What is SMT Surface mount technologyAn overview or tutorial about surface mount technology, SMT and surface mount devices SMDsSurface mount technology, SMT includes: SMT overview SMD component packages SMD resistor SMD resistor markings MELF SMD resistor SMD capacitor Quad Flat Package, QFP BGA, Ball Grid Array SMD PLCC

Virtually all of today's mass produced electronics hardware is manufactured using surface mount technology, SMT. The associated surface mount devices, SMDs provide many advantages over their leaded predecessors in terms of manufacturability and often performance. It was not until the 1980's that surface mount technology, SMT became widely used. Once SMT started to be used, the change from conventional leaded components to surface mount devices, SMDs took place quickly in view of the enormous gains that could be made using SMT.

Why SMT?Mass produced electronic circuit boards need to be manufactured in a highly mechanised manner to ensure the lowest cost of manufacture. The traditional leaded electronic components do not lend themselves to this approach. Although some mechanisation was possible, component leads needed to be pre-formed. Also when the leads were inserted into boards automatically problems were often encountered as wires would often not fit properly slowing production rates considerably. It was reasoned that the wires that had traditionally been used for connections were not actually needed for printed circuit board construction. Rather than having leads placed through holes, the components could be soldered onto pads on the board instead. This also saved creating the lead holes in the boards which added cost to the production of the bare PCBs.

Typical SMT board with transistors, and passive components As the components were mounted on the surface of the board, rather than having connections that went through holes in the board, the new technology was called surface mount technology or1

SMT and the devices used were surface mount devices, SMDs. The idea for SMT was adopted very quickly because it enabled greater levels of mechanisation to be used, and it considerably saved on manufacturing costs. To accommodate surface mount technology, SMT, a completely new set of components was needed. New SMT outlines were required, and often the same components, e.g. ICs were sold in both traditional leaded packages and SMT packages. Despite this, the gains of using SMT proved to be so large that it was adopted very quickly.

SMT board with typical IC packages

What are SMT components?Surface mount devices, SMDs by their nature are very different to the traditional leaded components. They can be split into a number of categories:

Passive SMDs: There is quite a variety of different packages used for passive SMDs. However the majority of passive SMDs are either resistors or capacitors for which the package sizes are reasonably well standardised. Other components including coils, crystals and others tend to have more individual requirements and hence their own packages. Resistors and capacitors have a variety of package sizes. These have designations that include: 1812, 1206, 0805, 0603, 0402, and 0201. The figures refer to the dimensions in hundreds of an inch. In other words the 1206 measures 12 hundreds by 6 hundreds of an inch. The larger sizes such as 1812 and 1206 were some of the first that were used. They are not in widespread use now as much smaller components are generally required. However they may find use in applications where larger power levels are needed or where other considerations require the larger size. The connections to the printed circuit board are made through metallised areas at either end of the package.

Transistors and diodes: These components are often contained in a small plastic package. The connections are made via leads which emanate from the package and are bent so that they touch the board. Three leads are always used for these packages. In this way it is easy to identify which way round the device must go. Integrated circuits: There is a variety of packages which are used for integrated circuits. The package used depends upon the level of interconnectivity required. Many chips like the simple logic chips may only require 14 or 16 pins, whereas other like the VLSI processors and associated chips can require up to 200 or more. In view of the wide variation of requirements there is a number of different packages available. For the smaller chips, packages such as the SOIC (Small Outline Integrated Circuit) may2

be used. These are effectively the SMT version of the familiar DIL (Dual In Line) packages used for the familiar 74 series logic chips. Additionally there are smaller versions including TSOP (Thin Small Outline Package) and SSOP (Shrink Small Outline Package). The VLSI chips require a different approach. Typically a package known as a quad flat pack is used. This has a square or rectangular footprint and has pins emanating on all four sides. Pins again are bent out of the package in what is termed a gull-wing formation so that they meet the board. The spacing of the pins is dependent upon the number of pins required. For some chips it may be as close as 20 thousandths of an inch. Great care is required when packaging these chips and handling them as the pins are very easily bent. Other packages are also available. One known as a BGA (Ball Grid Array) is used in many applications. Instead of having the connections on the side of the package, they are underneath. The connection pads have balls of solder that melt during the soldering process, thereby making a good connection with the board and mechanically attaching it. As the whole of the underside of the package can be used, the pitch of the connections is wider and it is found to be much more reliable. A smaller version of the BGA, known as the microBGA is also being used for some ICs. As the name suggests it is a smaller version of the BGA.

SMT in useSMT is used almost exclusively for the manufacture of electronic circuit boards these days. Now it is found that SMDs are far more widely used than traditional leaded components, and as a result, traditional leaded components are considerably less common. Some components, particularly high density ICs may only be available in SMT packages. While there is still a need for many traditional components, SMDs now form the main line stream for components

SMT / SMD component packages- an overview of the different SMD component packages used for surface mount technology, SMT componentsSurface mount technology (SMT) components come in a variety of packages. As technology has improved many packages have decreased in size. Additionally there is a variety of different SMT packages for integrated circuits dependent upon the interconnectivity required, the technology being used and a variety of other factors. To provide some degree of uniformity, sizes of most SMT components conform to industry standards, many of which are JEDEC specifications. Obviously different SMT packages are used for different types of components, but the fact that there are standards enables activities such as printed circuit board design to be simplified. Additionally the use of standard size packages simplifies the manufacture because pick and place machines can use standard feed for the SMT components, considerably simplifying the manufacturing process and saving costs. The different SMT packages can be categorised by the type of component, and there are standard packages for each.

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Passive rectangular componentsThese SMT components are mainly resistors and capacitors which form the bulk of the number of components used. There are several different sizes which have been reduced as technology has enabled smaller components to be manufactured and usedSMD Package type 1812 1206 0805 0603 0402 0201 Dimensions mm 4.6 x 3.0 3.0 x 1.5 2.0 x 1.3 1.5 x 0.8 1.0 x 0.5 0.6 x 0.3 Dimensions inches 0.18 x 0.12 0.12 x 0.06 0.08 x 0.05 0.06 x 0.03 0.04 x 0.02 0.02 x 0.01

Of these sizes, the 1812, and 1206 sizes are now only used for specialized components or ones requiring larger levels of power to be dissipated The 0603 and 0402 SMT sizes are the most widely used.

Tantalum capacitors SMD packagesAs a result of the different construction and requirements for tantalum SMT capacitors, there are some different packages that are used for them. These conform to EIA specifications.SMD Package type Size A Size B Size C Size D Size E Dimensions mm 3.2 x 1.6 x 1.6 3.5 x 2.8 x 1.9 6.0 x 3.2 x 2.2 7.3 x 4.3 x 2.4 7.3 x 4.3 x 4.1 EIA standard EIA 3216-18 EIA 3528-21 EIA 6032-28 EIA 7343-31 EIA 7343-43

Semiconductor SMD packagesThere is a wide variety of SMT packages used for semiconductors including diodes, transistors and integrated circuits. The reason for the wide variety of SMT packages for integrated circuits results from the large variation in the level of interconnectivity required. Some of the main packages are given below

Transistor packages

SOT-23 - Small Outline Transistor. This is SMT package has three terminals for a diode of transistor, bit it can have more pins when it may be used for small integrated circuits such as an operational amplifier, etc. It measures 3 mm x 1.75 mm x 1.3 mm. SOT-223 - Small Outline Transistor. This package is used for higher power devices. It measures 6.7 mm x 3.7 mm x 1.8 mm. There are generally four terminals, one of which is a large heat-transfer pad.

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Integrated circuit SMD packages

SOIC - Small Outline Integrated Circuit. This has a dual in line configuration and gull wing leads with a pin spacing of 1.27 mm TSOP - Thin Small Outline Package. This package is thinner than the SOIC and has a smaller pin spacing of 0.5 mm SSOP - Shrink Small Outline Package. This has a pin spacing of 0.635 mm TSSOP - Thin Shrink Small Outline Package. PLCC - Plastic Leaded Chip Carrier. This type of package is square and uses J-lead pins with a spacing of 1.27 mm QSOP - Quarter-size Small Outline Package. It has a pin spacing of 0.635 mm VSOP - Very Small Outline Package. This is smaller than the QSOP and has pin spacing of 0.4, 0.5, or 0.65 mm. LQFP - Low profile Quad Flat Pack. This package has pins on all four sides. Pin spacing varies according to the IC, but the height is 1.4 mm. PQFP - Plastic Quad Flat Pack. A square plastic package with equal number of gull wing style pins on each side. Typically narrow spacing and often 44 or more pins. Normally used for VLSI circuits. CQFP - Ceramic Quad Flat Pack. A ceramic version of the PQFP. TQFP - Thin Quad Flat Pack. A thin version of the PQFP. BGA - Ball Grid Array. A package that uses pads underneath the package to make contact wit the printed circuit board. Before soldering the pads appear as solder balls, giving rise to the name. By placing the pads underneath the package there is more room for them, thereby overcoming some of the problems of the very thin leads required for the quad flat packs. The ball spacing on BGAs is typically 1.27 mm.

SMD package applicationsSMT surface mount technology packages are used for most printed circuit designs that are going to be manufactured in any quantity. Although it may appear there is a relatively wide number of different packages, the level of standardisation is still sufficiently good. In any case it arises mainly out of the enormous variety in the function of the components.

SMD Resistor- an overview of surface mount technology SMT resistors, or SMD resistors, their packages and properties.Surface mount device , SMD, resistors are the most widely used electronic component. Every day many millions are used to produce the electronic equipment from cell phones to televisions and MP3 players, and commercial communications equipment to high technology research equipment.

Basic SMD resistor constructionSMD resistors are rectangular in shape. They have metallised areas at either end of the body of the SMD resistor and this enables them to make contact with the printed circuit board through the solder. The resistor itself consists of a ceramic substrate and onto this is deposited a metal oxide film. The thickness, and the length of the actual film determines the resistance. In view of the fact that the SMD resistors are manufactured using metal oxide, means that they are quite stable and usually have a good tolerance.5

SMD resistor packagesSMD resistors come in a variety of packages. As the technology has moved forward so the size of the resistor packages has fallen. The main packages with their sizes are summarized below: Package style 2512 2010 1812 1210 1206 0805 0603 0402 0201 Size (mm) 6.30 x 3.10 5.00 x 2.60 4.6 x 3.0 3.20 x 2.60 3.0 x 1.5 2.0 x 1.3 1.5 x 0.08 1 x 0.5 0.6 x 0.3 Size (inches) 0.25 x 0.12 0.20 x 0.10 0.18 x 0.12 0.12 x 0.10 0.12 x 0.06 0.08 x 0.05 0.06 x 0.03 0.04 x 0.02 0.02 x 0.01

It can be seen from the dimensions in Imperial measurements, that the package names correspond to the dimensions in hundredths of an inch. This an SMD resistor with an 0805 package measures 0.08 by 0.05 inches.

SMD resistor specificationsSMD resistors are manufactured by a number of different companies. Accordingly the specifications vary from one manufacturer to the next. It is therefore necessary to look at the manufacturers rating for a specific SMD resistor before deciding upon exactly what is required. However it is possible to make some generalisations about the ratings that might be anticipated. Power rating: The power rating needs careful consideration in any design. For designs using SMDs the levels of power that can be dissipated are smaller than those for circuits using wire ended components. As a guide typical power ratings for some of the more popular SMD resistor sizes are given below. These can only be taken as a guide because they may vary according to the manufacturer and type. Typical Power Ratings Package style Typical Power Rating (W) 2512 0.50 (1/2) 2010 0.25 (1/4) 1210 0.25 (1/4) 1206 0.125 (1/8) 0805 0.1 (1/10) 0603 0.625 (1/16) 0402 0.0625 - 0.031 (1/16 - 1/32) 0201 0.05 Some manufacturers will quote higher power levels than these. The figures given here are typical. Tolerance: In view of the fact that SMD resistors are manufactured using metal oxide film they available in relative close tolerance values. Normally 5%, 2%, and 1% are widely available. For specialist applications 0.5% and 0.1% values may be obtained.

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Temperature coefficient: Again the use of metal oxide film enables these SMD resistors to provide a good temperature coefficient. Values of 25, 50 and 100 ppm / C are available.

ApplicationsSMD resistors are used in many designs. Their size not only means that they are suitable for compact circuit boards, and for automatic assembly techniques, but it also ahs the advantage that they perform well at radio frequencies. Their size means that they have little spurious inductance and capacitance. Nevertheless care has to be taken when calculating their power dissipation as they can only dissipate small levels of power. ..............

SMD / SMT Resistor Markings- details of the SMD or SMT resistor markings and the resistor marking systems used to indicate the resistor values - including EIA SMD resistor marking scheme.Although not all SMD resistors, or SMT resistors are marked with their values, some are, and in view of the lack of space the SMD resistor making systems may not always provide an obvious indication of the resistor value. The SMT resistor marking systems provide are mainly used to enable service, repair and faultfinding. During manufacture the resistors are held either in tapes that are reeled, or in hoppers used for the surface mount machines. The SMD resistor markings can be used as a check to ensure the correct values are being fitted, but normally the reels or hoppers will be suitable marked and coded.

SMT resistor marking systemsMany SMD resistors do not have any markings on them to indicate their value. For these devices, once they are loose and out of their packaging it is very difficult to tell their value. Accordingly SMD resistors are typically used within reels or other packages where there is no chance of different values being mixed. Many resistors do have markings on them. There are three systems that are used:

Three figure SMD resistor marking system Four figure SMD resistor marking system EIA96 SMD resistor marking system

3 figure SMT resistor marking systemA three figure SMT resistor marking system is the one that is normally used for standard tolerance resistors. As the name indicates this SMD resistor marking system uses three figures. The first two indicate the significant figures, and the third is a multiplier. This is the same as the coloured rings used for wired resistors, except that actual numbers are used instead of colours.

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Therefore an SMD resistor with the figures 472 would have a resistance of 47 x 102 ohms, or 4.7k. However beware of resistors marked with figures such as 100. This is not 100 ohms, but it follows the scheme exactly and it is 10 x 100 or 10 x 1 = 10 .

Three figure resistor marking

Where resistance values less than ten ohms are used, the letter "R" is used to indicate the position of the decimal point. As an example, a resistor with the value 4R7 would be 4.7.

4 figure SMT resistor marking systemthe four digit or four figure SMT resistor marking scheme is used for marking high tolerance SMD resistors. Its format is very similar to the three figure SMT resistor making scheme, but expanded to give the higher number of significant figures needed for higher tolerance resistors. In this scheme, the first three numbers will indicate the significant digits, and the fourth is the multiplier. Therefore an SMD resistor with the figures 4702 would have a resistance of 470 x 102 ohms, or 47k.

Four figure SMT resistor marking

Resistors with values of less than 100 ohms are marked utilise the letter 'R', as before, to indicate the position of the decimal point.

EIA96 SMD resistor marking systemA further SMD resistor marking scheme or SMD resistor coding scheme has started to be used, and it is aimed at 1% tolerance SMD resistors, i.e. those using the EIA96 or E-96 resistor series. As higher tolerance resistors are used, further figures are needed. However the small size of SMT resistors makes the figures difficult to read. Accordingly the new system seeks to address this. Using only three figures, the actual characters can be made larger than those of the four figure system that would otherwise be needed. The EIA SMD resistor marking scheme uses a three character code: the first 2 numbers indicate the 3 significant digits of the resistor value. The third character is a letter which indicates the multiplier. In this way this SMD resistor marking scheme will not be confused with the 3 figure markings scheme as the letters will differentiate it, although the letter R can be used in both systems. To generate the system the E-96 resistor series has been taken and each value or significant figure set has been numbered sequentially. As there are only 96 values in the E-96 series, only two figures are needed to number each value, and as a result this is a smart way of reducing the number of characters required.8

EIA SMD resistor marking

The details for the EIA SMT resistor marking scheme are tabulated below:

Code

Multiplier

Z 0.001 Y or R 0.01 X or S 0.1 A 1 B or H 10 C 100 D 1 000 E 10 000 F 100 000 EIA SMT resistor marking scheme multipliers

Code 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Sig Figs 100 102 105 107 110 113 115 118 121 124 127 130 133 137 140 143 147 150 154 158 162 165 169 174

Code Sig Figs Code Sig Figs 25 178 49 316 26 182 50 324 27 187 51 332 28 191 52 340 29 196 53 348 30 200 54 357 31 205 55 365 32 210 56 374 33 215 57 383 34 221 58 392 35 226 59 402 36 232 60 412 37 237 61 422 38 243 62 432 39 249 63 422 40 255 64 453 41 261 65 464 42 267 66 475 43 274 67 487 44 280 68 499 45 287 69 511 46 294 70 523 47 301 71 536 48 309 72 549 EIA SMT resistor marking scheme significant figures

Code 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96

Sig Figs 562 576 590 604 619 634 649 665 681 698 715 732 750 768 787 806 825 845 866 887 909 931 953 976

For example a resistor that is marked 68X can be split into two elements. 68 refers to the significant figures 499, and X refers to a multiplier of 0.1. Therefore the value indicated is 499 x 0.1 = 49.9.9

MELF Resistor- details of the MELF resistor a surface mount device, SMD used to provide superior performance over SMT resistors in certain applications.Another form of SMD resistor that can be used is known as the MELF resistor - Metal Electrode Leadless Face. These resistors are not nearly as widely used as the standard SMD resistors, but in some instances they provide advantages and can be used.

MELF resistor basics & constructionThe MELF resistor is cylindrical in shape and have metallisation on both ends. Land pattern sizes for MELF resistors are the same as SMD chip resistors. The manufacture of MELF resistors is more complicated than the more standard thick film SMD resistors. A metal film is deposited onto a high dissipation ceramic former. To make the terminations tin plated terminating caps are fitted. The resistor is then adjusted to the correct value by producing a helical cut in the film. The body of the MELF resistor is finally protected by a lacquer coating.

MELF Resistor Outline

The MELF SMD resistors are used for a number of reasons:

MELF resistors provide a high level of reliability. A MELF resistor has a more predictable pulse handling capacity than other SMD resistors MELF resistors can be manufactured with tolerances as tight as 0.1% They can be manufactured with very low levels of temperature coefficient, sometimes as low as 5 ppm/C

Although the standard flat chip resistors are cheaper and much easier to handle during manufacture, the performance of MELF resistor can be an overriding factor making them a cost effective solution

MELF resistors in electronics manufactureWhile MELF resistors provide some significant and compelling technical advantages for use in certain applications, they are not always the easiest to handle in manufacture. The most common form of SMD resistor by far is the flat or cuboid format. These require one form of nozzle on a pick and place machine, however MELF resistors require a different one that allows the cylindrical shape of the MELF resistor to be accommodated. They also require a higher level of vacuum on the pick and place machine.

MELF SMD resistor markingsMELF SMD resistors are used on occasions in some designs. These resistors are cylindrical and do not lend themselves to characters being printed on the surface, although coloured bands are10

easy to use. As such the MELF SMD resistor marking code is effectively the same as that used for leaded resistors. There are three variations used:

Four band code: This system is used for resistors with tolerances up to 5% using the E24 resistor series. The first two bands provide the significant digits. The third band provides the multiplier and the fourth, normally wider, provides the tolerance.

MELF Resistor 4 band code

Sometimes an alternative colour banding system may be used where the bands are all grouped towards one end of the MELF resistor rather than having a wider band at the far end.

Alternative MELF Resistor 4 band code

Five band code: This system is used for higher tolerance resistors typically better than 1% that use the E48, E96 or E192 series values. The first three bands provide the significant figures. The fourth band gives the multiplier and the fifth band gives the tolerance.

MELF Resistor 5 band code

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Six band code: This code provides space for a temperature coefficient marking. As with the four band code the first three bands give the significant figures. Next is the tolerance band, and finally the fifth band provides the tolerance. .

MELF Resistor 6 band code

Tables showing the various colours and figures are given below:

Colour None Silver Gold Black Brown Red Orange Yellow Green Blue Violet Grey White

Digit

Colour Code Multiplier 10-2 10-1 100 101 102 103 104 105 106 107 108 109 20% 10% 5% 1% 2%

Tolerance

0 1 2 3 4 5 6 7 8 9

0.5% 0.25% 0.1%

Temperature Coefficient Marking Colour Code (6th Band) Brown Red Yellow Orange Blue Violet 100 50 25 15 10 5 TCR ppm/K

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SMT / SMD Capacitor- an overview of the Surface Mount Device, SMD capacitor, its performance, construction, mechanical details and other useful information.SMD capacitors are used in vast quantities. After SMD resistors they are the most widely used type of component. There are many different types of SMD capacitor ranging from ceramic types, through tantalum varieties to electrolytics and more. Of these, the ceramic SMD capacitors are the most widely used.

Ceramic SMD capacitorsThe ceramic SMD capacitors form the majority of SMD capacitors that are used and manufactured. They are normally contained in the same type of packages used for resistors.

1812 - 4.6 mm x 3.0 mm (0.18" x 0.12") 1206 - 3.0 mm x 1.5 mm (0.12" x 0.06") 0805 - 2.0 mm x 1.3 mm (0.08" x 0.05") 0603 - 1.5 mm x 0.8 mm (0.06" x 0.03") 0402 - 1.0 mm x 0.5 mm (0.04" x 0.02") 0201 - 0.6 mm x 0.3 mm (0.02" x 0.01")

Construction: The SMD capacitor consists of a rectangular block of ceramic dielectric in which a number of interleaved precious metal electrodes are contained. This structure gives rise to a high capacitance per unit volume. The inner electrodes are connected to the two terminations, either by silver palladium (AgPd) alloy in the ratio 65 : 35, or silver dipped with a barrier layer of plated nickel and finally covered with a layer of plated tin (NiSn). Ceramic capacitor manufacture: The raw materials for the dielectric are finely milled and carefully mixed. Then they are heated to temperatures between 1100 and 1300C to achieve the required chemical composition. The resultant mass is reground and additional materials added to provide the required electric properties. The next stage in the process is to mix the finely ground material with a solvent and binding additive. This enables thin sheets to be made by casting or rolling. For multilayer capacitors electrode material is printed on the sheets and after stacking and pressing of the sheets co-fired with the ceramic compact at temperatures between 1000 and 1400C. The totally enclosed electrodes of a multilayer capacitor guarantee good life test behaviour as well.

Tantalum SMD capacitorsTantalum SMD capacitors are widely used to provide levels of capacitance that are higher than those that can be achieved when using ceramic capacitors. As a result of the different construction and requirements for tantalum SMT capacitors, there are some different packages that are used for them. These conform to EIA specifications.

Size A 3.2 mm x 1.6 mm x 1.6 mm (EIA 3216-18) Size B 3.5 mm x 2.8 mm x 1.9 mm (EIA 3528-21) Size C 6.0 mm x 3.2 mm x 2.2 mm (EIA 6032-28) 13

Size D 7.3 mm x 4.3 mm x 2.4 mm (EIA 7343-31) Size E 7.3 mm x 4.3 mm x 4.1 mm (EIA 7343-43)

Electrolytic SMD capacitorsElectrolytic capacitors are now being used increasingly in SMD designs. Their very high levels of capacitance combined with their low cost make them particularly useful in many areas. Often SMD electrolytic capacitors are marked with the value and working voltage. There are two basic methods used. One is to include their value in microfarads (m F), and another is to use a code. Using the first method a marking of 33 6V would indicate a 33 F capacitor with a working voltage of 6 volts. An alternative code system employs a letter followed by three figures. The letter indicates the working voltage as defined in the table below and the three figures indicate the capacitance on picofarads. As with many other marking systems the first two figures give the significant figures and the third, the multiplier. In this case a marking of G106 would indicate a working voltage of 4 volts and a capacitance 0f 10 times 10^6 picofarads. This works out to be 10 FLetter e G J A C D E V H 2.5 4 6.3 10 16 20 25 35 50 Voltage

Ball Grid Array, BGA- an overview or reference tutorial providing the basics about what is a Ball Grid Array or BGA and BGA packages used for SMT technology circuit boards, and BGA rework and BGA repair.A Ball Grid Array or BGA package is a form of surface mount technology, or SMT package that is being used increasingly for integrated circuits. The BGA offers many advantages and as a result it is being used increasingly in the manufacture of electronic circuits. The Ball Grid Array, BGA package was developed out of the need to have a more robust and convenient package for integrated circuits with large numbers of pins. With the levels of integration rising, some integrated circuits had in excess of 100 pins. The conventional quad flat pack style packages had very thin and close spaced pins, and these were very easy to damage, even in a controlled environment. Additionally they required very close control of the soldering process otherwise the level of solder bridges and poor joints rose. From a design viewpoint, the pin density was such that taking the tracks away from the IC also proved to be problematic as there could be congestion in some areas. The BGA package was developed to overcome these problems, and improve reliability from the soldered joints.

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What is a BGA package?The Ball Grid Array, BGA, uses a different approach to the connections to that used for more conventional surface mount connections. Other packages such as the quad flat pack, QFP, used the sides of the package for the connections. This meant that there was limited space for the pins which had to be spaced very closely and made much smaller to provide the required level of connectivity. The Ball Grid Array, BGA, uses the underside of the package, where there is a considerable area for the connections. The pins are placed in a grid pattern (hence the name Ball Grid Array) on the surface of the chip carrier. Also rather than having pins to provide the connectivity, pads with balls of solder are used as the method of connection. On the printed circuit board, PCB, onto which the BGA device is to be fitted there is a matching set of copper pads to provide the required connectivity. Apart from the improvement in connectivity, BGAs have other advantages. They offer a lower thermal resistance between the silicon chip itself than quad flat pack devices. This allows heat generated by the integrated circuit inside the package to be conducted out of the device onto the PCB faster and more effectively. In this way it is possible for BGA devices to generate more heat without the need for special cooling measures. In addition to this the fact that the conductors are on the underside of the chip carrier means that the leads within the chip are shorter. Accordingly unwanted lead inductance levels are lower, and in this way, Ball Grid Array devices are able to offer a higher level of performance than their QFP counterparts.

BGA assemblyWhen BGAs were first introduced, BGA assembly was one of the key concerns. With the pads not accessible in the normal manner would BGA assembly reach the standards that could be achieved by more traditional SMT packages. In fact, although soldering may have appeared to be a problem for a Ball Grid Array, BGA, device, it was found that standard reflow methods were very suitable for these devices and joint reliability was very good. Since then BGA assembly methods have improved, and it is generally found that BGA soldering is particularly reliable. In the soldering process, the overall assembly is then heated. The solder balls have a very carefully controlled amount of solder, and when heated in the soldering process, the solder melts. Surface tension causes the molten solder to hold the package in the correct alignment with the circuit board, while the solder cools and solidifies. The composition of the solder alloy and the soldering temperature are carefully chosen so that the solder does not completely melt, but stays semi-liquid, allowing each ball to stay separate from its neighbours. As many products now utilise BGA packages as standard, BGA assembly methods are now well established and can be accommodated by most manufacturers with ease. Accordingly there should be no concerns about using BGA devices in a design.

Ball Grid Array, BGA, inspectionOne of the problems with BGA devices is that it is not possible to view the soldered connections using optical methods. As a result there was some suspicion about the technology when it was first introduced and many manufacturers undertook tests to ensure that they were able to solder the devices satisfactorily. The main problem with soldering Ball Grid Array devices, is that sufficient heat must be applied to ensure that all the balls in the grid melt sufficiently for every joint to be satisfactorily made.15

The joints cannot be tested fully by checking the electrical performance. It is possible that the joint may not be adequately made and that over time it will fail. The only satisfactory means of inspection is to use X-ray inspection as this means of inspection is able to look through the device at the soldered joint beneath.It is found that once the heat profile for the solder machine is set up correctly, the BGA devices solder very well and few problems are encountered, thereby making BGA assembly possible for most applications.

Ball Grid Array, BGA reworkAs might be anticipated, it is not easy to rework boards containing BGAs unless the correct equipment is available. If a BGA is suspected as being faulty, then it is possible to remove the device. This is achieved by locally heating the device to melt the solder underneath it. In the BGA rework process, the heating is often achieved removed in a specialised rework station. This comprises a jig fitted with infrared heater, a thermocouple to monitor the temperature and a vacuum device for lifting the package. Great care is needed to ensure that only the BGA is heated and removed. Other devices nearby need to be affected as little as possible otherwise they may be damaged.

BGA repairOnce removed, the BGA can be replaced with a new one. Occasionally it may be possible to refurbish or repair a BGA that has been removed. This BGA repair may be an attractive proposition if the chip is expensive and it is known to be a working device once removed. Undertake a BGA repair it needs to have the solder balls replaced. This BGA repair can be undertaken using some of the small ready-made solder balls that are manufactured and sold for this purpose.

PLCC, Plastic Leaded Chip Carrier- essential notes or overview about the SMD PLCC, Plastic Leaded Chip Carrier, an SMT package that can be soldered to a board or used with a socket.The SMD PLCC or Plastic Leaded Chip carrier is an SMD package that is widely used for many types of integrated circuit. However the SMD PLCC is particularly useful for applications where the integrated circuit may need to be removed on a regular basis as, for example, in the case of a chip containing firmware where no other means of re-programming may be available. The SMD PLCC also has the advantage that it can be soldered to the board. Having leads on all sides of the chip, the SMD PLCC offers a relatively high connection density.

SMD PLCC basicsAn SMD PLCC or plastic leaded chip carrier is a four sided flat integrated circuit package or chip carrier. Rather than using the gull wing leads that are used on the quad flat pack, the SMD PLCC uses a "J" lead format. Here the leads are in the form of a J that is positioned on the edge of the SMD PLCC package with the lower section of the J folding back under the package. As a result of the lead format the SMD PLCC offers a number of advantages:

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Space saving: The "J" lead of the SMD PLCC provides a useful reduction in board area when compared to the gull wing lead of the QFP. As the "J" lead effectively folds back under the package, this provides a significant reduction in real estate usage. Socket compatible: In some areas, especially when developing new products a socketed chip can be particularly useful, if new builds of a PLD or other chip may be needed. The PLD can be programmed off the board and added to the board to test the overall system operation. While many boards will allow on-board programming, this may not always be achievable. Heat resistance: In some limited instances, the heat experienced during the soldering process could cause damage to the chip. In this case a socket can be added to the board, and the PLCC inserted after soldering is completed, and no high temperatures will be experienced.

the SMD PLCC can have a variety of formats. Lead counts can vary from 20 up to 84 and body widths range from 0.35 to 1.15 inches. Pin or lead spacing is generally 0.05 inches, i.e. 1.27 mm.

PLCC socketsOne of the major advantages of an SMD PLCC is that the chip can be connected to the circuit via a socket. The same chip format can also be used in the standard SMT format, soldering the PLCC directly to the board. This can have significant advantages when a replaceable chip is needed for development, but then the same chip can be used in production where it can be soldered onto the board. PLCC sockets may either be surface mounted - the most common, or some through hole versions are also available. Some through hole PLCC sockets may be used with wire wrap techniques for prototyping. Although it is often possible to extract PLCCs using a small screwdriver, etc., it is far more preferable to use a PLCC extractor tool. This will make extraction of the PLCC far easier, and minimize the possibility of any damage.

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Resistor Types- Information, tutorial about the basics of the different types of resistors including fixed and variable resistors, carbon, film, carbon composition, metal film, etcResistor types includes: Resistor types summary Variable / adjustable resistor Thermistor LDR light dependent resistor MELF resistor

See also: SMT resistor

There are many different types of resistor available for use within electronic circuits. These different resistor types have somewhat different properties dependent upon their construction and manufacture. This makes the different types of resistor suitable for different applications. Over the years the resistor types used in mass electronics production have changed. Years ago, all the resistors used had leads and were relatively large, and by today's standards they offered a low level of performance. Today, the resistor types used are much smaller and offer much higher levels of performance.

Fixed & variable resistor typesThe first major categories into which the different types of resistor can be fitted is into whether they are fixed or variable. These different resistor types are used for different applications:

Fixed resistors: Fixed resistors are by far the most widely used type of resistor. They are used in electronics circuits to set the right conditions in a circuit. Their values are determined during the design phase of the circuit, and they should never need to be changed to "adjust" the circuit. There are many different types of resistor which can be used in different circumstances and these different types of resistor are described in further detail below. Variable resistors: These resistors consist of a fixed resistor element and a slider which taps onto the main resistor element. This gives three connections to the component: two connected to the fixed element, and the third is the slider. In this way the component acts as a variable potential divider if all three connections are used. It is possible to connect to the slider and one end to provide a resistor with variable resistance.

Fixed resistor typesThere are a number of different types of fixed resistor:

Carbon composition: These types were once very common, but are now seldom used. They are formed by mixing carbon granules with a binder which was then made into a small rod. This type of resistor was large by today's standards and suffered from a large negative temperature coefficient. The resistors also suffered from a large and erratic irreversible changes in resistance as a result of heat or age. In addition to this the granular nature of the carbon and binder lead to high levels of noise being generated when current flowed.18

Carbon film: This resistor type is formed by "cracking" a hydrocarbon onto a ceramic former. The resulting deposited film had its resistance set by cutting a helix into the film. This made these resistors highly inductive and of little use for many RF applications. They exhibited a temperature coefficient of between -100 and -900 ppm / Celcius. The carbon film is protected either by a conformal epoxy coating or a ceramic tube. Metal film / metal oxide: This type of resistor is now the most widely used form of resistor. Rather than using a carbon film, this resistor type uses a metal film deposited on a ceramic rod. Metals such as nickel alloy, or a metal oxide such as tin oxide are deposited onto the ceramic rod. The resistance of the component is adjusted in two ways. First the thickness of the deposited layer is controlled during the initial manufacturing stages. Then it can be more accurately adjusted by cutting a helical grove in the film. Again the film is protected using a conformal epoxy coating. This type of resistor has a temperature coefficient of around 15 parts per million / K, giving it a far superior performance to that of any carbon based resistor. Additionally this type of resistor can be supplied to a much closer tolerance, 5%, 2% being standard, and with 1% versions available. They also exhibit a much lower noise level than carbon types of resistor. Wire wound: This resistor type is generally reserved for high power applications. These resistors are made by winding wire with a higher than normal resistance (resistance wire) on a former. The more expensive varieties are wound on a ceramic former and they may be covered by a vitreous or silicone enamel. This resistor type is suited to high powers and exhibits a high level of reliability at high powers along with a comparatively low level of temperature coefficient, although this will depend on a number of factors including the former, wire used, etc.. Thin film: Thin film technology is used for most of the surface mount types of resistor. As these are used in their billions these days, this makes this form of resistor technology one of the most widely used.

The Wirewound ResistorPhil Ebbert, VP Engineering, Riedon Inc. reports on the wirewound resistor and the fact that it is widely used todayLike every component, the fabrication technology used in resistor manufacture has changed over time and resistive films have made a significant contribution in allowing the cost-effective mass production of devices that are increasingly miniaturized. Yet the traditional wirewound resistor, despite a substantial decline in the number of manufacturers of this component in recent decades, remains the best solution for many specialized applications. The wirewound resistor is still used in large quantities where particular elements of performance are required. In these areas, the wirewound resistor can greatly outperform many other resistor technologies.

Construction advantagesOne reason for the survival of wirewound resistors is that all of the alternative fabrication techniques have drawbacks. For example, the use of conductive inks to produce carbon film or thick film resistors can produce very low-cost components but the resulting devices have limited pulse handling, no better than 0.1% initial tolerance and poor long-term stability, typically 500 to 1000ppm/year. The resistance is temperature dependent, with a temperature coefficient of19

resistance (TCR) of around 50 to 100ppm/C. Moreover, relatively high current noise of -18 dB to -10 dB is typical, where: dB = 20 x log (noise voltage [in V]/DC voltage [in V])

Figure 1: Easy customization is one of the major advantages of wirewound resistor technology

Carbon composition resistors, made by binding conductive carbon powder and an insulating material (usually ceramic) in a resin are some of the earliest resistor types. The proportions of carbon and insulating material determine the desired resistance value. Its difficult to achieve accurate values so 5% is often the best initial tolerance available and they exhibit poor temperature stability with a TCR of some 1000ppm/C. These resistors also have high current noise (-12 dB to +6 dB ) and suffer from poor stability over time. Metal film types perform better. They deliver improved tolerance (as good as 0.01%), TCR of 10 to 200ppm/C and stability of 200 to 600ppm/yr. But these figures still cannot match those of wirewound alternatives, and their pulse handling capability is significantly inferior. As a result of the limitations of other technologies, wirewound components continue to be used in many applications. They can handle high level pulses and transients, can dissipate substantial amounts of power (some are rated at up to 2.5kW), and they can be made with great precision some have initial tolerances down to 0.005%. Just as importantly, they are stable (15 to 50ppm/yr), maintaining their precision over time because they are made with stable materials. Wirewound resistors are also among the lowest current noise resistors available at -38dB. The basic structure of a wirewound resistor has remained unchanged for many years. As the name suggests, a resistance wire is wound around a central core or former, usually made of ceramic. Metal end-caps are pressed onto the core, and the resistance wire welded to them. Finally, the assembly is encapsulated to protect it from moisture and physical damage.

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Figure 2: The fundamental construction of a wirewound resistor has changed little over time.

Wirewound construction also produces devices that are easy to customize, so engineers have the freedom to specify exactly what they need, even if the final quantities required are in the hundreds, rather than tens of thousands. And although familiar, the technology has not stood still. For instance, advances in materials science allow the construction of devices with tightly controlled response across a range of temperatures, with TCR as low as 1ppm/C. The individual components resistance is determined by the length, cross-sectional area, and material (and hence resistivity) of the resistance wire. In terms of material choice, a small diameter copper wire 30m long may have a resistance of a few ohms. In contrast, the higher resistivity of a nickel-chrome alloy means that a small diameter wire only 30cm long made of this material may have a resistance of several thousand ohms. Manufacturers of wirewound resistors offer a choice of metal alloys and sizes and the fabrication characteristics go a long way to explaining the advantages. When a high precision resistor is required, for example, a longer resistance wire can be used, allowing the value to be trimmed to great accuracy by removing a few centimetres (or even millimetres) of wire.

Temperature stabilityThe choice of material is also the major factor influencing the temperature characteristic of the resistor. For example, low-TCR RO-800 alloy is formulated to have a TCR of 5 to 10ppm/C. For comparison, pure nickel has a TCR of 6700ppm/C, and copper a TCR of 3900ppm/C. The material choice therefore allows the manufacturer to tailor the resistor to desired characteristics. In general, low TCR is desirable. However, in some situations, such as temperature sensing and compensation applications, the opposite may be true, since the specific purpose of these components is to respond to changes in temperature. Wirewound components are sometime chosen for their ability to continue operating in extreme temperatures. Devices such as Riedons UT series of axial resistors, for example, operate from 55C to 275C, and continue to function at even higher temperatures with de-rating. These capabilities make the technology well-suited for use in the aerospace industry, and in applications such as fire suppression systems. Power handling and energy dissipation characteristics are similarly linked to the physical construction of the device. As a general rule, a resistor with a larger mass can safely absorb and dissipate more instantaneous power and more energy overall, and this is another strength of wirewound technology.

Pulse performanceOne common use for wirewound resistors is in pulse handling. A device such as a medical defibrillator needs to dissipate a large amount of energy in a very short time, putting its electrical components under a high degree of stress. To protect these components from failure, engineers typically design-in a resistor that can absorb the energy of a significant millisecond current surge. In another application, wirewound resistors are used to protect a metering module installed in a solid state electricity meter.

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Here, the resistor absorbs the high current generated when a metal oxide varistor (MOC) clamps in response to a voltage surge on the grid. Surges can have many causes, including lightning, inductive loads (motors), capacitor banks, switchgear, or even switching heating and ventilation systems in and out of circuit. For these types of application, resistors in the UT series mentioned above are sometimes used. They can withstand over 1000 Joules. Values range from 0.02 Ohms to 260k with tolerances down to 0.01% and TCR down 20ppm/C. Determining the right pulse handling capabilities for a particular application is not always a straightforward task. Dealing with inrush current implies different requirements than transient suppression. It is not easy to capture within a datasheet all of the information required to make such a choice. For pulses of up to five seconds, the industry standard specification is a withstand of five-times rated power for five seconds, so a 5W resistor must be able to handle 25W for 5 seconds (125 Joules), regardless of package size or resistance value. For shorter pulses, the mass of the resistance wire determines the Joule rating, which is then dependent upon resistor value and package type, including its size and whether its an axial or surface mount component. Repetition rate and pulse shape - square, triangular or irregular also have to be taken into account.

Figure 3: Pulse shape, repetition rate and duration all need to be understood in order to calculate the required energy handling capabilities.

In current sensing applications, designers have different requirements. For example, monitoring battery life in a handheld device generally requires a small package, whereas measurements in industrial or medical equipment might necessitate high precision and high current withstand. Wirewound devices excel where accuracy is important. For instance, four-terminal components are available in values from 0.01 to 1k with tolerances down to 0.005% and current handling capability of up to 25A. The most commonly cited disadvantage of wirewound resistors, particularly with respect to high frequency applications, is their self-inductance. However, this can overcome with a bifilar winding technique, shown in Figure 4, in which the turns are arranged so that two opposing magnetic fields are created ( one clockwise and the other counter-clockwise ), cancelling out the22

inductance, except the residual amount accounted for by terminations and connecting leads. Inductance is typically reduced by 90% compared to a standard part.

Figure 4: Non-inductive winding can produce wirewound resistors with minimal self-inductance

Leaded and non-leaded resistor typesOne of the key differentiators for resistors, and many other forms of component these days is the way in which they are connected. As a result of the mass production techniques sued and the widespread use of printed circuit boards, the form of connection used for components, especially those to be incorporated into mass produced items changed. The two main forms of resistor type according to their connection method are:

Leaded resistors: This type of resistor has been used since the very first electronic components have been in use. Typically components were connected to terminal posts of one form or another and leads from the resistor element were needed. As time progressed, printed circuit boards were used, and the leads were inserted through holes in the boards and typically soldered on the reverse side where the tracks were to be found.

Typical leaded carbon resistor

Surface mount resistors: These resistor types have been used increasingly since the introduction of surface mount technology. Typically this type of resistor is manufactured using thin film technology. A full range of values can be obtained.

Typical SMD resistors on a PCB23

Variable / Adjustable Resistor or Potentiometernotes or overview about the adjustable resistor or variable resistor used as a trimmer resistor and the circuit symbolVariable or adjustable resistors are often needed within electronic circuits to act as a preset control within the circuit. The variable resistor, is also widely referred to as a potentiometer as a result of its configuration. While it is often considered poor design practice to include unnecessary adjustments in a circuit, the variations in circuit values may mean that a preset, or variable resistor may be required in order to set the circuit to function within its required limits. Additionally, variable resistors are used for controls - a prime example is the volume control on a radio, television of hi-fi unit.

Variable resistor basicsThe variable resistor comprises a fixed resistive element along which a slider passes. The variable or adjust able resistor forms a potential divider in which the overall resistance between the two end points remains the same, but the ratio of the two resistors in the legs changes. In view of the fact that the variable resistor is effectively a potential divider, it is called a potentiometer.

Variable resistor is effectively a potential divider

Variable resistor symbolThe variable resistor symbol used in circuit diagrams indicates its construction. Effectively it is a fixed resistor with a slider that can move along the length of the resistive element. In this way it forms a potentiometer as described before.

Variable resistor symbol for circuit diagrams 24

The variable resistor symbols depict the current version use din circuit diagrams today and the traditional format that may be seen on older circuit diagrams. When a true variable resistor with only two connections is needed, it is common practice to connect the slider to the remote end of the variable resistor as shown below.

Variable resistor element with two connections

Types of adjustable or variable resistorsThere are a number of different types of variable resistor that are available on the market. Each of these different types of variable resistor has slightly different properties and is suitable for different applications and situations.

Wirewound variable resistors: Wirewound variable resistors are able to give a high level of performance and as a result they are often the variable resistor of choice for many applications such as audio, etc.. Wirewound variable resistors are manufactured using very fine resistance wire. This is wound around a former that is almost torroidal. The most commonly used form of resistance wire used is a nickel chrome alloy. Which has some further additives to improve its electrical characteristics. Wirewound variable resistors offer a high level of linearity and close tolerance. Some very close tolerance versions may be able to offer linearity tolerances of 0.1%. These variable resistors are also stable over a wide temperature range. There are two main disadvantages with the wirewould variable resistor. The first is that often as the slider moves over the wires, the resistance changes have discrete steps. This may not be a problem in many applications, but it is a point to note. The second is that they are not suitable even for low frequency RF applications as the resistance wire forms a coil and has significant inductance.

Cermet variable resistors: Cermet variable resistors are widely used, particularly for trimmer resistors. The name cermet is derived from the fact that the resistive element is made from CERamic and METal. The resistive element is made from a mixture of fine metal oxides or precious metal particles and glass in a viscous organic material. The resulting paste is applied to the substrate and fired to solidify the mixture. Cermet variable resistors are ideal for trimmer resistors because they have a low to medium adjustment life, and they often have temperature coefficients of around 100ppm/C.

Carbon composition variable resistors: For the carbon composition variable resistor, a mixture of carbon powder and a binder are moulded under heat into the required shape. In some manufacturing processes the carbon composition element is moulded at the same time as the plastic substrate. 25

Carbon composition variable resistors are some of the least expensive types and they are widely used in many areas - they are a good all round general purpose variable resistor. The carbon composition variable resistor element can be tailored to give approximately linear, logarithmic or even anti-logarithmic characteristics. The logarithmic forms are particularly useful for audio applications because the hearing characteristics of the ear mean that a logarithmic curve is more useful. Carbon composition variable resistors can sometimes exhibit temporary resistance changes of up to around 10% if operated at very high or low temperatures. Typically there operating temperature range might be expected to be from -55C to +120C. These variable resistors can also become noisy after use as wear and dirt appear on the track. Often some switch cleaner improves the situation.

Conductive plastic variable resistors: Conductive plastic variable resistors are made using a conductive plastic ink. This ink contains carbon, resin, solvent and other materials specific to the manufacturer. It is applied to the substrate, either by screening or co-moulding. As the ink has a relatively low curing temperature, this enables a variety of substrate materials to be used. Conductive plastic variable resistors have a high rotational life as well as providing a low noise output. As a result, they are often used for position sensors in servo-controlled machines, etc.

Summary of characteristics of variable resistor typesThe different types of variable resistor have different characteristics and this enables them to be used in different situations. The table below summarises some of the major characteristics of the most commonly used types of variable resistor.Variable Resistor Type Wirewound Cermet Conductive Plastic Carbon composition Typical Resistance Ranges 10 - 50k 50 - 2M 50 - 2M 50 - 2M Typical Tolerance Typical Power Handling up to 1 Watt 500mW 250mW 250mW Typical Life (Rotations) 500 200 100 000 1000 Typical Temperature Coefficient (ppm/K) 50 100 500 ~10%/K

5% 10% 10% 20%

By the very nature of this table the characteristics for the various forms of variable resistor can only be taken as a guide - with developments in technology occurring, along with the differing specifications of components from the variety of manufacturers, there is a large variation of performance of components from different sources.

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Resistor colour code table- resistor colour code chart / table for the four band, five band and six band systems used to provide value, tolerance and temperature coefficient details

Resistor colour codes are used to indicate the value of leaded resistors. These resistor colours have been widely used for many years. The resistor colour code provides an easy and reliable method for value indication - often printing the values in figures can be obscured or erased during handling making identification difficult.

Resistor colour code basicsThe resistor colour coding is carried on a number of coloured rings placed around the resistor. As virtually all leaded resistors are cylindrical, it is difficult to print numbers on them, and they can also become obscured during handling and use. As the resistor colour code system relies on rings around the resistor, even if part of the coding scheme is marked, other areas can be seen and the values and other information deciphered. Dependent upon the tolerance and accuracy required for the resistor, there are a number of colour coding schemes that may be used. All the different resistor colour code systems are basically the same in outline, but there provide differing levels of information. The main resistor colour coding schemes that are seen are:

Four band resistor colour code scheme Five band resistor colour code scheme Six band resistor colour code scheme

Dependent upon the number of rings used, the different resistor colour code schemes are able to provide

Four band resistor colour code systemThe four band system is used for E6, E12, and E24 series values. It can accommodate values with up to two significant figures which is acceptable for the resistor value ranges up to E24 which normally accommodate tolerance values up to 2%. The resistor colour code bands give the value of the resistor as well as other information including the tolerance and sometimes the temperature coefficient. The band closest to the end of the resistor body is taken to be Band 1. The first two bands of the resistor colour code are the significant figures of the value, and the third of the resistor colour code is a multiplier.

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4 band resistor colour code

As an example the colours shown above are red, violet, and orange on the left - the forth band on the right is red. The value is given by the first three, red violet corresponds to the significant figures, 27, and then the orange corresponds to a multiplier of 1000. This gives the value 27k. The fourth band gives a tolerance of 2%. Note: If only three bands are present on the resistor, they will be the two significant figures, followed by the multiplier, i.e. no tolerance band.

Five band resistor colour code systemFor resistors where higher tolerances are needed, i.e. 1% and better and for the E48, E96 and E192 series resistors where three significant figures are required, an extra digit band is included. Otherwise this resistor colour coding system is the same as the four band colour code system.

5 band resistor colour code

Using the example in the diagram where the resistor colours are, orange; brown; blue; red; brown. From the first three resistor colour bands, it can be seen that the significant digits are 316, and the multiplier is 100. This gives 31600 or 31.6k. The final band or ring indicates the tolerance is 1%

Six band resistor colour code systemThe six band resistor colour code system provides the maximum amount of information about the resistor parameters. Like the Five band colour code system, this one is generally used with high tolerance values i.e. 1% and better and E$*, E96, & E192 series resistor values.

6 band resistor colour code

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The example of the six band resistor colour code system shown in the diagram has colours of where the resistor colours are, orange; brown; blue; red; brown red. From the first three resistor colour bands, it can be seen that the significant digits are 316, and the multiplier is 100. This gives 31600 or 31.6k. The fifth band or ring is brown and indicates the tolerance is 1%. The final red band indicates the temperature coefficient is 50 ppm/K.

Resistor Colour Code ChartThe resistor colour code table or chart below summarises the different colour codes used for resistors.

Colour Black Brown Red Orange Yellow Green Blue Violet Grey White Gold Silver None 0 1 2 3 4 5 6 7 8 9

Digits (Sig Figs)

Multiplier 100 101 102 103 104 105 106 107 108 109

Tolerance

Temp Coefficient ppm/K 100 50 15 25

1% 2%

0.5% 0.25% 0.1% 0.05% 5% 10% 20%

The resistor colour code is used in virtually all leaded resistors with power dissipation levels up to about a watt. Beyond this the resistors are generally large enough, and use a different form of construction allowing sufficient space for the values to be marked in figures. Nevertheless the resistor colour code is the most widely used system for leaded resistors. The same basic concept is also used on some capacitors.

Standard resistor values- standard resistor values given in the EIA E series - with explanations of the system & tables of these common resistor values.The values given to resistors fall into a number of preferred or standard resistor values. These standard resistor values have a logarithmic sequence related to the component accuracy, enabling the standard resistor values to be spaced according to the tolerance on the component. These standard resistor values are also applicable for capacitors and other components as well as resistors. Component values such as resistor values can never be manufactured exactly, each resistor has a tolerance associated with it. These may typically be 20%, 10% and 5%. Other tolerances such as 2% are also available. In order to ensure that standard values can be chosen from one of a variety of manufacturers, list of preferred values or standard resistor values have been devised. By using these preferred resistor29

value lists, common resistor values can be chosen from available components. This not only makes manufacture easier, but it enables stock holdings of manufacturers to be reduced by having a preferred resistor value range. As most component values need not be high precision special values, this is a particularly attractive idea.

E series of standard resistor valuesIn order to enable the common resistor values to be spaced apart according to their tolerance, a series known as the E series for standard or preferred values is used. Resistors are spaced apart so that the top of the tolerance band of one value and the bottom of the tolerance band of the next one do not overlap. Take for example a resistor with a value of 1 ohm and a tolerance of 20%. If the actual resistance of the component falls at the top of the tolerance band then it will have a value of 1.2 ohms. Take then a resistor with a value of 1.5 ohms. Again it is found that the value at the bottom of its tolerance band is 1.2 ohms. By calculating a range of values in this way a series can be built up. This is repeated for each decade. The series generated in this way for standard resistor values is known as the E series and these are preferred values. The most basic series within the E range is the E3 series which has just three values: 1, 2.2 and 4.7. This is seldom used as such because the associated tolerance is too wide for most of today's applications, although the basic values themselves may be used more widely to reduce stock holding. The next is the E6 series with six values in each decade for a 20% tolerance, E12 series with 12 values in each decade for a 10%, E24 series with 24 values in each decade for a 5% tolerance. Values for resistors in these series are given below. Further series (E48 and E96) are available, but are not as common as the ones given below. The E6 and E12 resistors are available in virtually all types of resistor. However the E24 series, being a much closer tolerance series is only available in the higher tolerance types. Metal oxide film resistors that are in common use today are available in the E24 series as are several other types. Carbon types are rarely available these days and in any case would only available in the lower tolerance ranges as their values cannot be guaranteed to such a close tolerance. The E series preferred or standard resistor ranges are widely used and have been adopted by standards organisations. The EIA (Electrical Industries Association) based in North America has, for example adopted the system and as such the values included are often referred to as the EIA preferred values. Summary of EIA Preferred or Standard Resistor Series E Tolerance Number of values in Series (Sig Figs) each decade E6 20% 6 E12 10% 12 E24 5% 24 [normally also available in 2% tolerance] E48 2% 48 E96 1% 96 E192 0.5%, 0.25% and higher 192 tolerances

Preferred and standard values of other components30

The system for adopting standard component values works very well for resistors. It is also equally applicable for other components. The same concept of using values in a standard list that are determined by the tolerance of the components is equally applicable. Accordingly the E series preferred values are also widely used for capacitors, where some of the lower order series are used - E3, E6 as the values on many capacitors do not have a high tolerance. Electrolytic capacitors typically have a very wide tolerance, although others such as many ceramic types have a much tighter tolerance and many be available in ranges conforming to the E12 or even E24 values. Another example of components that follow the EIA E series preferred values is Zener diodes for their breakdown voltages. The Zener diode standard voltages typically conform to the E12 values although E24 series voltage values are also available - especially 5.1 volt Zener diode for 5 volt rails.

Resistor E Series - E3, E6, E12, E24, E48, E96 Tables- chart and tables of standard resistor values in the E3, E6, E12, E24, E48, E96 ranges.The EIA preferred values can be summarised in tabular form to give the different values within each decade. When designing equipment, it is good practice to keep to the lowest E-series section, i.e. it is better to use E3 rather than E6. In this way the number of different parts in any equipment can be minimised. If decade values, i.e. 100R, 1K, 10, etc can be used so much the better. For many digital designs where the resistor is used as a pull up or pull down, the resistor value is of little consequence and this is easy. For analogue designs it is a little more complicated, and E12, or E24 values are needed. E48, E96 or even E192 series values are needed for high accuracy and close tolerance requirements. As the higher order series are used less, their costs are also normally higher.

Resistor E series tables of valuesE6 Standard Resistor Series 1.5 2.2 4.7 6.8

1.0 3.3

1.0 1.8 3.3 5.6

E12 Standard Resistor Series 1.2 1.5 2.2 2.7 3.9 4.7 6.8 8.2

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1.0 1.3 1.8 2.4 3.3 4.3 5.6 7.5

E24 Standard Resistor Series 1.1 1.2 1.5 1.6 2.0 2.2 2.7 3.0 3.6 3.9 4.7 5.1 6.2 6.8 8.2 9.1

1.00 1.15 1.33 1.54 1.78 2.05 2.37 2.74 3.16 3.65 4.22 4.87 5.62 6.49 7.50 8.66

E48 Standard Resistor Series 1.05 1.10 1.21 1.27 1.40 1.47 1.62 1.69 1.87 1.96 2.15 2.26 2.49 2.61 2.87 3.01 3.32 3.48 3.83 4.02 4.42 4.64 5.11 5.36 5.90 6.19 6.81 7.15 7.87 8.25 9.09 9.53 E96 Standard Resistor Series 1.02 1.05 1.10 1.13 1.18 1.21 1.27 1.30 1.37 1.40 1.47 1.50 1,58 1.62 1.69 1.74 1.82 1.87 1.96 2.00 2.10 2.16 2.36 2.32 2.43 2.49 2.61 2.67 2.80 2.87 3.01 3.09 3.24 3.32 3.48 3.57 3.74 3.83 4.02 4.1232

1.00 1.07 1.15 1.24 1.33 1.43 1.54 1.65 1.78 1.91 2.05 2.21 2.37 2.55 2.74 2.94 3.16 3.40 3.65 3.92

4.22 4.53 4.87 5.23 5.62 6.04 6.49 6.98 7.50 8.06 8.66 9.31

4.32 4.64 4.91 5.36 5.76 6.19 6.65 7.15 7.68 8.25 8.87 9.59

4.42 4.75 5.11 5.49 5.90 6.34 6,81 7.32 7.87 8.45 9.09 9.76

Tables of standard resistor values in the E series Virtually all resistors that are available fall into the standard resistor values that are given in the table above. Although resistors are specified up to the E96 series, for most applications a comparatively few number of resistor values is needed. By choosing from E3 or E6 series of standard resistor values, and not going to some of the higher order series, it can reduce the stock holding as there is a greater chance the same values may be used elsewhere in a design. Only where close tolerance types are required should resistors from the E24, or even E48 or E96 series of standard resistors should be used.

SMD Resistor- an overview of surface mount technology SMT resistors, or SMD resistors, their packages and properties.Surface mount technology, SMT includes: SMT overview SMD component packages SMD resistor SMD resistor markings MELF SMD resistor SMD capacitor Quad Flat Package, QFP BGA, Ball Grid Array SMD PLCC

Surface mount device , SMD, resistors are the most widely used electronic component. Every day many millions are used to produce the electronic equipment from cell phones to televisions and MP3 players, and commercial communications equipment to high technology research equipment.

Basic SMD resistor constructionSMD resistors are rectangular in shape. They have metallised areas at either end of the body of the SMD resistor and this enables them to make contact with the printed circuit board through the solder.

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The resistor itself consists of a ceramic substrate and onto this is deposited a metal oxide film. The thickness, and the length of the actual film determines the resistance. In view of the fact that the SMD resistors are manufactured using metal oxide, means that they are quite stable and usually have a good tolerance.

SMD resistor packagesSMD resistors come in a variety of packages. As the technology has moved forward so the size of the resistor packages has fallen. The main packages with their sizes are summarised below:

Package style 2512 2010 1812 1210 1206 0805 0603 0402 0201

Size (mm) 6.30 x 3.10 5.00 x 2.60 4.6 x 3.0 3.20 x 2.60 3.0 x 1.5 2.0 x 1.3 1.5 x 0.08 1 x 0.5 0.6 x 0.3

Size (inches) 0.25 x 0.12 0.20 x 0.10 0.18 x 0.12 0.12 x 0.10 0.12 x 0.06 0.08 x 0.05 0.06 x 0.03 0.04 x 0.02 0.02 x 0.01

It can be seen from the dimensions in Imperial measurements, that the package names correspond to the dimensions in hundredths of an inch. This an SMD resistor with an 0805 package measures 0.08 by 0.05 inches.

SMD resistor specificationsSMD resistors are manufactured by a number of different companies. Accordingly the specifications vary from one manufacturer to the next. It is therefore necessary to look at the manufacturers rating for a specific SMD resistor before deciding upon exactly what is required. However it is possible to make some generalisations about the ratings that might be anticipated. Power rating: The power rating needs careful consideration in any design. For designs using SMDs the levels of power that can be dissipated are smaller than those for circuits using wire ended components. As a guide typical power ratings for some of the more popular SMD resistor sizes are given below. These can only be taken as a guide because they may vary according to the manufacturer and type.

Typical Power Ratings Package style Typical Power Rating (W) 2512 0.50 (1/2) 2010 0.25 (1/4) 1210 0.25 (1/4) 1206 0.125 (1/8) 0805 0.1 (1/10) 0603 0.625 (1/16) 0402 0.0625 - 0.031 (1/16 - 1/32) 0201 0.0534

Some manufacturers will quote higher power levels than these. The figures given here are typical. Tolerance: In view of the fact that SMD resistors are manufactured using metal oxide film they available in relative close tolerance values. Normally 5%, 2%, and 1% are widely available. For specialist applications 0.5% and 0.1% values may be obtained. Temperature coefficient: Again the use of metal oxide film enables these SMD resistors to provide a good temperature coefficient. Values of 25, 50 and 100 ppm / C are available.

ApplicationsSMD resistors are used in many designs. Their size not only means that they are suitable for compact circuit boards, and for automatic assembly techniques, but it also ahs the advantage that they perform well at radio frequencies. Their size means that they have little spurious inductance and capacitance. Nevertheless care has to be taken when calculating their power dissipation as they can only dissipate small levels of power. ..............

SMD / SMT Resistor Markings- details of the SMD or SMT resistor markings and the resistor marking systems used to indicate the resistor values - including EIA SMD resistor marking scheme.Although not all SMD resistors, or SMT resistors are marked with their values, some are, and in view of the lack of space the SMD resistor making systems may not always provide an obvious indication of the resistor value. The SMT resistor marking systems provide are mainly used to enable service, repair and faultfinding. During manufacture the resistors are held either in tapes that are reeled, or in hoppers used for the surface mount machines. The SMD resistor markings can be used as a check to ensure the correct values are being fitted, but normally the reels or hoppers will be suitable marked and coded.

SMT resistor marking systemsMany SMD resistors do not have any markings on them to indicate their value. For these devices, once they are loose and out of their packaging it is very difficult to tell their value. Accordingly SMD resistors are typically used within reels or other packages where there is no chance of different values being mixed. Many resistors do have markings on them. There are three systems that are used:

Three figure SMD resistor marking system Four figure SMD resistor marking system EIA96 SMD resistor marking system

3 figure SMT resistor marking systemA three figure SMT resistor marking system is the one that is normally used for standard tolerance resistors.

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As the name indicates this SMD resistor marking system uses three figures. The first two indicate the significant figures, and the third is a multiplier. This is the same as the coloured rings used for wired resistors, except that actual numbers are used instead of colours. Therefore an SMD resistor with the figures 472 would have a resistance of 47 x 102 ohms, or 4.7k. However beware of resistors marked with figures such as 100. This is not 100 ohms, but it follows the scheme exactly and it is 10 x 100 or 10 x 1 = 10 .

Three figure resistor marking

Where resistance values less than ten ohms are used, the letter "R" is used to indicate the position of the decimal point. As an example, a resistor with the value 4R7 would be 4.7.

4 figure SMT resistor marking systemthe four digit or four figure SMT resistor marking scheme is used for marking high tolerance SMD resistors. Its format is very similar to the three figure SMT resistor making scheme, but expanded to give the higher number of significant figures needed for higher tolerance resistors. In this scheme, the first three numbers will indicate the significant digits, and the fourth is the multiplier. Therefore an SMD resistor with the figures 4702 would have a resistance of 470 x 102 ohms, or 47k.

Four figure SMT resistor marking

Resistors with values of less than 100 ohms are marked utilise the letter 'R', as before, to indicate the position of the decimal point.

EIA96 SMD resistor marking systemA further SMD resistor marking scheme or SMD resistor coding scheme has started to be used, and it is aimed at 1% tolerance SMD resistors, i.e. those using the EIA96 or E-96 resistor series. As higher tolerance resistors are used, further figures are needed. However the small size of SMT resistors makes the figures difficult to read. Accordingly the new system seeks to address this. Using only three figures, the actual characters can be made larger than those of the four figure system that would otherwise be needed. The EIA SMD resistor marking scheme uses a three character code: the first 2 numbers indicate the 3 significant digits of the resistor value. The third character is a letter which indicates the multiplier. In this way this SMD resistor marking scheme will not be confused with the 3 figure markings scheme as the letters will differentiate it, although the letter R can be used in both systems.

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To generate the system the E-96 resistor series has been taken and each value or significant figure set has been numbered sequentially. As there are only 96 values in the E-96 series, only two figures are needed to number each value, and as a result this is a smart way of reducing the number of characters required.

EIA SMD resistor marking

The details for the EIA SMT resistor marking scheme are tabulated below:Code Multiplier Z 0.001 Y or R 0.01 X or S 0.1 A 1 B or H 10 C 100 D 1 000 E 10 000 F 100 000 EIA SMT resistor marking scheme multipliers Code 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Sig Figs 100 102 105 107 110 113 115 118 121 124 127 130 133 137 140 143 147 150 154 158 162 165 169 174 Code Sig Figs Code Sig Figs Code 25 178 49 316 73 26 182 50 324 74 27 187 51 332 75 28 191 52 340 76 29 196 53 348 77 30 200 54 357 78 31 205 55 365 79 32 210 56 374 80 33 215 57 383 81 34 221 58 392 82 35 226 59 402 83 36 232 60 412 84 37 237 61 422 85 38 243 62 432 86 39 249 63 422 87 40 255 64 453 88 41 261 65 464 89 42 267 66 475 90 43 274 67 487 91 44 280 68 499 92 45 287 69 511 93 46 294 70 523 94 47 301 71 536 95 48 309 72 549 96 EIA SMT resistor marking scheme significant figures Sig Figs 562 576 590 604 619 634 649 665 681 698 715 732 750 768 787 806 825 845 866 887 909 931 953 976

For example a resistor that is marked 68X can be split into two elements. 68 refers to the significant figures 499, and X refers to a multiplier of 0.1. Therefore the value indicated is 499 x 0.1 = 49.9.37

MELF Resistor- details of the MELF resistor a surface mount device, SMD used to provide superior performance over SMT resistors in certain applications.Another form of SMD resistor that can be used is known as the MELF resistor - Metal Electrode Leadless Face. These resistors are not nearly as widely used as the standard SMD resistors, but in some instances they provide advantages and can be used.

MELF resistor basics & constructionThe MELF resistor is cylindrical in shape and have metallisation on both ends. Land pattern sizes for MELF resistors are the same as SMD chip resistors. The manufacture of MELF resistors is more complicated than the more standard thick film SMD resistors. A metal film is deposited onto a high dissipation ceramic former. To make the terminations tin plated terminating caps are fitted. The resistor is then adjusted to the correct value by producing a helical cut in the film. The body of the MELF resistor is finally protected by a lacquer coating.

MELF Resistor Outline

The MELF SMD resistors are used for a number of reasons:

MELF resistors provide a high level of reliability. A MELF resistor has a more predictable pulse handling capacity than other SMD resistors MELF resistors can be manufactured with tolerances as tight as 0.1% They can be manufactured with very low levels of temperature coefficient, sometimes as low as 5 ppm/C

Although the standard flat chip resistors are cheaper and much easier to handle during manufacture, the performance of MELF resistor can be an overriding factor making them a cost effective solution

MELF resistors in electronics manufactureWhile MELF resistors provide some significant and compelling technical advantages for use in certain applications, they are not always the easiest to handle in manufacture. The most common form of SMD resistor by far is the flat or cuboid format. These require one form of nozzle on a pick and place machine, however MELF resistors require a different one that allows the cylindrical shape of the MELF resistor to be accommodated. They also require a higher level of vacuum on the pick and place machine.

MELF SMD resistor markingsMELF SMD resistors are used on occasions in some designs. These resistors are cylindrical and do not lend themselves to characters being printed on the surface, although coloured bands are38

easy to use. As such the MELF SMD resistor marking code is effectively the same as that used for leaded resistors. There are three variations used:

Four band code: This system is used for resistors with tolerances up to 5% using the E24 resistor series. The first two bands provide the significant digits. The third band provides the multiplier and the fourth, normally wider, provides the tolerance.

MELF Resistor 4 band code

Sometimes an alternative colour banding system may be used where the bands are all grouped towards one end of the MELF resistor rather than having a wider band at the far end.

Alternative MELF Resistor 4 band code

Five band code: This system is used for higher tolerance resistors typically better than 1% that use the E48, E96 or E192 series values. The first three bands provide the significant figures. The fourth band gives the multiplier and the fifth band gives the tolerance.

MELF Resistor 5 band code

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Six band code: This code provides space for a temperature coefficient marking. As with the four band code the first three bands give the significant figures. Next is the tolerance band, and finally the fifth band provides the tolerance. .

MELF Resistor 6 band code

Tables showing the various colours and figures are given below:

Colour None Silver Gold Black Brown Red Orange Yellow Green Blue Violet Grey White

Digit

Colour Code Multiplier 10-2 10-1 100 101 102 103 104 105 106 107 108 109 20% 10% 5% 1% 2%

Tolerance

0 1 2 3 4 5 6 7 8 9

0.5% 0.25% 0.1%

Colour Code (6th Band) Brown Red Yellow Orange Blue Violet

Temperature Coefficient Marking TCR ppm/K 100 50 25 15 10 5

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Capacitor types- an overview, information or tutorial about the different capacitor types looking at different types of capacitor and their construction, specifications and parameters.Capacitor types includes: Capacitor types overview Uses and applications Electrolytic capacitor Ceramic capacitor Tantalum capacitor Polycarbonate capacitor Silver mica capacitor Glass dielectric capacitor Polystyrene capacitor Capacitor markings

Electronic capacitors are one of the most widely used forms of electronics components. However there are many different types of capacitor including electrolytic, ceramic, tantalum, plastic, sliver mica, and many more. Each capacitor type has its own advantages and disadvantages can be used in different applications. The choice of the correct capacitor type is of great importance because it can have a major impact on any circuit. The differences between the different types of capacitor can mean that the circuit may not work correctly if the correct type of capacitor is not used. Accordingly a summary of the different types of capacitor is given below, and further descriptions of a variety of capacitor types can be reached through the related articles menu on the left hand side of the page below the main menu.

Capacitor basicsthere are many different types of capacitor, but they all conform to the same basic physical laws. These determine the basic way the capacitor operates, its value, i.e. the amount of charge it will hold and hence its capacitance. In order to understand some of the reasons why various forms of capacitor are used, it is necessary to look at the basic theory behind capacitance.

Note on Capacitance:All capacitors conform to the same basic laws. Regardless of the dielectrics and many other enw developments made, the same laws apply. Click on the link for further information about Capacitance

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Capacitor types & dielectricsAlthough all capacitors work in essentially the same way, key differences in the construction of different capacitor types makes an enormous difference in their properties. The main element of the capacitor that gives rise to the different properties of the different types of capacitor is the dielectric - the material between the two plates. Its dielectric constant will alter the level of capacitance that can be achieved within a certain volume. Some types of capacitor may be polarised, i.e. they only tolerate voltages across them in one direction. Other capacitor types are non-polarised and can have voltages of either polarity across them. Typically the different types of capacitor are named after the type of dielectric they contain. This gives a good indication of the general properties they will exhibit and for what circuit functions they can be used.

Overview of different capacitor typesThere are many different types of capacitor that can be used - most of the major types are ou