chapter 7: production of printed circuit boards
DESCRIPTION
Chapter 7: Production of Printed Circuit Boards. Focus on automated production of printed circuits by Surface Mounting Technology (SMT) and Hole Mounting Technology (HMT). The course material was developed in INSIGTH II, a project sponsored by the Leonardo da Vinci program of the European Union. - PowerPoint PPT PresentationTRANSCRIPT
10.10.99 Electronic Pack….. Chapter 7
Production of PCBs. Slide 1
Chapter 7:Production of Printed Circuit Boards
• Focus on automated production of printed circuits by Surface Mounting Technology (SMT) and Hole Mounting Technology (HMT)
The course material was developed in INSIGTH II, a project sponsored by the Leonardo da Vinci program of the European Union
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Production of PCBs. Slide 2
Hole Mounting• Axial components:
Sequencing and mounting• Radial components:
Mounting• DIP components:
Mounting• Odd components:
Robot or hand mounting
Axial Components
Sequencing
Lead forming
Insertion
Cut-and-clinch
Wave soldering
DIP
Insertion
Lead forming
Cut-and-clinch
Radial Components
Insertion
Hand mounting ofspecial components
Electrical test
To customer
Faulty boards
Visual inspection
Cleaning
Robot mounting/hand mountingof odd compomnents
Repair
Fig. 7.1:The process for production of hole mounted PCBs
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Production of PCBs. Slide 3
Hole Mounting, continued
Fig. 7.2 a): Schematic example of the most efficient sequence of mounting the components of a particular PCB.
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Production of PCBs. Slide 4
Hole Mounting, continued
Fig. 7.2 b): The principle of sequencing.
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Production of PCBs. Slide 5
Hole Mounting, continued
Fig. 7.3: Sequencing machine.
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Production of PCBs. Slide 6
Hole Mounting, continued
Fig. 7.4: Axial inserter with two mounting heads.
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Production of PCBs. Slide 7
Hole Mounting, continued
Fig. 7.5: Simplified process in the axial inserter:
1): Cutting the components from the tape
2): Lead bending
3) - 4): Insertion
5): Cut and clinch
6): Return to starting position.
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Production of PCBs. Slide 8
Hole Mounting, continued
Fig. 7.6: DIP inserter.
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Production of PCBs. Slide 9
Hole Mounting, continued
Fig. 7.7: Manual mounting board with light guide.
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Production of PCBs. Slide 10
Hole Mounting, continued
Fig. 7.8:Wave soldering machine.
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Production of PCBs. Slide 11
Wave Soldering, principle
•Fluxing
•Pre-heating
•Soldering
•(Cleaning)
Fig. 7.9:
a): Principle of foam fluxer.
b): Control system for density and level of the flux bath.
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Production of PCBs. Slide 12
Wave Soldering principle, continued
Fig. 7.10: a): Principle of wave soldering.
b): The real shape of the wave.
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Production of PCBs. Slide 13
Wave Soldering, continued
Fig. 7.11:
a): Industrial in line cleaning machine.
b): The principle of ultrasound and vapour cleaning.
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Production of PCBs. Slide 14
ElectroStatic Discharge (ESD) Precautions
Fig. 7.12: An ESD protected working space. The resistors R normally are 100 Kohm - 1 Mohm.
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Production of PCBs. Slide 15
Surface Mounting• Soldering by wave solder process or by reflow process Fig. 7.13: Application of adhesive for SMD mounting by:
a): Screen printing
b): Dispensing
c): Pin transfer
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Production of PCBs. Slide 16
Surface Mounting: Wave Solder Process
• Apply adhesive by dispenser, screen printing or pin transfer• Cure by heat or UV• Turn board•Wave solder–Double-wave soldering machine common for SMT–Not all SMD components suitable for wave soldering
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Production of PCBs. Slide 17
Surface Mounting, continued
Fig. 7.14: a): Shadowing in SMD wave soldering.
b): Solder bridging on fine pitch package.
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Production of PCBs. Slide 18
Surface Mounting, continued
Fig. 7.15: Double wave for SMD soldering. The first is a turbulent wave that wets, followed by a gentle “lambda wave” that removes superfluous solder.
Lambda wave
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Production of PCBs. Slide 19
Surface Mounting, continued
Fig. 7.16: Temperature profile during wave soldering in a double wave machine.
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Production of PCBs. Slide 20
Reflow Solder Process
• Print solder paste
•Mount components
• Dry solder paste
• Solder by heating to melting of paste
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Production of PCBs. Slide 21
Solder Paste
• Consists of: –Solder particles (~ 80 % by weight)–Flux–Solvents and additives to give good printing properties (rheology)
• Typical mesh count in screen: 80 per inch
• Area ratio: Ao = a2 /(a+b)2
• Paste volume deposited: V = Vo • Ao • t
• "Solder ball test" for quality of solder paste and solder process
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Production of PCBs. Slide 22
Solder Paste, continued
Fig. 7.17: Microphotograph of Multicore solder paste type Sn 62 RMA B 3. The designation means 62 % by weight of Sn, 35.7% Pb, 2%, Ag, 0.3% Sb, RMA flux, 75 µm average particle size, 85% metal content, viscosity 400 000 - 600 000 centipoise.
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Production of PCBs. Slide 23
Solder Paste, continued
Fig. 7.18: Test of solder paste: The paste is printed through a circular opening with a diameter of 5 mm, in a 200 µm thick stencil. After reflow, the paste should melt into one body, without any particles spreading out.
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Production of PCBs. Slide 24
Screen Printing
• Woven screen (stainless steel or polyester) with organic photosensitive layer, which is patterned with holes (mask).• Metal stencil with etched or drilled openings.• Polyester stencil with punched or drilled
openings.• Definition and accuracy depends on type, mesh
count, thickness, tension, squeegee, speed, etc. Screen Printing is a complex craft!
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Production of PCBs. Slide 25
Screen Printing, continued
• Off-contact for screen printing, contact for stencil. Two-step stencil for best definition.
• The most advanced printers are fully automatic with vision system for alignment.
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Production of PCBs. Slide 26
Surface Mounting, continued
Fig. 7.19: Detail of printing stencil (left) and printing screen with fine line printing pattern.
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Production of PCBs. Slide 27
Surface Mounting, continued
Fig. 7.20: Detail of printing stencil with fine pitch printing pattern: Cross section of a stencil etched from both sides, with an acceptable, small amount of offset (40 x magnification).
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Production of PCBs. Slide 28
Surface Mounting, continued
Fig. 7.21: Two steps printing stencil.
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Production of PCBs. Slide 29
Surface Mounting, continued
Fig. 7.22: Printing through 0.3 mm diameter holes with Mylar stencil. To obtain the correct amount of solder paste two or three small holes may be used for each solder land.
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Production of PCBs. Slide 30
Surface Mounting, continued
Fig 7.23 a): Screen printer.
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Production of PCBs. Slide 31
Surface Mounting, continued
Fig. 7.23 b): The squeegee (DEK).
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Production of PCBs. Slide 32
IR Soldering
Fig. 7.24 a): IR furnace. Schematically with low temperature "area emitter".
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Production of PCBs. Slide 33
IR Soldering, continued
Fig. 7.24 b): Industrial IR furnace.
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Production of PCBs. Slide 34
Infrared Soldering
• Planck´s law:
W/A = k1/5 {exp(k2/T)-1}Shown on graph, where:W/A = emitted energy pr. second per m2
area per micrometer of radiation spectrum
k1 = 2 hc2 h = Planck´s constant
k2 = hc/k k = Boltzmann’s constantWavelength of max. radiation:
max = k3/T• Total radiated energy (Stefan
Boltzmann´s law): W/A = T4
= Stefan Boltzmann’s constant = emissivity (between 0 and 1)
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Production of PCBs. Slide 35
IR Soldering, continued
Fig. 7.25: Typical temperature profile for an IR furnace.
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Production of PCBs. Slide 36
Vapor Phase Soldering
• Newton´s law :
Q/t = h•A (Tf -Ts)
Where:• Q/t = energy transferred pr. sec. (W)
• A = total area
• h = heat transfer coefficient
• Tf = vapour temperature (boiling point)
• Ts = PCB temperature
• PCB temperature approaches Tf asymptotically:
(Ts -To) = [Tf -To]•[1 -exp (-t/to)]
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Production of PCBs. Slide 37
Vapour Phase Soldering
Fig. 7.26 a): Principle of in-line vapour phase soldering machine.
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Production of PCBs. Slide 38
Vapour Phase Soldering, continued
Fig. 7.26 b): Industrial in-line vapour phase soldering machine.
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Production of PCBs. Slide 39
Vapour Phase Soldering, continued
Fig. 7.27: Heat transfer coefficient for air and fluorocarbons. Boiling fluorocarbons, at the bottom, give 200 - 400 times more efficient heat transfer than
air.
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Production of PCBs. Slide 40
Vapour Phase Soldering, continued
Fig. 7.28: Temperature profile through in-line vapour phase soldering machine.
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Production of PCBs. Slide 41
Vapour Phase Soldering, continued
Fig. 7.29: Chemical composition of fluoro carbons for vapour phase soldering. Top: The liquid FC-5311 (3M): C14 F24 is derived from C14 H10. Bottom: The liquid LS 230 (Galden).
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Production of PCBs. Slide 42
Vapour Phase Soldering, continued
Table 7.1: Physical properties of some primary vapours for reflow soldering.
Property Units R113 FC-70 FC-5311 LS230Boiling point or range °C 47,6 215 215 230±5Molecular weight - 187 821 624 ~650Pour point °C -25 -20 -80Density of liquid at 25°C g cm3 1,57 1,93 2,03 1,82
Density of saturated vapour at BP mg cm3 7,38 20,3 15,6 19,5
Viscosity of liquid at 25°C cP 0,7 27 16 8Surface tension of liquid at 25°C mN/m 19 18 19 18Specific heat of liquid at 25°C J/gK 0,95 1,05 1,07 1,00Thermal conductivity at 25°C mW/mK 74 70 53 70Electrical resistivity Ohm cm 2 1015 >1015 1015
Heat of vaporisation, at BP J/g 67 68 63
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Production of PCBs. Slide 43
Other Soldering Methods
• Hot air soldering (Most used today)
• Impulse (hot bar-, thermode-) soldering
• Hot plate / hot band soldering (thick film hybrid)
• Laser soldering (too time-consuming single point soldering)
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Production of PCBs. Slide 44
Thermode Soldering
Fig. 7.31: Two types of thermodes for thermode soldering.
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Production of PCBs. Slide 45
Thermode Soldering, continued
Fig. 7.32: Temperature profile for thermode soldering.
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Production of PCBs. Slide 46
Component Placement
–Automatic, dedicated pick-and-place machines–Manual placement (prototypes, repair)–Semi-manual (light guided table, etc.)• Programmable robot• Elements of Pick-and-Place Machine
– Board magazine/feeder system– Mounting head(s) (with interchangable grip tools)– Programming/control unit– Component "storage" and feeder– Vision system (correct placement and control afterwards)
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Production of PCBs. Slide 47
Component Mounting
Fig. 7.33: SMD pick-and-place machine (Siemens).
The mounting head may also include an electronic vision system for very accurate placement of fine pitch components.
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Production of PCBs. Slide 48
Component Mounting, continued
Fig. 7.34: a): Mechanical gripper in a pick-and place machine. b): Detail of the component tape when a component is in position for picking.
c): Vibration feeder.
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Production of PCBs. Slide 49
Component Mounting, continued
Fig. 7.35: Fuji CP-II pick-and-place machine. The machine has magazine for over 100 types of small components, nominal speed up to 15 000 components per hour, placement accuracy 0.10 mm. It has a rotating head with 12 positions, bottom figure, and two alternative tools at each position. There are components at all 12 positions at any time, with a separate operation being performed. A CCD camera shows the accurate position and orientation on a CRT screen (Fuji).
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Production of PCBs. Slide 50
Component Mounting, continued
Fig. 7.36: Philips large hardware controlled pick-and-place machine.
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Production of PCBs. Slide 51
Solder faults
Fig. 7.38: Small SMDs standing on edge due to the "Manhattan-" or ”tombstone-" effect.
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Production of PCBs. Slide 52
Robot System for Placement
• Advantages:–Flexibility: Can handle most odd component types and boards, in low and high volumes–Uniform quality–High placement accuracy (~ 0.02 mm)–Non-manned operation (over night)–Can work in hostile environments–Tests and controls can be included in placement operation by special sensors on robot
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Production of PCBs. Slide 53
Robot Mounting
Fig. 7.39: Example of a programmable placement robot for electronics: The SCARA robot.
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Production of PCBs. Slide 54
Robot System for Placement
•Must be carefully considered:
• Cost, including the external equipment, fixtures, transport system
• Lower capacity than Pick-and-Place
• Requires careful planning, and often much dedicated surrounding equipment
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Production of PCBs. Slide 55
Robot Mounting, continued
Fig. 7.40: The main components of a robot system.
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Production of PCBs. Slide 56
Robot System Components
•Manipulator–Learning unit–Control unit
• Types of Manipulator Coordinate Systems–Cartesian–Cylindrical (including "Scara")–Spherical–"Human-like"
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Production of PCBs. Slide 57
Robot Mounting, continued
Fig. 7.41: Types of robot arms: a): Cartesian motion. b): Cylindrical. c): Spherical. d): "Human like". The SCARA robot is a special version of the cylindrical type.
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Production of PCBs. Slide 58
Robot System Components, continued
• Programming–"Lead-and-learn”–"Jog-and-learn”–"Synthetic programming"
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Production of PCBs. Slide 59
Robot Mounting, continued
Fig. 7.42: Multi gripper head.
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Production of PCBs. Slide 60
Robot Uses in Electronics
• Production–Component placement–Production of parts (coils, cables,....–Board feeding–Handling of boards, components in testing–Automatic trimming in test–Parts assembly for board, rack, chassis, etc.–Screw and glue operation–Soldering, welding• etc.
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Production of PCBs. Slide 61
Robot Mounting, continued
Fig. 7.43: Robot cell for electronic component placement (Adept)
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Production of PCBs. Slide 62
Types of Boards: SMD and Mixed Assembly
• SMD side A
• SMD side A and hole components side B
• SMD side A and B
• SMD both sides, hole components side B
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Production of PCBs. Slide 63
Process Sequences
Fig. 7.44 a -d): Process sequences for boards with different types of components on the two sides.
The steps marked "For all processes" on figure a) are not repeated on the other figures.
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Production of PCBs. Slide 64
Process Sequences
Fig. 7.44 a -d): Process sequences for boards with different types of components on the two sides. The steps marked "For all processes" on figure a) are not repeated on this figure.
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Production of PCBs. Slide 65
Process Sequences
Fig. 7.44 a -d): Process sequences for boards with different types of components on the two sides. The steps marked "For all processes" on figure a) are not repeated on this figure.
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Production of PCBs. Slide 66
Process Sequences
Fig. 7.44 a -d): Process sequences for boards with different types of components on the two sides. The steps marked "For all processes" on figure a) are not repeated on this figure.
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Production of PCBs. Slide 67
Board Testing
• Functional test
• "In-circuit" test
• NB: Good designs use one-sided testing–Test jigs are expensive–Two-sided jigs very compicated
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Production of PCBs. Slide 68
Testing of PCBs
Fig. 7.45: Two methods for single sided test of a board with components on both sides.
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Production of PCBs. Slide 69
Testing of PCBs
Fig. 7.46: Bed-of-nails test fixture.
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Production of PCBs. Slide 70
Testing of PCBsFig. 7.47:
a) Detail of single sided test fixture.
b) Double sided fixture.
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Production of PCBs. Slide 71
Testing of PCBs
Fig. 7.48: Two types of test pins.
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Production of PCBs. Slide 72
Testing of PCBs
Fig. 7.49: Unacceptable testing. The test point should be on the Cu foil on the board, not on the component lead.
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Production of PCBs. Slide 73
End of Chapter 7: Production of Printed Circuit Boards
•Important issues:– When manufacturing PCBs:
• Understand the basic manufacturing steps:– Sequencing and mounting of Hole Mounted Components– Wave soldering: Basics. Why we want to avoid (yield and reliability problems) When to
use it for Surface Mount Components (Mixed boards)– Reflow soldering process: Basics. Solder paste. Silk screen and stencil printing. Reflow
heating with hot air, IR, vapor phase, etc.• Component placement:
– Automatic, manual, semi-automatic, and using robots• Types of SMD boards manufactured: Understand and remember the basic flow
diagrams:– SMD side A– SMD side A and hole components side B– SMD side A and B– SMD both sides, hole components side B
• Board testing:– Functional test– In-circuit test
•Questions and discussions?