elec 6740 electronics manufacturing chapter 7: design for ...jevans/elec6740/chapter7.pdf ·...

ELEC 6740 Electronics ELEC 6740 Electronics ManufacturingManufacturing

Chapter 7: Design for Chapter 7: Design for Manufacturability, Testing & Manufacturability, Testing &

RepairRepairR. Wayne JohnsonR. Wayne JohnsonAuburn UniversityAuburn University

[email protected][email protected]

OutlineOutline!! DFM Organizational StructureDFM Organizational Structure!! General Design ConsiderationsGeneral Design Considerations!! Component Selection Considerations for ManufacturabilityComponent Selection Considerations for Manufacturability!! Soldering ConsiderationsSoldering Considerations!! Interpackage Interpackage Spacing ConsiderationsSpacing Considerations!! Via Hole ConsiderationsVia Hole Considerations!! Soldermask Soldermask ConsiderationsConsiderations!! Repairability Repairability ConsiderationsConsiderations!! Cleanliness ConsiderationsCleanliness Considerations!! Testability ConsiderationsTestability Considerations

DFM Organizational StructureDFM Organizational Structure

!! Sequential design vs. concurrent engineeringSequential design vs. concurrent engineering

Physical layout

Manufacturing

Test

Design

Physical layout

Logic design

Manufacturing

Test

Process engineers

Design

Reliabilityenginesrs

Productengineers

General Design ConsiderationsGeneral Design Considerations!! Standard form factor (board size, shape, tooling Standard form factor (board size, shape, tooling

holes)holes)!! Odd shapes can require special fixtures, etc.Odd shapes can require special fixtures, etc.!! Standard assembly panel size vs. board sizeStandard assembly panel size vs. board size

!!Optimization of boards per assembly panelOptimization of boards per assembly panel!!Optimization of assembly panels per PWB panelOptimization of assembly panels per PWB panel!!L/W L/W << 1.51.5

Scoring of PanelsScoring of Panels

Fiducials Fiducials or Alignment Marksor Alignment Marks

FiducialsFiducials or Alignment Marksor Alignment Marks

Component SelectionComponent Selection!! Use surface mount components that solve real estate Use surface mount components that solve real estate

constraints or reduce the number of manufacturing constraints or reduce the number of manufacturing steps and bear no cost premium.steps and bear no cost premium.

!! All surface mount components should be All surface mount components should be autoplaceableautoplaceable!! Tantalum caps with welded studsTantalum caps with welded studs!! ConnectorsConnectors!! Heat sinksHeat sinks!! SocketsSockets

Component SelectionComponent Selection!! Components terminations with solder plating are Components terminations with solder plating are

better than solder dippedbetter than solder dipped!! Select only components that can withstand the Select only components that can withstand the reflow reflow

temperaturestemperatures!! Use 1206 and 0805 components when possible, 0603, Use 1206 and 0805 components when possible, 0603,

0402 & 0201 components are harder to place0402 & 0201 components are harder to place!! Use X7R capacitors rather than Z5U when using wave Use X7R capacitors rather than Z5U when using wave

soldering to avoid crackingsoldering to avoid cracking

Component SelectionComponent Selection!! Do not wave solder capacitors larger than 1812 to Do not wave solder capacitors larger than 1812 to

avoid crackingavoid cracking!! Do not use ceramic parts larger than 0.250” on FRDo not use ceramic parts larger than 0.250” on FR--4 to 4 to

avoid CTE mismatch and potential reliability concernsavoid CTE mismatch and potential reliability concerns!! Use marked components if no cost premiumUse marked components if no cost premium!! For secondary side attachment in Type II or Type III For secondary side attachment in Type II or Type III

SMT use low profile SOT devices instead of high SMT use low profile SOT devices instead of high profile profile SOTsSOTs. Low profile are easier for adhesive . Low profile are easier for adhesive attachment, but high profile are easier to cleanattachment, but high profile are easier to clean

Component SelectionComponent Selection!! Avoid using MELF packages unless very cost Avoid using MELF packages unless very cost

driven (MELF package cheaper)driven (MELF package cheaper)!! Use Nickel barrier terminated capacitors and Use Nickel barrier terminated capacitors and

resistors to prevent leaching of termination into resistors to prevent leaching of termination into molten soldermolten solder

!! Avoid surface mount connectors & sockets Avoid surface mount connectors & sockets without over riding reasons without over riding reasons

Component SelectionComponent Selection!! Use qualified partsUse qualified parts!! Minimize the different types of componentsMinimize the different types of components

Soldering ConsiderationsSoldering Considerations

Soldering ConsiderationsSoldering Considerations!! OptionsOptions

!! Double sided Double sided reflow reflow + hand soldering+ hand soldering!! Reflow Reflow side 1 & wave solder side 2side 1 & wave solder side 2

!! May degrade reliability of side 2 SMT components during wave solMay degrade reliability of side 2 SMT components during wave solderder!! Flux can creep into SOIC and PLCC packagesFlux can creep into SOIC and PLCC packages

!! Double sided Double sided reflow reflow with DIP using butt jointswith DIP using butt joints!! Reliability of butt jointReliability of butt joint!! Not permitted for military and high reliability applicationsNot permitted for military and high reliability applications

!! Double sided Double sided reflow reflow with ‘pastewith ‘paste--inin--hole’hole’!! ReflowReflow side 1 & wave solder side 2 with shieldside 1 & wave solder side 2 with shield

Wave Solder ShieldWave Solder Shield

Solder ShieldSolder Shield!! Stainless Steel or TitaniumStainless Steel or Titanium

!! Titanium expensive & hard to machine but holds Titanium expensive & hard to machine but holds shape better for repeated useshape better for repeated use

!! Aluminum or copper shield contaminates solder Aluminum or copper shield contaminates solder potpot

!! High temperature plastics and composites are High temperature plastics and composites are also usedalso used

Savings by Converting SMTSavings by Converting SMT

No Savings by ConvertingNo Savings by Converting

Other Soldering ConsiderationsOther Soldering Considerations!! Place larger components on top (2Place larger components on top (2ndnd) ) reflow reflow side side

when using double sided when using double sided reflowreflow!! Wave solder is not cheaper than Wave solder is not cheaper than reflow reflow so wave so wave

solder can be considered if only SMT passives solder can be considered if only SMT passives on 1 sideon 1 side

!! Wave solder fills plated through holes allowing Wave solder fills plated through holes allowing vacuum to hold board down for automated testvacuum to hold board down for automated test

Component OrientationComponent Orientation

InterpackageInterpackage SpacingSpacing!! Use land patterns described in Chapter 6Use land patterns described in Chapter 6!! For mixed assemblies, For mixed assemblies, autoinsert autoinsert equipment equipment

requires about 0.100” clearance for through requires about 0.100” clearance for through hole deviceshole devices

!! About 0.075 to 0.085” clearance is needed for About 0.075 to 0.085” clearance is needed for automated and hand probe testingautomated and hand probe testing

!! The The interpackage interpackage spacing must allow for test spacing must allow for test probe at ATE. probe at ATE.

InterpackageInterpackage SpacingSpacing!! Automated cleaning with adequate pressure nozzles Automated cleaning with adequate pressure nozzles

(>30psi)(>30psi)!! Component shift during Component shift during reflow reflow soldering and soldering and

placement may be up to 25% of the pad width for placement may be up to 25% of the pad width for military and 50% for commercial applicationsmilitary and 50% for commercial applications

!! Solder joint melting of adjacent components is allowed Solder joint melting of adjacent components is allowed a total of 4 times (2 for assembly and 2 for rework)a total of 4 times (2 for assembly and 2 for rework)

!! Visual inspection ( board tilting)Visual inspection ( board tilting)

InterpackageInterpackage SpacingSpacing

Via HolesVia Holes!! Number decreased with switch to SMT, but did not go Number decreased with switch to SMT, but did not go

awayaway!! SMT SMT vias vias are smaller than Through Holes for are smaller than Through Holes for

componentscomponents!! Vias Vias are used for test probe contactare used for test probe contact!! Vias Vias must be filled (solder or solder mask) for vacuum must be filled (solder or solder mask) for vacuum

used in bedused in bed--ofof--nails ATE.nails ATE.!! Vias Vias should not be used in SMT padsshould not be used in SMT pads!! Via hole location a concern in Via hole location a concern in reflow reflow due to limited due to limited

solder volume, but not in wave soldersolder volume, but not in wave solder

Via HolesVia Holes

Tented Tented ViasVias

TentedTented ViasVias!! Dry filmDry film

!! Should not be used between pads of chip Should not be used between pads of chip componentscomponents

!! 0.0030.003--0.004” thick can lead to 0.004” thick can lead to tombstoningtombstoning!! Thinner dry film can be usedThinner dry film can be used!! Allows tentingAllows tenting

TentedTented ViasVias!! Wet filmWet film

!! Thinner, allows traces to be run between pads of Thinner, allows traces to be run between pads of passive componentspassive components

!! Vias Vias must be plugged before tentingmust be plugged before tenting!! Increases adhesive bond strength, and minimizes Increases adhesive bond strength, and minimizes

voids during adhesive curevoids during adhesive cure

Solder MaskSolder Mask!! Solder mask should not be used over Solder mask should not be used over SnSn//PbPb

!!Solder melts during Solder melts during reflow reflow causing solder mask to crack causing solder mask to crack entrapping flux and moistureentrapping flux and moisture

!! SMOBC SMOBC –– solder mask over bare coppersolder mask over bare copper

RepairabilityRepairability!! Hand repairHand repair!! Automated systems with hot airAutomated systems with hot air!! Maximum of 2 rework cycles to limit Maximum of 2 rework cycles to limit SnSn--Cu Cu

intermetallic intermetallic formationformation

RepairabilityRepairability

TestabilityTestability

TestingTesting!! In through hole technology, all leads are In through hole technology, all leads are

accessible on the bottom side of the boardaccessible on the bottom side of the board!! With SMT, test points must be provided for ‘inWith SMT, test points must be provided for ‘in--

circuit’ testcircuit’ test!! Test point take up spaceTest point take up space!! No test point, no inNo test point, no in--circuit testcircuit test

!! Functional vs. InFunctional vs. In--circuitcircuit

ATEATE!! Use 1 test point (TP) for ground and 1 TP for power Use 1 test point (TP) for ground and 1 TP for power

for every 10 ICs to reduce risk of ringingfor every 10 ICs to reduce risk of ringing!! Connect all unused pins to ground or power via a Connect all unused pins to ground or power via a

resistor to improve quality of testresistor to improve quality of test!! Whenever possible, avoid double sided test probe Whenever possible, avoid double sided test probe

approach to reduce approach to reduce fixturing fixturing and costand cost!! One TP is needed for every test node unless 100% One TP is needed for every test node unless 100%

capability is needed for individual componentscapability is needed for individual components

ATEATE!! Test point Test point spacings spacings should be 0.100” whenever should be 0.100” whenever

possible. Probes for smaller possible. Probes for smaller spacings spacings are fragile are fragile and prone to damageand prone to damage

!! For smaller For smaller TPs TPs (under 30 mils (under 30 mils diadia.) deposit .) deposit solder paste on the solder paste on the TPs TPs to form bumps for ease to form bumps for ease of probing with serrated test probesof probing with serrated test probes

!! Flux residue can interfere with probe contactFlux residue can interfere with probe contact

ATEATE

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