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What is Just Enough Test?
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TopicsBoard Test TrendsDifferent types of Test
Inspection/StructuralAdvantages/Disadvantages
Big Iron vs Low-CostDistributed TestFalse FailuresSampling
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Fault Spectrum and Issues
Solder Paste Height
Solder Missing
Solder BridgeIC Pin Lifted
IC Pin ShortedTrace Short
Trace Open
Not Enough Solder
Board MarkingsReversed Part
Bad Part
Missing Parallel Cap
Part Placement
Part Tolerance
On Power Testing
Wrong Part
Flash Programming
ECO Version
Transistor testing
Boundary Scan
Memory Programming
I2C Programming
GUID Programming
Programming Verification
Test Time
Test Costs
Schedule AOI
X-Ray
MDA
ICT
Flying Probe Functional Test
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Board Trends
Higher Speed PartsMore pins per deviceShort life cyclesHigher Reliability Parts
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Test TrendsTest is a commodity
Issues are mature – little difference between vendorsHigher density boards -lack of test probe access Verify assembly process not parts
Screened parts don’t fail (normally)Programmable devices (where to program)Designers using standard Test interfaces
Boundary ScanTree-TestingSPI, I2C, ISP (serial interface protocols)
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Parts Fail Less
Better Controlled Manufacturing ProcessHigher YieldsLess need for testHigher Reliability
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Why Test?
Verification of productBusiness ReputationLow Volumes – less control of processPay Me Now or Pay Me Later
Basic Rule of 10
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Test Considerations
TimeVolumeCostQualityThe earlier a fault is found in manufacturing process the cheaper it is to fix (Rule of 10)
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Modern SMT line – Quality & Efficiency
AOI MDA/ICT•Defective device•Wrong device•Power-Up•Programming
•Shorts•Opens•Lifted lead•Polarity
•Tombstone•Billboard•Skid/Skew•Marking•Insufficient/excessive solder
Mfg Issues
• Repair after solder is difficult and costly
• Not enough board real estate for ICT test points
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Inspection Testing
Solder Paste InspectionAutomated Optical InspectionX-Ray Inspection
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SPI Advantages
No fixture costIn-LineNo componentsBeginning of SMT process
Fast program development (less than 1 hr)
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SPI Defect Coverage
Solder Defects
• Solder bridge
• Insufficient solder
• Excessive solder
•Volume
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SPI Disadvantages
Requires Known Good Board (KGB)Unpopulated board100% success does not guarantee 0% faults
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AOI Advantages
No fixture costIn-Line100% Visual coverage vs humanEarly in SMT process
Fast program development (3 -7 hours)
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AOI Defect Coverage
Component Defects Solder Joint Defects Surface Defects
• Missing component
• Skid/Skew component
• Extra component
• Tomb-stoned component
• Bill-boarded component
• Alternative/Marking
• Lifted/bent lead
• Broken lead
• Solder bridge
• Insufficient solder
• Excessive solder
• Lifted/bent lead
• Broken lead
• Solder ball
• Through-hole pin
• Gold-finger contamination
• Scratch
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AOI Disadvantages
Higher False Failure RatesRequires Known Good Board (KGB)Requires 10-30 board to adjust programOnly Visual (shorts under part not found)BGA pin shorts/opens
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X-Ray Advantages
AOI advantages minus markings and polarity
Non-visible assembly faults BGA pin shorts and opensInner layer shorts and opens
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X-Ray Coverage
AOI coverageBGA pin coverageInterlayer assembly faults
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X-Ray Disadvantages
False Failures More Expensive than “Big Iron” ICT testerRequires KGBProgram development 3-10 days
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Structural Testing
Flying ProbeManufacturing Defect AnalyzerBoundary Scan (virtual connections)X-Ray Inspection
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Flying Probe Advantages
No fixture Physical verification• Basic shorts and opens• Basic R/L/C testing
1 day program development
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Flying Probe Coverage
Shorts & OpensR/L/C testing
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Flying Probe Disadvantages
Long test times up to 30 min Limited DiagnosticsLower quality measurementsPossible to miss some shorts
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MDA AdvantagesLow CostPhysical testing of board• Shorts• Analog• Open Pins (Vectorless & Clamping Diode)
Short test time1-2 Days to programBetter diagnosticsBetter measurements - guarding
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MDA Coverage
Shorts & Opens (Pins and traces)Passive Component Testing• R/L/C , diodes, transistors, fets
Component ValuesVector-less testing (digital presence)
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Open IC Pin Detection
Vector-less Testing
Clamping Diode Testing
Both offer low cost analog
measurement to detect an open IC pin
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MDA Disadvantages
Requires a fixtureUsually requires mid-high volume to justify fixture costs
Requires nodal access1-2 Days to programRequires 20-50 boards for stable program
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ICT Advantages
Most Bang for the Buck Highest Quality TestingMDA test advantagesPowered up testingShort test time (10-60 sec)Digital component testingBest component level diagnostics
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ICT Coverage
MDA coverage Powered up testingDevice programmingBoundary Scan and other industry standard interface testing (I2C, SPI)
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Easy to Use On Board Programming Software Modules
EEPROM Programming (Mac Address)
ISP Programming
SPI Programming
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ICT Disadvantages
Requires a fixtureRequires mid-high volume to justify fixture and program costs
Requires nodal access1-2 weeks to programMore device data requiredRequires 20-50 boards for stable program
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Fault Spectrum vs TesterFaultSolder Height X XSolder Quality X X XBd Markings XComp Placement XIC Pin Shorts X X X X XIC Pin Opens X X X X XTrace Shorts X X X XTrace Opens X X X XMissing Part X X X X XBad Part X X XPart Tolerance X X XTransistors X XPower UP X XProgramming X XBoundary Scan X XECO Version X XAt Speed Verfication X
SPI AOI X-Ray Flying Probe MDA ICT Functional100-250K 100-250K 300K-600K 100-200K 20-50K 100K-500K low to high CostLow-High Low-High Low-Mid Low Low-Mid High Low-High VolumeMinute Minute Minutes > 30 Minutes Minute< Minute Minutes-Hours Test Timehours hours days day day week days-weeks* DevelopmentNo No No No Yes Yes Box/Interface Fixture
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Traditional Test Choice
Big Iron ICT TesterFastest and largest pin count testerMost bang for the buckAlso costs the most bucksNot cost-effective with smaller volumes
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Low Cost Tester Options
MDAMDA with 3rd party (Boundary Scan)Combinational (MDA/ICT/Functional)Stand-alone Boundary ScanUsed Testers
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Pin Card Cost700 net board with 200 pin IC
$70,000$10,0008967328:2128Big Iron
$38,500$3,50070411641:164Combo
$12,000$2,00076861281:1128MDA
Pin Card Cost
Bd CostPins req
Bds req
Real Pins/bd
Mux Ratio
Pins/bdTester
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Pin Card Costs700 net board with 300 pin IC
$100,000$10,000128010328:2128Big Iron
$38,500$3,50070411641:164Combo
$12,000$2,00076861281:1128MDA
Pin Card Cost
Bd CostPins req
Bds req
Real Pins/bd
Mux Ratio
Pins/bdTester
* 1 drive/1 sense
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Software Costs
>$60KAwareMagicShared Wiring
Basic Scan/Scan Pathfinder/ Silicon Nails
Flash 70Opens Xpress/Test Jet
Big Iron
$10KincincFlash libTest JetCombo
$45KNAOption$15K ?
Option$10K ??
Test Jet$10K
MDA
TotalsOtherBScanFlashVector-less
Tester
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Tester Costs700 nets with 300 pin IC
Industry Standard
$260K>$60K$100K$100KBig Iron
Integrated Solutions
$99K>$10K$39K$50KCombo
Multi-vendor$77K$45K$12K$20KMDA
NotesTotalSoftwarePinsBaseTester
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Boundary Scan Issue
More acceptance than everBut most customers don’t implementPC motherboards don’t (Nand Tree)Cell phones have no test padsStill parts without compliant BSDL
Micro-controllersAutomotive industry likes CAN
Its has many versions
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Big Iron vs Low Cost
Big Iron is still the Tried and True standardDo you need 10MHz?Do you need timing sets?
Low Cost is worth investigating if new linesStill need standard driver/sensorsWhat about multiple vendor support
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Distributed TestUse strengths of different types of testAOI for presence/bypass & reverse capsPhysical test for shorts and valuesDigital test for program/verificationNo software talks to all vendors (assy/test)Testers need to be able to turn on/off any test
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Manufacturing Test
Once process is good little goes wrongWhy Test all partsMaybe test changes in processExample: Replacing a reel of partsWhy Test all parts on the reel
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Test SamplingTesters will ability to turn on/off testsRequired for distributed testDrawbacks
QualityCustomer ExpectationsWho takes the blame for a test escape
Could a report even be generated to explain what happened. If its dynamic the conditions changed by the time the fault is found
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Functional Failures
How many bad parts are found?Are the failures structural?Is any particular test better at catching these failures and why didn’t it?Did test introduce any failures?
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False FailuresWhat do False Failures cost?Rules usually state you must replaceAre the parts really bad?Reasons for False Failures
Marginally testFixtures/ProbesAllow retest and fixture recycling
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What will you do?
Same as usualKeep buying “Big Iron”Investigate Low Cost solutionsExplore Distributed Test
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Conclusion
Test is mature and is a commodityBoundary Scan only solutions are not viable if there aren’t any boundary scan partsTest can’t be more flexible with current mind sets –not necessarily a bad thingDistributed Test has a long way to go
More work to be done – mainly software and controlLow Cost solutions are viable and available
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