Thoughts on Test Strategies for Medium to High Complexity ... · Thoughts on Test Strategies for...

Test Strategies x6000

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Thoughts on

Test Strategies

for Medium to High

Complexity boards

April 2007


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Do you select the same test strategy?

11 components26 joints

1,689 components10,239 joints

Board A

Board B

Board B magnified


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Complexity Index

Complexity Index = [( #C + #J ) / 100] * D * M * S

#C = Number components

#J = Number jointsS = Double sided = 1, Single sided = 1/2M = High Mix = 1, Low mix = 1/2

D = Joint density = Joints per square inch / 100or Joints per square cm / 15.5

Low complexity Medium complexity High complexity

< 50 >= 50 and < 125 >= 125

6 inch

2 inchSide A, 800 joints

Side B, 600jointsD = [(800+600)/(2*6)] / 100 = 1.17

Example


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Many test strategy options....

AOI solder paste

AXI pre-wave

inspection

Manual Visual

Inspection

AOI post-reflow

AOI pre-reflow

Functional test

In-circuit test

AXI post-wave

inspection

.. which combination is

optimal?


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Other considerations

bDouble sided boards

bHigh reliability concerns – few warranty defects

bHigh quality requirements – few field failures

bWants high yield at ICT and Functional Test


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• Many test / inspection solutions available

• Defect prevention – defect containment

• Medium to high complexity boards –

many defect opportunities

• This presentation shares result from latest research and studies

Key points....


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Topics

• Introduction

• Defect levels, defects found by 3D AXI

• Defect prevention and random defects

• Test effectiveness

• Summary


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3D AXI RepairUser A

3D AXIUser B

User N 726,091 Boards Inspected

3,675,298,930 Joints Inspected

14 users

2 in Americas

Repair operator

3.7 Billion Solder Joints

3D AXI

Repair

Repair

::

4 in Europe8 in Asia

Most of the data is from early 2007

1,138 Board Types


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Data “clean up”

• Removed debug boards

• Serial Number = “Family”, “Component”

• Boards inspected > 1 time

• Serial Number obvious debug

• Data over around 500 million joints inspected


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Solder Joints inspected by company

• 14 companies/sites, total = 3.7 billion

0

100,000,000

200,000,000

300,000,000

400,000,000

500,000,000

600,000,000

A B C D E F G H I J K L M N

100M

200M

300M

400M

500M

600M

A B C D E F G H I J K L M N


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DPMO Repaired and process indicators

327 DPMO repaired

245 DPMO process indicator

572 DPMO combined

Average numbers

0

500

1000

1500

2000

2500

3000

A B C D E F G H I J K L M NA B C D E F G H I J K L M N

500

1000

1500

2000

2500

3000

PI

Rep.


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Calls per 10 topped called algorithms

This is showing calls after ART, only for the top 10 algorithms based on # of calls.

(Number of opportunities per algorithm is not recorded, therefore DPMO values can not be calculated)

0

50,000

100,000

150,000

200,000

250,000

FPGullwing BGA2 Connector Gullwing Chip Res Paste PCAP PTH Socket

PI

Rep.


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Estimated yields

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

2500 5000 7500 10000 12500 15000 17500 20000 22500 25000

50

100

200

327

500

1,000

Solder joints

DPMO

Yields

Yield = (1 – DPMO/1,000,000)^Defect opportunities


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Key points....

• 2007 data – 14 companies

• 3.7 billion solder joints in study

• Defect levels are still high

• 327 DPMO Defects• 245 DPMO Process Indicators

• 572 DPMO Combined

• A board with 3,500 solder joints has an average of > 1 defects per board

• Yields after reflow for medium and high complexity boards typically very low

• Defects on all type of solder joints


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Topics

• Introduction




• Summary


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Question

Are defects systematic?

And if so what percent are systematic?

1 billion solder joint study used to analyze this.


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Boards available for analysis

566 board types in data base – 1999 DPMO study

Selection criteria:>= 100 boards manufactured

>= 1000 joints inspected>= 20 components inspected

(# components inspected not in data, therefore >=20 referencedesignator in calls)

237 board types meet criteriaProduction volume from 103 to 188,360

10 boards were selected randomly


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What is a systematic defect?

Same reference designator called* on >= 3% of the boards

*Called with repair, repair later, or process indicator actions.

Factor that could increase # of systematic defectsSeveral RefDes same basic problem (DFM issue)

Factor that could decrease # of systematic defectsAll defect types for one RefDes considered systematic

In this analysis the following was used:

Objective with study is only to indicate ball park numbers.For precise analysis availability to boards with defects are needed.3% was selected on engineering judgment basis.


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Result

For 10 boards types randomly selected. Number of random defects 74%

Systematic

Random

(“Same” defect on less than 3% of the boards)


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Result

For 10 board types randomly selected. Number of systematic defects

>=3%

0%

10%

20%

30%

40%

50%

60%

70%

80%

1 2 3 4 5 6 7 8 9 10 11AverageBoard types

%Systematic

defects


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• In this study around 75% of all defects are random.

• Should defect prevention strategies be implemented? ABSOLUTELY, efforts should definitely be done to minimize systematic defects.

• However an effective test strategy for random defects is needed, especially for medium and high complexity boards.

• What is an effective test strategy?

Key points....


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Topics

• Introduction




• Summary


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Defect coverage

• Poor wetting

• Marginal Joints

• Voids

• Excess

• Shorts

• Opens

• Hidden parts

• Missing

• Gross Shorts

• Lifted Leads

• Bent Leads• Insufficient

• Bridging

• Tombstone

• Misalignment

• Bypass Caps, L’s

• Extra Parts

•Orientation

• Missing non-electrical parts

•Mark Inspection

•Paste Deposition Defects

• Polarity

• Inverted

• Missing Socketed Parts

• Dead part

• Wrong part

• Bad part

• PCB short/open

• Functionally bad

AOI

ICT AXI

ICT: In-circuit Test

AXI: Automated X-ray Inspection

AOI: Automated Optical Inspection –

including solder paste inspection

(SPI), pre-reflow and post-reflow.

This is a conceptual

diagram!

How do you get

accurate data? ….


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What is Test Effectiveness?

Test Effectiveness is a measure of the “goodness” of your test and your test /inspection equipment and programs.

TESTER(S)

10 DEFECTS 3 DEFECTS

Test Effectiveness = (10-3)/(10) = 70%


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Test or Inspection

Manually Categorizethe test inspection results

into defects, process indicators, and false calls

NO REPAIRS

2.

3.

Customer has final say on what is a defect, process indicator, or false call.

Building of boards,including wave.

1.

Test Effectiveness Evaluation Flowchart

No inspection/test or repairs for the boards in the

Study.

AllTest or Inspections

Steps done?4.

No

Only defects are included in Test Effectiveness data.

Yes


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Case Study

• Compilation of nine similar studies performed in nine separate

manufacturing facilities

• 421 assemblies tested

• No defects repaired between test/inspection steps (except

shorts at ICT)

• Only one defect per component

• 3D AXI and ICT always present in study

• One of AOI, Functional Test, and Manual Visual also present

Most of these studies have been done on medium to high complexity

boards with medium to low manufacturing volumes.


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Summary TE Studies – 421 boards

3D AXI

AOI, MVI, or FT

ICT67

536

73

30

3

53103

779

209

226

Total Defects: 865


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Summary TE Studies – Defect Coverage

3D AXI

AOI, MVI, or FT

ICT

90.1%

24.2%

26.1%

Total Defects: 865


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Test Effectiveness studies - Summary

Key learnings:

- 3D AXI Test Effectiveness 85% - 95%- AOI “ “ 25% - 75%- ICT “ “ 20% - 60%- FT “ “ 5% - 20%

These numbers includes both Agilent and non-Agilent systems

(3D AXI is Agilent 5DX only)

All systems are not equal!!


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A visual presentation

Of

Test/Inspection

Coverage


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Defect universe – All defects – No coverage


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Defect universe – ICT and AOI, MVI, or FT coverage

Defects not covered

Red =

ICT

AOI, MVI or FT



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Defect universe – AXI 3D, ICT and AOI, MVI, or FT coverage

3D AXI coverage

90.1%

Defects not covered

Red =

ICT

AOI, MVI or FT



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• 3D AXI has by far the highest defect coverage, around 90%

• Without 3D AXI around 50% of defects are shipped to the end customer. Some of those defects will create warranty and field failures.

• For medium and high complexity boards an effective implementation of 3D AXI in the test strategy is strongly recommended.

Key points....


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Topics

• Introduction




• Summary


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Summary – Medium & High Complexity boards

• Defect levels are still high > 300 DPMO

• High defect coverage is important and 3D AXI is by far the most effective test / inspection method.

• An effective defect prevention strategy is recommended

• A majority of defects are random

• To achieve high yields at ICT and FT and to minimize warranty and field failures,

3D AXI is strongly recommended

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