We buy good boards! (Improve yield from design to production)

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We buy good boards!(Improve yield from design to
production)

• Christophe LOTZ
• christophe.lotz_at_aster-technologies.com
• ASTER Technologies

BTW2009
IEEE 8th International Board Test Workshop
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Content

• Introduction
• Yield improvements
• Defect prevention vs. Defect detection
• Test Coverage vs. Test Efficiency
• Production model
• Technologies convergence
• Coverage Analysis
• Traceability Quality tools
• Test Innovation
• Conclusion

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The world changes

• Electronic design and production changes
• Functional complexity of electronic boards.
• Staggering board density.
• Outsourcing of board production.

SMD, fine pitch, BGA, buried via
Non-functional channels
Block 3
We buy good boards
Block 1
Block 2
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Yield improvements
Defect Prevention
Defect Detection

• For a lot of people, Quality is costly. However,
  Non-Quality can be fatal.
• When it is impossible to reduce the task, it is
  always possible to reuse the results for other
  purpose i.e. Test for Designability, Production
  line optimization, Repair Cycle, Product life
• Combine Design Re-Use with Test Re-Use

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Defect prevention

• Design Flow
• Electrical DfT rules checking from schematic.
• Probe optimization from schematic.
• Probe placement Mechanical DfT rules.
• DfM Design for Manufacturing.
• Coverage estimation
• Inspection AOI, AXI
• Structural test ICT,FPT,MDA,BST
• Functional test In-System test, Emulation
• Lack of automation/understanding between design
  and production center (The WALL)!

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Defect Prevention

• Manufacturing flow
• Assembly machine
• Feeder control/supply chain management,
• Passive measurement during placement.
• Traceability tools
• Work In Process,
• Box Building.
• Repair station
• CAD data,
• Fault ticket,
• Diagnosis.
• Defect occurrence/re-occurrence

Quality System mustbe able to reportthe amount
of defects by partnumber
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Defect Detection
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Defect Detection
MPS PPVS PCOLA/SOQ PCOLA/SOQ/FAIM
Material Value Correct Correct
Material Value Live Live
Placement Presence Correct Correct
Placement Live Live
Placement Polarity Orientation Orientation
Solder Solder Short Short
Solder Solder Open Open
Solder Solder Quality Quality
Function Function Feature
Function Function At-Speed
Function Function In Parallel
Function Function Measurements
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Defect Detection

• One coin/two sides Defect ? Coverage
• Drill-down on flows for more defect categories

MPS, PTC, PPVS, PCOLA/SOQ PCOLA/SOQ/FAIM
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Test Coverage

• Demonstration using an absurd example
• Board - 4 components 3 resistors, 1 BGA.
• The 3 resistors are measured with very high
  accuracy.
• No test on the BGA.
• Is the board test score really 75?
• 3 resistors / 4 components
• We need something to weight the coverage It must
  be credible, easy to update to reflect growing
  electronics complexity.

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Test Efficiency

• For each category (MPS) of defects (D), we
  associate the corresponding coverage (C).
• The test efficiency is based on a coverage
  balanced by the defects opportunities.

? DM ? CM ? DP ? CP ? DS ? CS
Effectiveness
? DM ? DP ? DS
We need a better coverage where there are more
defect opportunities!
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Test Efficiency

• Coverage
• Material0, Placement100, Solder100
• Massive production
• Material2PPM, Placement10PPM, Solder10PPM
• Test efficiency90.9
• High mix
• Material15PPM, Placement10PPM, Solder15PPM
• Test efficiency60.5

Everything is relative.
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Defect universe

• How to know your defect universe?
• Average number It is better than nothing as it
  make possible to differentiate a resistor from an
  IC.
• www.ppm-monitoring.com
• www.inemi.org
• DPMO collected from the real production line
• Placement defects andsoldering defects by
  package.
• Material defects by partnumber.

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Production model

• Summarize the coverage in a limited set of
  numbers that will guide the test strategy choice.
• The Escape is an effective way to measure the
  manufacturing quality.

Good
Products shipped
First Pass Yield
Escape
Bad
Pass
Test
Yield
False reject
Good
Fail
Products repaired
Fall-Off Rate
Bad
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Technologies convergence

• Design re-use is widely accepted throughout the
  electronics industry.
• Design test specification test development
  quality management are isolated in separated
  silos. Limited data exchange between silos.
• It is time for test-reuse and technologies
  convergence.
• It increases the test value.
• It decreases the test cost.

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Functional test

• Functional coverage could be managed as described
  in BTW06 paper.
• By Declaration

Schematic and layout viewers used to simplify
coverage declaration.
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Functional test

• By Inheritance

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Functional test

• For a complex board, it represents 3 to 5 days
  work to analyze the functional coverage if
  nothing has been prepared from design flow.
• Benefits
• Get the overall coverage (inspection
  structural functional),
• Identify overlapping (potential optimization),
• Identify lack of coverage (Failure Mode and
  Effects Analysis).

Tested?
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Test Innovation

• Functional test
• Functional Test coverage tool used as functional
  test specification tool.
• Define test strategy early in the design flow.
• Identify unique test contribution.
• Avoid un-required overlapping.
• Functional Blocks recognition make possible to
  develop an Automatic Functional Test Generator.
• Automate test development and coverage analysis
  in high-hierarchical design flow.
• Integrate Designer knowledge for repair purpose.

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Test Innovation

• Test line
• Test coverage results re-used in functional test
  repair station.
• The Pass tests tell us which defects are not on
  the board.
• The Fail tests tell us which defects could be on
  the board.
• Combined with historical data in order to guide
  diagnosis to the most probable source of defect.

Coverage Database
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Test Innovation

• Dynamic test program optimization driven by
  Quality management tool.
• When the test is the bottleneck of the
  production
• The Quality Management system is collecting DMPO
  in real time.
• Defect profile is used to tune the assembly line.
• According to the defect profile, the test program
  is dynamically optimized.

No need to maintain test on defect thatno
longer occurs !
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Conclusion

• From design, during production and in a more
  general way, through the whole product life
  cycle, coverage estimation permits the test
  process to be optimized.
• By deploying various testers in the best order,
  at the best time, with controlled levels of
  redundancy, costs can be reduced and quality
  levels raised.
• The economic challenges are critical the tools
  to meet them are available.