DFT / ATPG · All levels

ATPG & Pattern Generation: Tricky Q&A

Senior interview and review questions for ATPG & Pattern Generation.

Section Q&A bank

Use these drills after completing all topics in ATPG & Pattern Generation. Answer with metric, mechanism, evidence, owner, and regression plan.

Coverage is 98.5% but release is blocked. Why?

diagram

[INT][DFT][ATPG-PATTERNS]

Q: Coverage is 98.5% but release is blocked. Why?

A:
Coverage alone does not prove quality; untestable classes, model mix, and tester feasibility may still violate policy.

FOLLOW-UP TRAP: Using one coverage number as signoff.

When is adding a new fault model justified late schedule?

diagram

[INT][DFT][ATPG-PATTERNS]

Q: When is adding a new fault model justified late schedule?

A:
When defect risk and product quality needs outweigh added pattern and runtime cost, with explicit owner approval.

FOLLOW-UP TRAP: Always adding model depth by default.

Q&A drill guide

diagram

METRIC -> MECHANISM -> EVIDENCE -> FIX -> REGRESSION

Sketch while answering

diagram

ATPG FLOW

fault model -> constraints -> generation -> simulation -> coverage closure -> signoff

Key takeaways

State metric, lot/corner context, and pattern tag with every claim.
Treat timing, power, and quality as one signoff problem.

Common pitfalls

Chasing coverage without legality checks.
Ignoring test-power side effects of pattern changes.
Debugging silicon without reproducible tags.

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