DFT / ATPG · All levels
Scan Fundamentals: Tricky Q&A
Senior interview and review questions for Scan Fundamentals.
Section Q&A bank
Use these drills after completing all topics in Scan Fundamentals. Answer with metric, mechanism, evidence, owner, and regression plan.
Why does chain balance matter beyond tester time?
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[INT][DFT][SCAN-FUNDAMENTALS]
Q: Why does chain balance matter beyond tester time?
A:
Unbalanced chains increase shift time and often create route detours and hold-fix overhead.
FOLLOW-UP TRAP: Treating chain balance as only an ATE problem.What is the first check when scan coverage unexpectedly drops?
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[INT][DFT][SCAN-FUNDAMENTALS]
Q: What is the first check when scan coverage unexpectedly drops?
A:
Verify scan replacement legality and non-scan element list before tuning ATPG options.
FOLLOW-UP TRAP: Tweaking ATPG switches before checking architecture inputs.Q&A drill guide
diagram
METRIC -> MECHANISM -> EVIDENCE -> FIX -> REGRESSIONSketch while answering
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SCAN INSERTION FLOW
scan-ready RTL -> scan replacement -> stitch chains -> DRC -> ATPG handoffKey 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.