DFT / ATPG · All levels

Compression & Diagnosis: Tricky Q&A

Senior interview and review questions for Compression & Diagnosis.

Section Q&A bank

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

How can higher compression reduce debug quality?

diagram

[INT][DFT][COMPRESSION-DIAGNOSTICS]

Q: How can higher compression reduce debug quality?

A:
Aggressive compaction and X pressure can reduce diagnosis resolution and increase aliasing ambiguity.

FOLLOW-UP TRAP: Optimizing ratio without diagnosis evidence.

Pattern count jumps 2x overnight. What do you inspect first?

diagram

[INT][DFT][COMPRESSION-DIAGNOSTICS]

Q: Pattern count jumps 2x overnight. What do you inspect first?

A:
Constraint diffs, X-source changes, and compression channel configuration tags.

FOLLOW-UP TRAP: Assuming silicon quality changed overnight.

Q&A drill guide

diagram

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

Sketch while answering

diagram

COMPRESSION LOOP

EDT/decompressor -> compressed patterns -> compactor responses -> diagnosis

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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