DFT / ATPG · All levels

MBIST & LBIST: Tricky Q&A

Senior interview and review questions for MBIST & LBIST.

Section Q&A bank

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

Why can MBIST pass but yield remain poor?

diagram

[INT][DFT][MBIST-LBIST]

Q: Why can MBIST pass but yield remain poor?

A:
Repair programming, diagnosis mapping, or production flow integration can be broken despite clean insertion.

FOLLOW-UP TRAP: Assuming MBIST insertion equals yield closure.

What is a common LBIST signoff pitfall?

diagram

[INT][DFT][MBIST-LBIST]

Q: What is a common LBIST signoff pitfall?

A:
Ignoring random-pattern-resistant faults and overclaiming quality from signature checks alone.

FOLLOW-UP TRAP: Treating LBIST as a full ATPG substitute.

Q&A drill guide

diagram

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

Sketch while answering

diagram

BIST FLOW

insert MBIST/LBIST -> execute -> collect signatures -> diagnose/repair -> 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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