Interview drills

Interview Drills for Test Signoff Reports focuses on test readiness score, unresolved waivers, production release risk. The goal is to convert metric movement into mechanism, owner, and release decision.

PROMPT
You observe test readiness score, unresolved waivers, production release risk on Test Signoff Reports. Walk through diagnosis and release decision.

STRONG ANSWER
1. States context and run tags.
2. Explains mechanism: Test signoff consolidates coverage, timing, power, and diagnosis evidence into a release decision with explicit ownership and waivers.
3. Requests test signoff dashboard, waiver tracker, release review memo.
4. Proposes minimal fix and regression.

WEAK ANSWER
Jumps to tool switches without evidence quality, ownership, or regression plan.

Diagram to draw on the whiteboard

Test timing/power flow

test SDC -> shift/capture timing -> power/IR checks -> release

Root-cause narrative

ROOT-CAUSE TREE - Test Signoff Reports

test readiness score, unresolved waivers, production release risk regresses
        |
  setup changed?
    /        \
  yes         no
  |            |
constraint    silicon or
or ATPG       physical/test path
 /    \          |
SDC   model    chain/clock/power/diagnosis
diff  diff     isolate first failing signature

DFT deep dive

Test signoff fails when shift/capture timing and test power are treated independently.

Concept diagram

TEST SIGNOFF LOOP

test SDC -> shift/capture timing -> power-aware ATPG -> IR validation -> release

Metric graph

TEST CURRENT

functional current  baseline
scan shift current  peak-risk zone

Reports and artifacts

• test-mode STA report

• shift/capture split

• test power IR map

• waiver tracker

Mini case study

At-speed patterns passed timing but failed in production due to peak shift IR; staggered capture and power-aware fill resolved.

Debug branches

• Tag test and functional corners separately

• Check hold in shift mode

• Correlate fail bins with power hotspots

Senior review question

Ask: what evidence proves this DFT decision is safe for production?

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.

Principal DFT review addendum

Test signoff consolidates coverage, timing, power, and diagnosis evidence into a release decision with explicit ownership and waivers.

Metric: test readiness score, unresolved waivers, production release risk