Scenario: Coverage Storm: Interview Drills

Interview drills

Interview Drills for Scenario: Coverage Storm focuses on coverage shortfall under schedule pressure, pattern growth slope. The goal is to convert metric movement into mechanism, owner, and release decision.

PROMPT
You observe coverage shortfall under schedule pressure, pattern growth slope on Scenario: Coverage Storm. Walk through diagnosis and release decision.

STRONG ANSWER
1. States context and run tags.
2. Explains mechanism: Coverage crises require separating true untestable faults from constraint/model issues and choosing the smallest high-impact closure plan.
3. Requests coverage gap snapshot, fault bucket analysis, closure plan.
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

Coverage crisis triage

coverage gap
  -> untestable? constraint? model?
  -> targeted fixes
  -> pattern budget check

Root-cause narrative

ROOT-CAUSE TREE - Scenario: Coverage Storm

coverage shortfall under schedule pressure, pattern growth slope 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

Senior DFT interviews test tradeoff judgment under imperfect data.

Concept diagram

INTERVIEW ANSWER LOOP

state metric -> explain mechanism -> request evidence -> propose fix -> list regression

Metric graph

ANSWER QUALITY

mechanism clarity + ownership clarity + regression discipline

Reports and artifacts

• whiteboard rubric

• scenario scorecard

• trap checklist

• follow-up depth index

Mini case study

Candidate improved from tool-only answers to mechanism-first narratives by using metric->artifact->decision template.

Debug branches

• Always state assumptions

• Name cross-team owners

• Discuss risk and fallback plan

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

Coverage crises require separating true untestable faults from constraint/model issues and choosing the smallest high-impact closure plan.

Metric: coverage shortfall under schedule pressure, pattern growth slope