Pattern Signoff: Step-by-Step Walkthrough

Step-by-step analysis walkthrough

Use when you own Pattern Signoff in a DFT closure review.

1. Open release criteria and failing metric dashboard.

2. Partition failures by pattern family and operating context.

3. Inspect constraints, clocks, masks, and unknown handling.

4. Check architecture assumptions against implementation reality.

5. Review diagnosis evidence for repeatability.

6. Assign owner and propose smallest high-confidence change.

7. Run timing, power, and quality regressions.

8. Capture final signoff or waiver decision.

Artifacts to collect

• pattern signoff memo, tester format validation report, quality checklist

• pattern tag manifest

• tester program revision

• signoff checklist

• owner tracker

Decision memo template

DFT DECISION MEMO - Pattern Signoff
scenario:
metric:
hypothesis:
fix:
regression:
owners: DFT lead, ATPG owner, product test owner

Reference visuals

ATPG flow

fault models -> constraints -> generation -> coverage closure -> signoff

DFT deep dive

ATPG quality comes from fault model choice plus legal constraints, not raw pattern volume alone.

Concept diagram

ATPG FLOW

fault model -> constraints -> generation -> simulation -> coverage closure -> signoff

Metric graph

COVERAGE GAP

target coverage
  ^
  |      o before closure
  |          o after fixes
  +---------------------> iteration

Reports and artifacts

• fault model coverage

• untestable class report

• constraint legality errors

• pattern signoff memo

Mini case study

Transition coverage stalled due to clock constraints mismatch; updated at-speed capture definitions recovered target.

Debug branches

• Classify untestable faults

• Diff ATPG constraints each run

• Pair coverage with pattern budget

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

Pattern signoff validates that pattern sets meet quality, runtime, and tester format requirements before tapeout and production handoff.

Metric: final coverage, escaped fault estimate, tester-ready pattern quality