DFT / ATPG · All levels

Pattern Signoff: Comparison Matrix

Comparison Matrix for Pattern Signoff.

Comparison matrix

Fault model and constraint policy shape runtime and outgoing quality.

diagram

+------------------+----------------+----------------+----------------+
| Approach         | Strength       | Weakness       | Best when      |
+------------------+----------------+----------------+----------------+
| Conservative     | safe           | higher cost    | ramp-sensitive |
| Balanced         | practical      | needs rigor    | production     |
| Aggressive       | fast           | escape risk    | schedule pressure |
| Architecture     | durable        | slow           | repeated pain  |
+------------------+----------------+----------------+----------------+

When to choose each approach

Tie approach to product risk and tester constraints

Interview traps

Optimizing one metric only
No regression ownership

Evidence comparison

diagram

DFT EVIDENCE MATRIX - Pattern Signoff

+-------------------+------------------------+--------------------------+-------------------------+
| Evidence           | Tells you              | Does not prove           | Next action             |
+-------------------+------------------------+--------------------------+-------------------------+
| coverage report    | fault detect trends    | silicon root cause       | inspect bucket details  |
| pattern diff       | generation changes     | architecture quality     | replay suspect patterns |
| timing/power report| test closure margin    | diagnosis confidence     | correlate fail logs     |
| diagnosis summary  | likely defect classes  | ownership decision       | assign action owner     |
| signoff checklist  | process completeness   | correctness of evidence  | peer review artifacts   |
+-------------------+------------------------+--------------------------+-------------------------+

DFT deep dive

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

Concept diagram

diagram

ATPG FLOW

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

Metric graph

diagram

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

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