DFT / ATPG · All levels

Coverage Closure: Comparison Matrix

Comparison Matrix for Coverage Closure.

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 - Coverage Closure

+-------------------+------------------------+--------------------------+-------------------------+
| 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

Coverage closure uses targeted analysis of undetected faults, constraints, and design-for-test hooks to close quality gaps without exploding pattern volume.

Metric: coverage gap to target, dominant undetected classes, closure iteration count

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