DFT / ATPG · All levels

Pattern Volume Tradeoffs: Comparison Matrix

Comparison Matrix for Pattern Volume Tradeoffs.

Comparison matrix

Channel count, masking, and compaction trade tester cost and diagnosis precision.

diagram

+------------------+----------------+----------------+----------------+
| Approach         | Strength       | Weakness       | Best when      |
+------------------+----------------+----------------+----------------+
| Low volume       | cheap test     | coverage risk  | cost pressure  |
| Balanced         | good quality   | needs tuning   | production     |
| High quality     | coverage       | test time      | safety-critical |
| Adaptive         | flexible       | complex flow   | mature teams   |
+------------------+----------------+----------------+----------------+

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 Volume Tradeoffs

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

Compression saves tester time only when diagnosis observability remains credible.

Concept diagram

diagram

COMPRESSION LOOP

EDT/decompressor -> compressed patterns -> compactor responses -> diagnosis

Metric graph

diagram

PATTERN vs COVERAGE

coverage up   -> pattern count up
compression up -> pattern count down (until aliasing risk)

Reports and artifacts

compression ratio dashboard
pattern count trend
X-source report
diagnosis bucket summary

Mini case study

Compactor overflow plus unknown inflation caused false diagnosis; masking policy and channel map corrected.

Debug branches

Separate X issues from silicon defects
Replay failing patterns uncompressed
Track tester memory 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 volume is a tradeoff between coverage closure aggressiveness, X-handling policy, and compression settings constrained by tester resources.

Metric: pattern count, tester memory usage, test application time

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