MBIST/LBIST options trade area, runtime, and observability.
+------------------+----------------+----------------+----------------+
| 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 |
+------------------+----------------+----------------+----------------+Tie approach to product risk and tester constraints
Optimizing one metric only
No regression ownership
DFT EVIDENCE MATRIX - LBIST Overview
+-------------------+------------------------+--------------------------+-------------------------+
| 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 |
+-------------------+------------------------+--------------------------+-------------------------+BIST value is realized only when insertion, diagnosis, and repair are tied to production flow.
BIST FLOW
insert MBIST/LBIST -> execute -> collect signatures -> diagnose/repair -> signoffREPAIR EFFECT
yield
^
| o pre-repair
| o post-repair
+---------------------> lotMBIST insertion coverage
repair signature report
LBIST resistant fault list
BIST release checklist
Fuse programming mismatch blocked repair activation; corrected bring-up script recovered expected yield uplift.
Validate BIST reachability
Correlate fail maps to repair signatures
Audit in-field boot test budget
Ask: what evidence proves this DFT decision is safe for production?
State metric, lot/corner context, and pattern tag with every claim.
Treat timing, power, and quality as one signoff problem.
Chasing coverage without legality checks.
Ignoring test-power side effects of pattern changes.
Debugging silicon without reproducible tags.
LBIST uses on-chip pattern generation and signature compression for in-system logic test where external ATPG access is limited.
Metric: LBIST signature quality, random-pattern-resistant fault count, runtime budget
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