DFT / ATPG · All levels

LBIST Overview: Comparison Matrix

Comparison Matrix for LBIST Overview.

Comparison matrix

MBIST/LBIST options trade area, runtime, and observability.

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

DFT deep dive

BIST value is realized only when insertion, diagnosis, and repair are tied to production flow.

Concept diagram

diagram

BIST FLOW

insert MBIST/LBIST -> execute -> collect signatures -> diagnose/repair -> signoff

Metric graph

diagram

REPAIR EFFECT

yield
  ^
  |      o pre-repair
  |             o post-repair
  +---------------------> lot

Reports and artifacts

MBIST insertion coverage
repair signature report
LBIST resistant fault list
BIST release checklist

Mini case study

Fuse programming mismatch blocked repair activation; corrected bring-up script recovered expected yield uplift.

Debug branches

Validate BIST reachability
Correlate fail maps to repair signatures
Audit in-field boot test 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

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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