LBIST Overview: Inputs & Outputs

Inputs and outputs contract

Inputs & Outputs for LBIST Overview focuses on LBIST signature quality, random-pattern-resistant fault count, runtime budget. The goal is to convert metric movement into mechanism, owner, and release decision.

Treat these as a release contract. Ambiguity here creates expensive debug loops because teams optimize against different assumptions.

INPUTS
  - scan/ATPG architecture and constraints
  - fault model and quality target policy
  - pattern generation config + tester limits
  - timing/power/physical assumptions

OUTPUTS
  - quality metrics and closure status
  - signed artifacts and owner approvals
  - diagnosis evidence for residual risk
  - release, waiver, or escalation decision

Flow sequence

DFT FLOW - LBIST Overview

scan insertion -> chain stitch -> compression map -> ATPG -> tester apply -> diagnosis
      |                |                |            |             |
 controllability   shift balance    channel use   coverage     silicon correlation

Primary metric: LBIST signature quality, random-pattern-resistant fault count, runtime budget

Ownership map

OWNERSHIP MAP - LBIST Overview

artifact              owner
----------------      -----------------
architecture/report DFT architect
constraints/setup   safety owner
physical/test       product engineering owner

Name an owner for each failing metric cluster.

DFT deep dive

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

Concept diagram

BIST FLOW

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

Metric graph

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