Mechanism to understand

Mechanism for Test Logic Floorplan focuses on compression logic placement quality, test route detours, floorplan DFT ECO count. The goal is to convert metric movement into mechanism, owner, and release decision.

Placement of decompressors, compactors, and BIST controllers impacts routing quality, clocking, and timing closure effort. Think of DFT as a quality pipeline where setup quality determines what silicon evidence means.

• Identify where controllability/observability is introduced.

• Identify legal constraints and mode assumptions.

• Identify failure class: architecture, constraints, physical, or silicon.

Layered view

DFT CLOSURE FLOW - Test Logic Floorplan

scan/test architecture
        |
        v
ATPG constraints + fault models
        |
        v
pattern generation + compression
        |
        v
timing/power/physical validation
        |
        v
silicon diagnosis and release signoff

Debug rule: always state metric, run tags, and owning team with any claim.

Compression logic placement

decompressor/compactor placement too far from chains
  -> detours + skew + route pressure

Layer responsibilities

DFT OWNERSHIP LAYERS - Test Logic Floorplan

layer              owns                         failure mode
----------------   --------------------------   -------------------------
rtl/architecture   scanability hooks            uncontrollable logic
atpg/constraints   legal pattern intent         aborts, low coverage
physical/clocking  chain route + test clocks    shift hold/timing escapes
tester/program     pattern apply integrity      false binning / bad fails
quality signoff    release criteria             escapes or schedule slip

DFT deep dive

Physical integration quality decides whether DFT architecture survives implementation realities.

Concept diagram

PHYSICAL DFT FLOW

chain planning -> floorplan placement -> route -> test timing/power validation

Metric graph

ROUTING BURDEN

poor chain order -> longer routes -> more hold buffers

Reports and artifacts

• scan physical wirelength

• congestion heatmap

• test clock skew

• handoff issue tracker

Mini case study

Late scan reorder reduced route detours and eliminated a major shift hold cluster before signoff.

Debug branches

• Correlate chain order with congestion

• Place compression logic near chain clusters

• Keep DFT-PD handoff versioned

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.

Mechanism deep dive

Placement of decompressors, compactors, and BIST controllers impacts routing quality, clocking, and timing closure effort.