Chain order and placement strategy trade congestion and closure time.
+------------------+----------------+----------------+----------------+
| 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 - Scan Chain Physical Effects
+-------------------+------------------------+--------------------------+-------------------------+
| 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 |
+-------------------+------------------------+--------------------------+-------------------------+Physical integration quality decides whether DFT architecture survives implementation realities.
PHYSICAL DFT FLOW
chain planning -> floorplan placement -> route -> test timing/power validationROUTING BURDEN
poor chain order -> longer routes -> more hold buffersscan physical wirelength
congestion heatmap
test clock skew
handoff issue tracker
Late scan reorder reduced route detours and eliminated a major shift hold cluster before signoff.
Correlate chain order with congestion
Place compression logic near chain clusters
Keep DFT-PD handoff versioned
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.
Logical chain order interacts with placement and routing; poor ordering inflates wirelength, congestion, and shift hold fixes.
Metric: scan wirelength, congestion from chain ordering, hold buffer overhead
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