STA Mastery · All levels

ECO Timing Closure: Tricky Q&A

Senior interview and review questions for ECO Timing Closure.

Section Q&A bank

Use these drills after completing all topics in ECO Timing Closure. Answer with corner/mode/view, path group, metric, artifact, ECO, and regression.

Setup ECO effect on hold?

diagram

[INT][STA][ECO-CLOSURE]

Q: Setup ECO effect on hold?

A:
Increasing delay helps setup but often worsens hold — must re-run min analysis.

FOLLOW-UP TRAP: Setup-only signoff.

Logical vs physical ECO?

diagram

[INT][STA][ECO-CLOSURE]

Q: Logical vs physical ECO?

A:
Logical changes netlist; physical changes placement/route — different regression surfaces.

FOLLOW-UP TRAP: Skipping equivalence on logical ECO.

Q&A drill guide

diagram

CONSTRAINT -> VIEW -> PATH -> METRIC -> ECO -> REGRESSION

Sketch while answering

diagram

ECO LOOP

failing path -> fix -> setup check -> hold check -> SI -> MMMC matrix

Key takeaways

State corner, mode, view, and database tag with every slack claim.
Run setup and hold plus MMMC regression after every ECO.

Common pitfalls

Comparing STA runs with different SPEF or SDC tags.
Broad false_path to green-wash violations.
Setup-only ECO without hold check.

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