STA Mastery · All levels

SI ECO Fix Order: Design Space

Design Space for SI ECO Fix Order.

Design space exploration

For SI ECO Fix Order, closure options trade margin, schedule, and regression risk.

Option A — conservative

Conservative margin: helps safe signoff
Risk: over-pessimism, area/power
Validate with: first silicon

Option B — balanced

Balanced derate: helps reasonable margin
Risk: needs approval
Validate with: mature node

Option C — aggressive ECO

Aggressive ECO: helps fast WNS gain
Risk: hold/SI regressions
Validate with: late schedule

Option D — RTL restructure

RTL restructure: helps structural fix
Risk: schedule hit
Validate with: chronic paths

diagram

DESIGN SPACE — SI ECO Fix Order
margin <-> performance <-> schedule
pick based on post-ECO SI WNS recovery, reroute count, spacing violations cleared on product scenarios

Design pitfalls

ECO without regression matrix
Constraint change without audit

Tradeoff curve

diagram

BEFORE / AFTER ECO — SI ECO Fix Order

WNS (ps)
  0 |                    --- target
-50 |    ● regressed
-80 |         ● before ECO
-20 |              ● after ECO
    +-------------------------------> ECO iteration
Prove setup AND hold moved safely.

STA deep dive

Coupling makes delay a function of neighbors, not just wire RC.

Concept diagram

diagram

SI ON VICTIM

victim net delay = base_RC + coupling_from_aggressors

Metric graph

diagram

DELTA DELAY ON CRITICAL PATHS

no SI   ████████  1.2ns
with SI ██████████  1.35ns  (+150ps)

Reports and artifacts

delta delay report
aggressor list
noise peaks
SI WNS delta

Mini case study

Setup fixed by upsize but SI worsened — spacing ECO on bus bits recovered margin.

Debug branches

Re-run SI after every timing ECO
Shield wide switching buses

Senior review question

Ask: what corner/mode/view proves this topic is closed or failing?

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.

Principal STA review addendum

SI fixes use spacing, shielding, sizing, and reroute; order matters because a setup fix can worsen hold or noise elsewhere.

Metric: post-ECO SI WNS recovery, reroute count, spacing violations cleared

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