Interview drills

Interview Drills for Package SI/PI Contracts focuses on SI/PI margin violations, package-driven timing regressions. The goal is to map symptoms to boundary contracts, owner actions, and regression-proof closure.

PROMPT
You observe SI/PI margin violations, package-driven timing regressions in Package SI/PI Contracts. Explain root cause and closure plan.

STRONG ANSWER
1. Names baseline manifest and failing boundary.
2. Explains Package SI/PI constraints define return paths, impedance, and noise budgets that must be reflected in chip-level assumptions.
3. Requests SI/PI budget table, package model manifest, margin report.
4. Proposes minimal reversible fix + full regression scope.

WEAK ANSWER
Suggests broad optimizations or owner blame without baseline and artifact evidence.

Diagram to draw on whiteboard

SI/PI contract budget

PACKAGE SI/PI BUDGET

impedance target
return path quality
power droop budget
timing margin reservation

Root-cause tree to narrate

ROOT-CAUSE TREE — Package SI/PI Contracts

SI/PI margin violations, package-driven timing regressions regressed
         |
   same baseline manifest?
      /           \
    no             yes
    |               |
version/collateral  real integration
mismatch            contract break
 /       \            |
inputs    env      isolate domain
drift     drift    and first failure

SoC deep dive

Package assumptions must be treated as first-class chip constraints.

Concept diagram

PACKAGE CO-DESIGN
die io <-> package routing <-> board constraints

Metric graph

PACKAGE RISK MIX
SI margin █████
power integrity ████
lane mapping ███

Reports and artifacts

• bump map revision log

• SI/PI margin report

• IO co-design checklist

• package bring-up failures

Mini case study

Link degradation on product board came from package routing assumptions not reflected in pre-silicon model.

Debug branches

• Compare package model versions

• Audit lane mapping

• Correlate SI/PI margins to failures

Senior review question

Ask: what baseline, owner, and artifact prove this topic is truly closed?

Key takeaways

• State baseline manifest and owner with every closure metric.

• Run cross-domain regression after every top-level fix.

Common pitfalls

• Comparing results across different manifests.

• Unowned issues slipping through review cycles.

• Waiving risks without expiry and validation plan.

Principal SoC review addendum

Package SI/PI constraints define return paths, impedance, and noise budgets that must be reflected in chip-level assumptions.

Metric: SI/PI margin violations, package-driven timing regressions