Routing

Section goal

Achieve manufacturable, timing-clean connectivity with controlled DRC, SI, and EM risk across all route classes.

Mechanism to narrate

• Global route health predicts detailed route convergence and ECO effort.

• Antenna, via, and special-net strategy must be planned before brute-force cleanup.

• Routing closure is proven through category-wise DRC reduction and stable extraction-based timing.

Senior course bar for this section

• Every topic should end with a signoff decision, not only concept recall.

• Every fix should state expected metric movement and likely regression surface.

• Every open assumption should have an owner, tag, and review date.

• Every recurring issue should become a methodology guardrail or checklist item.

1. global-detailed-routing/ — Global and Detailed Routing Convergence

2. antenna-rules-fixes/ — Antenna Rules and Corrective Strategies

3. metal-layer-planning/ — Metal Layer Planning and Capacity Management

4. shielding-tie-cells/ — Shielding, Tie Cells, and Signal Hygiene

5. via-planning-and-via-ladders/ — Via Planning and Via Ladder Reliability

6. route-driven-timing-optimization/ — Route-Driven Timing Optimization

7. special-nets-and-power-routing/ — Special Nets and Power Routing Strategy

8. routing-drc-debug/ — Routing DRC Debug and Forensic Workflow

Related topics

• Clock Tree Synthesis hub

• Timing Closure hub

Key takeaways

• Treat routing as an evidence loop: classify violations, apply systemic fixes, and validate with extraction-backed reports.

Detailed section notes

Routing decides whether the placed design is manufacturable and extractable.

Reports and artifacts to inspect

• global route overflow by layer and region

• detailed route DRC/DRV summary grouped by rule

• antenna report: gate area, metal area, ratio, suggested diode

• post-route extraction delta on critical nets

Mini case study

Detailed route completes with 4,000 spacing violations around a macro channel. The design is not 'routed'. Cluster by rule and region, fix the channel or layer plan, then re-route locally.

Debug branches

• If antenna violations cluster on long lower-metal routes, jump to upper metal earlier or insert diode cells.

• If via violations dominate, inspect via arrays and preferred via stacks, especially on power transitions.

• If crosstalk worsens timing, space, shield, or layer-promote the victim nets.

Senior review question

Ask yourself: what single report line would prove this page's concept is either passing or failing?

What changes at 10+ years

• You are expected to predict what your fix can break before running it.

• You should recognize when the issue is methodology, not one block's implementation.

• You should communicate risk in tapeout language: owner, evidence, impact, mitigation, and decision date.

Principal-level review bar

Hub pages in this course should be read like real closure review material. For a 10+ year PD engineer, the bar is not remembering terminology; it is making a release-quality decision under ambiguity.

What excellent looks like

• Names the failing metric, corner/mode, database tag, and analysis switches before proposing a fix.

• Separates data, constraint, physical, tool, and methodology root causes instead of treating all failures as optimization problems.

• Chooses experiments by information gain and reversibility, not by habit.

• States regression blast radius across timing, route, power, PV, DFT, package, and tapeout manifest.

• Turns recurring failures into methodology guardrails, dashboards, or checklist items.

Closure note template

STAFF / PRINCIPAL CLOSURE NOTE

Context:
  stage: <pre-CTS | post-CTS | post-route | post-fill | signoff>
  tag: <database / netlist / SDC / library stack>
  failing metric: <exact report line>
  affected scope: <block / hierarchy / path group / power domain / region>

Hypotheses:
  H1: <most likely physical or constraint mechanism>
  H2: <competing explanation>
  H3: <methodology or input-data issue>

Decision:
  next experiment: <cheap check that can falsify H1>
  fix candidate: <minimal reversible change>
  rollback trigger: <metric that says the fix is wrong>
  regression set: <timing / route / power / PV / DFT / package>
  escalation owner: <team or reviewer>

Tradeoffs a senior engineer must discuss

Technical tradeoff

Routing decides whether the placed design is manufacturable and extractable. Explain not only the preferred fix, but what margin or schedule you are spending to get it.

Cross-team tradeoff

• What must RTL, synthesis, CAD, STA, DFT, package, IP, or foundry agree to before this decision is final?

• Which artifact becomes the source of truth after the decision: report, waiver, manifest, ECO script, or methodology deck?

• What is the cost of being wrong: one rerun, ECO churn, mask risk, performance loss, or silicon escape?

Leadership communication

"The current blocker is <metric> in <corner/mode/stage>. The leading cause is <mechanism>. I recommend <fix> because it is bounded and reversible. The regression surface is <domains>. If it fails, we escalate to <owner> with <evidence>."

Key takeaways

• Always connect the concept back to a measurable signoff artifact.

• A fix is not complete until you can name the regression checks.

Common pitfalls

• Optimizing by habit instead of reading the current report.

• Forgetting that a local fix can regress timing, routing, power, or PV elsewhere.