What must be clean before a routed block leaves the routing stage?

Short Answer

Connectivity has to be perfect: zero opens and zero shorts. DRC and antenna violations have to be zero or individually reviewed and accepted. Timing, transition, capacitance and signal integrity have to pass on routed parasitics in every active scenario, and the block has to be saved with the reports that prove it.

Technical Explanation

• Opens and shorts are hard stops. check_routes and check_lvs both need to report zero, with check_lvs -max_errors 0 so nothing is hidden by its default cap.
• Routing DRCs and antenna violations should be zero. If a few remain, each needs an owner and a reason, for example a known issue next to a macro that signoff DRC will judge.
• Timing has to be checked on routed parasitics, not estimates, in every active scenario. That means setup, hold, and the logical design rules: max transition and max capacitance.
• Signal integrity belongs in the gate: crosstalk delta delay included in timing, and noise within limits on sensitive nets.
• Redundant via rate and any DFM steps should be complete, and routing statistics recorded.
• Save the block with save_block along with the reports you used to decide. The next stage, and anyone debugging later, needs to know exactly what state was accepted.
• If anything changes after this gate, such as a late ECO, the whole checklist is repeated on the new database, not just the part you think you touched.

What To Check

• check_routes and check_lvs -max_errors 0: zero opens and shorts.
• DRC and antenna counts, with a written disposition for anything above zero.
• report_qor and report_constraints -all_violators in all active scenarios.
• A saved block and its reports, stored together.

Healthy, Suspicious & Hard-stop Results

• Healthy (illustrative): Zero opens, shorts, DRCs and antenna violations, all scenarios passing setup, hold and DRV, block saved with reports.
• Suspicious (illustrative): Fewer than about 10 DRCs left, each reviewed and assigned, with timing clean.
• Hard stop: Any open or short, any scenario not analyzed, or timing only checked on estimated parasitics.

What The Interviewer Is Testing

• Whether you separate hard stops from items that can be dispositioned.
• Do you insist on routed parasitics and all scenarios?
• A strong answer shows you keep evidence with the database.

Follow-up Question & Model Response

"Which of these items can you ever waive?"

Candidate Model Response: Opens and shorts cannot be waived; they are functional failures. A small number of routing DRCs sometimes can, if signoff physical verification shows they are false or they sit in an area owned by a macro team with a documented fix. Antenna violations can be waived only with an explicit reliability sign-off, which is rare. Timing items can be waived only with a signed-off timing exception, such as a proven false path, not because they are small.