1. Purpose of the gate
The design is frozen and the layout is complete; from here only fixes found by sign-off and verification are accepted, each one reviewed.
Sign-off and characterisation take time and must run on a stable layout. Every change after this point means re-running checks, re-extracting and re-characterising, and possibly moving the test chip date. The freeze therefore asks whether the design and layout are truly complete, not merely close.
The review checks that the layout has all planned features and matches the design, that pre-layout verification is complete with open issues waived or tracked, and that the reliability design review for protection against electrostatic discharge, latch-up and electromigration is complete. Trial sign-off results show how much work remains before a clean sign-off.
It also checks the contract with integrators: whether the footprint and pins still match the early abstract, and whether the metal layers used are those agreed. The test chip specification is approved here so the test chip can be built around the frozen layout.
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