1. Purpose of the gate
Product sign-off is the technical judgement behind the spend on the company's first full mask set. A full mask set on the production process, the wafers it starts and the months until silicon returns cannot be recovered if a fundamental error is found later. For many startups this is the first full product the company has signed off; the test chip was likely on a shared shuttle with a reduced scope. The review must therefore be at least as rigorous as in an established company, with fewer people and often with part of the work done by a design services partner.
The gate criteria are verification sign-off, with coverage and regression goals in the plan met or waived with reasons; physical sign-off, with timing, power integrity, physical verification and foundry checks clean or waived; test, with test patterns and coverage meeting the test strategy; and waivers reviewed and recorded with their reasons. The sign-off corners and margins are taken in this stage and frozen here, because every timing, power and reliability result in the review is only as good as the corners it was checked at.
The release of the database and the mask order are a separate decision at Product tape-out, which opens the next stage. Keeping them apart lets this review concentrate on whether the chip is right, and lets the release review concentrate on whether what is released is exactly what was signed off.
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