1. Purpose of the gate
For stacked products such as HBM, the stack architecture, base die interface, through-silicon via plan and bump map are frozen so the core and base dies and the package can be released together.
A stack is designed by several teams at once: the core die, the base die, the stack assembly and the package or interposer it sits on, often at another company. If the bump map, via positions or test access change late, every one of those designs changes with it. This gate freezes the shared interfaces so each team can finish its part.
It is also the point where the stack's physical limits are committed: the thermal path from the bottom die through the stack, the height and warpage the integrator can accept, and how the finished stack will be tested and repaired through the base die using IEEE 1500 and IEEE 1838 style access.
In practice the freeze is negotiated. Integrators want the stack early and stable; the memory team wants freedom to adjust as the core die design closes. A good review makes the trade explicit: which items are frozen now, which few remain open with a date, and how any later change will be handled through a single change board that both sides attend.
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