1. Purpose of the gate
Once a power device is approved by customers, every change to it is the customer's business. A new silicon carbide substrate supplier, a thinner wafer, a different epitaxy reactor, a die shrink at the same rating, a move to a second fab or assembly site, a new sinter paste or a reduced screen can all change reliability in ways that may only show after years in a vehicle or an inverter. This gate decides that the change has been qualified to a plan proportionate to its risk, that customers have been told in the agreed way and have approved where they must, and that implementation can begin.
The qualification plan for a change is built by comparing the changed product with the archived qualification baseline. Guidance such as the change tables in AEC-Q101 for discrete devices, and the requalification guidance in AQG 324 for modules, helps decide which stresses must be repeated for each kind of change. Changes to die attach or substrate usually need power cycling and thermal cycling again; changes to substrate or epitaxy usually need gate oxide, body diode and high voltage stresses again; changes to test or screening need data showing the outgoing quality is unchanged.
The gate criteria are that the change qualification passed to the agreed plan, that the process change notice was issued within the agreed notice period, and that customer approvals were received where required. The second-source materials and capacity decision is frozen here for the source being qualified.
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