1. Purpose and scope
The ramp turns a released product into reliable supply. For wide bandgap devices it is often limited by substrate and epitaxy supply and by yield learning on material defects rather than by fab capacity, and demand from vehicle programs can rise quickly once a platform launches. The purpose of this stage is to scale output to the agreed allocation, raise yield to its mature level and keep quality stable while volumes grow.
Quality in the ramp rests on several layers: statistical process control on critical steps with excursion response; production test at wafer and final level at high voltage and current; screens such as gate stress screening or burn-in where the plan requires them; statistical outlier screening such as part average testing to AEC-Q001; and field monitoring with customers so returns are analysed quickly.
In scope: the final process and assembly control plans, the capacity plan and allocation, yield learning, production test data, screening results, field monitoring and cost and yield reporting. Out of scope: planned cost-down changes, which follow in Cost-down & Sustaining.
Yield learning in a wide bandgap ramp has its own character. A large share of die loss can usually be traced to the starting material, so yield engineers join incoming substrate and epitaxy defect maps with wafer test maps die by die, separate killer defect classes from harmless ones and feed the result back to suppliers and to the material specification. Process-driven loss, such as gate oxide defects, implant or anneal non-uniformity and backside damage from thinning, is separated from material loss by tracking material identity through the flow. Assembly yield for modules, including void rates in die attach and bond quality, is tracked beside wafer yield, since a module carries several dies and loses all of them if one fails.
Field monitoring matters more for power devices than for many other parts, because a failure in a traction inverter or a solar inverter can be dramatic and expensive. Returns are analysed quickly, failure signatures are compared with the qualification failure modes, and any new mechanism triggers a review of screens, process controls and the lifetime model. Customers expect to hear promptly about issues that may affect parts already shipped, under the containment and notification terms of their agreements.
12 more sections for registered members.