1. Purpose and scope
The package often limits a power product's life more than the die. Every time a traction inverter accelerates, the dies heat and cool, and the different expansion of silicon carbide, copper, ceramics and solder stresses the die attach and the bonds on top of the die. Wire bonds lift and solder layers crack after enough cycles. Fast-switching wide bandgap devices also expose the package's stray inductance, which causes overshoot and ringing and limits switching speed.
The purpose of this stage is to design and industrialise packages and modules that suit the die and the application, and to release them for the qualification builds. For discretes this means choosing package families, sometimes top-side cooled or with a separate driver source connection. For modules it means the substrate, such as direct bonded copper on alumina or active metal brazed copper on silicon nitride, the die attach, such as solder or silver or copper sintering, the top-side interconnect, such as aluminium or copper wires, ribbons or bonded clips, the encapsulation, the baseplate and the interface to the cooler.
In scope: module design, electromagnetic, thermal and thermo-mechanical simulation, assembly process development, the assembly process specification, thermal models, the qualification build plan and the first module datasheet. Out of scope: die design, which comes before; application evaluation, which follows in Application Evaluation & Reference Designs; device and module qualification, which follow in Reliability & Ruggedness Qualification after that; and customer approval, which comes last.
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