Wire Bond Qualification Challenges and Development of First Stacked Die on Copper Clip for Multi-Die Controller MOSFET Package

Seremban QFN line has enjoyed continuous growth of production volume for Multi-die Driver/Controller MOSFET (DrMOS) package. Current production DrMOS device integrates a Driver/Controller, high-side MOSFET and low-side MOSFET into a 6 mm × 6 mm 40-pin QFN packaging. To be able to continue our fair share on the market though, new package and new case outline which comes into a 5 mm × 5 mm QFN32 project was recently developed for production. The new package consists of a FET die, Copper Clip and Controller die which are stacked to reduce the overall solution size. This paper elaborates specifically the wire bond challenges and corresponding improvements executed addressing the issues, hence making this package the reference for subsequent DrMOS with Stacked Controller Die on Copper Clip. To be able to define the allowable maximum loop height that can consistently meet the minimum stacked Controller die to Top Package clearance and marking depth requirements, package stack-up worst case analysis and loop height robustness study that can meet up to +6 sigma were evaluated. Since the Controller die is sitting on top of the FET die and Copper Clip, simulation on worst Controller die displacement scenario from different directions was also assessed to guarantee enough bonding wire to Copper Clip edge clearance. Reliability, bondability, wire bonding parameters characterization and cliff experiments were studied as well to ensure critical responses are well within pre-defined specification after implementation of new package design.