Optimization of Epoxy Molding Compound to Enhance the Solder Joints Robustness during Thermal Cycling for A Clip Bond Power Package

Abstract

Clip bonding technology is widely and increasingly used in microelectronic packages because of the increasing demand for high power and low loss automotive grade power package. Compared to wire bonding, clip bonding have much wider interconnection contact area which apply high lead solder with high thermal conductivity, exhibits lower electrical resistance and lower inductance. Meanwhile, large interface between different BOMs brings the stress management challenge during thermal cycling (TCT), especially under the increasingly higher automotive qualification requirements, solder crack including package level and board level solder crack during TCT is one of the key concerns of clip bond power package reliability.As most common encapsulation material, epoxy molding compound (EMC) provides strong mechanical protection and electrical insulation to electrical circuits, coefficient of thermal expansion (CTE) difference of EMC is one of the key factors contributing the overall package stress level. In most recent developments, EMC with high filler loading is preferred because of excellent moisture sensitivity level (MSL) performance and less CTE mismatch between EMC and silicon die. On the other hand, the CTE mismatch of EMC to Leadframe (LF) and package to printed circuit board (PCB) will be higher, resulting higher stress level to package internal bonding solder and external PCB solder. In this study, the consideration of EMC grades with different resin types, different mechanical properties, different CTE ranges and their impact to package integrity and reliability are discussed, optimization direction of EMC is proposed. The TCT performance of solder joint with different EMC materials are evaluated and investigated, advantages and disadvantages of different options are examined and discussed. Result shows that solder crack issue can be improved by preferred EMC types in suitable CTE range without negative effect, solder joint can survive under the thermal cycling longer than 4000 cycles. The TCT robust clip bond power package can be realized by the optimization of epoxy molding compound.