Impacts of solder voids on PQFN packages´ thermal and mechanical performances

Power Quad Flat No-lead (PQFN) packages are extensively used in automotive applications. Features such as solder die attach material, thick copper lead frame, exposed heat sink and heavy gauge aluminum wire, are adopted to ensure good thermal management and reliability performance. Solder voids, cavities formed between power die and lead frame during solder reflowing process, are major defects in die bonding process, and are detrimental to packages´ thermal, mechanical and reliability performances. In this study, the effects of solder voids on the thermal and mechanical performances of PQFN package are evaluated by numerical simulation. The thermal response of the package is predicted for different void sizes and locations. The solder voids raise slightly the junction temperature of the package when the voids do not cover a major portion of the die attach area. The effects of the solder voids on the package´s mechanical performance are assessed by carrying out mechanical simulations with different void sizes and locations. The void size does not have significant impact on power die stresses, whereas the location of voids, especially the large void at die edge/corner, raise the stress substantially.