Effects of Solder Voids on Thermal and Reliability Performances of PQFN Packages

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 performance of PQFN package are first 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. Then, the effects of the solder voids on the package’s reliability performance are assessed by carrying out two tests, Temperature Cycling (TC) and High Temperature Operating Life (HTOL), to the actual samples of different void sizes and locations. The electrical function inspection and Scanning Acoustic Microscope (SAM) inspection are performed to the samples at planned time points to find any electrical and mechanical failures. No functional failure or abnormal delamination has been observed throughout 500 cycles of the TC test and 408 hours of the HTOL test.