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Effects of Solder Voids on Thermal and Reliability Performances of PQFN Packages
Keywords: Solder voids, Thermal and reliability performance, Power QFN package
Power Quad Flat No-lead (PQFN) packages have been designed to meet the high power dissipation requirements of automotive and other applications. Features such as high lead contented die attach solder paste, thick copper lead frames, exposed heat sinks and heavy gauge aluminum wire, allow for efficient heat transfer out of the packages. Solder voids, formed between power die and lead frame during solder reflowing process, are a major defect in die bonding process, and more importantly, are detrimental to the packages’ thermal, mechanical and reliability performances. Therefore, it is necessary to investigate the effects of solder voids on the PQFN packages’ performance. The first part of this study is the numerical evaluation of the effects of solder voids on the thermal performance of a PQFN package in FLOTHERM. The thermal response of the package was predicted for different void size (ratio of void area to total die attach area) and location. It is found that the solder voids do not raise the junction temperature in the package significantly when the solder voids do not occupy the major portion of the die attach area. When the void size is less than 30%, the peak temperature increases is less than 10% compared with the peak temperature when no voids. The void location only slightly raises the peak temperature as well. The second part of the study is the actual reliability tests to the same PQFN package. Two tests, Temperature Cycle (TC) and High Temperature Operating Life (HTOL), were conducted to the real samples of different void size and location. The electrical tests and Scanning Acoustic Microscope (SAM) inspection were performed to find any electrical function failure and mechanical delamination in the tested samples at planned time points of the tests. The results show that all samples survived the tests and no function failure and significant delamination were observed throughout 500 cycles of the TC test and 408 hours of the HTOL test. The detailed numerical and experimental description, results and discussion will be presented.
Youmin Yu, Senior Packaing Engineer
Freescale Semiconductor
Tianjin 300385,
China


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