Molding compounds for thin surface mount packages and large chip semiconductor devices

It is noted that surface mounted devices have two major requirements: (1) resistance to the 'popcorn' phenomenon during the solder application process: and (2) minimization of stresses to the chip during the thermal shock process. Generally, there is a tradeoff relationship between these two properties. The range of importance of these two properties depends on the package types. Thicker surface mounted devices such as the PLCC (plastic leaded chip carrier) shows very little or no effect of the popcorn phenomenon. Cracks in passivation glass easily occur during thermal shock cycling. On the other hand TSOP or VQFP packages crack easily when subjected to the soldering process, while chip stresses are reduced during temperature shock cycling when compared to thicker packages such as PQFP and PLCC. The authors present analytical and experimental results for these two phenomena and discuss required properties for molding compounds or different types of surface mounted devices.<
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