Thin type packaging: an effective way to improve the popcorn resistance of plastic-packaged ICs

The popcorn resistance of a variety of thin quad flat packages (TQFPs) was studied. Both the package thickness and the die size were varied in order to understand the risks involved in this type of high-density packaging. Because of the typical moisture absorption behavior of TQFPs, a realistic preconditioning method was defined. The evaluation of the popcorn resistance made use of humidity tests as well as of acoustic inspection of package integrity on samples which were soldered after appropriate preconditioning. It was found that preconditioning at higher than realistic temperatures can overestimate the risk for popcorn damage if the correlation with real life conditions makes use of the measured total moisture uptake. When subjected to realistic stress conditions, the thinner TQFP types show a better popcorn resistance. Also, the samples with a larger die (and closer fitting diepad) perform better in the evaluation tests. The proposed failure mechanism for this type of package is moisture accumulation and expansion at the topside of the diepad next to the die, rather than at the bottom of the diepad.<
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