Warpage of molded plastic packages becomes a more serious consideration as their size increases. In this analysis we develop an analytical stress model for the evaluation of the thermally induced bow of large plastic packages due to the nonuniform distribution of temperature in the through-thickness direction after the molding cycle. This model enables one to determine the effects of the package geometry and material properties on the induced warpage. We show that the bow of the package is proportional to the edge length squared, and is inversely proportional to the package thickness. We show also that the coefficient of thermal expansion (contraction) of the molding compound has a strong effect on the bow, while its Young’s modulus has a small effect. The performed experimental work has indicated that different procedures for handling the packages after molding result in different temperature gradients leading to different bows. The obtained results are useful in the selection of the appropriate molding compound and rational physical design of thick plastic packages, as well as in the optimization of the handling procedures after molding and post-curing.

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