Effect of post-mold curing on package reliability

Silica filled epoxy resins as encapsulation in chip packages reveal a major influence on the reliability and functionality of microelectronic devices. In this study, the resulting effects of post-mold curing (PMC) on the thermomechanical and chemical properties of different mold compounds were observed. Polymer systems of the investigated mold compounds were based on two orthocresol novolacs (OCN), one biphenyl and one multifunctional resin (MFR). It could be shown, that longer thermal treatment after curing leads in general to further cross-linking of the polymer chains and increases the glass transition temperature T-g. Therefore, the temperature resistance of the mold for following process steps after package assembling, like soldering, can be improved as well as the reliability during temperature cycle tests. However, PMC treatment also increases the moisture absorption. Here, MFR mold exhibit the highest moisture absorption. Also the high T-g of the MFR mold is not much influenced by PMC. Hence, further thermal treatment after curing of the MFR mold is not necessary. In case of OCN and biphenyl mold types, the advantages of PMC are predominating.