Effect of Post-mold Curing on Package Reliability

Abstract

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 postmold 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.

Thermal test effect on fan-out wafer level package strength

“…The flexure strength of all EMC specimen increases rapidly after one-time passivation layer curing process. This phenomenon matches the previous research statements [11][12][13]. The increased glass transition could lead to the increase in flexural modulus of EMC.…”

Thermal aging of molding compounds

“…It was expected that after prolonged exposure to high temperatures the polymer chains would break down [3], resulting in a lower glass transition temperature and a lower modulus. However, in literature also studies which show an increase in the glass transition temperature can be found [4]. Preliminary experiments showed that this was also happening to our molding compound.…”

“…Apart from ref. [4], surprisingly little studies can be found which report this increase in glass transition temperature and accompanied other changes in mechanical properties after prolonged exposure to high temperatures.…”

Evaluation of fan-out wafer level package strength

“…The EMC strength may become stable after the 1,000 hours' hightemperature storage test (Xu et al, 2017d). The reason is the high temperature increases the EMC glass transition, and the increased glass transition leads to the EMC flexural modulus increase (Mengel et al, 2004;Zhang et al, 2016). The evaluation work of FOWLP strength also can be implemented by the finite element method, besides the experimental method.…”