Joachim Mahler

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 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 Tg. 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 Tg 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.

Degradation of moulding compounds during highly accelerated stress tests – A simple approach to study adhesion by performing button shear tests

High temperature storage can degrade moulding compounds for chip encapsulation to such an extent that the adhesion to surfaces like copper (lead frames) or polyimide (chip coating) decreases drastically causing delamination. Also during normal operation of electronic components heat is generated locally (bond wire or chip surface) degrading the moulding compound and reducing the adhesion which in extreme cases can destroy the metallisation or the bond wires.