Performance of epoxy encapsulants for optoelectronic packaging

The optical, mechanical and thermal properties of a specialty epoxy-anhydride molding compound are presented. Physical properties are compared to the performance of other types of epoxies (i.e. hisphenol A-and cycloaliphatic-based). This epoxy-anhydride system is demonstrated to have superior optical transmission properties upon accelerated heat aging. The adhesion to various lead-frame finishes is discussed and the effect of adhesion promoter demonstrated. Finally, approaches to toughen these materials through the use of a miscible thermoplastic polymer are discussed along with the effect on thermal cycling crack resistance of molded TO220 packages.