Robust encapsulation of hybrid devices

Abstract

An option for polymeric protection of bare ICs mounted directly to the surface of an alumina substrate is described. This robust package, with enhanced temperature-cycling performance and increased circuit survival rate under actual operating conditions, provides excellent protection throughout processing, handling, and field operation. The enhanced performance is the result of the high modulus and toughness of epoxy selective encapsulant-glob top. A combination of several physical enhancements in the material results from: (1) a higher silica filler content to lower the TCE (thermal coefficient of expansion) of the material, (2) the addition of elastomeric modifiers to improve the fracture toughness and dissipate stress, and (3) the definition of a cure schedule to optimize physical properties. The result of these factors is a good material formulation coupled with an enhanced cure schedule to yield a low-stress hybrid package. The final internal material stress, 3.2 MPa, is determined by the uniformly loaded beam method. The lower stress and lower TCE provide a four-fold improvement of temperature-cycling performance over older epoxy materials.<>