Chemistries for High Reliability in Electronics Assemblies

Abstract

This article provides a review of the attitude of the scientific community towards reliability in electronic packages, with emphasis on the prevailing mechanisms for package failure under highly stressed environmental conditioning. Once this failure mechanism is fully developed, approaches to the resolution can be more rigorously applied. Overall, the predominant evidence points to moisture, both diffusivity and equilibrium weight gain, as the key factor in reduced reliability performance. Other fundamental polymer properties are important, but generally, methods are well established for adjusting these parameters. Moisture uptake is somewhat inherent to a particular chemistry type and this can direct the use of resin systems that are more suited to particularly moist environments. Epoxy resin systems, while pervasive in the electronics industry, do have limitations under humid environmental test conditions. Cyanate ester resin chemistry is claimed to have low moisture uptake by virtue of a non-hydrophilic cure mechanism. However, certain aspects of the cure chemistry and side reactions with water can result in misleading predictions on humid environment performance. Siloxane-based materials present an attractive solution to many moisture related issues. Traditional condensation and addition cure silicone systems have, thus, found widespread use as packaging adhesives and encapsulants. Siloxane-functional polyimides have also been successfully utilized in a number of application areas. Relatively new siloxane/hydrocarbon resins, developed specifically for electronics applications, further address the shortcomings of classic silicone adhesives and coatings.