Chemistries for high reliability in electronics assemblies

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 conditi oning. Once this failure mechanism is fully developed, approaches to the re solution can be more rigorously applied. Overall, the predominant evidence points to moisture, both diffusivity and equilibrium weight gain, as the ke y factor in reduced reliability performance. Other fundamental polymer prop erties are important, but generally, methods are well established for adjus ting 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 Epoxy resin systems, while pervasive in the el ectronics industry, environments. do have limitations under humid environme ntal test conditions. Cyanate ester resin chemistry is claimed to have low moisture uptake by virtue of a non-hydrophilic cure mechanism. However, cer tain 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, fou nd widespread use as packaging adhesives and encapsulants. Siloxane-functio nal polyimides have also been successfully utilized in a number of applicat ion areas. Relatively new siloxane/hydrocarbon resins, developed specifical ly for electronics applications, further address the shortcomings of classi c silicone adhesives and coatings.