Combined Thermally and Electrically Conductive Adhesives

We are proposing the development of adhesives that will be capable of conducting heat and electricity at levels significantly above currently available systems while offering improved processability.A novel thermoplastic/epoxy hybrid paste adhesive will use an advanced formulation approach to achieve unusually high conductive filler and thermoplastic loadings while still maintaining a low viscosity. It will have a thermal conductivity of more than 15W/mK combined with an electrical resistivity of less than 40 microhm-cm. This is a combined performance better than the separate film adhesives currently used for the F-22 sub-array assembly. Further improvement of the electrical or thermal propertieswill be possible with additional development. A high thermoplastic content will allow rework and will provide unusual toughness to resist thermal cycling failure. The advanced formulation approach to both high filler and thermoplastic content will stillallow a material that flows like current pastes, thus allowing the productivity gains of automatic dispensing.In order to provide a technology backup and process alternative, we will also develop an epoxy film with both a thermal conductivity (>40 W/mK) and an electrical resistivity (<20 microhm-cm) better than solder. This z-axis film is the next generation oftechnology of our z-axis thermally conductive adhesive that has been developed for the BMDO/USAF. This will eliminate the need for separate adhesives for the F-22 sub-array assembly in areas of very high thermal or electrical transport across an adhesivebond line and will open many applications for solder replacement.The best thermally conductive adhesives are diamond filled and have a thermal conductivity of 10-12 W/mK with very high electrical resistance. The highest electrically conductive adhesives have a resistance of 100 to 500 microhm-cm and a thermalconductivity of 2-5 W/mK. Our proposed automatic dispensable paste adhesive will initially provide up to 20 W/mK thermal conductivity together with less than 40 microhm-cm electrical resistivity. A flowable paste adhesive with these much higherconductivities will open up many high performance electronic assembly applications due to the productivity improvements created by automated processing. The proposed z-axis film adhesive will be able to out perform solder in both thermal and electricalconductivity while requiring a sharply lower processing temperature. Such significant performance enhancement will find application in a variety of electronic packaging products and processes to reduce the yield loss caused by the high processingtemperature of solder.