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The thermal cycling endurance of three different die attach adhesives was investigated by measuring the increase in thermal resistance during a thermal cycling test. Testchips were bonded to three substrates with different coefficient of thermal expansion. The thermal resistance increased with increasing number of temperature cycles. A large mismatch in thermal expansion gave the fastest increase in thermal resistance. The study also revealed a significant difference in behavior between the different adhesives. IntroductionThe possibility of using adhesives in chip attach applications has been given increasing attention during the last years. Important material properties such as thermal and electrical conductivity, as well as mechanical behavior have improved. The primary advantages of the adhesives are high processing flexibility, low processing temperature, no need for flux cleaning and it is not an expensive technique. The adhesives are rather expensive compared to solders but the processing cquipment is cheap. The primary disadvantages are long cure times and that the technology is not as well characterized as the solder technology. A major concern with chip attach materials is their ability to withstand the thermomechanical stress induced due to the difference in coefficient of thermal expansion (CTE) between the silicon chip and the substrate. Since the substrates have a larger CTE than the silicon chip and there is a cooling from cure to room temperature, the

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A new hybrid substrate technology for power electronic applications has been characterised by thermal resistance and mechanical stress measurements. The new substrate utilises thermal spray technology for deposition of dielectric layer and electrical conductors. The results are compared with the more established technology of alumina substrates with direct copper bonding (DCB) metallisation. Silicon test chips for thermal resistance and mechanical stress measurement were used for the characterisation. The experimental results were compared with finite element analysis and a reasonable agreement was found.