Low moisture polymer adhesive for hermetic packages

The chemical and physical characteristics of a novel thermoset die-attach paste developed to meet the low moisture requirement of attaching Si chips to ceramic substrates in hermetic packages and its functional performance as a die-attach medium are discussed. The combination of a glass transition temperature around 240 degrees C and high thermal stability up to 360 degrees C provides significant performance enhancement over conventional epoxies. In addition, the material exhibits high adhesive strength and very low stress on the die. Experimental results show that the moisture content in the cavity of a Au-Sn solder sealed ceramic package is less than 1000 ppm. The low moisture characteristic is found to be an inherent property of the material. Reliability tests such as thermal cycling, high-temperature storage showed that the low moisture level is still maintained after 1000 cycles or 1000 h at 150 degrees C. Results of the thermal performance of the material on thermal test chips are discussed and compared to results for silver-filled glass.<
>