New snap cure materials

As uses for semiconductor devices and microsystems tend to increase, there is a growing demand for resin formulations useful in the manufacture of adhesives, underfills, encapsulants and the like. Resin compositions comprising cyanate ester and epoxy resins have been demonstrated to be useful as die attach adhesives, underfills and encapsulants. While the performance characteristics for such resin compositions are adequate for many applications, there is a continuing need to improve their manufacturing performance, especially. Critical problems to be solved are a too short pot life (less than 8 hours) and a too long cure schedule (e.g. 175/spl deg/C for more than 1hour). We encapsulated small particles (size in the range of 10 /spl mu/m) of effective hardeners to make them insoluble and non-reactive when mixed with the resin at room temperature. In this way, mixtures of the commercial liquid cyanate ester Primaset LeCy (Lonza AG) with encapsulated hardeners reach pot lifes of more than 3 months, whereas the cyanate ester gels and becomes solid within 30 minutes at room temperature, if the neat hardener is used instead of the capsules. At a certain elevated temperature, which mainly depends on the structure of the hardener, the capsules open and the curing reaction starts immediately. Curing temperatures and times as well as properties of the resulting thermosets depend on the structure and reactivity of the hardener and of the resin used, where a broad variety of combinations can be designed. Low-temperature systems with cure times less than 5 minutes at 80/spl deg/C reach glass temperatures of about 140/spl deg/C, whereas a glass temperature of 220/spl deg/C after 10 seconds cure can be achieved with another combination. The developed snap-cure resin systems can be easily mixed with a lot of common additives such as minerals, tougheners, metallic powders and others to cover a wide range of performance characteristics for use as adhesives, underfills, encapsulants - nd the like.