Recent advancements in olefin thermoset adhesive

Abstract

A paste adhesive system based on a modified cyclic olefin thermoset (MCOT) polymer was first introduced in 1997. MCOT consists of blocks of cyclic olefin (rigid) and linear olefin (soft). Due to its hydrophobic molecular structure, moisture absorption is inherently quite low, typically less than 0.1%; an order of magnitude lower than that of epoxies. Although its adhesive strength is less than that of epoxy, the MCOT based adhesive has been successfully used as die attach material for BGA packages. This paper describes our continued technology development to enhance the adhesion performance of MCOT material. The low adhesive strength is caused by the lack of reactive functional groups in the MCOT structure. Some desirable organic functional groups were identified, and grafted onto both the linear and cyclic olefin structures of MCOT. Using a Neural Network Analyzer model, we examined the effects of several variables such as the amount and type of reactive groups, and polymer molecular weight against key outputs such as adhesion, % moisture absorption, and viscosity. An optimized resin formulation with respect to these key elements was derived from this modeling approach. The improved MCOT composition shows at least twice the adhesion strength on various substrates with minimal impact on moisture absorption. Adhesion values are now comparable to epoxy. The new material with a unique combination of ultra low moisture and high adhesion appears to have the versatility to address a broad range of applications. It may promise to play an important role of the total material solution for many contemporary problems in polymer based packages.