An alternative to epoxy resin for application in isotropically conductive adhesive

Abstract

Isotropically conductive adhesive formulations predominantly include epoxy resin as the polymer matrix. Although epoxy has superior adhesion capability, it has a tendency to absorb moisture and is nonreworkable. The presence of water in ICA interconnects causes contact resistance degradation by means of galvanic corrosion. In this study, an alternative polymer matrix with low moisture absorption and potential for reworkability, is used in isotropically conductive adhesive (ICA) formulation. The contact resistance of this group of ICAs is measured throughout an accelerated aging process (85/spl deg/C/85%RH). The four point probe method is used to measure contact resistance on test coupons. Contact resistance stability of the ICAs is compared among test coupons of various surface finishes (OSP, Sn/Pb, Sn, and Ni/Au). SEM analyses are conducted on cross sections of coupons that fail early in the aging process and they are compared with coupons with stable resistance. Adhesion capability of this alternative polymer is compared with epoxy on various surfaces, e.g. OSP, Sn/Pb, Sn, and Ni/Au, using a die shear tester. Coupling agents are incorporated into the ICA formulations and their effects on adhesion and contact resistance stability are studied. Blends of epoxy and this alternative polymer are also evaluated. Contact resistance measurements of a thermoplastic-thermoset ICA blend are collected throughout the aging process. Adhesion data of the ICA blend is also collected using a die shear tester. Such a blend should produce a formulation with good adhesion and low moisture uptake, which will be verified by the experimental results.