Simulation of the aging behavior of isotropic conductive adhesives

Although, in numerous studies the changes of contact resistance during accelerated aging under elevated temperature and humidity were observed there is still a lack of understanding of degradation mechanisms. Some models illustrate connections between the contact behavior and parameters of the conductive filler. In addition to these considerations in our paper we describe the macroscopic behavior by considering the microscopic resistance change between the conductive particles themselves and between particles and contact pads. For this purpose, we calculated the electrical contact resistance with a two dimensional numeric simulation. Herein the conductive particles are modeled by randomly distributed ellipses placed between two parallel electrodes comparable to silver flakes as known from metallographic cross sections of our contact samples. The voltage and current distribution and the contact resistance as well are calculated by transforming this model into a resistor network. During a forced aging process different opposite effects occur in an adhesive joint. One effect is the increase of entire resistance due to a degradation of the interparticle contact. Another effect is the decrease of resistance caused by a post curing of the resin during aging of the adhesive joint. This behavior was experimentally determined in a previous investigation. In accordance to these effects we simulate the aging process of the joint by introducing different time dependencies of the interparticle resistance. The goal of this study is to provide a deeper understanding of the changes of the macroscopic contact behavior due to different environmental impacts.