Electronically conductive adhesives: Conduction mechanisms, mechanical behavior and durability

The objective of this paper is to add to the fundamental understanding of the conduction mechanisms and mechanical behavior of electrically conductive adhesives and their applications. Consequently, the research work to be presented involves two parts: (a) analysis of mechanical behavior, and (b) analysis of electrical behavior of conductive adhesives. Electrical and mechanical behaviors of both bulk conductive adhesives and single lap joints bonded with a conductive adhesive are studied. For bulk conductive adhesives, a model is established to predict the adhesive conductivity. The effect of film thickness on the conduction behavior of conductive adhesives is also presented, and it is shown that in thin flim adhesives the resistivity values in planar directions are much larger than those encountered in 3-D measurements for the same adhesive material. The thermal mismatch stress induced at the interface between the adhesive and the substrate is studied in closed form and by finite element analysis, and the mechanical properties of the filled adhesive composite are obtained for this purpose. Calculations for a typical adhesive interconnection reveals the possibility of failure initiation due to thermal mismatch. Silver fillers are considered in discussions and calculations. Consequently, the silver migration phenomenon and its dependence on environmental temperature is also studied. The migration time is shown to decrease with increasing voltage, and high temperature ambient conditions are shown to speed up the migration.