Modelling of the initial stages of the anisotropic adhesive joint assembly process

Industrial experience and academic studies to date indicate the initial stages of the assembly process for anisotropic adhesive joints are particularly significant to the successful formation and long term performance of the completed assembly. The consistency of the process is controlled by the early stages of compression and the resulting distribution of conducting particles is affected by the adhesive resin flow in the early stages of the assembly process. The bump geometry on flip chip assemblies has been found to be critical to the success of the process as it significantly affects the early stages of the adhesive film compression. This paper describes analytical and CFD models which explore the time required to squeeze out the adhesive as a function of applied pressure, temperature ramp rate, and adhesive viscosity. The results of a study on adhesive rheology are presented and used in the flow models. The paper also explores the flow of conducting particles within the adhesive, and hence the final particle distribution underneath the flip chip. This distribution has been shown in the past to significantly affect the probabilities of shorts and opens