Design Guidelines for Anisotropic Conductive Adhesive Assemblies in Microelectronics Packaging

Multiple parameters are involved in the design of anisotropic conductive adhesive assemblies, and the overlapping influences that they have on the final electrical contact resistance represent a difficult challenge for the designers. The most important parameters include initial bonding force $F$⁠, number of particles $N$⁠, the adhesion strength $GA$⁠, and modulus of elasticity $E$ of the cured resin. It is well known that as the bonding force increases, the contact resistance decreases. However, when the bonding force reaches a certain maximum value, the contact between conductive particle and conductive track is disrupted due to delamination of the cured resin during the elastic recovery. The authors have shown in previous studies that the delamination is caused by high residual stresses and that it largely depends on the adhesion strength of the assembly and on the modulus of elasticity of the cured resin. Additionally, the authors have provided a methodology to quantify the maximum threshold value of the bonding force for different numbers of particles trapped between mating conductive tracks. In this paper, the relationships between contact resistance $R$ and each one of these parameters are systematically investigated to create diagrams that give regions of robust design. Given the number of particles and their size, adhesion strength, and modulus of elasticity of the resin, the required bonding force can be found in order to achieve a desired range in contact resistance.