Flip-chip assembly using anisotropic conducting adhesives: experimental and modelling results

This paper presents the results of a programme of experimental and computational work aimed at understanding key issues involved in using anisotropic conducting adhesive (ACA) materials in fine pitch flip-chip assemblies. The experimental programme involved the construction of a number of assemblies with flip-chip devices (unbumped and bumped) at a pitch of 200 μm on ceramic and organic substrates. Measurements made on these assemblies show wide variations of conductivity at the electrical joints of the flip-chip assemblies, constructed under apparently the same experimental conditions. Attempts were made to identify reasons for the poor conductivity uniformity and to explain the origin of the unsatisfactory connections through experimental analysis of the linearity of the contact resistances and the effects of gap height on conduction within anisotropic conducting adhesive assemblies. In addition, computational models of metallic conduction in solid and polymer-cored particles were constructed to help further understand the conduction mechanism at electrical joints. Results indicate that flip-chip assemblies with larger conducting particles within the ACAs are able to produce higher yield than those with smaller conducting particles, while the experimental and computational analyses strongly suggest the presence of thin insulating films between particles and that give rise to nonuniform conductivity