Resistance characterization of flip chip joint formed using Au bumps and anisotropic conductive adhesives

In this paper, the resistance characterization of flip chip joints formed using Au bumps and anisotropic conductive adhesives (ACAs) is reported. A flip chip on glass (FCOG) test vehicle with indium tin oxide (ITO) conductive lines was used to study the effect of Au bump structure, bonding forces, bump size, conductive filler size and conductive filler loading on contact resistance. Both anisotropic conductive film (ACF) and anisotropic conductive paste (ACP) with varying filler sizes and filler loadings were used to assemble the FCOG test vehicle. Joint contact resistances were obtained by a 4-point measurement method. Results showed that ACP joints generally requires an order of magnitude lower bonding force than ACF joints to achieve consistent contact resistance values. Uncoined Au bumps are preferred for ACF and ACP joints because they offer lower contact resistance than coined Au bumps. This work has led to a better understanding of contact resistance in ACF and ACP joints.