Degradation mechanism and reliability of flip chip interconnects using anisotropic conductive adhesives for high current density packaging applications

In this paper, we investigated the degradation mechanism and the reliability behaviors of flip chip joint using anisotropic conductive adhesives (ACAs) and Au bumped chip under high current density. The current carrying capability and current stressing reliability of flip chip assembly using three different types of ACAs were performed to investigate the effect of thermal conductivity of ACA and the conductive particle type on the current carrying capability and current stressing reliability of ACA flip chip joints. For the ACA materials, we prepared two conventional ACAs with different conductive fillers, which are thermally non-conductive, and one thermally conductive ACA. For the conductive fillers, we incorporated Au coated polymer balls and metallic Ni balls in 5 /spl mu/m diameter. For the thermally conductive ACA materials, we incorporated thermally conductive fillers of silicon carbide with less than 1 /spl mu/m diameter in the conventional ACA formulation. The thermal conductivity and thermo-mechanical properties of three ACAs such as thermal conductivity, cure behavior, coefficient of thermal expansion (CTE) were measured in comparison. The current carrying capabilities and current stressing reliabilities of flip chip joints using ACAs with different conductive filler type, thermal conductivity and physical properties were investigated. The current carrying capability and electrical reliability of flip chip joints using enhanced thermally conductive ACAs were improved due to high thermal conductivity. The failure analysis including cross-section SEM works shows that the interface degradation and adhesive swelling are main degradation mechanism of the high current density interconnection of flip chip assembly using conventional ACA, in which high junction temperature enhance such thermally induced degradation mechanism. The improved current carrying capability and current stressing reliability of flip chip assembly using thermally conductive ACAs were due to reduced interface and adhesive degradation through easy heat dissipation of adhesive that bring slow down of thermally induced degradation mechanism. There were no degradations of ACA flip chip joints using Ni-filled ACA and Au-coated polymer-filled ACA up to 200 hrs under 3.0 A current stress.