Novel lead free nano-scale non-conductive adhesive (NCA) for ultra-fine pitch interconnect applications

Recently, non-conductive adhesive (NCA) bonding technology has attracted increasingly research interests as lead-free interconnect due to the fine pitch capability and low cost. The NCA usually requires no conductive fillers, but needs a relatively high pressure for bonding between the IC chip and the substrate coupled with heat. During bonding, the heat and pressure are applied for some time and the direct physical contact between the two surfaces of the IC bump and the substrate bond pad can be made with NCA resin curing/solidification. Contact of bottom and top pads/electrodes, via their up-and-hill (represents the uneven bond pads surfaces) surface structures, leads to the electrical conduction of NCA joints. In order to create the electrically conductive NCA joints, relatively high pressure and high degrees of the solidification of the polymer resin are required. This paper introduces a novel lead-free nano-scale NCA interconnect material with trace amount of in-situ formed nano conductive fillers. These uniformly distributed nanosized conductive fillers were in-situ formed in the epoxy resin and were well dispersed within the polymeric matrix. As such, the novel NCA joints were formed with lower bonding pressures and exhibited an improved electrical performance without sacrificing the fine pitch advantages of NCAs. The dramatic improvement was attributed to the enhanced interface properties by the nano-conductive fillers, which assisted the electrons tunneling and current flow.