Isotropic conductive adhesives with fusible filler particles

A new low-temperature assembly process using a new class of isotropic conductive adhesives (ICAs) with fusible filler particles was proposed to realize a low-temperature, fluxless and cost-effective, alternative, solder flip-chip interconnection technology. New ICA formulations were developed using two different resin materials and fusible filler particles. The curing behavior of the resin materials and the melting of the fusible filler were observed by differential scanning calorimetry (DSC). The coalescence and wetting states, the size distribution of the fusible fillers, and the formation of the conduction path in each ICA formulation were observed with a laser microscope. It was found that two different types of electrical conductive paths, necking type and bump type, were produced. The bump-type conductive path was more effective than that of the necking type in achieving a lower electrical resistance through resistance measurement. The reduction capability of the base resin material was effective for the coalescence and the wetting of the fusible fillers and affected the conductive path type. A good metallurgical connection was formed between the fusible fillers in ICAs and between the fusible fillers and the copper surface even at the lower filler-volume fraction of 30%.