In order to overcome several crucial limitations to the traditional electrically conductive adhesive bonding used in the electronics field, a novel low-melting-point alloy (LMPA)-filled ICA (Isotropic Conductive Adhesive) was synthesized. Also, a hybrid interconnection process using it was developed, which can be achieved by melting-coalescence-wetting behavior of LMPA fillers in ICA. In order to ensure excellent coalescence and wetting characteristics of the LMPA filler particles, the fluxing capability of the resin should have been sufficient to remove the oxide layer on the surfaces of the filler particles and the electrode materials. The effect of reductant on the hybrid interconnection formation was examined.
ICAs with and without reductant were formulated with a 40% volume fraction of filler. The QFP chip had a size of 14×14×2.7 mm and a 1 mm lead pitch. The test board had a 18 μm thick Cu daisy-chained pattern. Thermal characteristic of the ICA was observed by differential scanning calorimetry (DSC), and the temperature-dependant viscosity characteristic of the polymer matrix was observed by torsional parallel rheometer. Based on the results, the reflow profile of the interconnection process was determined. The dipping interconnection method was applied in the QFP bonding process. After the QFP bonding process, the electrical characteristic of ICA was measured with a multimeter. The wetting, bondability, coalescence characteristics of the LMPA filler particles and the morphology of the conduction path were observed by microfocus X-ray inspection systems and optical microscopy. As a result, the LMPA-filled ICAs with reductant had stable contact resistance, forming the metallurgical interconnection. A good electrical conduction path was achieved with the coalescence and wetting characteristics of the molten solder particles in the ICA.