Isotropic conductive paste based on epoxy with Ag coated Cu and SAC305 solder

摘要

Isotropic conductive paste (ICP) has been continuously developed to get a good electrical performance for the semiconductor packaging applications. The conductivity of the ICP material is simply determined based on the contact between adjacent metal particles in a polymer matrix. Therefore, the mechanical shock applied on the semiconductor package can be a bad point of the adhesive strength between the substrate and polymeric matrix in the ICP material. In the present research, an isotropic conductive paste based on epoxy with Ag coated copper and solder was investigated. An isotropic conductive paste, called a hybrid Cu paste (HCP), which is composed of fluxing resin, Ag-coated Cu flakes, and solder powder, is placed between the top and bottom substrates. With increase of process temperature, the solder particles placed between the Ag coated Cu particles, as well as between the metal pads and Ag coated Cu particles, are eventually melted, thereby performing electrical interconnections through solder wetting owing to the oxide on the surface of the solder particles and metal pads being removed by the fluxing resin matrix. Specially, nano Ag coated Cu flakes was used to decrease the electrical performance as well as to keep the minimum viscosity at room temperature. After completion of curing processing, the fluxing resin is solidified due to the chemical reaction of epoxy resin. The electrical and mechanical interconnections of the hybrid Cu paste are strongly dependent on the wettability of the solder as well as by the adhesion of the resin matrix between the metal substrate and conductive filler, while that of a conventional ICA with silver particles is only determined by the shrinkage and adhesion strength of the resin matrix during processing.