A novel low-melting-point solder (LMS) and high-melting-point solder (HMS)-filled solderable isotropic polymer composite (LH-SIPC) was developed to enhance the interconnection properties of a solderable isotropic polymer composite (SIPC) containing only LMS filler. To determine the effect of the LMS/HMS (i.e., Sn-58Bi/Sn-3.0Ag-0.5Cu) mixing ratio on the interconnection properties of LH-SIPC joints, LH-SIPCs with different mixing ratios of the LMS/HMS filler were formulated, and an interconnection test using a quad flat package was performed. The LH-SIPC joints having HMS content of less than 90 vol% in the filler formed a wide and stable conduction path through the proper internal flow, coalescence, and wetting behavior of molten fillers within the polymer composite with low viscosity owing to the decreased melting point of HMS caused by the interaction between the molten LMS and solid HMS. Moreover, the mechanical properties of LH-SIPC joints were linearly improved as the HMS content increased because of precipitation hardening and dispersion strengthen effects of the fine Bi phase and intermetallic compound particles distributed in the conduction path and refinement of grain size. However, LH-SIPCs with excessively high HMS content formed a poorly shaped conduction path because of excessive curing of the polymer composite, which resulted in the deterioration of the interconnection properties of the LH-SIPC joint.
