Investigation of bonding properties of solderable anisotropic polymer composite filled with low- and high-melting-point alloy fillers

The bonding properties of solderable anisotropic polymer composites (SAPCs) containing only low-melting-point alloy (LMPA) fillers need improvement. In this study, a new composite containing LMPA and high-melting-point alloy (HMPA) fillers, named LH-SAPC, was proposed, and the establishment of the conduction path and bonding properties of LH-SAPC were investigated for different LMPA/HMPA mixing proportions. Six types of LH-SAPC filled with different LMPA/HMPA mixing proportions (100:0, 80:20, 50:50, 20:80, 10:90, and 0:100) were formulated, and bonding tests were performed using the quad flat package. The LH-SAPCs containing less than 50 vol% HMPA within the LMPA/HMPA filler formed a proper and broad conduction path through of the excellent inner flowage of molten fillers within the polymer composite maintaining a low-viscosity condition, coalescence behavior between adjacent fillers, and a wetting behavior for the metallization. In addition, the mechanical bonding properties of the LH-SAPC joints improved with increasing HMPA content owing to the precipitation hardening and dispersion strengthening effects of the finely distributed Bi-rich phase and intermetallic compound particles within the conduction path and grain refinement. In contrast, as the HMPA content was excessive within the LH-SAPC, a poor conduction path was established because of the fluidity deterioration of the molten HMPA, which was attributed to the immoderate curing of the polymer composite; accordingly, the mechanical properties of the LH-SAPC joint degraded.