Improving the thermo-mechanical reliability of solderable isotropic conductive adhesive joints by using low- and high-melting-point solder fillers

In this study, we investigated the effect of adding a mixed low-melting-point solder (LMS)/high-melting-point-solder (HMS) filler on the thermo-mechanical reliability of solderable isotropic conductive adhesive (SICA) joints. To this end, we compared the properties and thermo-mechanical reliability of L-SICA (fabricated with LMS filler) and LH-SICA (fabricated with the mixed LMS/HMS filler). LH-SICA exhibited enhanced mechanical interconnection properties compared with L-SICA due to precipitation hardening and dispersion strengthening effects arising from the distribution of intermetallic compounds (IMCs) Ag ₃ Sn and Cu ₆ Sn ₅ , and Bi-rich phase particles within the joint. The results of thermal shock testing revealed that the electrical reliability of both SICA assemblies remained stable owing to the formation of a metallurgical conduction path between the corresponding leads and electrodes through the molten solder filler. Although the pull strength of SICA assemblies tended to decrease compared with their initial pull strength during thermal shock testing, LH-SICA exhibited improved thermo-mechanical reliability compared with L-SICA. This is due to the enhanced bonding properties, a reduction in microstructural coarsening, slower growth and flattening of the IMC layer at the bonding interface, and a reduction in the accumulated Bi-rich phase at the bulk solder/Cu ₆ Sn ₅ IMC interface resulting from changes in the composition of the LH-SICA joint.