Fabrication of SAC107 and Sn-0.7Cu lead free composite solder reinforced with Si3N4 via powder metallurgy route

Abstract

The composite technology is the new approach to improve the service temperature capabilities and thermal stability of the solder joints. Low-silver Sn98.3-Ag1.0-Cu0.7 (SAC107) and Sn99.3-Cu0.7 (Sn-0.7Cu) solders were used as matrix while silicon nitride (Si3N4) with different weight fractions (0, 0.25, 0.5, 0.75 and 1.0 wt. %) were added as reinforcement particles. The solder composites were prepared by using powder metallurgy method consists of mixing, compaction and sintering via microwave assisted rapid sintering. This microwave sintering approach results in more uniform heating with cost-effective and energy efficiency. The research project was divided into two phases. The first phase involves the fabrication and characterization of electrical, thermal, microstructural and mechanical properties of the bulk composite solder. The second phase was the studies on the properties of microstructural, solderability and mechanical properties as-reflowed solder joint/interconnection. It was noted that finer and well distributed reinforcement precipitates has led to higher microhardness and slightly decreased in melting point and electrical resistivity of bulk composite solder. The wettability performance of composite solder was improved. Correspondingly, the intermetallic compound (IMC) thickness was suppressed during the soldering. The dispersion strengthening effect enhances the shear strength and the fracture surface exhibit the ductile fracture mode with rough dimple surface instead of brittle fracture mode at the interface (substrate/solder) of composite solder joints. Overall, the addition of reinforcements into lead-free solder alloy matrix has improved all the listed properties of the solder materials.