Mechanical properties and microstructure evolution of Cu/Sn58Bi/Cu solder joint reinforced by B4C nanoparticles

Abstract

The mechanical mixed Sn58Bi solder reinforced by B4C nanoparticles for the interconnect of Cu/Cu same metal was studied. The hardness of solder alloy and shear strength of joints with Sn58Bi-xB4C (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) composite solder were tested. The feasibility of the solution was verified by the performance of melting characteristics, wettability, microstructure, and interfacial IMC structure. It is indicated that the proper amount of B4C nanoparticles can improve the mechanical properties of the solder joint, and the hardness of the solder alloy is decreased to 246.0 HV by 13.65% with the addition of 0.6 wt% B4C and the highest shear strength of the joint reaches 52.282 MPa, which is increased by 8.9%. The failure mode of fracture is mainly considered a brittle fracture. The preferred orientation of the β-Sn phase and Bi phase are (1 0 0) and (1 0 1), respectively, and the number of low-angle grain boundary and dislocation density are increased. The melting characteristics of the solder are less affected by B4C nanoparticles, which will not interfere with its normal use. When the amount of B4C is 0.6 wt%, the spreading area of the solder is increased by 35.44%. Besides, a moderate amount of B4C nanoparticles is able to refine the matrix structure of the solder and inhibit the growth of Cu6Sn5 IMC.