Microstructure and Shear Strength of Low-Silver SAC/Cu Solder Joints during Aging

Abstract

A new type of low-silver hypoeutectic SAC lead-free solder was prepared, and then hot dip soldering was used to form the joints of copper. The microstructure evolution of IMCs and the variation of shear strength of solder joints were investigated. The results have shown that the thickness of the IMC layer increased over time and the scallop-type IMC became a hump like shape during the aging process. The growth rates of the IMC layer were 0.61 × 10⁻¹⁴ cm²/s, 2.06 × 10⁻¹⁴ cm²/s, 4.83 × 10⁻¹⁴ cm²/s at 348 K, 373 K and 423 K respectively. The shear strength of solder joint fell sharply at first and then became slow, finally dropped from 40.94 MPa to 29.73 MPa after aging at 423 K for 12 days. Moreover, the fracture mode changed from ductile fracture to local brittle fracture with the increasing of aging time.