Effect of reflow time on microstructure and mechanical properties of soldered joints of pure copper substrate with Sn0.3Ag0.7Cu solder

Taking Sn0.3Ag0.7Cu as solder and pure Cu plate as substrate, Cu/Cu₃Sn/Cu₆Sn₅/Cu₃Sn/Cu multilayer structure all-intermetallic compound soldered joints were prepared by transient liquid phase diffusion welding process. Scanning electron microscope and energy dispersive spectrometer were used to analyze microstructure and composition of soldered joints, shear strength of soldered joints was tested, and growth mechanism of intermetallic compounds at interface was studied. The results showed that growth rate of Cu₆Sn₅ at the cold end was greater than that at the hot end due to the influence of temperature gradient. When reflow time was 5 h, all-intermetallic compound was formed in weld, interface of weld was relatively flat and free of defect, shear strength was reduced from 32.16 MPa to 21.29 MPa with a decrease of 33.8%, and fracture mode evolved from plastic fracture to brittle fracture.