Abstract: A 20 μm thick Sn-0.3Ag-0.7Cu solder paste was uniformly coated between two copper substrates. Transient liquid phase diffusion bonding tests were conducted at different reflow temperatures （240, 260, and 280 ℃） and different reflow time periods （0, 1, 2, 3, 4, and 8 h）. The interfacial microstructure and shear property of the joints bonded by different processes were investigated. The results show that by reflow 240 ℃, the amount of Cu₆Sn₅ intermetallic compound at the joint interface increased and then decreased with the extension of reflow time period, and its morphology was transformed from a scalloped shape to a layered structure. When the reflow time was 4 h, the weld seam was almost filled with Cu₆Sn₅, and a thin Cu₃Sn intermetallic compound layer was formed at interfaces between weld seam and base metal. After 8 h of reflow, large pores were formed in the weld seam, and the thickness of the Cu₃Sn intermetallic compound layer increased. The thickness of the intermetallic compound layer first increased and then decreased with the extension of reflow time or increase of temperature. The growth of the intermetallic compound was characterized by volume diffusion, with the diffusion coefficient increasing at higher reflow temperatures. The shear strength of the joint first increased and then decreased with the extension of reflow time. When the reflow time was 4 h, the shear strength was the highest. The reflow temperature had little influence on the shear strength.