Coexistent improvement of thermal and mechanical performance at Si/Cu joint by thickness-controlled Sn-Ag bond layer

In this study, sound Si-Cu joints with high thermal conductivity and mechanical property were achieved at 260 °C with thickness-controlled Sn-Ag bond layer. The microstructure evolution, thermal and mechanical properties were proposed systematically. The bond layer was fabricated by micro electroforming technology to precisely control the thickness and improve the bond ability. The electroformed Ag layer could protect the sputtered Cu film and restrict the diffusion of Cu elements, which could decrease the residual stress and remove the interface defects. At the joints, the electroformed Sn layer was consumed to form Ag3Sn and Cu6Sn5 intermetallic compounds. The thermal conductivity and shear strength both increased firstly and then decreased with the thickness of bond layer increasing. The highest thermal conductivity of 283.21 W/(m·K) and shear strength of 88.74 MPa were achieved synchronous with 15-μm-thickness Sn-Ag bond layers, which were attributed to the reduction of the interface stress and elimination of interfacial defects. This technology had potential to be applied in the microelectronic heat dissipation at the future.