Accelerated solid-liquid interdiffusion bonding of Cu joint using a Cu10Ni alloy mesh reinforced SAC305 composite solder

Abstract

High reliable packaging materials are essential for wide band-gap power devices due to the thermal and mechanical stresses arising from extreme environmental conditions. In this study, two-dimensional pure Cu mesh or Cu–10Ni (wt.%) alloy mesh reinforced SAC305 composite solders were employed to create solid-liquid interdiffusion (SLID) soldering of Cu substrates at 250 °C. The microstructure evolution behavior of the soldering seam was investigated based on EPMA and EBSD characterizations, and the strengthening mechanism of the joint was discussed. Results showed that the pure Cu mesh reacted slowly in the Sn matrix and large-sized Cu6Sn5 grains were formed in the solder seam; while for joints using Cu–10Ni alloy mesh, the addition of Ni causes the Cu–Ni mesh to quickly dissolve and promote the formation of the fine-grained (Cu,Ni)6Sn5 phase. Increasing the mesh number of Cu–10Ni alloy skeleton could enhance the metallurgical reaction rate of the soldering seam and the grain-size reduction of the (Cu,Ni)6Sn5 phase; ultimately, the joints were completely composed of fine-grained (Cu,Ni)6Sn5 phase and reaction-residual Cu–10Ni skeletons. The refining mechanism of the (Cu,Ni)6Sn5 grains was discussed in detail. The shear strength of the Cu alloy joints varied with changing alloy skeletons and soldering time, and the joint soldered with 300 mesh Cu–10Ni skeleton for 210 s obtained the highest shear strength of 47.8 MPa. The grain boundary strengthening effect of fine-grained (Cu,Ni)6Sn5 phase, synergized with the toughening effect of the alloy skeleton, ultimately achieving highly reliable joints.

Keywords

• Solid-liquid interdiffusion bonding
• Cu–10Ni (wt.%) alloy mesh
• SAC305 composite solder
• EBSD characterization
• Mechanical properties