Study on layer formation behavior of Ag joints sintered with pressureless sintering process

Abstract

This study focuses on investigating the relationship between sintering performance and bond layer thickness for the hybrid Ag paste consisting of micrometer-sized Ag particles and sub-micrometer Ag spherical particles. The surface morphology showed that the sub-micrometer Ag particles would contribute to improving the densification and bonding strength of the sintered Ag joint. The x-ray results indicated that the bonding quality was achieved when the bonding layer thickness was 50 μm, whereas a thinner or thicker bonding layer would lead to cracks or voids. Moreover, the microstructure of sintered Ag joints with different bonding layer thicknesses was found to be in good agreement with the results of x-ray by SEM observations. There are many cracks in the sintering structure due to the insufficient Ag paste when the bonding layer thickness is below 50 μm, while more voids appeared in sintered Ag joints when the thickness reached 120 μm, which was caused by the organic solvent volatilization. In addition, the poor densifications lead to low strengths of 7.6 MPa and 23.42 MPa for 15 μm and 30 μm thickness, respectively. The shear test results revealed that the highest shear strength was achieved on the bonding layer with a 50 μm-thick bonding layer. However, the bonding strength would decrease to 24.67 MPa and 18.64 MPa when the bonding layer thickness was 90 μm and 120 μm, respectively. The SEM observations indicated that many dimples were formed on the fracture surface with a thickness of 50 μm, which was the reason for the enhancement of bonding strength in the sintered Ag joint.