The bonding properties of various surface finishes with Cu paste for pressure sintering

This study suggests a newly developed pressure type Cu sinter paste as a bonding material for power electronics. Our previous study on ECTC2019 showed high bonding strength and high reliability between Ag metallization and Cu sintered layer. Bonding mechanism is also reported. In this study, we investigated bonding property between Cu paste and two kinds of surface finishes, Ni/Au and Ni. Ni/Au and Ni were electro plated on Cu substrate. For device, an Ag metalized 5mm by 5mm Al
₂
O
₃
mechanical die is used. Sintering temperature was 280°C in N
₂
. The sintering time and pressure are different in each condition. Ni/Au substrate was 5 minutes with 9 MPa pressure. Ni plated substrate was 20 minutes with 15 MPa. After sintering, all the samples were evaluated by sound acoustic tomography (SAT) and shear strengths were measured. The shear strengths were over 80 MPa in both surface finishes. Our previous results with Cu surface finish were also over 80 MPa. The energy dispersive spectroscopy (EDS) was analyzed for each bonding state between Cu paste and surface finishes. The mutual diffusion (MD) is observed between Cu paste to Au layer, and also between Cu paste and Ni layer. The MD depth of Cu to Au is deeper than that of Cu to Ni layer. This newly developed Cu paste demonstrates promising adaptability for various surface finishes for power electronics as a bonding material.