TZ2018003), the National Science Foundation of China (No. The work was supported by the Science Challenge Project (No. To enhance the bonding, the substrate surface roughness should accommodate the viscosity, particle size, and shrinkage of the silver paste Acknowledgments The shear strengths first increased with surface roughness because of increased contact area for metallic bonds and mechanical interlock, and then decreased with surface roughness, most likely due to localized debonding. ![]() The effects of surface roughness on die-shear strength of pressureless in-air sintered-silver die-attach on copper substrates were studied. The shear strengths first increase Conclusions 1 shows the plots of die-shear strength versus surface roughness. Results and discussionĪs with the Ag-sintering on Cu substrates, only the metallic bonds (between sintered-Ag and Cu) and mechanical interlock (from the perspective of surface roughness effects) are considered in this study, since the contributions of the other forces (such as physical adsorption and electrostatic force etc.) to the total bonding strength are negligible by an order-of-magnitude comparison. The surface roughness on Cu substrates were obtained as R a = 0.15–8.41 µm and R z = 1.22–50.97 µm by polishing with 60–2000 grits sandpapers. The surface roughness on die was R a = 0.2 μm and R z = 1.5 μm. The surface roughness was measured using an optical surface profilometer (Zygo, NewView™ 9000). Samples were fabricated by attaching Ag-plated silicon dice (3 × 3 mm 2) using sintered nanosilver paste (average diameter of Ag particles is 0.6 μm) on Cu substrates with different surface roughness. The results presented in this study could help to prepare DBC substrates with optimized surface roughness for well using the Ag-sintering die-attach technology. The findings helped us to achieve the high bonding strength in excess of 50 MPa in the case of surface roughness R a slightly larger than the Ag particles, by likely generating full contacts for strong metallic bonds and mechanical interlock. In this study, we did die-attach on Cu substrates with different surface roughness using nanosilver paste pressureless sintered in air. Therefore, it is crucial to find out the effects of surface roughness on the bonding strength of sintered-Ag die-attachment. , however, reported higher bonding strength using substrates with a rougher surface. , obtained higher bonding strength using substrates or devices with a smoother surface. It has been reported that the surface roughness greatly influences the bonding strength of sintered-Ag die-attachment. ![]() ,, , while cold-spray typically generates very rough surfaces with R a of 5–20 µm and R z of 20–60 µm. In general, relatively smooth surfaces with R a < 5 µm and R z < 20 µm can be obtained by eutectic-bonding, active-metal-brazing (AMB), and metal-casting-direct-bonding (MCB) method etc. The surface roughness is typically characterized using arithmetical mean surface roughness ( R a) and maximum roughness depth ( R z). The Cu surface could have a wide range of surface roughness due to the various processing techniques for bonding Cu sheets on ceramic insulation layer during DBC substrate manufacturing,. It has been reported that the strong die-attach on low-cost copper (Cu) surface can be obtained by pressureless silver-sintering in air, which has great significance in power electronics. With the development of wide-band-gap devices targeting for high-temperature and high-power applications, die-attachment by low-temperature sintered-silver was increasingly used as an alternative to solders or epoxies, due to its high-performance and high-reliability,. This work could help to prepare DBC substrates with optimized surface roughness to accommodate the viscosity, the particle size, and the sintering shrinkage of the silver paste for well using the sintered-Ag die-attach technology. When the surface roughness ( R a of 0.65 μm) is slightly larger than the silver nanoparticles (diameter of 0.6 μm), the high shear strength in excess of 50 MPa was achieved, likely due to both strong metallic bonds and mechanical interlock. ![]() In this study, we did die-attach on Cu substrates with surface roughness R a = 0.15–8.41 µm and R z = 1.22–50.97 µm by pressureless sintering of nanosilver paste in air. It is crucial to find out how the surface roughness influences the bonding strength of the sintered-silver (Ag) die-attachment. The Cu surface in direct-bond-copper (DBC) substrates could have a wide range of surface roughness due to the various processing techniques. It is significant to attach power devices on low-cost copper (Cu) substrates by pressureless silver-sintering in air.
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