Point-Contact Bonding of Integrated 3D Manifold Microchannel Cooling within Direct Bonded Copper (DBC) Platform

A microchannel heat sink integrated with a three-dimensional manifold using Direct Bonded Copper (DBC) is promising for high power density electronics due to the combination of low thermal resistance and reduced pressure drop. However, this requires much progress on the fabrication and high-quality point-contact bonding processes of the microchannel substrate and 3D manifold DBCs. In this study, we have developed processing techniques for surface preparations and high-quality point-contact solder bonding between the two DBC substrates. We utilized chemical polishing followed by electroless plating to prevent excess solder from blocking the microchannels. We performed a parametric study to investigate the impact of bonding time and surface roughness on the tensile strength of the bonding interface. The bonding strength increased from 1.8 MPa to 2.3 MPa as the bonding time increased from 10 to 30 minutes while reducing the surface roughness from Rz = 0.21 to 0.05 µm, resulting in increasing the bonding strength from 0.16 MPa to 2.07 MPa. We successfully tested the microcooler up to the inlet pressure of 70 kPa and pressure drop of 30 kPa, which translates to the tensile strength at the bonding point contacts, which remains well below the 2.30 MPa. We achieved the junction-to-coolant thermal resistance of 0.2 cm2-K/W at chip heat flux of 590 W/cm2. Thus, our study provides an important proof-of-concept demonstration towards enabling high power density modules for power conversion applications.