Cold Gas Spraying Copper Metal on AlN Ceramics as an Alternative to Thick Direct Bond Copper Substrates for Power Electronics

Abstract

This study investigates the use of cold gas spraying (CGS) as a low-temperature additive manufacturing method to bond copper onto aluminum nitride (AlN) substrates for electronic packaging of high-power applications. While the direct bond copper (DBC) technique is commonly used, it has limitations due to the large mismatch in the coefficient of thermal expansion, which affects substrate reliability. This work employed CGS to mechanically bond Cu on AlN. The study explores the effect of multiple sprays, spray angle, and spraying direction on deposition thickness, coating surface roughness, and deposited volume through a factorial design of experiments (DOE). The results, based on optical and scanning electron microscopy combined with profilometry data, showed that coatings sprayed at a 60 deg angle had a smoother profile topography and less surface roughness than those sprayed at a 90 deg angle. After depositing ten layers, a surface roughness (Sa) of around 30 μm and a coating thickness of over 300 μm were successfully attained. These findings provide valuable insights into the processing factors affecting the growth and quality of copper coatings on AlN substrates via multiple sprays, thus enabling the realization of CGS technology as a potential solution to DBC substrates for electronic packaging of wide-bandgap semiconductors.