Soldering characteristics of active metal brazing ceramic substrates with various surface finishes

Herein, the solder bond characteristics of various surface finishes in the presence or absence of a vacuum of the active metal brazing (AMB) ceramic heat-dissipation substrates were analyzed. On Cu/Si 3 N 4 /Cu substrates bonded using AMB technology, the surfaces were finished under three conditions: Cu, electroless nickel immersion gold (ENIG), and electroless Ag. Subsequently, solder bonding between the surface-finished AMB substrate and dummy chip was performed using a Pb-rich solder preform (Pb–5Sn–2.5Ag, wt.%). Surface characteristics and cross-sectional analysis of the AMB substrates revealed the formation of a plating layer with a thickness similar to the designed plating under all conditions. The cross-sections and microstructures of the solder joints with different surface finishes under various conditions and reflow profiles revealed that the presence of a vacuum in the heating area during the reflow process reduced the density of voids formed in the solder joints. As their volume fraction increased, the voids formed in the solder joints increased the overall joint thickness. Moreover, the higher the density of the voids formed in the solder joints, the lower the mechanical strength. The solder joint analysis with different surface finishes of the AMB substrates revealed that a thick interfacial compound layer formed when using an Ag surface finish compared with the Cu and ENIG surface finishes. Thus, the Cu and ENIG surface finishes, which demonstrated relatively low reactivity, exhibited superior interfacial properties and bonding strength compared to the Ag surface finish, which was highly reactive with Sn in the Pb-rich solder.