Low-temperature air-fireable glass-free metallic thick-film electrical conductor materials

Low-temperature air-fireable glass-free metallic thick-film electrical conductor materials were developed for interconnections in electronic packaging. The thick film with composition (by weight) 96.60%Ag, 1.38%Cu, 0.28%Al, 0.35%Ti, and 1.39%Sn used Ti-Al as the active binder. After firing in air at 500°C it exhibited low electrical resistivity (6.2 × 10^-6Ω·cm), good scratch resistance and strong bonding with the alumina substrate, with no pinholes. The firing caused complete melting of the particles in the film. Firing in argon rather than air degraded both electrical and bonding properties, due to the absence of oxygen, which helped to burn out the vehicle. The use of Ti rather than Ti-Al as the active binder resulted in holes in the thick film due to incomplete melting of the Ti-rich particles and also resulted in poor scratch resistance and weaker bonding to the substrate. Tin in the composition was important for promoting melting and protecting the active particles from oxidation during firing.