Binder chemistry,adhesion and structure of interfaces in thick-film metallized aluminium nitride substrates

Aluminium nitride substrates from three different sources were metallized by standard thick film processing using gold conductor pastes, Pd-Ag paste, and a ruthenium oxide resistor paste. Screen printed pastes were fired in a typical three-zone furnace to obtain metallized AIN substrates. Interfacial reaction zones were studied by microscopic (optical and scanning electron microscopy) and electron beam microprobe analysis techniques. The elements in the binder materials in thick film pastes form amorphous phases at the interface which influence the adhesion of thick films to the AIN substrate. The lack of certain elements (Cd, Zn, Ca) in the binder of the gold thick-film paste led to weaker adhesion and severe degradation of the thick-film adhesion during thermal cycling.