Porosity development of RuO 2 filled glass thick films on aluminum nitride substrates at elevated temperatures

Abstract

This study is focused on the evolution of the interfacial blisters appearing when a glass-filled resistor thick film is coated on polycrystalline AlN and fired over a temperature range of 600 to 800 °C. The AlN substrates used include those of the as-received form (hereafter termed the “bare” substrate) and thermally pre-oxidized form. Microstructural observations reveal that the film-substrate adhesion is critically influenced by the gas products formed at the interface during heating. A method is then proposed which involves a composite structure of the film to provide open porosity serving as a conduit for facilitating gas liberation at lower temperatures. This hypothesis is confirmed by the reduced blister occurrence at the interface when “rigid” (i.e., non-sintering) inclusions were blended into the resistor paste before coating on the bare substrate. The film with inclusion fractions less than 10 wt % densifies with improved film integrity as the firing temperature is raised above the gas-forming temperature, indicating that the porosity is transient in character.