Thick film adherence fracture energy: influence of alumina substrates

Abstract

The adherence of a glass bonded Pt-Au thick film conductor to various alumina substrates is degraded by changes in the surface composition of and by the presence of (0001) crystallographic texture in the substrate. Using the critical fracture energy (γ_IC) required to separate the thick film from the substrate, it was found that γ_IC was reduced from a maximum of 3.7 J m⁻² using an as-received 96+ wt% alumina substrate to ∼2J m⁻² using an as-received 99+ wt% alumina. In addition, the thick film adherence γ_IC using (0001) sapphire substrates was less than that using (11¯23) sapphire. The 96 wt% substate exhibited essentially a random crystallographic surface texture and a considerable amount of surface silicates. The as-received 99+ wt% Al₂O₃ substrate was charactarized by a high (0001) surface texture and, while exhibiting a similar composition silicate layer as that of the as-received 96 wt% alumina, the total amount of the glass layer is greatly diminished. Fractographic analysis of the separated thick films and substrates showed that changes in the substrate crystallographic texture and the glass layer diminish the interpenetrating nature of the glass—metal interface and weaken the glass—substrate interface. Such changes in thick film microstructure lead to poorer thick film adherence.