Influence of ceramic surface treatment on peel-off strength between aluminum nitride and epoxy-modified polyaminobismaleimide adhesive

Peel-off strength between aluminum nitride (AlN) ceramics and a polyaminobismaleimide (PABM) adhesive is investigated after surface treatments. The surface treatments of the AlN substrates were oxygen plasma exposure, K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution immersion and a combination of the two. Each of the three methods increases the peel-off strength compared to that in the case of no surface treatment. In the case of the combination of oxygen plasma exposure for 60 s and K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution immersion for 10 min, average peel-off strength was over 1.6 N/mm, whereas that in the case of no surface treatment was 0.14 N/mm. Oxygen plasma exposure and K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution immersion decreased the relative amounts of carbon and hydrocarbon on the surface of as-sintered AlN substrates. On the other hand, the relative amount of hydrophilic groups, such as COO, C=O, and C-O relatively increased. This chemical change is effective for increasing peel-off strength. The results of measurement of surface free energy of the AlN substrate surface indicate that these surface treatments increase surface energy of AlN substrates from about 47 to 60 mJ/m/sup 2/. When AlN substrate was immersed in K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution, tiny protrusions were formed on the AlN grain surfaces. The approximate height and pitch of the protrusions were about 30 nm and 60 nm, respectively, in the case of immersion for 10 min. Most AlN grains were etched, although not all. This change in shape of grains brings about resistance to peeling and contributes to enlargement of the surface area. Due to these effects, average peel-off strength of AlN substrates with both oxygen plasma exposure and K/sub 2/O/spl middot/n(B/sub 2/O/sub 3/) aqueous solution immersion was 1.1 N/mm even after 800 cycles of thermal cycling and the value is still larger than that required for the practical package application.