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 polyaminobi smaleimide (PABM) adhesive is investigated after surface treatments. The su rface treatments of the AIN substrates were oxygen plasma exposure, K2O .n( B2O3) 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 ex posure for 60 s and K2O .n(B2O3) aqueous solution immersion for 10 min, ave rage peel-off strength was over 1.6 N/mm, whereas that in the case of no su rface treatment was 0.14 N/mm, Oxygen plasma exposure and K2O .n(B2O3) aque ous solution immersion decreased the relative amounts of carbon and hydroca rbon on the surface of as-sintered AIN substrates, On the other hand, the r elative amount of hydrophilic groups, such as COO, C=O, and C-O relatively increased, This chemical change is effective for increasing peel-off streng th. The results of measurement of surface free energy of the AIN substrate surface indicate that these surface treatments increase surface energy of A IN substrates from about 47 to 60 mJ/m(2), When AIN substrate was immersed in K2O .n(B2O3) aqueous solution, tiny protrusions were formed on the AIN g rain surfaces, The approximate height and pitch of the protrusions were abo ut 30 nm and 60 nm, respectively, in the case of immersion for 10 min. Most AIN grains were etched, although no all. This change in shape of grains to brings about resistance to peeling and contributes to enlargement of the s urface area. Due to these effects, average peel-off strength of AIN substra tes with both oxygen plasma exposure and K2O .n(B2O3) aqueous solution imme rsion was 1.1 N/mm even after 800 cycles of thermal cycling and the value i s still larger than that required for the practical package application.