Ion beam modification of metal-polymer interfaces for improved adhesion

The surfaces of Lexan Polycarbonate (PC) and ABS polymers were treated with low energy (300 eV) ion bombardment prior to and during deposition of a thin (200 nm) Al film. The effects on the adhesion characteristics, the type of ions used (Ar, N), and the type of bombardment (sputtering or during deposition) were studied for eight different deposition conditions for each polymer. The adhesion characteristics were compared by the tape and stud pull tests. The ion beam treatment caused substantial improvement in adhesion strength in all seven cases where sputtering was involved. In the case of the stud pull test for the PC samples, the failure was along the interface for the non-sputtered case only. In all others, with sputtering, we observed cohesive failure within the polymer, as confirmed by SEM. This suggests that the actual interface strength in all the sputtered cases was higher than that of the polymer itself. SEM, RES, and profilometry were used to study the failure modes, Al film quality, and the effect of morphology on adhesion characteristics, respectively. Surface roughness did not seem to be an important factor for adhesion improvement. XPS studies suggest that the Al is bonded in identical ways at the bombarded and virgin interfaces. Improved adhesion is likely due to surface sputter cleaning.