Direct metallization of PMMA with aluminum films using HIPIMS

• HIPIMS for direct metallization of PMMA
• Excellent adhesion without any pretreatment
• Influence of peak current on adhesion
• Coating-substrate interface investigations

Ionized sputtering like high power impulse magnetron sputtering HIPIMS opens new horizons for cost effective, environmental friendly plastic metallization with excellent adhesion. First reports on HIPIMS deposited films on polymer foils, textiles, and different untreated plastics showed significant adhesion improvement of the metallic or oxide coatings applied. Plexiglas (PMMA) is a very attractive substrate material due to its properties for several commercial applications. Since PMMA is very sensitive to the UV radiation of technical plasmas, direct metallization of the surface by sputtering is conventionally not possible. Using ionized sputtering it is shown that the adhesion can be enhanced to excellent level, passing a combined cross cut and tape test without any failure. The study of the interface correlated to the different peak current densities of the HIPIMS processes shows some trends for the significant adhesion improvement. With increasing peak current in the HIPIMS discharge, i.e. increasing degree of ionized species forming the film, the adhesion is significantly improved. The failure mechanism changes from adhesive failure and poor adhesion to a cohesive failure and excellent adhesion. Furthermore, the surface of the polymer was modified as a result of the increasing ionization. The PMMA surface reorganizes and roughens due to ions forming the film and additionally electrons providing local thermal annealing by recombination.