The effect of adhesion promoter layer thickness on the adhesion strength between silicone rubber and aluminium

Abstract

The effect of adhesion promoter (primer) layer thickness on the peel strength was investigated on Al/adhesion promoter/silicone rubber samples. The thickness of the primer layer was determined by ellipsometry and mechanical step-height measurement on reference Si-wafers. The analysis proved that dip coating results in a smooth layer of continuously varying thickness, while brush coating gives a highly non-uniform coating. A 45-250 nm layer thickness was produced by spin-coating technique. Thinner layers (down to 8 nm) were made by evaporation, thicker layers by repeated coating. Multiple and brush coated layers are laterally inhomogeneous. The refractive index of the adhesion promoter gradually increases with thickness. Adhesion promoter coatings thinner than 80 nm did not improve adhesion between A1 and silicone rubber. In the range of 80 nm and 250 nm layer thickness, a continuous improvement of adhesion was observed. In best cases the interface did not fail at all during the peel test: the rubber sample slipped out of the clamp of the tensile tester. Brush coating and multiple layers resulted in decreased strength and increased scattering.