Characterization of the adhesion of SU-8 and Epoclad

In this paper, the adhesion of SU-8 and Epoclad polymers to silicon substrates is quantified as an energy release rate, and the effect of a chromium coating as an adhesion promoter is studied. The intention is to quantify the adhesion strength for processing parameters that were previously optimized to yield good adhesion for various patterns and layer thicknesses. To do so, a custom tool is built to measure the force to shear off a square button of the epoxy from the substrate. Silicon and the silicon wafers coated with chromium were used as a substrate. Fracture mechanics is used to model this test and an energy release rate for different combinations of epoxies and substrates is determined. The energy release rates between SU-8 and Si and between SU-8 and Cr are measured to be 1.7 x 10(2) +/- 0.3 x 10(2) J m(-2) and 2.6 x 10(2) +/- 0.5 x 10(2) J m(-2), respectively. The energy release rates between Epoclad and Si and between Epoclad and Cr were determined to be 2.8 x 10(2) +/- 0.4 x 10(2) J m(-2) and 35 +/- 6 J m(-2), respectively.