Adhesion Measurement on Thin Evaporated Films

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Abstract
Methods to evaluate the adhesion of thin evaporated films to their substrate were devised. One was to pull down and the other to twist off a rod whose bottom was cemented with epoxy to the film. The critical force or torque to strip off the film from the substrate was taken as a measure of the adhesion. It was important to maintain adequate temperature and humidity [16 °C (61 °F) and below 60 percent] during the cementing and measurement, to assure the high adhesion of the cement and the reproducibility of the result. The adhesion of thin films of aluminum, silver, and copper to substrates of mild steel and glass was studied, along with the adhesion of epoxy and other cements. It was found that the critical force and torque were proportional not to the 3rd power as expected but rather to the 2.5 ∼ 2.9th power of the rod diameter. In the case of thin films, the dispersion of the measured values was very large. The dispersion and also the ratio of tensile to shear adhesive strength increased rapidly with the decrease in adhesion. This is contrary to the effects of the small dispersion, the independence of the dispersion, and the ratio on the adhesion in the case of cement itself. Also mentioned is an experiment on the fracture of brittle substrates such as silicon wafers which sometimes happened during the measurement.

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