Measurement of thin film adhesion

Three methods of measuring thin film adhesion have been developed and evaluated. The well established 'scratch test' using a hemispherical diamond stylus, loaded tangentially to the plane of the surface, which offers a high degree of reproducibility, at the expense of information about the adherent qualities of the film. A quantitative 'peel test' has been found to yield useful data on thin fims whose adhesion is worse than that of commercially available adhesive tape. For cases where adhesion is considerably better than this, a 'pull test' has been developed, using an electronic force gauge and cyanoacrylate and epoxy resin adhesives. This has been found to give the most reliable results over the widest range of adhesive forces, though the maximum measurable force obtainable from this test is equal to the maximum bonding strength of available adhesives. Results are presented to show the reproducibility of each of these methods on films having identical adhesion. Further results are presented from an experiment designed to show the effect of thickness of film on the measured adhesive forces.