Improved method to evaluate the adhesion properties of thin film conformal coatings

Conformal coatings are widely used by the electronics industry to protect sensitive equipment from moisture and corrosion [i]. Of these, parylene thin-film coatings have many material properties such as low dielectric and dissipation factors, high operating temperatures, excellent conformability and low moisture permeability, which make them an attractive conformal material for numerous applications. However, adhesion of parylene coatings is critical to the overall reliability of the coating and is especially problematic on inorganic surfaces. A number of techniques can potentially improve adhesion including adhesion promoters and plasma treatment, but a robust method for evaluating adhesion has been lacking. In response, we developed a method based upon a standard dieshear test that can calculate the adhesion strength of different interfaces when multiple failure modes are active. This process uses pre-shear and post-shear images to calculate the area of each failure mode. Those areas are then used in combination with the measured breaking load to calculate the adhesion strength of the different interfaces using an iterative solver. This method provides an accurate, quantitative measure of thin-film adhesion even when mixed failuremodes are active.