Effects of Environment On Measurements of Adhesion of Polyimide to Silicon

We have studied the effects of liquid environments on measured adhesion of PMDA-ODA polyimide to a silicon substrate by the blister and peel tests. The debonding pattern and adhesion strength were very sensitive to the liquid. For example, introducing pure methanol at the crack tip caused stick-slip debonding, with a high debonding angle, and severe plastic deformation of the polyimide film in blister tests, and greatly increased the adhesion strength in the peel test. The effects were progressively enhanced for water/methanol mixtures as the content of methanol increased, or for pure alcohols as the molecular size decreased. Evidently, as the wettability between the environment fluid and the surfaces involved improves, transport of the fluid to the crack tip region increases, allowing more diffusion of the fluid into the film, which causes a considerable decrease in its yield stress. Under these conditions, local plastic deformation and consequent blunting of crack tip are facilitated, resulting in larger crack opening displacements, which requires more energy and increases likelihood of unstable stick-slip propagation.