Effect of the environment on the measured values of the adhesion of polyimide to silicon

We have studied the: effects of liquid environments on the measured adhesio n of PMDA-ODA polyimide to a silicon substrate by the blister and peel test s. The debonding pattern and adhesion strength were very sensitive to the l iquid. For example, introducing pure methanol at the crack tip caused stick -slip debonding, with a high debonding angle, and severe plastic deformatio n of the polyimide film in blister tests, and greatly increased the adhesio n strength in the peel test. The effects were progressively enhanced for wa ter/methanol mixtures as the content of methanol increased, and for pure al cohols as the molecular size decreased. Evidently, as the wettability betwe en the environment fluid and the surfaces involved improves, transport of t he fluid to the crack tip region increases, allowing more diffusion of the fluid into the film, which causes a considerable decrease in its yield stre ss. Under these conditions, local plastic deformation and consequent blunti ng of the crack tip are facilitated, resulting in larger crack opening disp lacements, which requires more energy and increases the likelihood of unsta ble stick-slip propagation.