HUMIDITY EFFECT ON POLYIMIDE FILM ADHESION

Abstract

A 90-degrees peel tester with substrate heating capability has been built to evaluate the adhesion strength of polyimide film to silicon substrate. The peel strength of polyimide film is not only a function of film thickness or peeling rate, but also a function of ambient humidity. A mechanism is proposed. The peel strength decreases with increasing relative humidity due to the hydrolysis of polyimide, reaches a minimum, and then increases with increasing relative humidity due to the hydrogen bonding at the weak boundary layer. In a high-humidity environment, peel crack tips are attacked by moisture and result in weak adhesion measurement. Water adsorbed by polyimide film near the crack tip and diffused into the peel crack tip is the main mode of moisture attack. The peel behaviour of polyimide film at the elevated temperature is almost the same as peeling at room temperature in a low-humidity environment.