Effects of CO₂ laser pretreatment conditions on adhesion properties of Cu/Ti films and polyimide substrates

Polyimide is widely used as an insulating substrate for flexible printed circuit boards. However, the metallic thin films deposited on polyimide readily undergo debonding during deformation. In this study, a carbon dioxide (CO₂) laser pretreatment was performed to enhance the adhesive strength between metal films and polyimide substrates. Cu/Ti films were formed on polyimide substrates with a thickness of 125 µm, which had previously been irradiated with a CO₂ laser at powers of 1, 3, and 5 W. The interfacial adhesion between the Cu/Ti films and the irradiated polyimide substrates was quantitatively evaluated using peel tests. Carbides and micropores formed on the surfaces of the polyimide substrates after the CO₂ laser pretreatment. For CO₂ laser powers of 1, 3, and 5 W, the interfacial adhesion increased by approximately 55%, 73%, and 92%, respectively, with respect to that before the laser pretreatment. Thus, the CO₂ laser pretreatment significantly improved the metal–polyimide interfacial adhesion and should be suitable for improving the performance of flexible printed circuit boards.