Surface modification of polyimide by combining swelling and TiO₂ photocatalytic treatments for adhesion improvement of electroless Cu

In order to enhance the adhesion strength between the PI film and the electroless copper film, a combination of swelling and TiO2 photocatalytic treatments was used to modify polyimide (PI) film. The effects of the swelling solution composition and TiO2 photocatalytic condition on the surface performance were investigated. After the optimal swelling and photocatalytic treatment, the surface contact angle of the PI film decreased from 85 to 28.7°, and the surface average roughness of the PI film only increased from 1.3 to 13.6 nm, indicating no obvious change for the surface topography of PI film after the photocatalytic treatment. However, the adhesion strength between electroless copper film and the PI film reached to 0.6 KN·m−1. The FT-IR spectra and XPS analyses indicated that –COOH group was formed on the PI surface after the treatment, and the surface hydrophilicity was improved, which improved the adhesion strength between the PI film and the electroless copper film.