Improved adhesion between plasma-treated polyimide film and evaporated copper

The surface of polyimide film, Kapton H, was modified with Ar, N2, NO, NO2, O2, CO, and CO2 plasmas to improve its adhesion to evaporated copper. The plasma treatments led to bond scission of the imide groups in the Kapton film to form carboxyl and secondary amide groups, and, as a result, the surface of the Kapton film changed from hydrophobic to hydrophilic. The Ar-, NO-, and NO2-plasma treatments enhanced the adhesion between the Kapton film and copper, but the O2-, CO-, and CO2-plasma treatments did not. The roughness profile determined with an atomic force microscope showed that the plasma treatment removed a surface layer of the Kapton film, and the surface contained needle-shaped protuberances. The ATR IR spectra for the copper side torn-off from the Kapton film/copper joints showed the formation of coordinate bonds between carboxyl groups and copper atoms at the interface of the Kapton film and evaporated copper. The improved adhesion may be due to the formation of coordinate bonds between carboxyl groups and copper atoms, and the mechanical interlocking by penetration of the copper layer into the deep valleys between the protuberances.