Surface treatment for Cu metallization on polyimide film by atmospheric pressure dielectric barrier discharge plasma system

Atmospheric pressure plasma (APP) surface treatment method was applied to surface modification of polyimide (PI) films to enhance the adhesion between copper layer and PI surface by electroless plating. Also, APP was ignited by radio frequency (RF; 13.56 MHz) plasma power supply. In this study, nontoxic gases (nitrogen, oxygen, and NO (nitrogen:oxygen = 1:1)) plasma effects were mainly investigated instead of toxic gas such as NH3. The influences of APP treatment on chemical composition of the PI surface were investigated by using Fourier transform infrared spectroscopy (FT-IR). The wettability was also investigated by water contact angle measurement. The changes of binding energy of PI substrate were investigated by X-ray photoelectron spectroscopy (XPS). The contact angle results show that was dramatically decreased to below 30° from 58° (bare PI). Electroless copper depositions were carried out with the free-formaldehyde method using glyoxylic acid as the reducing reagent and mixture palladium chloride, tin chloride as activation solution. Adhesion property between polyimide surface and copper layer was investigated by tape test. Also, scanning electron microscope (SEM) images show the morphologies of electroless plated Cu layers with/without APP pre-treatment. None pre-treated Cu layer and Cu layer with O2 and N2 + O2 (NO) plasma pre-treatment shows voids and cracks in Cu foil on PI substrate. Only N2 plasma pre-treated Cu foil shows smooth and dense surface.