Polyimide film has the desirable properties of thermal stability, good chemical resistance and excellent mechanical strength and has been widely applied to complicated electronic devices and products. Considering the cost issue, we developed a palladium-free process which employs complexed copper ion as catalyst precursor of electroless copper deposition to metallize polyimide film. In this work, electroless Cu was pre-deposited on the polyimide as a seed layer and then followed by copper electroplating. Herein, we used complexed copper ion as the catalyst precursor. After chemical reduction step, the complexed copper ion was reduced to metallic copper (i.e., copper nanoparticle), which is a good catalyst for electroless copper deposition. Therefore, we call the process to be palladium-free process because palladium is a usual and expensive catalyst for electroless copper deposition. The ratio of the complexing agents to the copper ions and optimal temperatures of the solution were investigated in order to enhance the adhesion strength of copper metal film on the polyimide film. The amounts of complexed copper ion on the polyimide surface and the morphology of electroless copper were measured by atomic absorption spectrometry (AA) and imaged by scanning electron microscope (SEM), respectively. X-ray photoelectron spectroscopy (XPS) was used to examine the elements on the polyimide. The results showed that complexed copper ion has the function of catalyst after chemical reduction for the electroless copper deposition on polyimide. The temperature of the catalyst exhibits significant effect on the adhesion strength of the deposited copper metal film on the polyimide film.

Keywords:

Polyimide, Catalyst, Electroless copper deposition

Reference:

[1] Makoto Kohtoku, Hideo Honma and Osamu Takai, J. Electrochem. Soc., 161, D806-D812 (2014).