Electroless and eletroplating copper on liquid crystal polymer (LCP) for high frequency applications

Copper metallization on LCP was carried out by means of electroless plating followed by electroplating and the effect of pretreatment on the adhesive strength of the Cu-plated LCP was investigated in detail. Compared with the other etching agents used here, potassium permanganate was found to be the most effective and the optimum etching time is 20min. With potassium permanganate as the etching agent, the adhesion strength could reach 12.08MPa, which is much higher than the reported maximum adhesion strength of 8.0MPa. Furthermore, it is more environment-friendly to use potassium permanganate as an etching agent compared with the other common chromium-containing chemicals like Chromic Acid. ATR FT-IR spectra of LCP film indicated that hydrophilic groups were introduced into the LCP surface by etching, creating a nanometer-scale surface roughness and improving the wettability between copper and LCP. SEM and AFM observations revealed that the distinctly increased adhesion strength could be attributed to the improved wetting and the mechanical interlocking effect. The failure mode of Cu-plated LCP film was found to be dependent on the etching time and it was adhesive failure for the short etching time and cohesive failure for the long etching time.