The effect of pretreatment on adhesive strength of Cu-plated liquid crystal polymer (LCP)

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 20 min. With potassium permanganate as the etching agent, the adhesive strength could reach 12.08 MPa, which is much higher than the reported maximum adhesive strength (lower than 8.0 MPa). XPS 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 adhesive 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. When the etching time was short, the failure mode of Cu-plated LCP film was mainly adhesive. As the etching time increased, cohesive failure gradually occurred, causing an adhesive/cohesive mixed failure mode.