Metallized liquid crystal polymer with low interfacial roughness and excellent adhesive strength based on semi-additive process for high-frequency signal transmission

Fifth-generation communication (5G) with the feature of high frequency puts forward harsh requirements on the roughness of the transmission lines due to the skin effect. Metallization liquid crystal polymer (LCP) with low interfacial roughness and high adhesive strength simultaneously poses a huge challenge for the modern electronics. Herein, based on semi-additive process, molecular grafting is reported to highly bridge smooth LCP substrate and thickened copper layer by chemical bonds. The process comprises the wettability of LCP surface tuned via oxygen plasma with negligible roughness changes. gamma-aminopropyl triethoxysilane (APTES) plays a role in the integration of LCP substrate and metal layer. Followed by electroless plating, a thin nickel is planted on LCP as conductive seeds for electroplating copper. Compared with addition manufacturing, which directly coarsens the interface of circuits, semi-addition process just etches the edge of circuits. Through APTES grafting, 10 mu m thick copper on LCP substrate reaches to the level of 5B according to the criteria of ASTM D3359, overcoming the trade-off between low interfacial roughness and high adhesive strength of existing techniques. Additionally, the interfacial strengthening mechanism of APTES grafting is carefully investigated. The proposed grafting-assisted semi-additive process is potentials for scalable fabrication of high-frequency electronics on various substrates.