Low temperature bonded Cu/LCP materials for FPC and its characteristics

New cladding process has been developed by means of a Surface Activated Bonding (SAB) technique. In this process, Surfaces of materials to be bonded are immediately cleaned, activated by Ar ion sputter etching, and rolled with low distortion at room temperature in vacuum [1]. It is found that this process is available not only for cladding metals but also for laminating polymer film on metal without any adhesives. We have already reported copper (Cu) clad laminating (CCL) materials using Liquid Crystal Polymer (LCP) and showed its possibility by means of the SAB [2-5]. Interface of the LCP/Cu produced by the SAB was flat and smooth when comparing to that by conventional method. Therefore, the laminated material showed high electric property and excellent etching property [4,5]. In this study, it was investigated that the transition of chemical bonding state around interface between Cu foil and LCP film after heat treatment. It has been already reported that interface of Cu side was oxidized by heat treatment [2]. The XPS analysis showed that the ratio of C=O bonding on the LCP film side also interface increased with an increase in heat treatment temperature. So it was revealed that the heat treatment at high temperatures oxidize not only the Cu interface formed by Cu foil and sputtered Cu, hut also the LCP film side interface. We also have reported that Cu sputtering on the LCP film before laminating improved bonding strength [4,5]. However in heat-resistant test, the bonding strength significantly decreased because of oxidization around the interface and of softening of Cu foil due to re-crystallization. To improve the heat resistance, we used Cu-O.O2%Zr alloy foil having high re-crystallization temperature and sputtered Cu-Ni alloy or Ni-Cr alloy on LCP Tim instead of Cu sputtering. The improved materials also showed high frequency property and good etching property.