Processes for forming conductive vias between circuit elements formed on either side of a flexible substrate are disclosed. In one embodiment, the inventive process starts with a flexible film polyimide substrate on each side of which is arranged a layer of copper. Both of the copper surfaces are coated...http://www.google.com.hk/patents/US6039889?utm_source=gb-gplus-share專利 US6039889 - Process flows for formation of fine structure layer pairs on flexible films
