Hdhesiveless copper on polyimide sub-strates are commonly used for fine-line and high density electronic interconnection applications. Medical, hard disk drive, and COF applications often require line and space features 2-mil and finer. Adhesiveless materials can facilitate fine feature formation because thin copper is available and because the interface between copper and dielectric is smooth. Both attributes result from the fact that adhesiveless materials are manufactured by direct metallization of fully cured polyimide film. Adhesion between copper and polyimide is an important consideration because there is no copper profile or nodular bond treatment to promote mechanical interlocking. Good adhesion is achieved for these materials by plasma pretreating the polyimide surface and by applying a thin metal tiecoat between copper and polyimide. Common tiecoat metals include chromium and nickel alloys.
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