Application of an acrylic acid tie-coating layer on a flexible copper clad laminate

An acrylic acid, which is the same polymeric material as a polyimide substrate, is used as a tie-coating material instead of commercial Ni-Cr. The acrylic acid was evaporated as a monomer and was introduced into a vacuum chamber; then, it was polymerized and deposited among the RF plasma. On it, the Cu was deposited and electroplated. For the fabricated PI/acrylic acid/Cu-type flexible copper clad laminate, we investigated the effects of plasma pre-treatment of the polyimide substrate, the deposition time, the pressure of the acrylic acid and the optical heating on the adhesion of Cu to polyimide. The adhesions of Cu with and without the plasma pre-treatment were 15 gf/mm and 35 gf/mm, respectively. This is an opposite result from the case of Ni-Cr tie coating. As the deposition time was increased, the polymerized acrylic acid layer started to cover the polyimide; after entire coverage, the surface became hydrophilic; then, it grew a chain thickness and made the surface porous. On the other hand, better polymerized and hydrophilic acrylic acid was obtained at a lower deposition pressure. When the evaporated acrylic acid was heated by using halogen lamp, better adhesion was realized. Under optimized conditions, we could obtain a maximum adhesion of 105 gf/mm with acrylic acid tie-coating, which is comparable to the 120 gf/mm with Ni-Cr tie-coating. This identifies the possibility of acrylic acid polymerization for a non-Cr tie-coating layer.