Effects of Additives on Copper Layer Stress Electroplated on Polyimide

Thursday, 5 October 2017: 17:00
Chesapeake G (Gaylord National Resort and Convention Center)
L. J. Lin and W. P. Dow (National Chung Hsing University)
Flexible printed circuit board (FPCB) made of polyimide film as an insulator with a low dielectric constant, good mechanical strength and excellent chemical resistance has been widely applied to complicated electronic devices and products such as chip on flexible printed circuit (COF) and laptops. Because of economic advantage, we developed an all-wet process to metallize polyimide film. In this work, electroless Ni was predeposited on the polyimide as seed and barrier layer, and then followed by copper electroplating. The copper electroplating bath contained chloride and acidic copper sulfate as well as a suppressor and an accelerator. We used various copper electroplating formulas in the plating bath to reduce the surface roughness and intrinsic stress of the electroplated copper film on the polyimide film for a high reliability, such as high adhesion and good thermal reliability. The intrinsic stress, preferred crystalline orientation and surface morphology was analyzed by the Bent Strip Method (Deposit Stress Analyzer System), measured by an X-ray diffraction (XRD), and examined by scanning electron microscope (SEM), respectively. As a result, we found that the peel strength between the plated copper film and the polyimide depends on the copper plating formula.