Recently, electronic products pursue nanoscale, lightness, thinness, miniaturization and multi-function products, so the demand for flexible printed circuit board (FPCB) and rigid-flex PCB has grown substantially. Polyimide (PI) is dynamic and rollable products, because it has thin and flexible characteristics, also, it has high thermal stability, good mechanical strength. However, the line width and space is about five and five micrometer on FPCB, so FPCB with fine pitch would be manufactured by semi-additive process (SAP) PI-SAP will not use copper foil anymore. Instead, PI will directly be metallized by electroless deposition and then electroplating to form conducting lines. Because the copper line on the PI surface is very thin and micro-scaled, the peeling strength is a very critical target in this metallization. In this study, we used an overall wet process to directly metallize the PI film. Electroless deposition of Co-W-P films was performed on a PI film as seed and barrier layer followed by copper electroplating. The aim of our work was to develop an optimal electroless plating composition and process parameters to increase the adhesion between the Co-W-P layer and the PI film. Scanning electron microscopic (SEM) examination shows that the surface morphologies of Co-W-P films. FE-TEM and XPS confirm that Co-W-P films deposit can serve as a perfect diffusion barrier layer to prevent Cu diffusion from the surface layer into the PI film. SEM with energy dispersive spectroscopy (SEM/EDS) data indicates the composition of Co-W-P film. Tensile strength measurement tool can explain the adhesion between the Co-W-P layer and the PI film.

Keywords:

Electroless deposition, Barrier layer, Co-W-P thin films, Polyimide

Reference:

[1] R. Tarozaitė, Z. Sukackienė, A. Sudavičius, R. Juškė nas, A. Selskis, A. Jagminienė, E. Norkusė, Materials Chemistry and Physics, 117 (2009) 117-124.