Recently, progress of semiconductor packaging is drastic and multi-pinned devices such as Fan-out Wafer Level Packages (FOWLPs) attract much attention. For those applications, photosensitive polyimides (PSPIs) are applied as redistribution layers (RDLs) and they are required to have high level of properties such as adhesion to metal and reliability. We developed novel low-temperature curable positive-tone photosensitive polyimides (posi-PSPIs) with high elongation, strong adhesion to the copper RDLs, and high chemical resistance for establishing the multi RDLs by improving the base-polyimides and incorporating polyimides with cross-linkers and adhesion promoters.
We successfully developed redistribution structure by using photosensitive polyimide and all wet Cu plating processes. To obtain the structure, patterned Cu was obtained by nonelectrical plating on photosensitive polyimide layer with a mask of photo-resist. Various types of surface treatments on polyimide layer were investigated to obtain good adhesion between Cu and polyimide. In this work, we coated the photosensitive polyimide by a slit coater and found a suitable wet surface treatment to obtain good adhesion to plated Cu. The all wet Cu processes are composed of wet activation process and electro-Cu plating process. By combining all these processes, 40µm line and space Cu pattern was obtained by using a 500-600 mm glass panel. In addition, 2µm line and space Cu pattern was obtained on an 8 inch glass wafer.
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