Today's PWB manufacturers are being challenged by their customers to develop printed circuits boards that have greater functionality and lower cost. This results in a need for photoresists that will enable the production of boards with finer circuits (greater functionality) and higher yield (lower cost). Current resolution requirements are ≥ 75 μm. Over the next one to two years, these requirements are expected to decrease to 50 μm and below. Finer resist resolution can be obtained by reducing the resist thickness. Thinner resists also improve the quality and latitude for etching fine copper traces. However, reducing the resist thickness will result in poorer conformation during lamination to the copper substrate. This can be offset by applying a thin layer of water to the substrate surface before lamination. The water plasticizes the resist at the interface allowing it to flow and conform to the substrate surface. Here we describe the development of a new thin dry film photoresist that has been optimized for good conformation using wet lamination, and the development of new equipment for applying consistent low levels of water to the substrate surface before lamination. Yield improvement data will be shown from multiple PCB manufacturing sites.
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