Photographic masks, bearing the image corresponding to an electrical circuit, are known as photo tools. To make the phototool, a photosensitive emulsion layer is applied to a plate and the image created by means of an exposure apparatus, such as a photo-plotter. The phototool is then placed face down on a photoresist layer used to manufacture the circuit board and a contact print is made by exposing the photoresist to high intensity light. Such phototools are prone to scratching and require time-consuming microscopic checking. One method of protection is to provide a clear coating, but they can suffer from poor adhesion and resistance to sticky photoresists.
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