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US 4,610,941 AGranted
Method for photographically improving the resolution of screen printed photopolymer images
OwnerDonald F. Sullivaninventor
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OwnerDonald F. Sullivaninventor
Estimating the term…
A process is described for improving the quality of images which have been formed by screen printing a liquid photo curable photopolymer. Images formed by screen printing, especially heavy coatings such as solder masks on printed wiring boards, inherently have indistinct boundaries, and may have feathered edges and photopolymer smears. These indistinct boundaries are removed and the resolution improved by a process which utilizes the oxygen inhibition effect characteristic of selected photopolymers. Thus, a screen printed image can be 0.001 inches thick at the center of a line, tapering off to 0.0001 inch thick smears, and these smears may be eliminated by irradiating the entire image with a moderate amount light energy, which cures the thick image portion and leaves a liquid boundary layer on the order of 0.0001 inch thick due to the oxygen effect. When washed with a mild solvent the liquid layer is removed, including the smears, leaving the thick image portion undisturbed. In a preferred embodiment a phototransparency is interposed over and out of contact with the images and then irradiated with non-collimated UV light so as to harden the thicker image sections while indistinct boundary areas are shielded by opaque phototransparency areas. Light undercutting due to the use of non-collimated light does not polymerize the smears because of the oxygen-inhibition effect and the thinness of the smears, and thus only the undersirable smears will be inhibited and left in the liquid state for removal to improve the resolution.
The process of improving resolution of printed photopolymer patterns of low resolution because of smears at the pattern edges, comprising the steps of:
The method of forming patterns of good resolution upon a substrate with liquid photopolymers of the type that oxygen inhibits polymerization, comprising the steps of:
A process for curing a liquid photopolymer including the steps of, depositing a layer of liquid photopolymer on a substrate, irradiating the layer with a predetermined amount of radiant energy that hardens substantially the entire layer thickness except for a thin surface layer portion, and removing the unhardened surface portion.
A process for removing excess portions of liquid photopolymer patterns previously placed on a substrate surface by a screen printing step thus leaving low resolution smears at the edges of the pattern, including the steps of, depositing said liquid photopolymer patterns on the substrate surface, irradiating the photopolymer pattern through a phototransparency spaced from the photopolymer pattern surface with a transparent image thereon defining a high resolution pattern within the confines of the photopolymer pattern on the surface, transmitting radiation through the image to harden the photopolymer in a high resolution pattern leaving the smears in unhardened liquid form, and removing the unhardened portions of the photopolymer pattern after radiation to produce a high resolution pattern on the substrate surface.
Dependencies are inferred from the claim text.