GB1384167A - Shadow mask colour picture tube and method of fabrication - Google Patents

Abstract

1384167 Luminescent screens RCA CORPORATION 23 May 1972 [28 May 1971] 24104/72 Heading H1D In the manufacture of a multi-dot or multiline colour television screen by a photo-resist process, the sizes of the leaving tolerance (shortest distance from a beam landing area to the edge of the phosphor area) and of the clipping tolerance (shortest distance between a phosphor area and an adjacent beam landing area on a different colour phosphor) may vary undesirably over the area of the screen; such variation is measured and corrected by varying the sizes of the phosphor areas without altering their shape. In the case of circular phosphor dots the clipping tolerance can be increased and the leaving tolerance reduced by reducing the diameter of the dot; conversely the clipping tolerance can be reduced and the leaving tolerance increased by increasing the diameter of the dot. A completed screen is examined with a microscope and the variations in dot diameter required for each colour are measured at various points over the area of the screen; the variations may be designed to equalize clipping and leaving tolerances or to make the clipping tolerance always larger than the leaving tolerance. From the measurements, contours of equal variation are plotted separately for each colour and used to produce filters which are incorporated in the "lighthouse" used in the photo-resist process to produce a corresponding variation in light intensity which will vary the dot sizes as required.