GB1535813A - Multi-layer circuit board - Google Patents

Abstract

1535813 Masters for printed circuits N C R CORP 18 June 1976 [3 July 1975] 25344/76 Heading G2X [Also in Division H1] In a multi-layer printed circuit board 1 with at least one internal circuit layer, desired patterns of outer circuit layers 5, 10, Fig. 2, are produced from artwork masters generated from layout patterns initially made to a first degree of layout precision, by altering these patterns, the alterations being effected to a second degree of layout precision which is less than the first. As shown, the initial circuit patterns of the outer layers 5, 10 to the first degree of precision include mutually perpendicular sets of parallel conductor runs 38, 54, Fig. 13, interconnecting pads, and signal pads 42, 62, Fig. 2 shorter conductor runs 44-46 and 64-66 between the pads and the main runs 38, 54 are produced to the second degree of accuracy resulting in the particular configuration desired for the intended circuit use. Connections through the board from one circuit pattern 5 to the other 10 are made by plated through-holes 14, Fig. 2. As shown in Fig. 13, initial artwork layouts for the circuits 5, 10, e.g. produced on an automatic X-Y plotter, are superposed and the necessary alterations e.g. traces 45, 64 are marked on a transparent sheet 110 laid over the patterns. The marked sheet 110 is then used as an underlay and the alterations are transferred to the artwork layouts to produce the masters corresponding to circuit layers 5, 10, Fig. 14, 15 (not shown). One of the internal circuit patterns 6-9, Fig. 2, e.g. a ground plane circuit 8, is used to ensure correct dimensional control in the photoreduction of the completed artwork masters. The plated through holes 14 are made from a drilling template and the components are then installed on the board.