GB1456378A - Electrical circuit artwork - Google Patents

Abstract

1456378 Setting out work POST OFFICE 7 Feb 1975 [21 Dec 1973] 59321/73 Heading B4X [Also in Division G2] Solder-denoting pads 24 are manually located on a printed circuit board artwork sheet 12 by means of a stylus 32 see also Fig. 2 (not shown), which is used to engage the pads by means of a time 34 extending from a spring-loaded stem (42) of the stylus, the stem being thereafter inserted selectively in apertures 22 in a template 20, see also Fig. 4 (not shown), which is accurately located above the sheet 12 by spigot 16 on a frame 14 secured to a light box 10, the spigots engaging location sockets 18 in the template and the stylus being pressed against the sheet 12 to deposit the pads at their selected locations. The pads have adhesive undersurfaces engaging the sheet. The sockets 18 are so spaced that by selective engagement of the spigots 16 in pairs of the sockets 18 the template can be selectively positioned relative to the sheet 12 in positions which are spaced from each other by distances which are fractions of the distance between the apertures 22. Thus if the movement of the template 20 is to be in N equal incremental parts of the pitch P of the apertures 22 then N<SP>2</SP> sockets 18 must be provided in an array with complementary mutual spacings which are N-aliquant multiples of P/N, viz. multiples of P/N which cannot be divided by N without a remainder. For example, if N equals 2 then 4 sockets 18 are required to permit stepwise movement of the template by a distance equal to ¢ P in either or both longitudinal and lateral directions of the template. This permits a template 20 having apertures 22 at a minimum acceptable pitch to be used to locate the pads 24 at points on a grid having a pitch which is a fraction of the pitch of the apertures 22. The spigots 16 are preferably spaced by an N-aliquant multiple of P/N and sockets 18 are preferably provided at both lateral areas of the template so that by inverting the template further closer spacings of the location points of the pads are provided. Below the sheet 12 is an undersheet having thereon a representation of the required printed circuit, a grid of appropriate pitch and different coloured marks to indicate approximate required positions of the pads 24, and the template 20 is located relative to the sheet 12 by a sighting device 48, see also Fig. 3 (not shown), having a sighting bead (54) at the end of a plug (50) which is inserted in any aperture 22 to align the bead with the selected colour and location indicia on the undersheet.