Patent GB-1512793-A (GB)
Title: Manufacture of micro-wiring printed circuit arrangements
IPC: H05K3/40
Filed: 1975-09-05
Abstract: 1512793 Printed circuits SIEMENS AG 5 Sept 1975 [27 Sept 1974 2 July 1975] 36565/75 Heading H1R In fabricating a micro wiring printed circuit arrangement for contacting semiconductor circuits, superimposed on a flexible insulant carrier strip 1; a copper foil 2 is adhesively secured thereto and a series of transport holes 100 and assembly openings 101 are punched in the strip both sides thereof, being dip coated with positive photosensitive varnish layers 3, 4. The latter also covers these areas of the foil exposed by openings 101. The varnish layer 3 is exposed and developed on one side with removal of those areas corresponding to the required wiring structure to uncover areas 300 of the foil 2; development being by flotation of the strip on an alkaline developer both with layer 3 immersed to prevent dissolution of layer 4. (Fig. 2). An etch resistant, e.g. tin layer 5 is electrodeposited on the exposed areas of foil 2 the rear of which is protected against depositon by layer 4 (Fig. 3, not shown) and the residual layer 3 is removed by secondary exposure followed by one-sided secondary development, or by one sided layer removal by flotation on an alkaline varnish removal both with layer 3 immersed and subjected to a flow towards the surface (Fig. 4, not shown). The resultant wiring structure 200 (Fig. 5) is subsequently etched out of foil 2 with removal of varnish layer 5, while the rear face of the foil 2 exposed in openings 101 is protected by varnish layer 4 during etching. Layer 4 is finally removed in a known varnish removal bath. An apparatus for one sided development and varnish removal (Figs. 6, 7) comprises a developer bath 7 or varnish remover bath 70 in an open dish 8, whose walls are surrounded by an overflow channel. The strip 10 coated on each side with photosensitive varnish is guided over the dish so that the layer to be removed or developed is surface wetted by the appropriate bath; the strip being positioned by lateral flanges of guide rollers 11, 12. The strip overlaps the side walls of the dish at each side, and a flow is generated by pump 13 from channel 9 and directed to the surface of the bath and the immersed layer of the strip to be developed or removed. The walls of the dish are chamfered at 76 for uniform overflow. In a complete plant (Fig. 8) for development and/or varnish removal the strip 17 is unwound from supply reel 18 over guide rollers 19, 20 to a position at the surface of a developer or layer removal bath 21, 210 to immerse the layer to be processed. Then the strip passes over rollers 22, 23, 24 to spray wash 25 and to air drying zone 28; after which it traverses toothed drive drum 29 to take up reel 31. The process bath 21, 210 is contained in a funnel shaped vessel 23 containing a perforated plate under the surface and a surrounding overflow channel 35, whose outlet 36 is connected over throttle valve 38 to reservoir 39, whose bottom is connected to discharge valve 42, and to the suction of pump 44 delivering over filter 46, shut off valve 47, and regulating valve 48 to the inlet 33 at the bottom of the process bath. The transit speed of the strip over the process bath surface is adjustable by drum 29 for optimum process conditions, and valve 48 regulates the circulation and the flow directed towards the surface. Process liquid flows out over the edge of vessel 32 into channel 35, and returns to reservoir 39; the valve 38 being adjusted to develop back pressure of liquid in the overflow channel. Residues and foreign matter are extracted by filter 46, and plate 34 improves the uniformity of the flow towards the surface.