Patent GB-1476885-A (GB)
Title: Flexible planar printed circuit fabrication process
IPC: H05K1/16
Filed: 1975-05-07
Abstract: 1476885 Printed circuits G J LICHTBLAU 7 May 1975 [24 May 1974] 19273/75 Heading H1R Plural individual planar resonant tags comprising integral LC tuned printed circuits, e.g. for electronic security systems comprise on one side of a substrate a rectangular conducting spiral extending from an inner to an outer conductive area (Fig. 1, not shown) through an intermediate conductive area, and on the other side of the substrate conductive areas registering with the opposed inner and intermediate areas interconnected by a conductive path, and a further conductive area registering with the opposed outer area and connected to the remainder over a narrow fusible conductive path capable of electrical destruction during operation as described in Specification 1,406,500 (Fig. 2, not shown). The conductive paths define inductors L 1 , L 2  and capacitors C 1 , C 2  of which L 1 , L 2 , C 2  are tuned to a detection frequency and L 1 , C 1  is tuned to a destruction frequency at which link 28 is fused (Fig. 3). Thus the presence of a tag in a controlled zone due to illicit removal is indicated by resonance at detection frequency causing an alarm, while permissible removal is preceded by fusible destruction of the link by energy at a second frequency, to permit removal without alarm. In fabrication a substrate web 44 of, e.g. polythene, polypropylene, polyisobutylene is extruded through die 42 into cooled metal plate 46, treated with corona discharge at 50, 52 and wound on reel 56. Thereafter aluminium (or silver or copper) films 58, 60 from reels 62, 64 are laminated on respective sides of the web 44 from reel 66 by heated rolls 68, 70 and the laminate is wound on reel 74. The patterns required for the respective sides of the tags are respectively printed along both sides of the laminate by rollers 78, 80 on surface 76, followed by drying at 88, and rollers 84, 86 acting on opposite surface 82 followed by drying at 90; using a vinyl or nitrocellulose ink to produce a series of circuit patterns 91 on one side with corresponding circuit patterns on the other (Fig. 7); registration marks 92 being provided for electronic sensing, and alignment holes 96 being punched for mechanical registration. The laminate 98 is then etched (Fig. 8) by passing through an etchant, e.g. FeCl 3  spray from nozzles 108, 110 pumped from source 102, washed at 112, and dried at 114; the laminate is then split longitudinally for further processing, in which an electrosonic welder 116 has a four sector tip 118 (Fig. 10, not shown) applied to the circuit 120 against a heated base to electronically interconnect the confronting circuit patterns by welding through the substrate and ink layer. Cold welding may also be used for this purpose using a chisel shaped tip and sufficient pressure. Laminate 126 (Fig. 11) bearing the appropriate circuit patterns successively on the opposed faces is pressure adhesively attached to a paper film 132 and release sheet 134 by pressure rollers 128, 130 and fed to a rotary cutter 136 removing waste material without cutting the release sheet 134. The waste is stripped off on sheet 132 while the separated tags 138 remain adherent to release sheet 134 wound on reel 142 (Figs. 11, 12) which may be split into reels of single tags.