Patent GB-912980-A (GB)
Title: Production of laminates embodying electrically conductive patterns
IPC: H05K3/04
Filed: 1958-01-13
Abstract: 912,980. Electric heating resistances. EISLER, P. Jan. 13, 1959 [Jan. 13, 1958], No. 1149/58. Class 39 (3). [Also in Group VIII] A laminate of insulating material embodying an electrically conductive pattern is produced by making a first sequence of cuts in a thin electrically conductive sheet, the cuts of the first sequence being spaced from one another side by side and only partially delineating the desired pattern, without any removal of conductive material or separation of the conductive sheet into pieces, interleaving a first thin insulating sheet so that it passes alternately under and over the portions of the conductive sheets between neighbouring cuts, the insulating sheet extending at least substantially to the ends of the cuts, consolidating this interleaved structure, making a second sequence of cuts spaced from one another side by side, the second sequence overlapping the first and serving in conjunction therewith to complete the delineation of the pattern, but without any removal of conductive material or separation of the interleaved structure into pieces, interleaving a second thin insulating sheet so that it passes alternately under and over the portions of the interleaved structure between the neighbouring cuts of the second sequence, the second insulating sheet extending at least substantially to the ends of the outs of the second sequence, and then consolidating the whole structure. The electrically conductive sheet may be of metal, e.g. lead or aluminium, or may be a thin carboncoated or graphite-coated fabric. The insulating sheets may be of paper impregnated with a, preferably modified, phenolformaldehyde resin. As shown in Fig. 9, metal foil from roll 21 passes through cylindrical cutter 22. Alternate pairs of meander arms are lifted by means not shown, over an entry roller 23 which guides in the interleaving sheet P1 from roll 24. The lifted pairs of meander arms are then brought back on to the web, which then passes between heated rollers 26 to be consolidated. These operations are then repeated, using a second cylindrical cutter 27, a second entry roller 29 which guides in the sheet P2 from roll 28, and heated consolidating rollers 31. As shown in Fig. 11, foil from a stock roll (not shown) is cut at Cl at the first station and then advanced to the second station, where alternate pairs of meander arms are lifted and a sheet PI of insulating material inserted. The web is consolidated by passing it between the hot rollers 33 to a third station where it is cut at C2. At the fourth station, a second sheet P2 of insulating material is inserted, and the web then passed between hot rollers 34. The conductivity of the conductive sheet may be increased locally, e.g. in the links connecting adjacent arms, e.g. by plating or by applying a coating of solder or of conductive material such as graphite. Conversely, its resistance may be increased locally by thinning it, or by making holes in it. Perforations may be made at any stage, or a small perforation may be made in the finished laminate within the area of an earlier larger perforation through the conducting layer, so that an insulating ring is left round the hole. When, as in the embodiments of Figs. 9 and 11 the cuts form a regularly repeating pattern, the . product can be cut to produce a structure including a desired number of repeats. The conductive sheet may be a crimped foil, with its crimps substantially perpendicular to the cuts. Parts of the conductive sheet may be folded over before lamination, and the foldedover parts coated with a material, e.g. graphite or silicone grease, to which binder in the insulating sheets will not adhere, so that the folded-over portions can subsequently be folded back and electrical connections made thereto. Alternatively, a binder may be used that forms, with the conductive sheet a bond that can be broken without substantial damage to the conductive sheet, or the overlying layersmay include a brittle region that can readily be broken away. A water-soluble glue or gum can be used to provide the readily breakable bond or the brittle region. In another embodiment, the layer laminated over the pattern is apertured to provide access to terminals. These apertures may be temporarily filled with easily removable composition, which may be coloured for easy location. The laminate may have further insulating layers bonded to one or both sides; electrical connections may be made after bonding one of these but before bonding the other. The further insulating layers may be marked to indicate the positions of terminals, or of the boundaries between " repeats " or may be decorative. The laminate may have an insert moulded into it against a folded tab of the conductive layer. This insert is coated with graphite, talcum powder or silicone grease, or made of polytetrafluorethylene so that it does not bond to the other layers. It can be removed and a flat push-in connector inserted in its place. As shown in Fig. 19, the cuts of the first sequence form intercepts in a sector a of a spiral, a first sheet 51 of insulating material is interleaved and consolidated, a second series of cuts in the sector # completes the spiral, and a second sheet 52 is interleaved and consolidated. Specifications 900,515, 900,516, 900,517, 900,519 and 905,867 are referred to.