Patent GB-822826-A (GB)
Title: Printed circuitry laminates and production thereof
Inventor: WERBERIG CORNELIUS
IPC: B32B27/00
Filed: 1956-10-22
Abstract: 822,826. Laminates; coating webs. ST. REGIS PAPER CO. Oct. 22, 1956, No. 32139/56. Class 140. [Also in Groups XV and XXXVI] A thermoset resinous laminate having pattern areas of thin sheetmetal, which may form an electric circuit or part thereof, embedded in at least one surface of the laminate, is produced by forming or providing on one surface of a thin sheet of metal a self-supporting, firmly adhering, insulating film, resist printing the opposite surface of said metal sheet to define said pattern areas, removing the unprinted portions of said metal sheet by etching, leaving only said metal pattern on said film, superimposing said film, with said metal pattern exposed, on to a stacked assembly of sheets of fibrous material impregnated with a thermosetting resin, and hot pressing said assembly and superimposed film between platens to consolidate the same into a unitary, thermo-set laminate having said metal pattern embedded flush with the laminate in a surface thereof. As shown, in Fig. 1, a continuous strip 10 of thin copper foil is fed from a roll 11 between rolls 13 and 14. Roll 14 is partially submerged in a bath 15 of liquid plastic material, e.g. a solution of an alkylated phenol-formaldehyde resin and a polyvinyl butyral resin in a solvent such as acetone, methyl iso-butyl ketone or other low-boiling ketone, and deposits a coating of this solution on the foil. The coated foil is conducted past a bank of infra-red lamps 17 to evaporate the solvent and then over a roll 18 where it is sprayed with a photo-sensitive resist, through a nozzle 20, mounted in a housing 19 and connected through a pipe-line 21 with a reservoir 22 filled with the photo-resist. The foil then passes a second bank of drying lamps 25 to dry the photo-resist. The foil then passes about a drum 26 having transparent areas in its periphery in the form of the metallic pattern required in the finished laminate, the remainder of the periphery being opaque. The drum is rotated and has a mercury arc or equivalent lamp 28 in its interior to produce a photographic image on the photo-resist coating. The foil then passes over guide rolls through successive tanks containing (a) a solvent to dissolve off the unexposed portions of the photo-resist, (b) an etching-agent (e.g. 40% solution of FeCl 3 ) to dissolve away the thus-exposed areas of the copper foil, and (c) water in each of two successive wash tanks. The material is passed between squeegee rolls as it emerges from each of the solvent and etching tanks and from the second wash tank. After washing, the material is fed over an inspection unit 51, provided with a light source 52 for indicating any flaws. It is then passed through a cutting-device which cuts the strip into lengths corresponding with the pattern areas, the cut lengths being stacked at 55. The plastic material may be applied as a preformed continuous film instead of in liquid form, or a suitable resist may be printed on in the required pattern by means of a print roll instead of using the photo-sensitive resist. A cut length of the etched strip is used as the surface sheet of a laminating assembly, the unetched metal being on the outside. The other surface sheet of the assembly may be a similar sheet bearing a different pattern. Between the two surface sheets is interposed an assembly of sheets of fibrous material (e.g. kraft paper) impregnated with thermosetting (e.g. phenolformaldehyde) resin. The complete assembly is pressed between the platens of a heated press to cure the resin and press the metal pattern flush with the surface of the laminate. To align the circuit patterns on the two faces, when two are employed, the patterned areas may include copper foil corner-tabs 65 (Fig. 3) and border outlines 66. When assembling the laminate the edges are clamped together, as by stapling, and holes punched through the corner tabs, as at 67, in which are inserted plastic aligning pins. After hot pressing the stapled edges of the laminate are sheared off. The photo-resist is removed after etching by means of toluene, xylene or similar solvent, either before or after laminating. Specification 639,178, [Group XXXVI], is referred to.