Patent GB-776343-A (GB)
Title: Improvements in the production of two-dimensional electric circuits or circuit elements on a supporting base
IPC: G03F7/027
Filed: 1953-08-04
Abstract: 776,343. Photographically produced electrical circuits; relief photographs; bichromated colloid processes. BLAUPUNKTWERKE GES. Aug. 4, 1953 [Aug. 2, 1952], No. 21555/53. Class 98(2) A flat or laminated electrical circuit or circuit element is formed on an insulating support as a wash-off developed exposed radiation-sensitive colloid relief which either (a) contains initially as a finely dispersed material, e.g. a powder or a colloidal dispersion, the functional material, i.e. that forming the circuit or circuit element, or (b) is swollen by immersion in a solution of a substance which reacts with a second solution or a substance incorporated in the colloid layer to deposit the functional material in the relief which may include initially an absorbing material such as colloidal silica or a largely insoluble reduction or oxidation agent. The colloid layer may be gelatin, albumen, animal glue, fish glue, dextrin, gum arabic- or polyvinyl - alcohol, - chloride, - acetate,. polystyrene, methacrylic acid derivatives, phenol-formaldehyde or silicone resins, cellulose, cellulose nitrate or acetate, and is exposed to harden it right through to the support which may be of plastic, e.g. polystyrene, glass, mica, or ceramic. Typically the sensitizers used may be alkali metal or ammonium bichromates or diazo and/or amino group containing compoents, e.g. N-methyl N-(6 [1:2:3:4-tetrahydronaphthyl]) p - phenylene diamine. In certain cases the sensitizers may be applied in the form of a vapour or by spraying or sputtering. If the layer is largely opaque to visible light due to the materials included in it, it may be exposed from front and rear through mirror image negatives. To decrease the overall heating which long exposure involves and which itself causes uniform hardening of the colloid, the face of the negative directed to the light may be white or reflecting in its opaque portions. Alternatively the exposure may be made with ultra-violet, or X-rays or a radioactive source using a radiation-opaque negative, e.g. of lead, or a phosphor such as zinc and/or cadmium sulphides or silicates may be used, being excited with ultra-violet or X-rays. A suitable phosphor for infra-red exposure is of the kind which after excitation and the usual afterglow stores energy which is released as light when the material is stimulated with infra-red. Since the swellability of the layer depends on the degree of exposure, different parts' of the colloid layer may be given different exposures to vary the deposit of functional material in case (b) above. Development, which may be assisted by the addition of acid or alkali, by mechanical vibration of audio or ultrasonic frequency, or by heating, is effected with hot water for gelatin and other natural soft colloids, cold water for polyvinyl alcohol, alcohol for shellac, and a mixture of acetone and methyl acetate for polystyrene. For case (a) above, the functional material may be ground up with the colloid and homogenized with ultrasonics. The functional materials may be powdered silver, copper, iron, nickel, or cobalt for conductors, carbon black, graphite, or carbides for resistors: oxides such as ferrosoferric oxide or manganese oxide or mixtures thereof for semi-conductors; ground glass, mica, kaolin, bentonite, felspar talcum, aluminium or magnesium oxides for insulators; titanium or zirconium compounds, such as barium titanate or barium or strontium zirconate for capacitors; " complex oxides such as ferrites and manganites for magnetic shields. For case (b) above, for conductors, the layer may be immersed in a " functional metal " salt solution e.g. silver nitrate followed either by an alkali metal carbonate and the silver carbonate reduced to silver by heating, or by a hydrazine e.g. phenylhydrazine to precipitate metallic silver. Alternatively the exposed layer may be impregnated with the metal salt and reduced to metal with nitrogen, hydrogen, hydrazine vapour or ammonia gas or solution, or oxidized with oxygen, ozone or with hydrogen peroxide or solutions of per salts such as perborates and permanganates. To assist the continuity of the functional material, especially for conductors, the layer is seeded with a solution of an alkali metal salt, e.g. a sulphate, so that on immersion in the "functional metal" salt, e.g. silver nitrate, nuclei of an insoluble salt are immediately precipitated and serve as deposition centres when the second treating solution is applied. Conductors so formed may be electroplated, the colloid being hardened by heating to prevent swelling and penetration by the electrolyte. If seeding is used for the production of electrode leaves in the manufacture of capacitors, the seeding ions should finally be removed by dialyses or electrodialysis. The finished circuit or circuit element may be given a protective lacquer coating which may serve as a transfer sheet which may be peeled off the support providing the circuit elements adhere to it more strongly than to the support. If a polystyrene support is used, capacitiative and magnetic coupling may be effected through the support between circuit elements on opposite sides of it.