| 摘要 |
894,256. Etching. HANLET, J. M. N. July 22, 1958 [July 22, 1957], No. 23494/58. Class 100(2) [Also in Group XXXVI] In a method of making printed circuits (see Group XXXVI), a printing plate is formed of magnesium, chromium or of a ferro-chromium alloy and is coated with a film of nickel oxide Ni 2 0 3 by heating in a vessel in the presence of vapours of nickel bromide, iodide or chloride in ethyl alcohol. A negative of the required circuit pattern is next formed on the oxide-coated surface by applying asphalt or bitumen by the silk screen process to the parts not corresponding to the conductors in the finished circuit. The following photo-etching process is described as an alternative to silk-screening: The oxide coating is sprayed with a photo-sensitive emulsion containing fish glue, erythrosin, ammonium bichromate, and ammonia. After drying, a contact print of a positive transparency of the required circuit is made on the plate using an ultraviolet source. The plate is developed in warm water which removes all the unexposed emulsion. The plate is then heated and the parts of the oxide coatings not protected by emulsion are then etched away by spraying the plate with an aqueous solution of sodium nitrate, sodium pyrophosphate, methyl alcohol and powdered zinc. Hydrochloric acid is then poured over until the zinc is dissolved. This process reduces the oxide to expose the parts of the metal corresponding to the conductors of the finished circuit. The resist is then removed with turpentine or hot water. Alternative materials Complex coatings of iron, bismuth and antimony oxides may be substituted for nickel oxide. |
