Patent GB-846204-A (GB)
Title: Improvements in or relating to the etching of copper
IPC: C23F1/46
Filed: 1958-10-09
Abstract: 846,204. Regenerating etchant solutions. WESTERN ELECTRIC CO. Inc. Oct. 9, 1958 [Oct. 28, 1957], No. 32260/58. Class 41. [Also in Group XVI] Copper is etched in a bath of a metallic bromide or chloride, the bath containing an excess of the halide ions over metallic ions, the copper reacting with the halide to form cuprous bromide or chloride which reacts with the excess halide ions to form a complex. The bath is then electrolytically regenerated in a cell by maintaining a low current density at the anode and a high density at the cathode, concentration polarisation at the cathode causing cuprous ions to be oxidised to cupric ions at the anode which are physically free to migrate to the cathode, and cuprous and cupric ions to be reduced to copper at the cathode. The bath may comprise cupric or ferric chloride, with added hydrochloric acid, sodium, ammonium, potassium, or lithium chloride, or cupric, sodium, ammonium, potassium or lithium bromide, or hydrobromic acid, e.g. 2 molar cupric chloride saturated with sodium chloride, with 20 grams per litre of added copper. The bath is regenerated subsequently or simultaneously, using a larger anode than cathode, the area ratio being preferably greater than 5:1 and usefully up to 45:1. The current may be 1 amp at 1 volt, and a small amount of colloid such as dextrin may be added. The minimum current density at the cathode should be 60 amps/sq. ft., 90 amps/sq. ft. and 50 amps/sq. ft. respectively where sodium chloride, ammonium chloride, and hydrochloric acid respectively are added. A thin flexible inert metallic tape, such as platinum, 23, Fig. 7, is passed, by drive wheel 21 and rollers 27 of polystyrene through an etching bath 24 (in which copper is being etched), a wash-water bath 25, and a stripping bath 26. A copper wheel 28 connected to a source of electricity biasses the tape so as to be cathodic relative to an anode in the bath 24 and anodic relative to a cathode in the bath 26. The tape receives copper in the bath 24 and deposits it on the cathode in the bath 26. The regeneration process thus consists of oxidation of cuprous to cupric ion at the anode and removal of a portion of cupric and cuprous ions from the solution as copper at the anode. In another form, the stripping bath 26 is omitted and the copper on the tape is removed by a mechanical scraper. In another form, Fig. 6, etching liquid to be regenerated is placed in a glass container 18 having as a core a hard rubber rod 15. The cathode is a platinum cylinder 11, 1À5 square inches in area, soldered to a brass ring fitted to a phenolic support rod 12, and sealed with adhesive to expose only its outer surface. Electrical contact is made by a wire within the rod 12 to the contact ring 13 and phosphor-bronze spring contacts 14 riding thereon. The anode is a cylindrical platinum gauze member 17 having a surface area about twentyfive times that of the cathode and spaced about “ inch therefrom. The rod 15 is drilled to receive the rod 12 and a wire leading to the anode. The rod 12 is rotated by a motor to actuate a stirring vane 19. After regeneration, the potential is removed and copper deposited on the anode allowed to re-dissolve.