Patent GB-1376785-A (GB)
Title: Method and apparatus for etching copper and copper alloys
IPC: C23F1/46
Filed: 1972-02-29
Abstract: 1376785 Liquid level control and indication; measuring density electrically H HOLLMULLER 29 Feb 1972 [8 March 1971 11 Aug 1971 21 Jan 1972] 9254/72 Headings G1H and G1N [Also in Divisions B6 and G3] An ammoniacal etching solution containing chloride ions (e.g. ammonium hydroxide and ammonium chloride) for etching copper or copper alloys is regenerated by adding controlled amounts of an ammonia-containing compound (e.g. ammonium hydroxide) and a chlorine-containing compound (e.g. hydrochloric acid), the former in an amount to maintain the pH at 8À5-10À0 and the latter in an amount corresponding to the formation of copper (I) during etching. Etching solution 5 on the way to an etching machine is passed through a container 1. A pH measurer 29 controls a valve 14 to admit ammonium hydroxide from a container 8 to the container 1, a specific gravity measurer 30 controls a valve 15 to admit water from a container 9, and a redox potential measurer 28 controls a valve 16 to admit hydrochloric acid from a container 10. The maximum liquid level 4 in the container 1 and the minimum level 27 in the containers 8, 9, 10 are maintained by means of level-control switches 6, 26, the latter controlling the supply to the containers 8, 9, 10. In another form, Fig.2 (not shown), the measurer 30 controls all the valves 14, 15, 16 and the measurer 29 controls an additional valve (33) for further addition of ammonium hydroxide. In another form, Fig.3 (not shown), the container 8 is replaced by an inlet for ammonia gas, said inlet having a valve controlled by the pH measurer, while the valves 15, 16 are controlled by the measurer 30. In another form, Fig.4 (not shown), the solution is regenerated in the etching chamber, ammonia gas and ammonium chloride being introduced through valves controlled by the measurers 29, 30 respectively. The specific gravity measurer 30 comprises a closed cylinder 54, Fig.5, having an inlet 55 and an outlet 56 for the solution, in which floats a rod-shaped float 59 having a titanium extension 61. If the specific gravity of the solution rises to an undesirable level, the extension 61 moves further away from an inductive switch 62, which opens the circuit of a relay 63, thus closing a relay switch 65 in the circuit 66 of the solenoid valve 15, to open the latter. In another form, Fig.6 (not shown), the circuit 66 controls all the valves 14, 15, 16, and the pH measurer 29 controls a changeover switch which, when the pH value drops, excludes the valve 15 from and includes the valve 33 in the circuit 66. The level-control switch 6 (or 26) comprises a housing 169, Figs.8 and 9, separated from the container 1 (or 8, 9, 10) by a disc 70 having a plurality of apertures. The housing 169 contains a float 167 in which is secured an annular magnet 168. To the bottom of the housing is secured a closed trough 71 in which is fixed a closed glass tube 75 containing an electric switch 72 which comprises a stationary contact 73 and a movable contact 74 which are normally spaced apart. When the level of the liquid in the container sinks, the magnet approaches the switch and causes the contacts to close and initiate the supply of further liquid to the container.