Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating selected area
Reexamination Certificate
2001-10-02
2004-11-23
Andrews, Melvyn (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating selected area
C205S584000, C205S586000
Reexamination Certificate
active
06821404
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the technical field of recovering an etch bath from an etching process in which printed boards coated with copper are etched with the alkaline etch bath and then rinsed with water. The recovery of copper from such an etch bath as well as the recovery of the etch bath itself are known per se, but the invention relates to the recovery of copper in a manner that is completely new in this connection and very advantageous.
BACKGROUND OF THE INVENTION
Today, electronics are primarily composed of components which are soldered onto printed boards. The manufacture of these printed boards has increased rapidly. Advanced electronics, such as computers, require very complicated printed boards and the manufacture thereof has resulted in the emergeing of a special industry.
A printed board consists of a plate made of a base material, which is often a plastic material, e.g. epoxy. This plate is coated with a thin (e.g. about 15-20 &mgr;m) copper layer on both sides.
The manufacture of these printed boards may, for instance, be carried out in the following manner. According to a predetermined pattern, holes of different size are drilled into the plates so that ducts are formed between the two sides and so that holes are formed, in which components can be mounted. After that, all surfaces are coated with a copper layer which has a thickness of about 2-4 &mgr;m and which is applied in a chemical manner instead of electrochemically. This is necessary since the walls of the holes consist of a material (e.g. epoxy) on which it is not possible to use electrochemical plating. As a result, an integral and continuous copper surface is obtained, which can subsequently be coated by means of electrochemical plating.
The next step in the manufacture of printed boards is to make the desired conductive pattern. To this end, the surfaces which are to be free from copper are coated with a non-conductive protective film, and the boards are fed into a so-called electroplating line. This line comprises a number of different baths, into which the boards are dipped.
In one of these baths, the exposed copper surfaces are coated with additional copper to provide the desired thickness of conductors, after which the same surfaces are coated with a tin layer, which will serve as a protection during the subsequent etching.
After that, the etching of the printed boards in question takes places, which is usually carried out by means of alkaline solutions. Preferably, they are ammoniacal and contain free ammonia as well as one or more ammonium salts (e.g. NH
4
Cl, NH
4
HCO
3
). When etching, copper is removed from the surfaces of the printed board, on which the copper layer is exposed to the solution. Gradually, the copper content of the bath rises to a level, on which the speed of etching drastically decreases and the bath is no longer usable. Usually, the upper limit of the copper content is about 150-170 g/l, depending on the composition of the bath. After the etching, the printed boards are rinsed with water to be clean.
The boards are then passed on to be stripped of tin and coated with varnish, wax, etc.
A method for regenerating the etch bath in & process of this kind is known from EP-B1-0005415. This method may be directly connected to the etching process and it involves in short the regeneration of the etch bath for renewed use in an etching process, copper being removed from the etch bath by extraction. The method also allows treatment of the rinsing water so that it may subsequently be let out in an environmentally suitable manner.
The copper which is extracted from the etch bath and preferably also from the rinsing water is recovered as metallic copper by electrolysis.
DESCRIPTION OF THE INVENTION
The present invention relates to a new and, in this connection, extremely advantageous process for recovering copper from an alkaline etch bath of the above-mentioned kind. According to the invention, it has thus surprisingly been found that it is possible not only to recover copper from the etch bath and preferably also from the rinsing water in an alternative new manner but also to reuse recovered copper-in the plating process. Generally, the process according to the invention makes it possible to directly reuse a copper-containing solution which is obtained after the extraction from the alkaline etch bath in the plating of the printed boards, if a flow is diverted from the copper-containing acid solution which is obtained from the re-extraction step and the balance of the copper content is adjusted between this flow and the acid solution which is withdrawn for recovering copper, e.g. metallic copper by electrolysis. As a result, the need for cost-demanding electrolysis for recovering metallic copper is reduced, at the same time as the need for additives of expensive anode copper is reduced or eliminated in the plating. In addition, it is possible to directly and in the same place use the recovered copper which previously could only be sold at a price of about ¼ of the price of said anode copper while achieving a plating quality which is at least equally good or even better than the quality obtained in plating according to the plating technique which was previously commercially used.
Moreover, one condition of successful plating, i.e. with a satisfactory evenness of surface and satisfactory coating in holes and the like, in connection with commercial methods previously used for electroplating has been the addition of a number of different chemicals. Besides the fact that these chemicals to a certain extent have not been compatible with reagents which are used in the extraction, and therefore must be removed according to prior-art technique, which has complicated the process and made it more expensive, it has thus been found that the use of these chemicals may be reduced or completely eliminated in the process according to the present invention, if the plating is carried out under special conditions, in particular pulse plating. According to the invention, it has thus been found that at least equally good results as according to prior-art technique may be achieved by this new method according to the invention, which results in considerable advantages in terms of both costs and environment. Besides the fact that the process is simpler and cheaper, the process according to the invention also allows a completely closed or continuous process, in which also the plating step may be included in the prior-art etching and recovery process.
Further advantages of the invention will appear from the description below.
In this connection, it can be added that pulse plating of printed boards is known per se from Processing of Advanced Materials (1994) 9, pp 148-154, but this publication does not in any way disclose or even suggest that such plating could be integrated in a process of the kind involved in the present invention and even less so under the same circumstances and with the same results as in the case of the present invention.
Thus, the process according to the invention is a process for recovering copper from an alkaline, preferably ammoniacal, etch bath from an etching process in which printed boards electroplated with copper are etched with the alkaline etch bath and then rinsed with water, a part of the copper content of the alkaline etch bath being removed by extraction with an organic solution containing a reagent, which forms with copper a complex compound, which is extracted by the organic solution, the alkaline etch bath being recirculated to renewed etching, the copper-containing organic solution being contacted, in a re-extraction step, with an aqueous solution of acid, preferably sulphuric acid, so that copper passes from the organic solution to the aqueous solution, and the organic solution being recirculated from the re-extraction step to renewed extraction. The process according to the invention is characterised by the steps of passing the copper-containing acid solution obtained from the re-extraction step to a copper recovery operation, preferably f
Lidmer Gunnar
Pacholik Robert
Andrews Melvyn
Burns Doane Swecker & Mathis L.L.P.
Mercer Holdings Corp.
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