DE4024909A1 - Selective alkaline etching soln. for copper and copper alloys - useful in brasses and bronzes, even when lead is present, completely removes copper to exclusion of nickel - Google Patents

Abstract

An effective etching soln. is claimed for the selective removal of Cu or Cu alloys from a Ni substrate. This soln. is alkaline (pH adjusted to 9-11 by NH3) and contains, (g/l) a metal or NH4 chlorite 3-90; and a metal or NH4 carbamate 50-200. USE/ADVANTAGE - Fully removes Cu to the exclusion of Ni. Useful in situations when other etching agents cannot be used, e.g. for certain bronzes and brasses, and esp. when Pb is present. In an example, precisely weighed plates of the purest Cu and different Cu-Zn alloys (including those contg. Pb) and Cu-Sn alloys were mechanically treated by ultramilling to a Ra value of less than 15 micron, then galvanically coated with Ni on one side. The Cu was then removed by placing in a soln. made from deionised water and contg. (g/l) NaClO230 and (NH4)(OCONH2) 122, and the pH adjusted to 10 by NH3 at room temp. for more than 1 hr. until the Cu concn. in the soln. was constant. The plates were then removed, rinsed clean, and reweighed. No Ni ions were detected in the spent etching soln., and screening electron microscopy of the etched plates' surface showed that no corrosive action of the soln. on the Ni had taken place.

Description

The invention relates to an alkaline etching solution for copper or containing copper alloys

• a) metal or ammonium chlorite
• b) metal or ammonium carbamate
• c) ammonia or aliphatic amine or aliphatic Polyamine

A selective alkaline etching solution for copper is from the US PS 38 44 857 known. This etching solution consists of the alkali metal or ammonium salt of a chlorine oxygen acid, esp special from sodium chlorite, copper amine chloride, an ammonia Salting as a buffer and ammonia in an amount that a pH from 8 to 12 is reached.

Another alkaline caustic solution for copper is described in US Pat 39 19 100. This etching solution contains copper ions, Sulfamate ions and ammonium ions at a pH greater than 7, preferably 8 to 12.

In the case of etching solutions which, like the aforementioned, have an ammonial potassium contain Cu (II) chloride solution, there is a risk that besides copper, nickel is also attacked. The selectivity against nickel and the etching rate are pH-dependent. Furthermore, a dense, poorly soluble CuCl coating can be found the copper layer to be etched the further attack of the etch prevent diums. Even if you consider the etching conditions, above al lem the pH value and the dwell time of the counter to be etched levels in the etching bath are strictly controlled, who must be expected the fact that nickel parts are attacked at the same time.

In the event that copper alloys, e.g. B. brass or bronze These etching solutions fail completely to be etched especially if lead is present as an alloy component.  

The well-known acidic etching solutions for copper based on Iron chloride, for example according to DE-OS 36 23 504, are opposite Nickel not selective.

The object of the invention is a selective etching solution for copper or to propose copper alloys that have the disadvantages of does not have known etching solutions and in particular the Surface of nickel objects due to erosion or corrosion not worsened. The etching solution is also said to be copper alloys containing lead, brass and bronze can sen without attacking nickel. The etching solution should be free of copper ions.

Accordingly, the etching solution defined at the outset was found.

Particularly suitable etching solutions are described in the subclaims as well as a particularly preferred application wrote.

The etching solutions according to the invention are preferably used in the galvanic impression of microstructure bodies applied.

Here, a microstructured body, which by Be radiate with X-rays and then remove them of the irradiated areas was molded.

The microstructured body consists of a base plate, on which microstructures emerge from an X-ray resist appropriate polymer polymer. The structural reason exists made of metal and is used for galvanic impression as cathode switches so that between the microstructures and also also a suitable metal, especially nickel can divorce. So that the resulting nickel body more easily can be separated from the microstructured body, the sen structural base coated with at least one separating layer. Often a very thin gold is first on the structural base  layer deposited, which is then covered with a copper layer is covered.

After the galvanic impression of the ready in this way The microstructured body with nickel is created separated the nickel body. This nickel body has the above-mentioned Kup layer and remains of the gold layer. Since such nickel bodies can display tools, of which a high precision sion, especially a smooth and undamaged surface is required, the copper layer must be removed in a way be that the underlying nickel surface is not attached is gripped.

For this purpose, the etching solutions according to the invention are very good is suitable.

In addition to pure copper, its alloys, in particular other brass and bronze, which in turn also contain lead can, as well as lead-containing copper with the same selectivity be removed from the nickel surface.

An essential advantage of the etching solutions according to the invention be stands in the greatly simplified process control of the etching gangs.

It is sufficient to put the etching solution on before using it a pH of about 9 to 11, preferably 10 put; control and readjust the pH rend the etching process is unnecessary as long as the etching solution in Excess is used. Also the concentration of chlorite and the carbamate need not be monitored. Further the residence time of the object to be treated in the Etching solution should not be checked, because even after long etching time nickel is not attacked.  

The end point control is the concentration trace of the copper in the etching solution.

As soon as the copper concentration no longer increases, the Reaction ended. This endpoint control is facilitated by the fact that the etching solution itself does not contain copper holds.

The invention is described below with the aid of implementation examples play explained in more detail.

example 1

Precisely weighed platelets made of pure copper and various which copper-zinc alloys (also containing lead) and copper Tin alloys were made after mechanical processing on one ultra mill down to Ra <0.15 µm with nickel on one side galvanically coated.

The copper was then etched as described below solution removed:

The following were dissolved in deionized water:
30 g / l sodium chlorite NaClO ₂ , as well as
122 g / l ammonium carbamate (NH ₄ ) (OCONH ₂ ).

The pH was adjusted to approximately 10 using an NH ₃ solution.

The treatment was carried out at room temperature for a few hours until the measured copper concentration of the solution remains constant stayed. After the etching treatment was completed, the sample was again weighed and the nickel removal checked. It did find no removal. An examination of the caustic solution Nickel ions were also negative. The one on the grid electro  inspection of the nickel surface by a microscope Traces of corrosion showed no attack from the etching solution.

Example 2

Using the LIGA process (X-ray lithography-galvanic Impression) was made using a synchrotron radiation from PMMA (Polymethyl methacrylate) generated primary structure by electroplating Forming from nickel a molding tool for the plastic Mi Kroabformtechnik manufactured. To the impact of the Unterplat tion (it manifests itself as a fine metal fringe that free structure protrudes and in the molding process as unim desired undercut) has been avoided a suitable sequence of sub-µm to a few µm thick Me intermediate layers applied before the actual Mi Crostructed and galvanized to form an impression tool was built.

One of these intermediate layers consists of copper and serves after the electroforming of the impression tool as a separating layer for separating the nickel part from the substrate on which the Underplating remains.

The mold insert was used to remove the copper intermediate layer for a few hours at room temperature in the be in Example 1 treated etching solution.

The end point control was carried out as in Example 1 by the Track the increase in copper concentration.

To check the nickel surface, the mold insert on Scanning electron microscope examined: the nickel layers showed no corrosion attack.

Instead of ammonium carbamate, a metal, e.g. B. Na-, K or Li carbamate can be used.  

Ammonia can be generated by an aliphatic amine or an aliphati cal polyamine to be replaced. The etching solution can also be a non-ionic, alkali-insensitive surfactant for better loading wettability included.

Claims (6)

1. Selective alkaline etching solution for copper or copper alloys containing

• a) Metal or ammonium chlorite
• b) metal or ammonium carbamate
• c) ammonia or aliphatic amine or aliphatic polyamine.

2. etching solution according to claim 1, characterized by a Chlorite concentration in the range between 3 g / l and 90 g / l. 3. etching solution according to claim 1, characterized by a Carbamate concentration in the range between 50 g / l and 250 g / l. 4. etching solution according to claim 1, characterized by a pH Value in the range from 9 to 11. 5. etching solution according to claim 1, characterized in that it contains a non-ionic, alkali-insensitive surfactant. 6. Use of the etching solution according to one of claims 1 to 5 for the selective removal of copper or copper alloys from a nickel base.