WO1998007903A1

WO1998007903A1 - Device for electroplating electronic printed circuit boards or the like

Info

Publication number: WO1998007903A1
Application number: PCT/EP1997/003895
Authority: WO
Inventors: Thomas Kosikowski
Original assignee: Hans Höllmüller Maschinenbau GmbH
Priority date: 1996-08-22
Filing date: 1997-07-20
Publication date: 1998-02-26
Also published as: DE19633797A1; DE19633797B4

Abstract

A device for electroplating electronic printed circuit boards, in particular those which contain a plurality of bores, has in a manner known per se a machine housing (1) with an electrolyte sump (9) in its bottom area. The printed circuit boards are transported in the horizontal position by a transport system along a path of displacement through the device. At least one anode (7, 8) and a container (13) that surrounds the anode and is provided with an inlet slot (14) and with an outlet slot (15) are arranged in the area of this path of displacement. Electrolyte from the sump (9) is fed by a pump (10) into the inner chamber of the container (13) so that the inner chamber is filled with electrolyte in dynamic balance between inflow and outflow. Contact and transport rollers (6) which extend over the whole working width of the device across the direction of displacement of the electronic printed circuit boards, thus exercising a damming effect on the electrolyte flow, are part of the transport system. This damming effect leads to varying pressure conditions in the area of the electronic printed circuit boards which improve the flow through the bores contained therein. The contact and transport rollers (6) are provided over at least part of their outer surface with a metallic coating connected to the negative pole of the electroplating current source.

Description

Device for electroplating electronic circuit boards or the like

The invention relates to a device for electroplating electronic printed circuit boards or the like, in particular those containing a plurality of bores

a) a machine housing, in the lower area of which there is a sump for an electrolyte;

b) at least one electroplating current source;

c) Contact and transport means, which are electrically connected to the negative pole of the galvanizing power source, act on the electronic circuit boards in such a way that their metallic coatings are also at negative potential, and along the electronic circuit boards in a substantially horizontal orientation lead a path of movement through the device;

d) at least one anode located near the path of motion and connected to the positive pole of the galvanizing power source;

a container surrounding at least part of the path of movement and the anode (s) and having an inlet and an outlet slot for the electronic circuit boards; at least one pump which takes electrolyte from the sump and feeds it to the container in such a way that its interior is filled with electrolyte in the dynamic equilibrium between inflow and outflow.

With devices of this type, there is the double problem of how on the one hand the electronic circuit boards which are moved continuously through the electrolyte in a horizontal orientation can be driven and on the other hand brought to the required negative potential. This problem is solved in a known device of this type in that the lateral edges of the electronic circuit boards are gripped by clip-like contacts which are attached to endless chains on both sides of the movement path and are themselves at a negative potential. These contact clips hold the printed circuit boards firmly and guide them through the electrolytic bath along a part of their path of movement. The clips on the edges of the printed circuit boards are closed by suitable cam devices at the beginning of the part of the movement path in question and opened again by corresponding cam devices at the end of the part of the movement path, so that the printed circuit boards, which have in the meantime been galvanized, are released and in a different way Transport system can be handed over. This known device has the advantage that the contact point between the contact clamps and the electronic circuit boards does not perform any relative movement, so that the coating on the circuit boards is protected. On the other hand, the cam devices that are required to open and close the contact clips, as well as the endless chain, to which the individual contact clips are attached, and their drive are very complicated and expensive components. Moreover This type of contacting and promotion of the electronic circuit boards presupposes that a corresponding metallic contacting plug is provided at the edge of the electronic circuit boards, which generally requires a special "design" of the circuit boards.

It is also known to make contact with electronic circuit boards via contact rollers which roll on the edges of the circuit boards which are otherwise moved by a conventional conveyor system. However, even with this type of contacting, the lateral metallic hem on the printed circuit boards already mentioned above is required.

In both cases of the prior art, the electrolyte flowing over the printed circuit boards is stowed exclusively at the inlet and outlet of the container in which the "standing wave" is formed, that is to say in practice at a distance of 5 to 6 meters. It was therefore not recognized that the congestion of the electrolyte flow is also important in view of the formation of a uniform thickness of the electrodeposited layer. Therefore, in the prior art it is inadequate to achieve a constant thickness of the electroplated layer over the entire printed circuit board. This also applies in particular to the lateral surfaces of bores, which are generally present in the electronic circuit boards and also have to be galvanized.

The object of the present invention is to design a device of the type mentioned at the outset in such a way that the means used for contacting and conveying are inexpensive and simple to use and that, moreover, the devices which are deposited on the electronic circuit boards which metallic layers have a more uniform thickness, especially in the bores.

This object is achieved in that the contact and transport means are designed as rotatably driven contact and transport rollers, which extend transversely to the direction of movement of the electronic printed circuit boards over the entire working width of the device, at least partially have a metallic coating on their outer surface, which is connected to the negative pole of the galvanizing power source, and which are each designed to bear against a main surface of the electronic circuit board, such that each contact and transport roller forms a dust barrier for the flowing electrolyte, as a result of which locally dynamically varying pressure differences occur on the circuit boards to adjust.

According to the invention, means are provided as contact and transport means-driven rollers, which extend across the entire working width of the device, transversely to the direction of movement of the printed circuit boards. Such contact and transport rollers can be easily integrated into conveyor systems known per se, which work with driven rollers, and set in motion by the same mechanism that is usually used to drive the conveyor rollers. The fact that these contact and transport rollers extend over the entire working width of the device results in jamming effects for the electrolyte flowing off. These congestion effects lead, partly due to the locally different flow velocities, to locally varying pressures which act on the printed circuit boards, whereby the electrolyte flow through the holes in the circuit boards is improved. These have locally varying prints not originated in the feed pump. Rather, a variation of the local flow velocity of the electrolyte according to the principles of the Bernoulli see equation ensures a local variation of the static pressure. In this context, the contact and transport rollers serving as dust barriers mean local narrowing of the flow path for the electrolyte, at which relatively high flow velocities and consequently relatively low local static pressures occur.

With the help of the contact and drive rollers spanning the full width of the circuit boards, power can also be supplied to the circuit boards at any desired location, even at several locations. Voltage drops within the circuit board, which would lead to an uneven coating with metal, can be avoided in this way.

In general, the electronic circuit boards are to be galvanized on both opposite main surfaces. In this case, it is advisable to design the device according to the invention in which the contact and transport rollers are provided in pairs, the partners of which are designed to bear against opposite main surfaces of the electronic circuit boards. The latter are thus pulled through the gap between the opposite contact and transport rollers; the partners of a pair of contact rollers and transport rollers rotate counterclockwise.

In the simplest case, the contact and transport rollers are provided with a metallic coating over their entire axial dimension. Hereby the most uniform thicknesses can be achieved in the layers deposited on the electronic circuit boards, since voltage drops across the direction of movement of the circuit boards cannot occur in their coatings at all. However, such contact and transport rollers can be relatively expensive if the material used for their metallic coating is itself expensive.

For this and another reason, which will be discussed further below, it is therefore advisable in many cases that the contact and transport rollers are provided with a metallic coating in only a part of their outer surface in a certain geometric pattern. The geometric pattern mentioned is determined experimentally in such a way that the desired uniform layer thickness results in the electroplated layers, but that unnecessarily much metal is not required in the production of the contact and transport rollers. In the non-metallic coated areas of the lateral surfaces of the contact and transport rollers there is a plastic base body, e.g. made of polypropylene, free.

If additional precautions are to be taken to ensure that no "shadow formation ¹ " occurs in the galvanizing process due to metallic coatings applied to the contact and transport rollers only in certain areas, contact and transport rollers can be combined with different geometric patterns of the metallic coating in a special embodiment of the device according to the invention On their way through the electrolyte, the electronic printed circuit boards are first moved by one or two contact and transport rollers with a first geometric pattern and by this or these transfer to one or two contact and transport rollers, the outer surface of which is provided with such a geometric pattern that the electronic circuit boards are now contacted at another location on their main surface.

It is known that, without special precautionary measures, metal ions accumulate in the electrolyte of electroplating devices of the type described here, that is to say their concentration increases in an undesirable manner. Although the concentration in the electrolyte can be kept constant by adding appropriate chemicals and water, this has the disadvantage that the amount of electrolyte contained in the device increases over the course of the operating time (the electrolytic bath "calves"). In order to avoid this "calving", it is known to provide an auxiliary cathode on which metal is electrolytically deposited in order to keep the metal ion concentration in the electrolyte constant. One also makes use of such an auxiliary cathode in a device according to the invention

Use, the configuration is recommended in which the metallic coatings of the contact and transport rollers serve as auxiliary cathodes and their total area is selected so that the desired constant concentration of metal ions in the electrolyte results during the operating time. In this way the undesirable effect that metal is deposited on the contact and transport rollers from the electrolyte is turned into a positive: by a suitable choice of the total area of the metallic coatings (ie by a corresponding "design" of the geometrical used Patterns of these metallic coatings) can be achieved that the metallic coatings of the contact and transport rollers take over exactly the function of the auxiliary electrode, so that without special precautionary measures the desired constant concentration of metal ions in the electrolyte is ensured.

Another known undesirable phenomenon in devices of the type of interest here is that not only the electronic circuit boards but also these contact means are provided with a metallic coating by the electrolysis. In order to avoid that the contact means must be freed from deposited metal at regular intervals (for which the device should be shut down and the contact means would have to be removed), it is known to provide at least one decoupling cathode in the vicinity of the contact means and in the same electrolyte more negative potential than the contact means. In this way, a "secondary electrolysis" takes place between this decoupling cathode and the contact means, under the influence of which the metal deposited on the contact means goes back into solution and (instead) is deposited on the decoupling cathode. If you use this very useful

Thoughts also with a device according to the invention, the embodiment in which the metallic coatings of the contact and transport rollers are provided with a coating of catalytically active metal has proven particularly advantageous. The coating need only have a very small thickness (in the range of a few μm). The efficiency of the decoupling electrolysis can be greatly improved by this coating: even at a fraction of the otherwise required current, the metallic coatings of the contact and transport rollers can be kept free of undesired metal deposits in the long run. An advantageous side effect of this catalytically active metal is that the adhesion of the temporarily formed galvanic metal deposits is better and the deposits are not spongy, as is often the case on titanium surfaces. Spongy or porous deposits could loosen metal particles and get onto the circuit boards, which would become scrap in this way.

The catalytically active metal can e.g. gold, palladium, iridium or an alloy of these components.

Finally, a particularly preferred embodiment of the invention is characterized in that, viewed in the direction of movement of the printed circuit boards, several individual anodes are provided, between each of which a pair of contacts and transport rollers is provided. In this way, the anodes can be arranged very close (with a distance that is smaller than the diameter of the contact and transport rollers) to the path of movement of the printed circuit boards. This improves the efficiency of the electrolysis and at the same time achieves a more uniform thickness of the electroplated layers. The interruptions between the individual anodes are without disadvantage, since the anode regions above these contact and transport rollers would also be shaded and would therefore be essentially ineffective even in the case of an anode running in one piece above the contact and transport rollers.

Embodiments of the invention are explained in more detail below with reference to the drawing; show it

Figure 1: a vertical section through a device for electroplating electronic circuit boards;

Figures 2 and 3: side views of two contact and Transport rollers, as they can be used in the device of Figure 1.

In Figure 1, a device is shown in vertical section, in which electronic circuit boards, which are provided with holes, can be provided with a metallic coating by galvanic means. This metallic coating should in particular also cover the lateral surfaces of the holes in the circuit board, so that e.g. an electrical over these lateral surfaces

Connection between the wiring patterns on the upper and lower side (the "main surfaces") of the circuit board can be created.

The device shown in Figure 1 comprises a machine housing 1 with an inlet slot 2 and an outlet slot 3. The electronic circuit boards are fed in a horizontal orientation in the direction of arrow 4 of the device and, after passing through the inlet slot 2, first meet four pairs of nip rollers 5, in which treatment liquid still adhering to the circuit boards and originating from previous processing operations is largely removed.

The printed circuit boards are transferred from the squeeze roller pairs 5 to a first contact and transport roller pair 6. The exact design of these contact and transport rollers 6 will be discussed in more detail below. The contact and transport rollers 6 advance the circuit board further in the conveying direction. These pass between an upper anode 7 and a lower anode 8. In the exemplary embodiment shown, these anodes 7 and 8 are designed as anode baskets which can be pulled out laterally from the machine housing 1 in the manner of a drawer. However, any other can be used Use types of anodes, such as inert anodes made of expanded titanium. After passing the anode baskets

7 and 8, the printed circuit boards are in turn gripped by a pair of contact and transport rollers 6, which further advances the printed circuit boards so that they again pass between an upper anode basket 7 and a lower anode basket 8. The circuit boards covering the distance between the latter anode baskets 7 and

8 have passed, are picked up by a last pair of contact and transport rollers 6 and again on four

Pass squeeze roller pairs 5, which largely remove the electrolyte in which they were located from the printed circuit boards (see the following description below). The printed circuit boards are finally discharged from the device through the transport system, of which the contact and transport rollers 6 are part, via the outlet slot 15 and fed to a subsequent treatment station.

In the lower area of the machine housing 1 there is a sump 9 in which the electrolyte used for the electrolysis collects. A pump 10 continuously removes electrolyte from the sump 9 and guides it through a filter 11, a valve 12 and lines 16a, 16b upwards into a container 13 which rolls the plane of movement of the printed circuit boards in the area of the contact and transport rollers 6 as well as the Anode baskets 7 and 8 surrounds. The container 13 also has an inlet slot 17 and an outlet slot 18, which, however, are largely sealed off by the adjacent pinch roller pairs 5 serving as accumulation rollers and bulkheads sliding against them. In the dynamic equilibrium between the supply of electrolytes into the interior of the container 13 and the discharge from the container 13, the container 13 is largely filled with electrolyte, so that the circuit board between the right-most contact and transport roller pair 6 in FIG. 1 and the left-most contact and transport roller pair 6 in FIG. 1 move within a constantly exchanging electrolyte. These processes are known to the person skilled in the art under the term "standing wave".

Specifically, the electrolyte from the pump 10 is supplied via a first branch line 16a to distribution channels 17 in the area of the upper anode baskets 7 and via a second branch line 16b to distribution channels 18 in the area of the lower anode baskets 8. From the distribution channels 17, individual nozzle channels 19 lead down to nozzle openings 20, 21, which are located in the vicinity of the plane of movement of the printed circuit boards. The electrolyte is ejected via the nozzle openings 20 at an angle deviating from 90 degrees against the surface of the printed circuit boards passing by, while the electrolyte flows vertically downwards from the nozzle openings 21, that is to say it strikes the printed circuit boards passing by at a right angle.

The further course of the electrolyte from the lower distributor channels 18 upwards is essentially similar to that which has already been described for the path of the electrolyte from the upper distributor channels 17.

However, it should be noted that the obliquely directed nozzle openings 20 above the path of movement of the printed circuit boards are each opposed by a vertically oriented nozzle opening 21 below the path of movement of the printed circuit boards or vice versa. In this way it is avoided that the migrating circuit board is subjected to electrolyte on both sides under the same pressure, which would hinder the flow through the holes.

Each contact and transport roller 6 is a copper removal - assigned to cathode 22. This can be a rod-like structure made of titanium, which extends parallel to the associated contact and transport roller 6 and is at (more) negative potential than the latter.

The device described above works as follows:

With the help of the pump 10, electrolyte is removed from the sump 9 in the machine housing 1 and fed in the manner already described to the interior of the container 13 such that it is filled with electrolyte in dynamic equilibrium. The circuit boards to be electroplated are fed via the inlet slot 2 and the pinch roller pairs 5 to the contact and transport system which is formed by the contact and transport rollers 6. The contact and transport rollers 6 extend over the full width of the machine, that is, they also capture the printed circuit boards over their entire transverse dimension. The contact and transport rollers 6 are at least partially coated on their outer surface (see below for this). This metallic coating is connected to the negative pole of the galvanizing current source (not shown in the drawing) via suitable brushes or grinders, the positive pole of which is in turn connected to the various anode baskets 7, 8. By touching the metallic coatings on the contact and transport rollers 6, the metallic coatings on the electronic circuit boards also receive negative potential. An electrical field therefore builds up between these metallic coatings on the electronic printed circuit boards and the anode baskets 7, 8 as the electronic printed circuit boards pass through. This is where electrolysis takes place in a known manner, in the course of which the surfaces of the printed circuit boards, but in particular also the jacket surfaces of the holes contained in the printed circuit boards, be provided with a metallic (generally copper) coating. By running through a galvanization path between two anode baskets 7, 8 several times, the required layer thickness is built up on the electronic circuit boards in several stages. The number of sections to be traversed one behind the other between opposite anode baskets 7, 8 can in principle be of any size; it depends exclusively on the required thickness of the metallic coatings desired on the printed circuit boards. In the case of the printed circuit boards passing through the contact and transport rollers 6 lying furthest to the left in FIG. 1, it can therefore be assumed that the desired layer thickness of the metallic coating has been reached. These printed circuit boards can then leave the galvanizing module via the pinch roller pairs 5 and the outlet slot 3 and be fed to a further processing.

As is known, the electrical field causing the galvanization acts not only between the anode baskets 7, 8 and the printed circuit boards passing by in each case, but also between the anode baskets 7, 8 and the respectively adjacent contact and transport rollers 6. This has the consequence that even those with negative galvanization - Potential metallic coatings of the contact and transport rollers 6 are galvanically provided with a metallic coating, which is not completely avoidable even with good mechanical shielding of the contact and transport rollers 6 against the electrolyte. For this reason, the decoupling electrodes 22 are provided, which are at an even more negative potential than the metallic coatings of the contact and transport rollers 6. Between the copper removal electrodes 22 and the metallic coating I

lines of the contact and transport rollers 6 there is therefore an electrolysis process, in the course of which the metal coatings of the contact and transport rollers 6 bring electrodeposited metal back into solution and then deposit it on the decoupling cathodes. In this way it is possible to keep the metallic coatings of the contact and transport rollers 6 free of undesired deposits over long operating times.

In principle, it is possible to provide the contact and transport rollers 6 with a metallic coating, for example a titanium coating, over their entire axial dimension. However, this is not always necessary. In many cases it is sufficient if the contact and transport rollers 6 are provided with metallic coatings only over a part of their axial dimension. Such an example is shown schematically in FIG. 2. The contact and transport roller 106 shown here comprises a cylindrical base body 130 made of plastic material, e.g. Polypropylene, which carries only two ring-like lateral areas 131, 132 with a metallic coating.

The area ratio between the metallic coating and (unclad) plastic base body as well as the geometric pattern of the metallic coating can be changed as desired according to expediency. Thus, in the exemplary embodiment of a contact and transport roller 206 shown in FIG. 3, half is axial

Dimension provided with a metallic coating 231, while in the second half of the axial extent of the plastic base body 230 is exposed.

The pattern and size of the metallic coating, 1 ⁽ j

which is in each case on the contact and transport rollers 6, is selected in accordance with the geometry of the conductor tracks applied to the printed circuit boards and the arrangement of the bores in such a way that a shadow-free, uniform formation of the galvanic precipitate results in particular on the lateral surfaces of the bores. As seen in the direction of movement of the circuit boards, different contact and transport rollers 6 can be combined. Thus, for example, the contact and transport roller 206 of FIG. 3 could alternately be installed alternately in the device of FIG. 1 by 180. It would also be conceivable to combine contact and transport rollers, as shown in FIG. 106, with contact and transport rollers 206 according to FIG. 3 in the same device.

When choosing the total area of the metallic coatings on the contact and transport rollers 6, it is advisable to consider the following point of view:

It is known that in the case of electroplating devices of the type described here, the electrolyte accumulates in the course of the operating time with ions of the metal to be deposited on the electronic printed circuit boards, that is to say generally of copper. In order to avoid an increase in the metal ion concentration in the electrolyte, two countermeasures are known: either the electrolyte is regenerated by adding chemicals and water so that the desired metal ion concentration is restored. However, this has the disadvantageous consequence that the amount of electrolyte in the device increases, that is, the electrolytic bath "calves". Therefore, the second countermeasure is preferred: Here, an auxiliary electrolysis is used which continuously removes metal ions from the electrolyte by means of electrodeposition withdrawn at an auxiliary cathode.

In the device described here, the inherently undesirable deposition of metal ions from the electrolyte on the metallic areas of the contact and transport rollers 6 can be used in the sense of this auxiliary electrolysis. The total amount of metal which is deposited on the metallic coatings of the contact and transport rollers 6 depends on the total area of these metallic coatings. In general, it is always possible to determine the area of the metallic coatings on the contact and transport rollers 6 by means of appropriate tests for the respectively processed electrolytes and electronic printed circuit boards, in which the

Concentration of metal ions in the electrolyte remains constant.

According to what has been said above, the metal thus removed from the electrolyte does not remain on the metallic coatings of the contact and transport rollers 6, but is detached from them again by the auxiliary electrolysis mentioned above and finally deposited on the decoupling cathodes 22.

In the simplest case, the metallic coatings of the contact and transport rollers 6 can consist of titanium, a metal which is anyway very widespread in electroplating devices of the type of interest here. However, it has been found that the efficiency of the decoupling electrolysis, that is to say the amperage required to "keep bright" the metallic coatings of the contact and transport rollers 6, can be kept very much lower if the metallic coatings of the contact and transport rollers 6 are included 10

are coated with a catalytically active metal. Gold, palladium, iridium and the like are particularly suitable. The layer thickness of this catalytically active metal need not be greater than a few μm. Experiments have shown that this

In this way, the current required to carry out the decoupling electrolysis can be reduced to up to a quarter of the value that would be required if metallic coatings of the contact and transport rollers 6 made of titanium were used. The galvanic deposits temporarily formed on such catalytically active coatings are compact; there is therefore no danger that metal particles can come loose from these deposits and get onto the printed circuit boards.

Regardless of what metal the metallic coatings of the contact and transport rollers 6 are made of, and regardless of what percentage these metallic coatings occupy on the outer surfaces of the contact and transport rollers 6, it is important that the contact and Transport rollers 6 extend across the entire width of the processed electronic circuit boards. In this way, a congestion effect and a dynamic flow behavior of the electrolyte on the electronic circuit boards is caused, which generates locally different pressures acting on the electronic circuit boards and thus the flow through the holes in the circuit boards and thus also the uniformity of the coating of the The lateral surfaces of these holes ("scattering") improved. Details in this connection have already been discussed above.

Claims

claims

1. Device for electroplating electronic circuit boards or the like, in particular those which contain a plurality of bores, with

b) at least one electroplating current source;

c) Contact and transport means, which are electrically connected to the negative pole of the galvanizing power source, attack the electronic circuit boards in such a way that their metallic coatings are also at a negative potential, and along the electronic circuit boards in a substantially horizontal orientation lead a path of movement through the device;

e) at least part of the movement path and the anode (s) surrounding container, which has an inlet and an outlet slot for the electronic circuit boards;

f) at least one pump, which from the sump electrolyte removed and fed to the container such that its interior is filled with electrolyte in the dynamic equilibrium between inflow and outflow,

characterized,

that the contact and transport means are designed as rotatably driven contact and transport rollers (6; 106; 206) which extend transversely to the direction of movement of the electronic printed circuit boards over the entire working width of the device, at least in some areas a metallic coating on their outer surface ( 131, 132; 231), which is connected to the negative pole of the galvanizing power source, and which are each designed to bear against a main surface of the electronic circuit board, such that each contact and transport roller (6; 106; 206) has one Forms a dust barrier for the flowing electrolyte, which results in locally dynamically varying pressure differences on the circuit boards.

2. Device according to claim 1, characterized in that the contact and transport rollers (6) are provided in pairs, the partners of which are each designed to bear on opposite main surfaces of the electronic circuit boards.

3. Apparatus according to claim 1 or 2, characterized in that the contact and transport rollers (6) are provided with a metallic coating over their entire axial dimension.

4. Apparatus according to claim 1 or 2, characterized in that the contact and transport rollers (106; 206) only over part of their outer surface in a certain geometric pattern with a metallic coating (131, 132; 231).

5. The device according to claim 4, characterized in that in its contact and transport rollers (106, 206) with different geometric patterns of the metallic coating (131, 132; 231) are combined.

6. The device according to claim 4 or 5, in which an auxiliary cathode is provided, on which for

Keeping the metal ion concentration constant in the electrolyte

characterized in that

the metallic coatings (131, 132; 231) of the contact and transport rollers (6; 106; 206) serve as auxiliary cathodes and their total area is selected so that the desired constant concentration of metal ions in the electrolyte results during the operating period .

7. Device according to one of the preceding claims, in which at least one decoupling cathode is provided, which are at a more negative potential than the contact and transport means and are arranged in the vicinity such that metal deposited on the contact and transport means again in solution goes and precipitates on the decoupling cathode, characterized in that the metallic coatings (131, 132; 231) of the contact and transport rollers (6; 106; 206) are provided with a coating of catalytically active metal.

8. The device according to claim 7, characterized in that that the catalytically active metal is gold, palladium, iridium or an alloy of these components.

9. Device according to one of the preceding claims, characterized in that, seen in the direction of movement of the printed circuit boards, several individual anodes (7, 8) are provided, between each of which a contact and transport roller pair (6) is arranged.