Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating selected area
Reexamination Certificate
1996-07-01
2001-01-23
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating selected area
C205S128000, C205S133000, C205S137000, C205S145000, C205S150000, C205S152000, C205S640000, C205S686000, C204S212000, C204S22400M, C204S22400M, C204S275100, C204S283000, C204S284000
Reexamination Certificate
active
06176995
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of electrolytically metallising or etching material.
The economic operation of electrolytic metallising and etching methods essentially depends on the maximum current density at which an industrially useful treatment result may still be obtained. The maximum current density is above all dependent on the speed at which fresh treatment agent (electrolyte solution) can reach the surface of the material to be treated. During electrolytic metallisation, the precipitated metal ions are consumed in the direct vicinity of the material for treatment. This reduces the metallising speed, and the process decelerates. The same also applies to other electrolytic treatment methods, for example electrolytic etching.
In order to provide assistance here, flesh treatment solution can be supplied continuously trough flow tubes which in electrolytic metallisation are disposed between the anode and the material for treatment (cathode), on to the surface of the material for treatment. This procedure however is subject to certain fluidic limits; the exchange of liquid in the direct vicinity of the surface of the material for treatment (diffusion layer) may only be increased to a restricted degree. Apart from this, such a procedure is disadvantageous, as the flow tubes disposed between the anodes and the material for treatment screen the electrical field between the anodes and cathodes, so that metal is irregularly deposited on the material. This disadvantage is particularly serious when the space between the flow tubes and the surface of the material is small. On the other hand, for fluidic reasons a small space between the flow tubes and the material surface would be preferable, in order to achieve controlled flow direction and the highest possible current density. In this case high current densities would occur at some points on the surface of the material, so that the additives conventionally included in electrolytic metallising baths would become oxidised.
Plate-shaped material for treatment, particularly printed circuit boards, is preferably processed in horizontal treatment installations.
The material is grasped in a horizontal position and passed through the installation in a horizontal direction, thus being electrolytically treated. In such installations, rollers are normally used for transporting and guiding the material. These also are located in the area between anode and cathode. Particularly in the case of extremely thin films, guide members are also necessary in order to transport them efficiently, in order to prevent the films from slipping off the transport track and becoming wound around the transport rollers. Such constructional members, like the transport rollers mentioned, also hinder the current flow between the anode and the material for treatment.
Soluble anodes, produced from the metal to be precipitated, are normally used for electrolytic metallisation. Their positioning inside the metallising installation and their normal shape and size give rise to considerable difficulties in finding simple constructive solution to the named problems. When using insoluble anodes, there is on the other hand the possibility in horizontal installations of making these in a longitudinally-extended form, and of disposing them in such a way that the screening actions described do not occur. For example, in such arrangements, in repeated sequences of adjacent insoluble anodes, at least one flow tube may be disposed for supplying fresh treatment agent to the surface of the material, and to transport rollers. The positioning of these individual members is so selected that the material s moved slowly past them during the metallising process. The length of such an installation is determined by the geometrical dimensions of the three members, their necessary spacing apart from one another, and by their overall number. Such treatment installations are therefore extremely long and relatively expensive.
DESCRIPTION OF THE PRIOR ART
In the German Disclosure Document 36 03 856 there is described a method for continuously electroplating flat workpieces such as printed circuit boards, in which the workpieces are passed horizontally through an electroplating installation, and are grasped and transported inside the electroplating installation by a cathodically-incorporated rotating pair of rollers, and in which the electrolyte solution is transferred on to the workpiece from a likewise rotating pair of rollers, located in the vicinity of the cathodic roller pair, and incorporated as anode, the surface of the said anodic pair of rollers being capable of absorbing liquid and rotating at a narrow interval from the surface of the workpiece, so that the electrochemical deposition of metal is effected in the gap between workpiece surface and the surface of the anodic roller pair. In this case the electrolyte solution is sprayed from spray heads over the anodic rollers, so that the surface of the material for treatment is permanently supplied with enriched electrolyte solution. By means of the rapid rotation of the rollers, the solution however is centrifuged in all directions, and caught by the plastics screens located above the spray heads and the anode rollers. Large quantities of the electrolyte solution are indeed transported into the working area. However, only a small proportion thereof reaches the locus of the treatment point having the largest current density. This point lies between the anode roller and the surface of the material. Controlled direction of flow at this point is not possible.
In the case of roller-shaped anodes, the greatest current density occurs in the vicinity of the surface line of the anode lying closest to the material for treatment. Vertically on either side of the surface line, it reduces sharply. This leads to a situation in which the electroplating speed, seen in the direction of the transport path, fluctuates intensely. In order to obtain a sufficient medial current density over the entire treatment path, therefore, the maximum current density beneath the surface line of the anode must be high. This demands a controlled and effective exchange of electrolyte at the diffusion layer at that point; this cannot be realised by the abovenamed method.
A further disadvantage in this case is that, at the point of highest current density, gases such as hydrogen, oxygen and chlorine are formed. These gases attack the anode material. Therefore this material must be provided with coatings of noble metal in order to restrict their corrosion. In addition, the gases have to be removed by an additional flow of electrolyte solution over the anodes. This requires further technical outlay on the installation.
In the publication EP 0 210 072 A1 there is described an apparatus with a rotating metallising brush for selectively metallising metal parts, and in which a roller-shaped anode surrounded by a porous hydrophobic material serves as a counter-electrode for the metal pats to be coated, the metal parts being slidingly moved along the surface line of the anode, electrolyte solution being caused to flow from the interior of the anode through the hydrophobic material on to the metal parts.
In the essay “Elektrolytische Hochleistungsverzinkung von Stahlband durch mechanische Grenzschichtbeeinflussung” (Electrolytic High-performance Galvanisation of Steel Strip by Mechanical Influence on the Boundary Layer) by B. Meuthen and D. Wolfhard in the specialist periodical “Metalloberfl{umlaut over (a)}che”, vol. 36 (1982) pages 70-75, there is described a method for high-performance galvanisation of steel strip. The laboratory installation illustrated comprises a cathodically-incorporated circular sheet metal disc which is passed in a rotating fashion along a perforated anode, fibre fleece attached to the anode being wiped on its surface during rotation of the cathode. Fresh electrolyte solution is continuously passed on to the cathodic metal disc by the anode.
The abovementioned documents disclose methods and apparatus in which the surface of the mat
Atotech Deutschland GmbH
Paul & Paul
Valentine Donald R.
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