Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating moving substrate
Patent
1997-05-19
1999-08-03
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating moving substrate
205145, 205 81, 205 82, 204297R, 204202, 118503, 19834107, C25D 500
Patent
active
059320818
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a method and device for galvanizing plate-shaped products in horizontal continuous plants, particularly for electrolytic treatment of printed circuit boards and printed circuit films.
2. Brief Description of the Prior Art
An arrangement of this type is described in the European Patent Specification 0254030 B1. The products are transported horizontally through the electrolytic plant. The anodes are located along the transport path in the form of plates or cages, which are filled with the metal to be deposited. During its passage through the electrolytic plant, the product is coated in a known way by this metal.
As it enters the electrolytic plant, the plate-shaped product is grasped at its edge by transport members in the form of clamps. The clamps release the product again at the end of the electrolysis chamber. The clamps, secured on an endless revolving transport means, are returned to the inlet to the electrolytic plant.
Apart from transport, the clamps serve also for cathodic contacting of the product during its horizontal passage through the electrolytic plant. For this purpose the plants comprise an electrically conductive material. Furthermore, each clamp is provided, outwith the electrolysis cell, i.e. above the bath level, with a wiper arrangement for transmitting the electrolytic current. Due to the cathodic polarity of the clamp, it is coated with a metal to be deposited within the electrolysis cell just like the product. In order to avoid continual coating during each revolution, the clamps are again de-metallized in a de-metallizing chamber during the return journey. For reasons of system technology, the de-metallizing chamber can only contain the electrolyte which is also located in the electrolysis cell. The electrolyte is optimised for metallization, but not for de-metallization. The massive deposition of metal is frequently not entirely removed by electrolytic de-metallization. In the manufacture of printed circuit boards, it also appears as a disadvantage that the clamps, which are highly electrically conductive and cathodically poled, act as a "thief cathode". The consequence is that the layer deposited on the printed circuit board in the vicinity of the clamps is insufficient. This undesired deposition of metal gives rise to additional consumption of anodes and of energy, particularly for de-metallization.
A further horizontal continuous plant for electroplating printed circuit boards is described in DE 42 12 567 A1. This system uses as a contacting means rods with grippers, which grasp the plates not at the side but at the front edge, drawing them through the plant. The rods are likewise cathodically poled. As a result they are electroplated just like the product. Here also de-metallization is carried out as the rods return to the initial point. The disadvantages named also apply to this contacting means.
In order to avoid the named disadvantages, according to prior art the clamps or rods are covered with an electrically insulating material. This coating covers at least the area of the clamps or rods which projects into the electrolysis cell. Only the area in actual contact with the product, e.g. a printed circuit board, remains without insulation. Materials known in electroplating installations, such as PTFE, are considered as insulating materials; other suitable materials are glass, ceramics and enamel.
It has now become apparent in practice that, in spite of the electrical insulation on the clamps or rods, metal is to some extent still partially deposited. The causes of this are faults in the insulating layer, damage to this layer during use and the necessarily bright metal contact. At these points the field densities are so concentrated that disproportionate metallization takes place. This then cannot be entirely removed in the following de-metallization process, even if attempts are made to operate at this point with a higher current density. When the current density is too high, the electrically conductiv
REFERENCES:
patent: 4668358 (1987-05-01), Ball
patent: 4776939 (1988-10-01), Blasing et al.
patent: 5292424 (1994-03-01), Blasing et al.
patent: 5324406 (1994-06-01), Anderson et al.
Kopp Lorenz
Scharrer Helmut
Atotech Deutschland GmbH
Gorgos Kathryn
Nicolas Wesley A.
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