Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating moving substrate
Reexamination Certificate
1999-10-20
2001-04-17
Gorgos, Kathryn L. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating moving substrate
C204S206000, C205S136000
Reexamination Certificate
active
06217736
ABSTRACT:
DESCRIPTION
The invention relates to an apparatus for electrolytically treating a board-shaped substrate to be treated, as well as relating to a method of electrically shielding edge regions of the item to be treated. For the electroplating or etching of printed circuit boards and conductor foils, the apparatus and the method are preferably used in continuous systems with the item to be treated being horizontally or vertically aligned during its passage therethrough.
Substrates to be treated, of varying widths, are generally produced in continuous electroplating systems. The anodes in the systems must be so dimensioned that even the widest boards and foils can be treated without any problems. If, in these circumstances, relatively narrow boards or foils are electroplated in the system transversely relative to the direction of conveyance of the item to be treated, considerably thicker metal layers are produced in the edge regions thereof than in the center, because the electrical field lines are concentrated in these edge regions. A specific tolerance for the metal layer thickness is usually prescribed, so that the region which is usable in practice on the metallized boards and foils is smaller than the overall width thereof. Only a low tolerance for the metal layer thicknesses is permissible for the production of printed circuit boards and conductor foils, which thicknesses result from requirements for the subsequent processing of boards and foils. Furthermore, printed circuit boards generally involve expensive materials. In consequence, it is desirable to achieve maximum utilization of the electroplated bare printed circuit boards, which are also called blanks. In consequence, a uniform layer thickness as far as the edge region of the printed circuit boards or conductor foils is to be achieved. A known measure for influencing the layer thickness in the edge region of the item to be electroplated resides in electrically screening these edge regions by using electrically non-conductive screens.
Apparatus for screening field lines in an electroplating system for treating printed circuits boards, more especially, are described in DE-P 39 37 926 C2. Screens are illustrated in FIGS. 2 and 3, contained therein, and comprise a plurality of partial screens which are individually adjustable per se. By rotating the partial screens about an axis, the screening effect of each individual partial screen can be increased or reduced. The edge covering can be set in optimum manner when the individual screens are narrow enough and, in consequence, when there is a sufficiently large number of these screens.
A disadvantage which has to be tolerated, however, is that there remains a residual screening over the region of the printed circuit boards which should not actually be shielded. Furthermore, the structural outlay for achieving this apparatus is considerable. In consequence, a level screen between the anodes and the edge region of the item to be treated is preferred in practical usage, as illustrated in FIG. 4 in the above-mentioned publication. With this arrangement of the screens, however, an optimum profile-like screening is not possible, with the result that the required layer thickness tolerances cannot be achieved in a relatively large edge region on the blank. Moreover, the high level of technical outlay is also disadvantageous for this arrangement.
The electroplating operation requires strong constructions. In consequence, a flat, displaceable screen similar to that known from JP-A-62/151 593 has proved successful in practical usage. The screens used there are displaced by a linearly acting drive between the anodes and the edge region of the item to be treated.
These and similarly flat screens reduce the concentration of field lines in the edge region of the item to be treated in dependence on the covering of the item to be treated by the screen and on the spacing between the screen and the anode, or respectively the surface of the item to be treated. The spacing between the anodes and the item to be treated as well as the anodic and cathodic current densities are also significant for the electrolytic treatment. The position of the screen during the electrolytic treatment constitutes a compromise based on these parameters, so that the optimum screening has to be determined in complex experiments. An object is to achieve a large usable area within the permissible tolerance range without burning the edges in the event of high current densities. In the case of fine printed circuit boards and average current densities, the non-usable edge has a width of about 30 mm in practical usage. In the case of current densities up to 15 A/dm
2
, the non-usable edge with this screen already has a width of about 50 mm.
An electroplating arrangement is described in U.S. Pat. No. 3,862,891 and has an electroplating frame and anodes, as well as an electrically non-conductive shielding screen for distributing the concentration of field lines evenly along the item to be electroplated, which is mounted on an article carrier. The shielding screen comprises a plurality of screen portions, which are securedly connected to the arrangement, in that they are secured on the lateral walls and screw-connected in suitable guides. The screen portions are orientated parallel to one another and parallel to the item to be electroplated and the anodes. The screen portions protrude partially into the space between the item to be electroplated and the anodes, whereby the screen portions situated closer to the anodes protrude further than the screen portions situated closer to the item to be electroplated. It is stated that, with this arrangement, a uniform electroplating layer thickness can be achieved in the plane of the electroplating frame.
It is not possible, with this arrangement, to treat items of varying external dimensions electrolytically in optimum manner, since a prescribed tolerance of the metal layer thickness is not achieved, only on as narrow an edge region of the item to be treated as possible, while the remaining surface of the item to be treated meets the requirements for the uniformity of the metal layer thickness at all locations. A continuous operation is especially desirable in order to render possible a minimal setting period.
In consequence, the basic object of the present invention is to avoid the disadvantages of prior art and, more especially, to provide an apparatus for electrolytically treating a board-like item to be treated, by means of which apparatus the boards or foils can be continuously electrolytically treated, and the apparatus can also be adapted to changing formats/widths of the boards or foils to be treated at any time rapidly in an automatic manner or possibly in a manual manner, in order to achieve an even distribution of the metal layer thickness on the board or foil surfaces. During the continuous operation, the edge region of the boards or foils, where prescribed layer thickness tolerances cannot be maintained, should be as small as possible. In addition, however, an extra requirement is to use as high an electrolytic current as possible in order to permit the boards or foils to be electrolysed with a short treatment time, so that a high throughput of the items to be treated per unit of time becomes possible with the arrangement. Even with a large electrolytic current, the thickness of the metal layer on the item to be treated is always to be kept as uniform as possible as far as the edge region.
The apparatus according to the invention substantially constitutes a continuous system, through which the item to be treated is guidable in a plane of conveyance in a substantially horizontal direction of conveyance. Counter-electrodes are disposed in this continuous system and are situated substantially parallel to one another opposite the plane of conveyance, and screens for shielding from high current density fields in the edge region of the item to be treated are disposed between the plane of conveyance and the counter-electrodes. The screens are each in the form of at least two fl
Kopp Lorenz
Plöse Wolfang
Wachter Ralf-Peter
Atotech Deutschland GmbH
Gorgos Kathryn L.
Paul & Paul
Smith-Hicks Erica
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