Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Contacting coating as it forms with solid member or material...
Reexamination Certificate
1998-10-13
2002-05-28
Bell, Bruce F. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Contacting coating as it forms with solid member or material...
C204S198000, C204S202000, C204S203000, C204S22400M, C204S227000, C204S275100, C205S125000, C205S137000, C205S148000, C205S150000, C205S222000, C205S920000
Reexamination Certificate
active
06395163
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates, first, to a process for the electrolytic processing of printed circuit boards with drillings, which are taken through a treatment bath or to a processing station by conveyor means, in which there are means for reducing the thickness of a metal-ion-depleted region (diffusion zone), which are in contact with the printed circuit boards. The preferred area of use for the invention is galvanization, which will be discussed in more detail below. The invention can also be used in electrolytic etching.
2. Discussion of the Prior Art
The surface of the items to be processed or their diffusion layer becomes depleted of metal ions in a disadvantageous manner during processing, because the cathode draws more ions to it than usually come out of the surrounding treatment bath. This leads to a reduction in the acceptable specific current density, and thus means that in order to achieve such a metal coating having a particular thickness, a correspondingly long treatment time is needed.
In order to overcome this disadvantage, the so-called “high-speed” process can be used, in which the electrolyte is conducted at great speed and in great quantity along the cathodic surface between this surface and the anode (see European Patent 0 142 010 and German Patent 35 25 183, for example). It is true that using this process, an improved, i.e. increased, current density of the metal coating on the cathodic item is achieved. However, the production, control and discharge of such an electrolytic current is relatively expensive. The creation of the flow channels necessary for this requires added constructive expenditures. In addition, the manner of conveying the items to be processed can be complicated. For these reasons, it has become known only for continuous items to be processed, such as strips or wires.
In the article “Electrolytic High-Power Overgalvanization of Steel Strip through Boundary Layer Control” (“Electrolytische Hocheistungoverzinkung von Stahlband durch mechanische Grenzschichtbeeinflussung”) by D. Meuthen and D. Wolfhard in the journal
Metal Surface
36 (
Metaloberfläche
36) (1982, pp. 70-75), a process for the electrolytic galvanization of steel strip is described, in which the strip surface to be galvanized is pressed against and moved relative to a nonwoven fabric, similarly to in the so-called tampon or brush galvanizing process. The coating electrolyte is rinsed through the nonwoven fabric onto the steel surface. Higher current density is achieved through this process during electrolytic zinc deposition.
A similar principle is also described in European Patent Application 0 210 072 for the electrolytic coating of small metal parts which are coated with noble metals, especially for use as plug-type connectors.
Furthermore, a process for the coating of surfaces is known from U.S. Pat. No. 3,706,650, in which non-conductive, fluid-storing, porous, compressible means are pressed against the surfaces to be coated and moved relative thereto, whereby the counter-electrode to the object to be coated is located in the interior of these means. The electrolytic fluid flows from the outside to the contact surfaces between the porous, compressible means and the surfaces to be coated. The porous, compressible means also contains hard non-conductive particles, which somewhat roughen the surfaces of the metal work piece to be coated.
In the three aforementioned documents, no reference is made to the flow through drill holes required in the manufacture of printed circuit boards, because in all cases the surfaces to be coated are either flat or merely curved.
In the German Document for Public Inspection 14 46 045, a process for galvanization with simultaneous electrolytic cleaning of metal surfaces and a device for implementing this process are disclosed. What is involved in this case is the coating of large drillings in steel with the help of an inner electrode, the outer areas of which are rubbed on the inner areas of the drillings. A device of this type is not suitable, however, for the electrolytic processing of printing circuit boards with drillings.
From DE-OS 36 03 856, a process and a device for galvanizing flat items such as printed circuit boards are known. The flat items are grasped and transported by a cathodically connected roller pair rotating at a relatively slow rotational speed. The electrolyte is applied to the item by an anodically connected roller pair, the surface of which can absorb fluid. A small distance is deliberately maintained between the surface of the item and the surface of the anodic rollers. The rotational speed of the anodic rollers is relatively high, in order to attain a correspondingly fast electrolytic movement along the surface of the item. In this way, an increase in current density is achieved, compared to conventional immersion bath galvanization. Thus rotating, insoluble roller pairs as anodes are described. The metal is supplied in soluble fashion via the electrolyte. The anodic roller pairs are not located below the level of the bath; therefore the electrolyte must continuously be applied to the galvanization location. The quantity of supplied electrolyte is limited, not least of all due to the close plastic screenings over the rollers. This also limits the possible galvanization current density. The plastic screenings are needed, however, in order to delay an undesired galvanization of the other, cathodically-connected roller pairs, which serve to transport the circuit boards.
Because the rotating anodic roller pairs do not touch the upper sides of the circuit boards, the diffusion layer located on the surface is not mechanically disturbed. However, the space between the anodic roller and the upper side of the circuit boards and thus the space between the pairs themselves is needed, to allow the galvanizing currents for the two sides of the circuit boards to be individually set. During galvanization of the conductor path image, this is always necessary, because the two sides of the circuit board, in practice, have uneven copper areas. For this reason, the anodes of the upper side of the circuit board are fed from one bath current rectifier and the anodes of the bottom side are fed from a different rectifier. Each rectifier can be individually set in respect to current.
Another disadvantage of the aforementioned invention is the very poor flow through fine holes in the printed circuit boards. On board sides located opposite to one another, electrolyte is applied in a small quantity in an almost pressure-free manner. This prevents the flow from going through the holes, resulting in inadequate galvanization of the hole walls even to the point of burns in the holes.
SUMMARY OF THE INVENTION
The invention is based on the problem of designing a generic process so as to achieve the desired reduction in thickness of the ion-depleted border layer on the anode surface or cathode surface (diffusion layer), and to thus attain a correspondingly increased current density of the galvanization current flowing from the electrolyte onto the anodic or cathodic item, while avoiding, however, the constructive and process-related expenses of the so-called “high-speed” flow technique.
This problem is solved and this object attained, first, starting from the generic prior art, in that in the presence of an anode and cathodic items to be processed, or in the presence of anodic items to be processed and a cathode, the surface to be treated of the items is wiped continuously by machine and the electrolyte is conveyed by a component vertical to the plane of the items and is passed through the drillings or drill holes (referred to hereinafter for the sake of simplicity as “drill holes”) of the items.
This wiping of the area or areas in question serves, in a simple, advantageous and industrially implementable manner, to counteract the disadvantageous depletion of metal ions in the diffusion layer. The diffusion layer is largely destroyed, and thus the ion-depleted zone on the surface or surfaces in question
Kosikowski Thomas
Schneider Reinhard
Schroeder Rolf
Wolfer Klaus
Atotech Deutschland GmbH
Bell Bruce F.
Cohen & Pontani, Lieberman & Pavane
Leader William T.
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