Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-11-22
2001-05-29
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S22400M
Reexamination Certificate
active
06238529
ABSTRACT:
DESCRIPTION
The invention relates to an apparatus for electrolytically treating printed circuit boards and conductor foils in horizontal or vertical continuous electroplating systems by using direct current or pulse current. The apparatus is especially suitable for the uniform electrolytic deposition of metal layers with optimised metal-physical properties.
It is well-known, for electrolytic metallisation, that electrolytic fluid must be brought to the surface of the item to be metallised in order to counter-control the consumption of the required metal ions. In such case, the requirement for metal ions per unit of time increases with an increasing current density. For such purpose, according to known methods, a flow of fluid is utilised, which is directed towards the surface of the item to be treated in order to reduce the thickness of the diffusion layer, which abuts against the surface, and thus to accelerate the conveyance of metal ions to the surface of the item to be treated. In practical usage, however, there are limits for directing the flow to the surfaces, which limits exist because of the design of the electroplating system and the nature of the item to be treated. It is not even possible, for example, to treat thin and, hence, mechanically inadequately stable conductor foils with desirably intense fluid jets. Ideally, the conveyance of the treatment fluid should be able to pass as uniformly as possible to all of the surface locations of the item to be treated situated in the electroplating system.
Furthermore, where possible, electrical screening by components of the system should be avoided. In known electroplating systems, however, this is not achieved. Whilst the item to be treated passes through the system, considerably different local current density values are often set at the treated locations, and such values result from the system components, for example electrolyte inlet pipes and nozzles, and/or from gaps between the anodes.
More especially with so-called high-performance electrolytes, which are particularly well-suited for depositing metal at high current densities, variable current densities have a considerable effect on the quality of the metal layers deposited. In consequence, high-quality printed circuit boards can practically only be produced with these electrolytes when the current density remains identical at all of the locations of the item to be treated during the entire electrolysis. If the current density is not kept within a narrow range, layers are formed, for example, with an unsatisfactory breaking elongation and surface quality. Varying current densities also, of course, lead to a non-uniform layer thickness distribution both from board to board and at various locations of the same printed circuit board. For example, only matt and rough layers are deposited during the deposition of copper with a current density of 7.5 A/dm
2
when the deposition electrolyte has a composition whereby a high-quality layer can be produced at a current density of 5 A/dm
2
.
In DE 42 12 567 A1, an electroplating arrangement for printed circuit boards is described, in which the printed circuit boards are guided along a horizontal continuous path through a treatment chamber, contacting means being provided, which are disposed in the region of the continuous path and grip the printed circuit boards at the front edge in their continuous path. Soluble anodes are provided opposite the plane of conveyance, in which the printed circuit boards are guided. It is also stated that surge nozzles are disposed between the individual anodes and direct the treatment fluid towards the surfaces of the printed circuit boards. However, a system of this type of construction is not suitable for depositing metal at high current densities and for meeting high demands regarding quality.
A horizontal continuous system for electrolytically treating printed circuit boards is described, inter alia, in DE 43 44 387 C2, wherein the printed circuit boards are guided through the system in a horizontal plane of conveyance and direction of conveyance, and insoluble anodes are provided opposite the plane of conveyance. Suitable contacting means in the treatment chamber are used for current supply purposes. During the conveyance of the printed circuit boards through the system, the treatment fluid is conveyed towards the surfaces of said boards via flood tubes. According to the statements made in this publication, the flood tubes and the supply lines for the flood tubes are formed from plastics material in order to minimise the effect of the electrical field between anode and cathode. However, it is assumed that an effect occurs, but the electrical screening effect is estimated to be minimal because the item to be treated would move slowly through the system and, in consequence, would continuously be exposed to the variable electrical fields.
A continuous system for coating plastics material films with metal is described in DE 42 29 403 C2. The item to be treated is drawn through chambers, which can be charged with electrolyte, anodes being disposed opposite the film. The treatment fluid is conveyed through bores in the anodes, which bores are provided so as to lead to the film and so as to extend in an inclined manner when viewed with respect to the direction of conveyance, and said fluid is directed onto the film surfaces. Moreover, an open-pore plastics material is provided internally of the chamber and is brought into contact with the drawn-through film. Furthermore, squeeze rollers are provided in the publication for partitioning the chamber, which rollers serve to prevent the escape of treatment fluid and are disposed at the inlet and outlet of the film. Moreover, it is described that a plurality of chambers are connected in series with one another. It has become apparent that, with such a system, it is not possible to deposit any high-quality metal layers and, more especially, this is not possible when high mean current densities are used.
A horizontal continuous system for treating printed circuit boards is also mentioned in DE 44 02 596 A1. To increase the usable current density, electrolyte from the nearest vicinity is conveyed to the surface of the printed circuit board, in that a rotating flood electrode is used which travels along the surface of the printed circuit board, and the electrolyte emerges from said surface under pressure. This electrode simultaneously also serves as the counter-electrode. Alternatively, the electrolyte may also be removed by suction via the flood electrode. An intense flow at the surfaces of the printed circuit boards is also produced thereby. However, it has become apparent that, when the rotating flood electrodes are used, no high-quality metal layers can be deposited at a high mean current density.
An apparatus is described in DE 43 24 330 A1, which is similar to that in DE 44 02 596 A1. As distinct from the latter, the flood electrode does not travel along the surfaces of the printed circuit boards in a non-slip manner. Rather, the flood electrode is wiped over the surface of the printed circuit board, so that the thickness of the diffusion layer is additionally disturbed with the possibility of a further increase in the limiting current density. However, this apparatus has other disadvantages. For example, the wiping movement leads to an increased wear of the wiping means on the electrode periphery, so that the electrolyte and, hence, the item to be treated easily become contaminated. Moreover, the wiping means needs to be replaced frequently, as a consequence, so that the apparatus has to be maintained with an increased outlay. In this case, it has also been ascertained that metal layers could not be deposited with a high degree of quality when the operation was accomplished with a high mean current density.
A system for electrolytically coating strip steel with metals is described in JP-A-58123898, wherein the strip steel is conducted continuously through an electrolytic chamber and guided closely past anodes. Electrolyte is guided, via pipelines,
Geissler Jens
Kopp Lorenz
Rydlewski Thomas
Schneider Reinhard
Wachter Ralf-Peter
Atotech Deutschland GmbH
Gorgos Kathryn
Paul & Paul
Smith-Hicks Erica
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