Etching a substrate: processes – Nongaseous phase etching of substrate – Etching inorganic substrate
Reexamination Certificate
1998-06-29
2001-04-17
Mills, Gregory (Department: 1763)
Etching a substrate: processes
Nongaseous phase etching of substrate
Etching inorganic substrate
C216S096000, C216S083000, C216S057000, C216S053000, C205S640000
Reexamination Certificate
active
06217787
ABSTRACT:
FIELD OF THE INVENTION
The invention is based on a method of removing and/or applying conductive material in accordance with the precharacterizing clause of the independent claims.
BACKGROUND OF THE INVENTION
We are familiar with etching printed circuit boards chemically by providing their copper layer with an etching mask and etching copper away chemically at those points where the etching mask is not present. This is disadvantageous, e.g. from environmental standpoints, because the chemical liquid is, in addition, enriched with copper, and, when the liquid has been used, it cannot be purified again, or can be purified only with a large input of energy and resources, and is also difficult to dispose of.
In addition, we are familiar with depositing metal layers on metal surfaces electrically in order to adapt their properties to specific requirements.
The invention is based on the object of providing a method of either applying conductive material to an insulating support or removing it from the latter electrically. This object is achieved by the invention disclosed in the independent claims. Advantageous developments of the invention can be found in the subclaims.
SUMMARY OF THE INVENTION
The inventive method of removing electrically conductive material from a printed circuit board having an etching mask, which covers the conductor structure, arranged on it, and in which the desired conductor structure allows non-cohesive areas to form, is characterized by the fact that the following steps are carried out:
a) the printed circuit board, together with an electrode, is placed in an electrolytic liquid,
b) voltages of suitable different potential are applied to the printed circuit board and the electrode, and
c) electrically conductive material is removed from the printed circuit board.
In this case, it is advantageous that no chemical means are used, but instead etching is carried out by electrolysis. The electrically conductive material is preferably copper and is removed from the board by the potential difference between the cathode and the anode, and is deposited on the cathode. The electrolyte is used so that a conductive connection is produced between the board, which forms the anode, and the electrode, which forms the cathode. The conductive connection is to be understood such that the different potentials cause the Cu and So
4
ions to migrate in the electrolyte so that they reach the negatively charged cathode. The electrolyte is an aqueous copper sulphate solution, for example.
In addition, the method can be characterized in that the printed circuit board passes through a first zone containing only the electrolytic liquid and the electrode, and in that the printed circuit board passes through a second zone containing, in addition to the electrolytic liquid and the electrode, a brush which is at the same potential as the printed circuit board, and in that, on passing through the second zone, a large area electrical contact is made with all regions of the printed circuit board.
Passing through the two zones has the advantage that copper is removed over a large area in the first zone and, in the second zone, the remnants are removed which have formed in the shape of an island. The shape of an island should be understood as meaning that not all the copper has been removed. As there is then no direct contact with the positive voltage either, this island is not removed as such. By passing through the second zone with the brushes, this is again possible, however, because the bristles of the brushes convey the positive voltage to the island surface, there is thus a potential difference between the anode and the cathode again, and the island can then be removed. The bristles of the brushes should be produced from a chemically very resistant material in order to ensure good contact and a long life.
In addition, the method can be characterized in that the printed circuit board is initially located outside the electrolyte and is introduced into the bath during the process as etching progresses, and/or in that an insulation layer is inserted between the electrode and the printed circuit board, and in that a border zone is thus obtained between the electrode and the printed circuit board.
Furthermore, the method can be characterized in that a linear electrode is moved past the printed circuit board at a short distance, which forms a moving etching zone on the printed circuit board.
It is advantageous that the brushes do not have to be used while producing the border zone. The border zone produces a potential difference over a large area at a particular point, so that island formation is virtually precluded here. The same result is obtained if the electrode is designed as a rod. In this case, the potential difference is then also increased for a particular region, so that the copper is removed.
A printed circuit board produced using the method is characterized by the fact that the conductive material which was covered by the etching mask remains on the printed circuit board.
The inventive method of applying electrically conductive material to a printed circuit board having the conductor structure mapped on it is characterized by the fact that a brush and an electrode are placed in an electrolytic liquid and a different potential is applied to the brush and the electrode, the printed circuit board, which has been seeded beforehand, is moved along underneath the brushes and there is direct contact with the brushes, and electrically conductive material is applied to the printed circuit board.
The electrode is preferably designed as a copper electrode and forms the anode, since the positive voltage is applied. The brushes are provided with a negative voltage and form the cathode. The boards are seeded with palladium, i.e. the conductor tracks which are to be covered with copper are activated in this manner. If the voltage is now applied via the brushes to the surface seeded with palladium, ions detach themselves from the anode and implant themselves in the surfaces seeded with palladium. This is how the copper conductor track layer is obtained. As a result of the fact that the board passes through a number of brushes and there is constant contact between the brush and the conductor track, ions will also continue to flow from the positive anode in the direction of the copper conductor track and be deposited there. An advantage of this is that it uses only that copper which is really needed.
Furthermore, the method can be characterized in that, after the printed circuit board has been removed from the electrolytic liquid, the potential of the electrode and the brush are interchanged and the conductive material is passed from the brush back to the electrode.
As the copper is deposited on the board, on the one hand, but also on the brushes, on the other, reversing the polarity of the anode and the cathode ensures that the copper migrates from the brushes in the direction of the electrode.
A printed circuit board produced using the method is characterized by the fact that conductive material is applied at those points corresponding to the mapped conductor structure.
The inventive method of applying and removing conductive material to and from a previously activated printed circuit board is characterized by the fact that
a) a brush and an electrode are placed in an electrolytic liquid, voltages of different potential are applied to the brush and the electrode, the printed circuit board is moved along underneath the brushes and there is direct contact with the brushes, and a thin layer of electrically conductive material is applied to the printed circuit board,
b) there is no brush arranged between the electrode and the printed circuit board in the electrolytic liquid, and a thick conductive layer is applied at those points where there is no etching mask, and
c) a brush and an electrode are placed in an electrolytic liquid, voltages of different potential are applied to the brush and the electrode, the printed circuit board is moved along underneath the brushes and there is direct contact with
Deutsche Thomson-Brandt GmbH
Irlbeck Dennis H.
Mills Gregory
Tripoli Joseph S.
Zervigon Rudy
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