Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Patent
1990-07-20
1991-07-16
Powell, William A.
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With microwave gas energizing means
156627, 156642, B44C 122, C23F 100
Patent
active
050322044
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an installation for etching objects, in particular printed circuit boards, with the etching medium being enriched with metal; depleted; etching medium between the etching machine and the electrolytic cell so that the density of the etching medium in the etching machine is substantially constant.
In known etching installations of this type, only a single control circuit is provided, which attempts to keep the density of the etching medium in the etching machine constant by appropriate operation of the electrolytic cell. This control system operates relatively slowly, so that this may lead to considerable shortages or excesses of the metal concentration in the etching medium located in the etching machine. Moreover this results in a discontinuous operation with frequent starting and stopping of the electrolytic cell, which has an unfavourable influence on the quality of the copper separated. Loosening of the copper layer may also occur, which may lead to short-circuits.
It is the object of the present invention to develop an etching installation of the aforementioned type so that the density of the etching medium in the etching machine as well as of the electrolytic cell can be kept at a constant value with low hysteresis and high accuracy.
An etching installation according to the invention, by which this object is achieved, is characterised by outlet of the electrolytic cell and the inlet of the etching machine; the outlet of the etching machine and the inlet of the electrolytic cell; medium in the etching machine and on exceeding a predetermined density value supplies depleted etching medium from the first buffer tank to the etching machine and removes a corresponding quantity of enriched etching medium from the etching machine into the second buffer tank; medium in the electrolytic cell and on falling below a predetermined density value supplies enriched etching medium from the second buffer tank to the electrolytic cell and removes a corresponding quantity of depleted etching medium from the electrolytic cell into the first buffer tank, tanks and operate independently of each other.
Thus, according to the invention the electrolytic cell operates completely independently of the etching machine. On account of the buffer tanks provided, the quantities of depleted etching medium required for maintaining the correct density can be supplied to the etching machine in a problem-free manner and at any time, independently of whether the electrolytic cell makes or does not make available just depleted etching medium. In a corresponding manner enriched etching medium can be removed from the etching machine independently of whether the electrolytic cell is ready to receive enriched etching medium or not. In turn, the electrolytic cell may operate completely independently of the yield of etching medium to be depleted from the etching machine or of the requirement of the etching machine for depleted etching medium. It is stopped when the second buffer tank is empty. Starting and stopping of the electrolytic cell is required solely at relatively great intervals due to the buffer action of the buffer tanks.
For safety reasons, the electrolytic cell should also be shut down in the case of a second density value, which lies below the above-mentioned density value.
It is appropriate if the electrolytic cell is put out of operation whilst voltage is applied, by switching off the pump, which circulates the etching medium through the electrolytic cell, the contents of the cell flowing into the associated storage tank.
If, as explained in claim 4, the etching medium supplied to the etching machine from the first buffer tank and the etching medium supplied to the second buffer tank from the etching machine are passed through a heat exchanger, energy is saved. The etching medium introduced from the first buffer tank into the etching machine must be brought to the working temperature at that point; the necessary heat can be removed from the etching medium to a considerable extent, which is removed from the
REFERENCES:
patent: 4190481 (1980-02-01), Goffredo
patent: 4576677 (1986-03-01), Faul et al.
patent: 4741798 (1988-05-01), Haas
patent: 4772365 (1988-09-01), Haas
Hans Hollmuller Maschinenbau GmbH & Co.
Philpitt Fred
Powell William A.
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