Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means
Patent
1990-07-20
1991-07-30
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
050357654
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 installations of this type, the capacity of the electrolytic cells is adapted to the maximum capacity of the etching machine, the control system always setting the electrolytic cell in operation when the density of the etching medium in the etching machine exceeds a certain value. These etching installations sometimes also contain several electrolytic cells connected in parallel, however this is for manufacturing reasons, since then a uniform type of electrolytic cell can be used for etching machines of the most varied capacity. All the electrolytic cells are always operated as a unit. In these known etching installations, the following is a drawback: if etching machines, which have a larger capacity, are operated with a low instantaneous etching capacity ("load"), the connected electrolytic cells very frequently switch on and off. However, such non-continuous operation of the electrolytic cells leads to a poor formation of the metal layer on the cathodes. In addition, the control of the density of the etching medium to the desired value for each new switching-on of the electrolytic cells only begins late, since the latter are normally put out of operation by discharge of the etching medium and a considerable time lapses until re-filling of the etching medium. The considerable control fluctuations of the density of the etching medium in the etching machine connected therewith have a disadvantageous effect on the etching result.
It is the object of the present invention to design an etching installation of the aforementioned type so that the switching-on of the electrolytic cells takes place with better adaptation to the instantaneous load of the etching machine and the frequency of switching-on and off of the electrolytic cells is reduced.
The solution of this object according to the invention is characterised by etching machine and integrates it over a predetermined time; are stored, as there are electrolytic cells in the installation; cell is set in operation or on falling below each limit value of the integral a (further) electrolytic cell is put out of operation; etching medium is removed from the etching machine in the predetermined time.
Thus, according to the invention, several electrolytic cells of lower capacity are used intentionally, not solely for manufacturing reasons, as was the case in the prior art. These electrolytic cells are not all connected as a unit; on the contrary, the number of electrolytic cells which are in operation at any time, is determined by the quantity of etching medium removed from the etching machine over a predetermined integration time. With a very small quantity of etching medium, thus solely a single electrolytic cell is in operation, which is then connected to a further electrolytic cell, when the amount of etching medium exceeds the first limit value of the integral and so on. This has the result that the frequency of switching the electrolytic cells on and off is considerably reduced. The build-up of the metal layer on the cathodes is considerably better than in the prior art. Considerably lower control fluctuations in the density control of the etching medium in the etching machine also result, which in turn leads to better etching results.
In a particularly preferred embodiment, the device which takes over the control of the electrolytic cells, has a mechanical construction. In this case, it comprises a buffer tank, into which the enriched etching medium removed from the etching machine is introduced, the buffer tank in each case being connected by way of a line, in which a pump is located, to each electrolytic cell and a different level of the filling height in the buffer tank being associated with each of these pumps so that it is oper
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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