Note: Descriptions are shown in the official language in which they were submitted.
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PRECIPITATION, PROCESS ~ND APPARATUS USING A MULl'I-CELL
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El.ECTROLYTIC TANK
The invention relates to a process for the precipita-
tion of e.g. copper from a liquid electrolyte by passage of
the liquid stream metered through an inlet into the multi-cell
electrolytic tank, whence it exits from an outlet after
precipitation of the copper.
The invention further relates to an appara-tus for
the practice of this process.
In the older processes and apparatus, the liquid
electrolyte was conducted through the multi-cell electrolytic
tank in such a way that uniform precipitation on the electrodes
did not occur. This irregular precipitation results if the
liquid distribution in the tank is not absolutely uniform.
15. In electrolysis installations which possess in a
common tank a plurality of anode and cathode plates connected
electrically one behind the other, uniform supply /to/ and
flow through the individual cells is of greatest importance.
Due to the uniform precipitation of e.g. copper from the
liquid electrolyte on the electrodes, the precipitated copper
can then immediately be used again in the etching process.
Here, therefore, it is a recycling process that is to be
achieved, among other things.
In one of these known devices the sensor was located
in the etching fluid, which is circulated continuously. Even
if one places the sensor into stagnating areas of the etching
tank, the measured result is still so imprecise that the
purpose of the invention, namely to obtain an optimum etching
rate, is not achieved. By immersion of circuit boards into
the etching fluid, its physical and chemical composition
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changes. It has been ~ound that to get an optirnum etching
rate, certain pararnete~s of the chemical and/or physical
constltution of the etching fluid must exist.
In the present process ecophile etching is
concerned, i.e. the etching fluid is circulated
continuously. It is not exchanged, as in known processes,
when it is used up, but is regenerated or is given additions
which ensure that always an optimum etching rate exists.
The object of the invention is, therefore, to
conduct the process so and to design the apparatus so that an
absolutely uniform distribution of the liquid electrolyte
over the electrodes takes place, the liquid electrolyte to be
optimally adjusted with respect to its chemical properties.
The solution of the problem of the invention now
consists in that -- proceeding from the known processes for
the precipitation of e.g. copper from a liquid electrolyte by
conduction of the liquid stream, metered through an inlet
into the multi-cell electrolytic tank, whence it issues from
an outlet after precipitation of the copper -- the liquid
stream passes through a liquid receiver forming a controlled
liquid stream before the inlet located under the liquid level
of the electrolytic tank. For example, a liquid-buffer tank
can be used to control the flow of electrolyte through the
indlvidual cells of the electrolytic tank with uniform
distribution.
Here an entirely new route is taken. Heretofore the
liquid electrolyte was indeed allowed to flow into the
electrolytic tank metered and as uniformly as possible in a
free jet, and via a drain or overflow the liquid stream, from
which e.g. copper had now been removed, left the tank again.
It turned out that on the electrodes a very uneven
precipitation occurred~ or where the flow was especially
strong, no precipitation at all took place.
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With the new process the llquid elect~olyte no
longer flows freely lnto the tank. It gets into the tank
only via a liquid receive~. The velocit~ of the liquid
stream bet~een the inle~ and the outle-t is very low. The
admission oF the liquid stream on the inlet side is uniforrn
and the discharge of the stream is also uniform in order -to
fully use the area of the anode and cathode plates -- and
thereby achieve a uniform precipitation.
The solution of the problem, namely to achieve an
accuratet i.e. flow-independent measurement and adjustment of
the etching fluid by a sensor, is effected in that the sensor
is arranged in a by-pass to the cycle line of the etching
fluid between etching tank and electrolytic cell, which is
connected at adjustable intervals of time with the cycle
line, e.g. via a valve, and the switching phase of the sensor
takes place with the valve closed, i.e. in the by-pass during
repose of the etching Fluid.
Here an entirely new method is employed. Measuring
is no longer done continuously, as is customary in such
processes, but intermittently. The intervals of time result
by taking from the liquid a sample, transferring it into a
measuring vessel and then measuring this liquid very
accurately in the static state, independent of flow. As a
function of this measured result the etching fluid is then
regenerated or modified until an optimum etching speed exists.
A realization according to the invention consists in
that the sensor is a float known in itself, with inductive or
capacitive tap.
Further the sensor is appropriately contained in an
overflow vessel disposed in the by-pass line.
This overflow vessel assures that the quan-tity of
sample liquid remains always exactly constant.
Appropriately the valve is arranged in the inflow to
the overflow vessel.
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For automatic operation, the valve may be an
electromagnetic valve whose open and closed position is
program-controlled.
In a preFerred realization, in which the copper
content in the etching fluid is adjusted to a certain amount,
it is important that -the sensor adjusts the current supply of
the electrolytic cell, e.g. via an amplifier.
The electrolytic cell is used for copper precipita-
tion, and depending on an adjusted value one is -then in a
p~sition to assign to the etching fluid a certain specific
gravity according to a specific copper content.
Another possibility is that the sensor regulates the
liquid supply to the electrolytic cell, e.g. via a valve and
an amplifier.
If not only the copper content is to be adjus-ted by
a switchable electrolytic cell, but if other parameters are
selected which are to be adjusted to achieve an optimum
etching rate, there results a process for etching circuit
boards by continuously monitoring the etching fluid in its
tank; the teaching of the invention then consists in that the
etching fluid is intermittently replenished by additions -
depending on the number of etching operations ~ until an
optimum etching rate is obtained. This is possible as a
sensor monitors the state of the etching fluid in a control
vessel which is filled at selected intervals of time, and as
the measuring phase of the sensor is shifted to the static
phase of the measured liquid in the control vessel.
A preferred device which solves the problem of
obtaining a uniform distribution of the liquid electrolyte
includes a liquid-buffer tank formed by a partition within
the tank and generally parallel to the inlet side of the
electrolytic tank. The partition defines a flow path to the
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tank to provide a uniforrn distribution of electrolyte
therethroughou-t.
This device is suitable for use wl-th -top or bottorn
inlets.
One possibility consists in that the inflow into -the
liquid-buffer tank occurs from below under hydrostatic
pressure.
By using a buffer tank, therefore, it is here
achieved that under hydraulic pressure, a very uniforrn
distribution takes place.
The design of the buffer tank or of the dividing
walls may vary. ûne possibility is that the upper edge of
the partition extends above the liquid level of the
electrolytic tank and the inlet openings in the partition are
arranged below the liquid level.
Depending on the size of the electrolytic tank and
the type of liquid electrolyte, the inlet openings may be
arranged approximately at mid-height of the liquid level so
that they introduce the liquid stream evenly between the
electrodes.
A plurality of inlet openings may be combined to
form one slit. In another arrangement several partitions
form a siphon type receiver.
The outlet side also has one or more partitions and
the discharge below the liquid level through individual
openings and/or slits occurs in a similar manner as at the
inlet.
A variety of designs on the inlet side can be
combined with designs on the outlet side. For example, on
the inlet side one might use two dividing walls and on the
outlet side only one dividing wall, or the same type of
distribution device for the liquid stream at the inlet side
and outlet side. The inlet openings in the partitions or
dividing walls on the inlet side rnay be arranged at the top,
but still bel~w the liquid level, while on the outlet side
openings are located far-ther down. In thls rnar,ner, tne li4Uid
goes in and out of the electrolytic tank through openinys,
slits, overflow edges or the li~e, w~lich are located ~elow the
liquid level.
Preferred embodiments of the invention are shown in
` the drawings, wherein:
o Figure 1 is a plan view of an electrolytic tank
showing the flow pattern;
Figure 2 is a side view illustrating the electrolytic
tank provided with a partition;
Figure 3 is a partial perspective view of a second
lS embodiment of the partition;
Figure 4 is a partial perspective of a thir~
embodiment of the partition;
Figure 5 is a side view illustrating an etching tank
with an electrolytic cell and measuring device; and
Figure 6 is an enlarged side view illus~rating the
mesuring device of the etching tank.
In Figure 1, the arrow direction 1 shows the liquid
stream of the liquid electrolyte through the electrolytic tank
3 The liquid stream enters on the inlet side 6 and leaves the
tank on the outlet side 18. Electrodes 16 are connected one
behind the other as anodes and cathodes. In this connection
the uniform supply to and flow through the individual cells is
of greatest importance.
According to the invention, in Fig. 2 e.g. the liquid
stream is charged in arrow direction 1 from above through a
feed 14. In this case a preceding preconnected buffer tank 13
must be present, through which the liquid stream flows in
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arrow direction 24 by passing through a thruway in partition 17
defined by openings 17a near the bottorn of the partition. It
then enters the liqui~-buffer tank 5~ sweeping the partition 17,
from below. The liquid-buffer tank is limited by a partition 7,
whose lateral edges lû, 11, as shown in Fig. 3, ano the lower
edge 9 are connected liquidproof with tank 3, so as to form a
dividing wall. In this par-tition 7 inlet openings 4 are
arranged. These inlet openings may be arranged either at the
top, in the center, or distributed in any manner. If desired,
1~ tests will be made to determine how the most uniform admission
of the individual plates is achieved during the precipitation.
The only essential point is that the inlet openings are located
always below the liquid level. Then the electrolyte is
conducted in arrow direction 25 through the individual cells in
such a way that the individual electrodes 16 experience a
uniform distribution of the liquid stream. In Fig. 2 the upper
edge 15 of partition 7 is above the liquid level 2, but the
inlet openings or slits 4 will be below the liquid level 2. It
is possible also that the upper edge 8 of partition 7 lies below
the liquid level 2 and the partition then has no inlet
openings. The supplied liquid stream will then flow below the
liquid level 2 in arrow direction 26 over this edge 8.
It is indicated schematically in Figure 2 that instead
of the upper inflow or upper feed 14 a lower inflow 12 may be
provided. In that case the preceding buffer tank 13 would be
omitted.
In Fig. 4 it is illustrated once more perspectively how
e.g. inlet openings 4 under the liquid level 2 may be arranged
in the upper region inside the partition 7.
In Fig. 2 the outlet side 18 may be designed in the
same manner as the inlet side. In the embodiment, to achieve
regulation of the liquid level 2, drains 21 are arranged in a
partition 2û. These drains may again be circular, slit type,
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I or adapted to the flow in some other way. In the embodirnent,
t the liquid flow arrlving in arrow directlon 25 then passes in
I arrow direction 27 into the buffer tank 28 on the outlet
¦ side, which may be designed analogously to the buffer -tank 5
¦ 5 on the inlet side. An additional partition 19, which is
arranged at the distance 29 from the bottom of tank 3, then
permits the draining liquid to enter the aF-ter-connected tank
23 in arrow direction 30. There an overflow 22 automatically
maintains level 2 constant.
qlthough the embodiment described in the following
is applicable also to an arrangement according to Figures 1
to 4, for better comprehension the organization of the
measuring device is described in a modified embodiment.
~ In Figure 5, according to a further embodiment,
t 15 circuit boards are illustrated schematically, which are
immersed by immersion in arrow direction 43 into the etching
tank 32 in a manner known in itself for the production of
electric circuits. The etching tank 32 is coupled with an
electrolytic cell 33. A sensor 34 is arranged in the by-pass
36 of a recycle line 37. A valve 38 regulates the inflow to
an overflow vessel 40. Further details are shown in Figure 6
where a float 35 is located in flow control vessel 40 and is
actuated by a program control 42. In the embodiment the
float has an inductive tap 39 known in itself, i.e. the
measuring arrangement switches on or off via its contact
terminals 44 when the contact 39 attached to float 35, e.g. a
reed contact, gets out of the magnetic field of the exciter
coils 45 in the stationary part~
The mode of operation is then the following:
The etching fluid 46 is drawn by pump 48 in arrow
direction 47 and thus gets into the cycle line 37. In the
embodiment of Figure 5 the cycle line contains further a
water jet pump 49, which draws partial quanti-ties of
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regenera~ed ~tching fluid out of the electrolytic cell ~3 in
arrow direc~ion 50. The purnp -then conveys the partially
regenerated etching fluid fur-ther in arrow direction 51 back
into the etching tank 32. The feed to the electrolytic cell
33 occurs via a branch 52 when valve 53 is open. Valve 38 is
opened at intervals of time, e.g. by a program control 4~.
Thereby a sample quantity is taken from the etching fluid
present in the cycle line 47 and is passed in arrow direction
54 (cf. ~ig. 6) into an overflow vessel 40. The overflow 55
in this vessel sees to it that the quantity to be measured in
the measuring tank 56 remains the same. If this measuring
tanl< 56 is full 9 the excess sample quantity runs in arrow
direction 57 back into the etching tank 32.
Depending on the measurement result, float 35 now
moves in arrow direction 58, so that the contacts 54 e.g.
turn off the current supply of the electrolytic cell when the
copper content in the etching fluid becomes too high, or turn
it on again when it becomes too low.
Additionally or separately further valves 59, 60 may
be switched, which via lines 61, 62 feed additions into the
etching tank 32. Depending on the type of etching fluid
and/or the materials of the circuit boards, known additives
may be used for bringing the etching rate to an optimum.
Although various preferred embodiments of the
present invention have been described herein in detail, it
will be appreciated by those skilled in the art, that
variations may be made thereto without departing from the
spirit of the invention or the scope of the appended claims.
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