Method and apparatus for replenishing an electroplating bath with metal to be deposited

For replenishing a plating bath with copper or other metal to be electrodeposited with the use of an insoluble anode, scrap metal such as copper wires is received in a makeup tank, into which are passed the gases generated within the plating tank with the progress of electroplating operation. The plating solution in the plating tank is also directed into the makeup tank and sprayed on the scrap copper wires, thereby dissolving same. The dissolved copper is then filtered, heated, and introduced into the plating tank.

CROSS-REFERENCE TO RELATED APPLICATIONS 
Applications entitled "Apparatus for Electroplating Strip Material without 
Current Leakage" and "Semiclosed Electrolyte Recovery System for 
Electroplating Apparatus", both assigned to the assignee of the present 
application, are filed substantially concurrently herewith. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
My invention pertains to the art of electroplating with the use of anodes 
of the nonconsumable type, commonly known as insoluble anodes, and in 
particular to a method of and apparatus for replenishing a plating 
solution with the metal to be deposited in such electroplating operation. 
The method and apparatus according to our invention have particular 
utility in conjunction with continuous electroplating or electroforming 
apparatus of the type disclosed in Yamashita et al. U.S. Pat. No. 
4,053,370 dated Oct. 11, 1977, of the type described and claimed in 
Yamaguchi U.S. Pat. No. 4,119,516 dated Oct. 10, 1978, and of the type 
described and claimed in the above referenced application entitled 
"Apparatus for Electroplating Strip Material without Current Leakage". 
2. Description of the Prior Art 
The above cited U.S. Pat. No. 4,119,516, for example, proposes 
electroplating apparatus useful for the fabrication of metal foil, for use 
in the manufacture of printed electronic circuitry, or printed circuit 
patterns on a continuous strip of electrically conductive material such as 
stainless steel or nickel. The apparatus comprises a cathode under which 
the continuous strip is fed slidingly and thereby made cathodic, and two 
insoluble anodes underlying the cathode, with an interelectrode gap 
between each anode and the conductive strip traveling under the cathode. 
An electroplating solution for use in the prior patented apparatus contains 
the metal to be deposited, notably copper. Made to flow turbulently 
through the interelectrode gaps, the solution speedily and uniformly 
deposits the metal on the downward-facing surface of the conductive strip 
advancing continuously over the successive anodes. The surface of the 
conductive strip must previously be masked with a plating resist for the 
fabrication of circuit patterns and can be blank for foil production. 
With the progress of the electroplating or electroforming operation the 
bath becomes gradually depleted of its metal content. A periodic 
replenishment of the bath is therefore a necessity to keep the metal 
concentration therein within required limits. Toward this end the plating 
industry has had to purchase a soluble compound of the metal, for 
introducing its solution into the bath. In the case of an acid copper 
plating bath, for example, copper has been added in the form of a solution 
of purchased copper sulfate. This practice is objectionable for the 
following reasons: 
1. The added copper sulfate solution inordinately increases the volume of 
the bath if the electroplating apparatus incorporates an electrolyte 
recovery system such as that proposed by the above noted application 
entitled "Semiclosed Electrolyte Recovery System for Electroplating 
Apparatus". The bath volume increases even more in the case where 
insoluble anodes are used. 
2. With the use of insoluble anodes, sulfate ions increase, lessening the 
solubility of copper sulfate and causing its recrystallization and 
consequent settling down to the bottom of the plating tank. 
3. The copper sulfate solution can introduce such cation contaminants as 
iron, nickel, zinc, and chromium, increasing the internal stress of the 
electrodeposited copper, decreasing its elongation ability and 
malleability, and impairing its hardness and other properties. 
4. Copper sulfate is not so cheap as can be desired. 
Ultimately, therefore, the plating solution must be discarded. Thus the 
conventional method of bath replenishment is not, or at least hardly, 
compatible with the electrolyte recovery system. 
SUMMARY OF THE INVENTION 
It is an object of my invention to provide an improved method of and 
apparatus for replenishing a plating bath with the metal to be deposited 
with the use of an insoluble anode or anodes, far more economically than 
has been feasible heretofore. 
Another object of my invention is to provide such a method and apparatus 
which does not increase the volume of the plating solution in adding the 
metal thereto. 
A further object of my invention is to provide such a method and apparatus 
which makes use of the gases emitted as a result of the electrolysis 
within a plating vessel, instead of allowing them to escape from the 
vessel and so to pollute the work environment. 
A still further object of my invention is to provide such a method and 
apparatus which is compatible with an electrolyte recovery system of the 
type disclosed in the separate application mentioned previously. 
In summary my invention proposes, for replenishing a plating bath with a 
metal to be deposited, the use of the metal in a solid state. Preferably, 
and particularly in the case of copper, our invention suggests the use of 
scrap wires because of their availability, cheapness, and ready 
solubility. For dissolving the scrap metal, the plating solution within a 
plating tank and the gases generated therein with the progress of plating 
operation are both passed into an enclosed space accommodating the scrap 
metal. In the case of an acid copper plating bath the scrap copper wires 
can be dissolved into a copper sulfate solution, which can then be 
introduced into the bath. 
The copper sulfate solution should preferably be heated prior to its 
introduction into the bath. In a preferred embodiment, therefore, the 
copper sulfate solution is directed from the enclosed space into a heater 
tank in constant communication therewith. The heater tank serves the dual 
purpose of heating the copper sulfate solution and allowing sedimentation 
of solids that may be contained therein. The heater tank is also in 
constant communication with the plating tank, and the copper sulfate 
solution overflows from the former to the latter. 
The above and other objects, features and advantages of my invention and 
the manner of attaining them will become more apparent, and the invention 
itself will best be understood, from the following description which is to 
be read in connection with the accompanying drawings.

DETAILED DESCRIPTION 
General 
The following detailed description of my invention pre-supposes the use of 
an acid copper electroplating bath and associated equipment for continuous 
fabrication of copper foil or printed circuit patterns, by way of one 
possible application of the invention. The bath is therefore to be 
replenished with copper by the method and means of our invention. 
With reference first to FIG. 1 the apparatus illustrated therein can be 
broadly divided into electroplating means and bath-replenishing means. The 
electroplating means include a tank or vessel 10 containing an acid copper 
electroplating solution 12. The bath-replenishing means comprise a makeup 
tank 14 for producing a copper sulfate solution by dissolving scrap copper 
16, and a heater tank 18 for heating the copper sulfate solution to a 
required temperature range before its introduction into the plating tank 
10. 
The configurations of the plating tank 10, the makeup tank 14 and the 
heater tank 18 will hereinafter be described under the respective 
headings. The operational description of the overall apparatus will follow 
the descriptions of the three tanks and will serve also as a disclosure of 
the inventive method. 
Plating Tank 
The illustrated electroplating equipment including the plating tank 10 is 
described and claimed in the aforementioned separate application entitled 
"Apparatus For Electroplating Strip Material without Current Leakage". A 
brief description of the electroplating equipment will therefore suffice, 
further details being disclosed in that application. 
As shown in both FIGS. 1 and 2, the plating tank 10 contains a cathode 20 
and, thereunder with some spacing, an insoluble anode 22. The cathode 20 
has formed in its bottom surface several depressions 24 communicating with 
respective passageways 26 extending vertically through the cathode. These 
passageways 26 communicate with a vacuum pump 28 via vacuum conduits 30. 
A strip 32 of electrically conductive material, on which copper foil or 
circuit patterns are to be electrodeposited, passes horizontally under the 
cathode 20 in the direction of the arrow in FIG. 2 or toward the viewer in 
FIG. 1. At 34 in FIG. 1 is shown an entrance opening into the plating tank 
10 for the conductive strip 32. During such travel of the conductive strip 
32 through the plating tank 10, the vacuum pump 28 creates a partial 
vacuum in the cathode depressions 24 thereby exerting suction on the 
conductive strip. Thus the conductive strip 32 advances in sliding contact 
with the bottom surface of the cathode 20 and in sufficient electrical 
contact therewith to become cathodic. 
A suitable interelectrode gap 36 exists between insoluble anode 22 and 
conductive strip 32 traveling under the cathode 20. The plating tank 10 
receives the acid copper plating solution 12 to a level considerably lower 
than the interelectrode gap 36. 
Mounted next to one end (upstream with respect to the predetermined 
traveling direction of the conductive strip 32) of the insoluble anode 22 
is a solution inlet block 38 defining a solution inlet 40. The plating 
solution 12 is to be fed from this inlet 40 into the interelectrode gap 36 
so as to flow turbulently therethrough along the conductive strip 32. The 
solution inlet 40 communicates by way of conduits 42 and 44 with a 
solution feed pump 46 located external to the plating tank 10. The 
solution feed pump 46 has an inlet conduit 48 communicating with the 
interior of the plating tank 10 at a point below the level of the plating 
solution 12 contained therein. 
A diffuser plate 50 is fixedly mounted in the solution inlet 40. Perforated 
to permit the plating solution to pass therethrough, the diffuser plate 50 
functions to make constant in the transverse direction of the conductive 
strip 32 the degree of turbulence of the plating solution flowing through 
the interelectrode gap 36. 
Over the solution inlet block 38 there is mounted a shield block 52 for 
shielding the conductive strip 32 traveling thereover from premature 
copper deposition due to current leakage. The shield block 52 is molded 
integral with a pair of parallel spaced sealing bars 54 disposed on 
opposite sides of the interelectrode gap 36, with the shield block 
bridging the sealing bars at their upstream ends. The pair of sealing bars 
54 have rounded top edges 56 for sliding but practically fluid-tight 
contact with the opposite side end portions of the downward-facing surface 
of the conductive strip 32. 
The entire U-shaped unit comprising the shield block 52 and sealing bars 54 
is mounted on the insoluble anode 22 and solution inlet block 38 via a 
lifter tube 58 of elastic material. The lifter tube 58 can be placed in 
and out of communication with a compressor (not shown) via an air conduit 
60. Upon delivery of compressed air into the lifter tube 58, same 
increases in diameter thereby lifting the U-shaped unit to such an extent 
that the pair of sealing bars 54 make sliding but fluid-tight contact with 
the conductive strip 32. The sealing bars 54 thus bound and seal the 
opposite sides of the interelectrode gap 36, constraining the flow of the 
plating solution only in the longitudinal direction of the conductive 
strip 32. 
Makeup Tank 
Like the plating tank 10 the makeup tank 14, including a removable top 
cover 62, is made of steel and has linings 64 of acid-resisting synthetic 
material such as polyvinyl chloride (PVC). The makeup tank 14 provides an 
enclosed space for accommodating a supply of scrap copper 16 to be 
dissolved and added to the plating solution 12 within the plating tank 10. 
For efficient dissolution of the scrap copper 16 its surface area should be 
as large as possible in comparison with its weight. Two possible forms of 
the scrap copper 16 meeting this requirement are wires and thin sheets or 
foils. Wires are preferred, especially those not more than three 
millimeters in diameter, partly because of their ready availability. Such 
scrap copper wires 16 rest upon a filter 68 forming the bottom of the 
makeup tank 14. The filter 68 has pores such that it admits the passage of 
the dissolved copper therethrough, arresting the smallest pieces of wire 
produced with the progress of its dissolution. 
The dissolution of the scrap copper wires 16 requires the plating solution 
12 and oxygen-enriched atmosphere, both obtainable from the plating tank 
10. To this end the makeup tank 14 communicates with the plating tank 10 
by way of conduit systems 70 and 72. The conduit system 70 has a pump 74 
and an on-off valve 76. With this valve 76 opened, therefore, the plating 
solution 12 can be pumped from the plating tank 10 into the makeup tank 
14. 
The conduit system 70 communicates with a spray nozzle assembly 78 suitably 
mounted inside the top cover 62 of the makeup tank 14. The spray nozzle 
assembly 78 comprises piping 80, as of PVC, of suitable arrangement 
communicatively jointed to the conduit system 70, and a plurality or 
multiplicity of spray nozzle units 82 communicatively coupled to the 
piping 80. The spray nozzle units 82 are of such relative placement that 
the plating solution pumped up from the plating tank 10 can be sprayed 
over the complete scrap copper wires 16 on the filter 68. 
The aforesaid conduit system 72 has a built-in blower 84 for drawing out of 
the plating tank 10 oxygen and other gases produced as a result of the 
electroplating operation. The blower 84 delivers such gases into the 
makeup tank 14. The conduit system 72 is connected to the plating tank 10 
in the adjacency of the interelectrode gap 36 where copper 
electrodeposition takes place. 
Under the filter 68 at the bottom of the makeup tank 14 there is mounted a 
funnel 86 for collecting and directing downwardly the filtered solution of 
the scrap copper wires 16. The lower extremity of this funnel 86 is 
located some distance above the level of the plating solution 12 within 
the plating tank 10. 
Heater Tank 
The heater tank 18 is in constant communication with the makeup tank 14 by 
way of an L-shaped conduit 88. This conduit is coupled to the funnel 86 on 
one hand and, on the other hand, to the heater tank 18 at a point above 
the level of the plating solution 12 within the plating tank 10. Thus the 
filtered solution of the scrap copper wires 16 flows by gravity from the 
makeup tank 14 to the heater tank 18. The heater tank 18 is also in 
constant communication with the plating tank 10 by way of an overflow 
conduit 90, permitting the scrap copper solution to overflow into the 
plating tank. The level of the solution within the heater tank 18 is 
therefore substantially equal to the plating solution level within the 
plating tank 10. 
An upstanding partition 92 divides the interior of the heater tank 18 into 
an upstream chamber 94 on the side of the makeup tank 14 and a downstream 
chamber 96 on the side of the plating tank 10. The top end of the 
partition 92 rises above the level of the solution within the heater tank 
18, and its bottom end is spaced from the bottom of the heater tank. The 
solution is therefore free to flow under the partition 92 from the 
upstream 94 to the downstream 96 chamber. Both heater tank 18 and 
partition 92 are of steel, complete with PVC linings. 
Within the upstream chamber 94 of the heater tank 18 a heater is provided 
for heating the solution prior to its overflow into the plating tank 10. 
In this particular embodiment the heater is shown as a simple electric 
heater 98 with a rod-shaped quartz envelope. Alternatively the heater tank 
18 may itself be constructed to include a built-in steam heater. 
A conduit system 100 communicates the heater tank 18 with a dual mist 
extractor 102. The conduit system 100 has a blower 104 for drawing 
mist-laden gases out of the heater tank 18 and forcing them into the dual 
mist extractor 102. This mist extractor forms a part of the recovery 
system for the plating solution 12 which is described and claimed in the 
above referenced separate application entitled "Semiclosed Electrolyte 
Recovery System for Electroplating Apparatus". 
Operation 
For the continuous fabrication of copper foil or circuit patterns by the 
electroplating means shown in FIGS. 1 and 2, the conductive strip 32 is 
fed at constant speed in the arrow-marked direction through the plating 
tank 10, in sliding contact with the cathode 20. The downward-facing 
surface of the conductive strip 32 has previously been masked with a 
plating resist for the production of circuit patterns and is blank for 
foil manufacture. 
The pump 46 delivers the plating solution 12 to the solution inlet 40 and 
thence to the interelectrode gap 36. Direct current is introduced through 
the insoluble anode 22 thereby causing copper deposition on the 
downward-facing surface of the conductive strip 32 traveling under the 
cathode 20. The turbulent flow of the plating solution 12 through the 
interelectrode gap 36 is effective to prevent any undue decrease in copper 
ion concentration in the adjacency of the conductive strip 32 and hence to 
speed the deposition of copper thereon. 
With the progress of the electroplating or electroforming operation the 
plating solution 12 emits gases including oxygen and sulfuric acid gas. 
The gases are highly toxic and strongly irritant to tissues. If they were 
not passed into the makeup tank 14 in accordance with our invention, the 
gases would escape as through the strip entrance opening 34 of the plating 
tank 10 thereby polluting the plant atmosphere. The loss of the gases is 
also undesirable from an economic point of view because they serve useful 
purposes as well. My invention utilizes these gases for dissolving the 
scrap copper wires 16, by directing them into the makeup tank 14 through 
the conduit system 72. 
The dissolving of the scrap copper wires 16 can be commenced as, with the 
on-off valve 76 opened, the plating solution 12 is pumped into the makeup 
tank 14 through the conduit system 70. Sprayed with the plating solution 
by the spray nozzle assembly 78 in the presence of the gases from the 
plating tank 10, the scrap copper wires 16 dissolve into the form of a 
copper sulfate solution in accordance with the formula: 
##EQU1## 
The heat required for this reaction derives from the plating solution 
itself, which normally is maintained in a temperature range of 60.degree. 
to 65.degree. C. within the plating tank 10. The higher the temperature of 
the sprayed plating solution, and the larger the surface area of the scrap 
copper in relation to its weight, the faster will be the rate of copper 
dissolution. 
FIG. 3 graphically demonstrates the dissolving rate of copper wires with a 
diameter of one millimeter versus the temperature of the plating solution 
sprayed thereon. The dissolving rate is given in grams per square meter of 
the total surface area of the copper wires per hour, and the temperature 
in degrees centigrade. 
The copper sulfate solution produced in the makeup tank 14 is then filtered 
by the filter 68, collected by the funnel 86, and directed into the heater 
tank 18 by the conduit 88. Since the temperature of the solution flowing 
into the heater tank 18 will have dropped below the required range of 
60.degree. to 65.degree. C., the heater 98 rapidly reheats the solution 
while it is flowing through the upstream chamber 94. The partition 92 
within the heater tank 18 also serves to allow sedimentation of the minute 
pieces of scrap copper that have somehow passed the filter 68 of the 
makeup tank 14, before the solution passes on into the plating tank 10. 
Thus heated and freed from solid particles, the copper sulfate solution 
flows under the partition 92 into the downstream chamber 96 and thence 
overflows into the plating tank 10 through the conduit 90. Copper being 
electrodeposited on the conductive strip 32 is thus added as required to 
the plating solution 12. 
While I have herein shown and described our invention in what we have 
conceived to be the most practical and preferable embodiment, it is 
recognized that this embodiment is by way of example only, for our 
invention is applicable to electroplating or electroforming apparatus of 
other than the illustrated type. It is also understood that not only 
copper but also other metals and alloys, notably including nickel, cobalt, 
and nickel-cobalt alloy, can likewise be added to their plating baths in 
accordance with our invention. Since nickel and cobalt are less soluble 
than copper, however, the capacity of the makeup tank may be suitably 
increased, and there may be employed the scraps of such metals that have 
as large surface areas as possible per unit weight. 
My invention is therefore not to be limited to the details disclosed herein 
but is to be accorded the full scope of the appended claims so as to 
embrace any and all equivalent forms.