Electroplating apparatus and method

An electroforming or electrodeposition system in which the depleted metallic component in the electrolyte is replenished by an electrolyzing unit having an anode chamber communicating with the electroforming electrolyte receptacle and separated by an ion-exchange membrance from a cathode chamber. An anode in the anode chamber is dissolved electrolytically to furnish the metallic component. The electroforming current is measured to indicate the rate of depletion of the metallic component from the electroforming electrolyte, the measurement signal being used to control the electrolyzing current to dissolve the metallic component from the anode so that the ionic concentration of the metal in the receptacle is maintained substantially constant.

FIELD OF THE INVENTION 
The present invention relates to an electroforming apparatus and, more 
particularly, to an improved system for electrolytically forming a 
metallic deposition in a layer on a mold shaped to a predetermined 
pattern, the deposited layer being subsequently removed to form a desired 
article. 
BACKGROUND OF THE INVENTION 
The execution of an electrodeposition process with stability to gain 
satisfactory results requires a proper monitoring of the composition of an 
electrolyte furnishing the depositing metal. In an electroforming 
operation, a large amount of metal is deposited and the electrolyte tends 
to alter the concentration quickly. It is desired to inspect the 
composition and to replenish the consumed metal in the electrolyte. The 
common practice effects replenishment by adding a corresponding metal salt 
to the solution tending to be depleted of the depositing metal upon 
inspection from time to time. This procedure has been found to give rise 
to problems because of possible introduction of impurities which may 
hinder or even be detrimental to satisfactory metal deposition. 
OBJECT OF THE INVENTION 
It is accordingly an important object of the present invention to provide 
an improved electroforming apparatus or system whereby the aforementioned 
problem is overcome. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided an 
electroforming apparatus comprising: a mold; at least one electrode 
juxtaposed with the mold to form an electrodeposition gap therebetween; a 
receptacle for an electroforming electrolyte containing a metal to be 
electroformed or deposited upon the mold; pumping means for circulating 
the electrolyte through the electrodeposition gap to supply the latter 
with the electrolyte; an electroforming power supply connected across the 
mold and the electrode for passing an electrodeposition current through 
the gap supplied with the electroforming electrolyte to electrolytically 
deposit the metal upon the mold from the electrolyte; and electrolyzer 
means for electrolytically replenishing said metal in the electrolyte in 
the receptacle, the electrolyzer means including: an anode composed of the 
metal; an anode chamber defining the region of the anode; an ion-exchange 
membrance separating the region of a cathode immersed in a cathode bath of 
the electrolyzer means from the anode chamber; and an electrolyzing power 
supply connected across the anode and the cathode for electrolytically 
dissolving the metal from the anode into the anode chamber, the anode 
chamber and said receptacle being interconnected to allow the 
electroforming electrolyte to circulate therebetween. The apparatus 
preferably includes means responsive to the electrodeposition current for 
acting on the electrolyzing power supply to control the electrolytic 
dissolution of the metal from the anode in the anode chamber so that the 
ionic concentration of said metal in said receptacle is maintained 
substantially constant.

SPECIFIC DESCRIPTION 
In an improved system according to the invention, an electroforming unit 
comprises a receptacle which is generally denoted at 1, a mold 3 fixedly 
mounted on a table or base 2 and a plurality of electrodes 4.sub.1, 
4.sub.2, . . . , 4.sub.n juxtaposed with the mold 3 along a cavity 3a 
thereof. An electroforming power supply comprises a direct-current source 
5 having parallel output branches whose common terminal is connected to 
the mold 3 and other terminals are connected to electrodes 4.sub.1, 
4.sub.2, . . . , 4.sub.n via power switches 6.sub.1, 6.sub.2, . . . , 
6.sub.n (shown by transistors), respectively. The switches 6.sub.1, 
6.sub.2, . . . , 6.sub.n are adapted to be successively turned on and off 
by a signal pulse generator 7 so that gaps G.sub.1, G.sub.2, . . . G.sub.n 
formed between the mold cavity 3a and electrodes 4.sub.1, 4.sub.2, . . . , 
4.sub.n, respectively, are successively energized with a pulsed 
electrodeposition current. This arrangement allows a uniform deposition 
over the cavity 3a. 
The common circuit connection between the DC source 5 and the mold 3 is 
shown to include a sensing resistor 8 designed to detect the 
electrodeposition current. 
The electroforming (deposition) electrolyte containing a desired deposition 
metal, e.g. copper or nickel in the receptacle 1 is drawn by a pump 10 and 
thereby supplied through a nozzle 9 over the mold cavity 3a while 
dynamically traversing the gaps G.sub.1, G.sub.2, . . . , G.sub.n. The 
electrolyte is then returned by gravity to the receptacle 1 for recycling. 
An electrolyzer bath is shown generally at 11, comprising a cathode 13 and 
an anode 14 separated from each other by an ion-exchange membrane 12 so 
that two isolated chambers are formed, a cathode chamber 13a and an anode 
chamber 14a. The membrane 12 is here of anion type but may be of cation 
type when a double structure is employed. 
The anode chamber 14a communicates with the receptacle 1 so that the 
electrodeposition or electroforming electrolyte such as CuSO.sub.4 in the 
latter should fill the chamber 14a. When CuSO.sub.4 is used as the 
deposition electrolyte and hence also as an anode bath in the chamber 14a, 
the cathode chamber 13a may then contain H.sub.2 SO.sub.4 as a cathode 
bath. The anode 14 should then be composed of copper. The cathode 13 may 
be copper or another material. 
The anode 14 and the cathode 13 are shown energized by an electrolyzing 
power supply 15 via a switch 16 whose switching operation is controlled by 
a control circuit 17. The control circuit 17 operates in response to a 
signal furnished by the sensing resistor 8. 
The electrodeposition of a desired metal on the mold cavity 3a is effected 
advantageously in the system shown with a pulsed current which is 
furnished successively to the electrodes 4.sub.1, 4.sub.2, . . . , 4.sub.n 
through the divided gaps G.sub.1, G.sub.2, . . . , G.sub.n when the 
respective switches 6.sub.1, 6.sub.2, . . . , 6.sub.n are turned on and 
off in succession. The pulse electrodeposition is especially advantageous 
in forming a thick deposition layer quickly and efficiently. The quick 
deposition may result in a quick drop in the ion concentration of the 
desired metal, e.g. copper, in the electrolyte which is circulated through 
the receptacle 1. Since the electrolyte is here also free to pass into and 
away from the anode chamber 14a of the electrolyzer unit 11, this drop is 
effectively replenished by ions of the same metal electrolytically 
dissolved from the anode 14. The ion-exchange membrance 12 disposed 
between the anode chamber 14a and the cathode chamber 13a effectively 
checks the dissolved metal ions from depositing on the cathode 13 and acts 
to enhance the concentration of the metal ions in the anode chamber 14a. 
Thus, all the metal ions dissolved from the anode 14 are introduced into 
the electrodeposition or electroforming electrolyte in the receptacle 1. 
The rate of introduction of the metal ions of interest is controlled in 
proportion to the electrolysis in the bath 11 and thus to the 
electrolyzing current therein. 
An important feature of the invention resides in controlling the 
replenishment of the metal ions by the electrolyzer unit 11 proportionally 
in accordance with the exhaustion of the metal ions by the electroforming 
operation in the receptacle 1. Thus, the sensing resistor 8 is provided in 
the electrodeposition power supply circuit to measure the precise rate of 
deposition and hence the precise rate of exhaustion of the metal ions. The 
control circuit 17 is provided to respond to this rate as an electrical 
signal and the switch 16 provided in the electrolyzing power supply 
circuit is controlledly operated by the controller 17 to control the 
electrolyzing current which is supplied by the source 15 on the anode 14 
so that the concentration of the metal ions in the receptacle 1 is 
maintained substantially constant. 
There is thus provided an improved electroforming apparatus wherein the 
replenishment of the depletion (makeup) of the metallic component in the 
electroforming electrolyte is effected by electrolyzing means which 
advantageously checks against introduction of impurities into the 
electroforming electrolyte. This allows the metallic deposition upon the 
mold to build up uniformly to a desired thickness to yield a 
satisfactorily homogeneous and densified structural layer. Furthermore, 
the measurement of the rate of exhaustion is effected automatically or on 
an in-process basis followed by the automatic replenishment operation so 
that a separate task of inspection and addition as in the conventional 
procedure may be advantageously eliminated.