Localized Electroplating Method

Abstract

An improved electroplating process is disclosed wherein a metal is deposited in the form of a predetermined pattern upon a continuously advancing strip of electrically conductive substrate. The process involves providing a potential difference between an anode and a cathode wherein the cathode is the strip of electrically conductive substrate, and the current density at the cathode is at least about 300 amperes per square foot per feet per minute of the advance of the cathode, and circulating an electroplating solution containing the metal to be deposited between the anode and the cathode at a velocity of at least 6.5 ft./sec. at the cathode. In addition, an apparatus is disclosed that comprises a means of continuously advancing the strip of electrically conductive substrate past at least one electroplating station that comprises a housing having one face adapted for contact with the strip, an anode recessed in the housing, a channel having specific dimensions and connecting the anode and the strip and a pair of passages at opposite ends of the channel that are in close proximity to the channel, the passages have one end terminating at the face that is in contact with the strip and the other end terminating at a face other than the one that is not adapted for contact with said strip and a container for an electroplating solution and a means for circulating the electroplating solution through the electroplating station and a means for receiving the electroplated strip.

Description

BACKGROUND OF THE INVENTION

This invention relates to a process and equipment useful in electroplating a metal upon a continuous strip of electrically conductive material. More particularly it relates to an improved process and equipment that will continuously selectively electroplate a metal upon the strip of electrically conductive substrate in a desired pattern.

In the manufacture of various material, notably in the manufacture of parts useful in the electronic industry, it is often desirable to have a particular pattern of a metal deposited upon a base of electrically conductive material generally metallic. The substrate is often a long continuous metal strip that can be formed in a particular fashion to have perforations in a particular manner, or can be a solid continuous strip of material. It is often desirable to have a pattern of a different or similar metal deposited in a pattern upon the strip, as for example, a stripe of metal deposit extending the length of the strip but covering only a narrow width of the total metal strip. The methods heretofore used have several disadvantages. For example, one method employed a rotating wheel that contained a reservoir of electroplating solution that rotated in the same direction and the same speed as the continuously advancing strip. The electroplating solution is applied to the metal strip via ports in the wheel and an anode is immersed in the solution and the advancing strip serves as a cathode. While the pattern that is formed is suitable for some purposes, the method outlined above has some serious disadvantages. For example, close uniform contact between the rotating wheel and the advancing strip of metal is hard to maintain. The result is that a uniform pattern is not achieved, that is, the pattern can vary in thickness and in width. As can be appreciated, uniformity is desired from both a functional and economic standpoint.

Other methods that have been tried but have serious disadvantages, include depositing the metal or solution over a larger pattern than desired then removing the undesired portion of the pattern. The removal can be done in a variety of ways, however, in practice a nonuniform pattern has been achieved, or adherence is poor or production rates are low. In many instances, mechanical damage to the base material can occur. These deficiencies are caused by a number of reasons. For example, often the electroplating solution is applied at one station, excess portion removed at another station and electroplated at a third station. Application, removal or electroplating steps can each effect the finished product.

It is an object of this invention to provide an improved process for electroplating a predetermined pattern of a metal upon an electrically conductive substrate.

It is a further object of this invention to provide apparatus for conducting an improved electroplating process.

It is still a further object of this invention to provide an improved electroplating station.

It is an additional object of this invention to provide an apparatus that can be used to deposit a uniform pattern upon a continuously advancing strip of electrically conductive substrate.

It is a further object of this invention to provide an apparatus that can be used upon substrates that are either solid or perforated.

SUMMARY OF THE INVENTION

In accordance with one aspect of this invention, there is provided a process comprising (a) providing a potential difference between an anode and a cathode that is a continuously advancing strip of electrically conductive material and the current density at said cathode is at least about 300 amperes per square foot per feet per minute of advance of the strip or cathode, and (b) circulating an electroplating solution containing the metal to be deposited between said anode and said cathode at a velocity of at least about 6.5 feet per second at the cathode. In accordance with another aspect of this invention there is provided an apparatus for continuously depositing a relatively uniform metal pattern upon a strip of electrically conductive material, said apparatus comprising (a) means for continuously advancing a strip of electrically conductive material, (b) at least one electroplating station that comprises a housing of an electrically insulative material, one face of the housing being in contact with the strip of material, an anode recessed in the housing, a channel connecting the anode and the strip, the width of the channel being approximately equal to the width of the desired pattern and the length of the channel preferably being approximately equal to the length of the anode, and a first and second passage for the electroplating solution at opposite ends of the channel, one end of each passage terminating in close proximity to the corresponding ends of the channel and the other end of each passage terminating at one of the faces that is not the face that is in contact with the strip, (c) a container for an electroplating solution, (d) means for circulating the electroplating solution from the container and to the following elements in series, the first passage, the channel and the second passage and (e) means for receiving the electroplated strip after it has past the electroplating station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view of the apparatus with parts in section;

FIG. 2 is a cross-sectional view of the electroplating station taken along the line 2--2 of FIG. 1;

FIG. 3 is a cross-sectional view of an alternate embodiment of an electroplating station for use in electroplating a solid strip of electrically conductive material;

FIG. 4 shows a segment of a preformed strip that has been processed by this invention; and

FIG. 5 shows a segment of a solid strip that has been processed by this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above description of some of the aspects of this invention and the above-described drawings.

An improved selective electroplating process upon a continuously advancing strip of electrically conductive material is achieved by maintaining a relatively high current density at the cathode (the strip) in relationship to the speed of travel of the strip and by maintaining a relatively high velocity of the electroplating solutions past the cathode.

In the process of this invention an electroplating solution is circulated at a relatively high velocity between a cathode and an anode. The volume between the anode and cathode is kept at a minimum. The current density at the cathode is thereby maximized for a given potential. It is to be noted that the volume between the cathode and anode is reduced from that generally employed and the current density for a given potential is thereby increased. In many instances, however, it is necessary for practical design reasons to keep the volume at a level to keep the pressure drop in the electroplating solution circulation system at a reasonable level.

The cathode used is the continuously advancing electrically conductive strip upon which a pattern of metal is to be deposited. In general, the process can be employed to electroplate any electrically conductive material. Such materials suitable for substrates are known in the art. Materials that have heretofore been electroplated and are satisfactory cathode materials include stainless steels, copper, nickel, various alloys, metallic coated plastics and the like.

The anodes are, in general, the nonconsumable type, that is the anode does not furnish the metal to be coated. Selection of the material for the anode will be dependent upon the metal that is being deposited on the strip of material and are known to those skilled in the electroplating art. The shape of the anode will depend upon several factors, such as the width of the pattern, the length of the channel connecting the anode and cathode and other features of the particular production unit desired.

A relatively high current density is used. Current densities above about 300 amperes per square foot (a.s.f.) per foot per minute of advance of the strip of material are used. It is preferred to employ a current density of from at least about 375 a.s.f. per ft./min. of advance of the strip of material when silver is being deposited and at least about 350 a.s.f. per ft./min. of advance of the strip of material when gold is being deposited from the commercially available gold and silver electroplating solutions. Although higher current density can be used, it will seldom be necessary to exceed about 1,000 a.s.f. per ft./min. of advance of the strip.

The electroplating solution is kept at a relatively high velocity past the cathode, that is a velocity of at least about 6.5 ft./sec. is maintained. Generally velocities from about 6.8 to about 10 ft./sec. are employed. Lower velocities result in nonuniform deposits and low production rates. Higher velocities can be used but no additional beneficial results are achieved, thus increased power costs result.

It is preferred to have the flow of electroplating solution in an opposite direction or countercurrent to the direction of movement of the continuously advancing strip of material. In this manner the desired velocities of the electroplating solution can be achieved at less power costs and somewhat better uniformity and adherence is achieved.

The electroplating solutions that are useful in the process of this invention are known in the art. For example, gold patterns are deposited from an electroplating solution containing a gold concentration of about 8 to 10 ounces per gallon, generally in the form of basic aqueous solution of potassium gold cyanide. An example of a suitable gold plating solution is sold by the Sel-Rex Corporation under the trade name "Temperex." A suitable silver aqueous electroplating solution comprises about 25 to about 30 ounces per gallon of silver, about 9 to about 12 ounces per gallon of potassium cyanide and about 2 to about 4 ounces per gallon of potassium hydroxide. Any metal, such as nickel, tin and the like, that is generally deposited upon a base metal via electroplating, can be deposited in the process of this invention.

As was previously mentioned, the current density used is dependent upon the rate of advance of the strip of material past the electroplating station. For example, when depositing silver upon a base metal strip of material when the strip of material is traveling at about 0.5 ft./min., the preferred current density is about 200 a.s.f. and at 1.0 ft./min. the preferred current density is about 400 a.s.f. Although in general the speed of travel of the strip of material can be increased to any level as long as there is a corresponding increase in current density to maintain the before-mentioned relationship of the variable, for practical mechanical reasons the speed of advance is kept below about 8 ft./min. and generally at about 5 ft./min. In most instances it will be desired to have the strip of material advancing at a rate of at least above about 0.5 ft./min. Thus the current density will be kept within the corresponding level.

Although a single electroplating station can be used in many instances, multiple stations can be used either in series or in parallel. If a relatively thick pattern is desired, then stations can be used in series. If parallel patterns are desired, stations can be used in parallel. Additionally, both sides of a strip of material can be electroplated by the use of two electroplating stations.

With particular reference to FIG. 1, there is shown an electroplating apparatus. An electroplating solution is stored in the container 10. It is circulated to the electroplating station 12 that comprises a housing 14 having an anode 16 recessed from the face 18 that is in contact with the continuously advancing strip of material 20 of the electrically conductive material that serves as the cathode. The electroplating solution flows from the solution-circulating means 22 to a first passage 24 in the housing 14. The solution then flows through a channel 26 that connects the anode 16 and the strip of material 20. The solution is kept at a velocity of at least 6.5 ft./sec. past the strip or cathode 20. The electroplating solution exits from another face 27 of the electroplating station 12 via second passage 28 and returns to the storage container 10. The strip of material 20 is advanced past the electroplating station 12 by the advancing means 29. Contact between the strip of material 20 and the electroplating station 12 is maintained by the guide means 30 and by the plate 31. The electroplated strip after being electroplated by the station 12 is received by the receiving means 32.

With particular reference to FIG. 2, there is shown a cross section of the electroplating station 12 taken along line 2--2 of FIG. 1. The width of the channel 26 is essentially the same width as the pattern that is desired on the strip of material 20.

With particular reference to FIG. 3 there is shown an electroplating station 12 that is adapted for use in electroplating a solid strip 33. The station is essentially the same as that described in reference to FIG. 1 with the exception that there is not provided a plate and the shape of the face is slightly curved.

In FIG. 4 and FIG. 5 there is shown two types of electrically conductive strips that can be produced by this invention. With particular reference to FIG. 4 there is shown a preformed electrically conductive strip 34 and a pattern 35 in the form of a stripe is deposited on the preformed strip 34. The width of the stripe 35 is approximately equal to the width of the channel 26 (shown in FIG. 2). With particular reference to FIG. 5 there is shown a solid electrically conductive strip 36 upon which a pattern 38 has been deposited.

In order to more fully illustrate the invention, the following detailed examples are presented. All parts, percentages and proportions are by weight unless otherwise indicated.

EXAMPLE I

A nickel strip about 1.15 inches wide, is advanced past an electroplating station at the rate of about 2 feet per minute. An aqueous silver electroplating solution containing about 20 ounces per gallon of silver and with a cyanide content of about 21 ounces per gallon at a temperature of about 180.degree. F., is circulated to the electroplating station. The solution is circulated at a sufficient velocity of about 8 ft./sec. past the strip that serves as the cathode. The current density at the cathode is about 800 amperes per square foot with a rate of strip advance of about 2 ft./min. A stripe of silver of about 0.14 inch wide and about 0.000250 inch thick is deposited in a uniform pattern.

Samples of the strip containing the deposited pattern are placed upon a hotplate at 900.degree. F. to determine if any blistering will occur. Samples are additionally subjected to a 90.degree. bend test to determine the adherence of the deposit. On samples produced and tested in the above manner no blistering or flaking of deposit is observed.

Similar runs are made using the following rates of advance and current densities with equally satisfactory results:

Current density Speed of advance Thickness of deposit (ft./min.) (millionths of an inch) __________________________________________________________________________ 0.5 200 250 1.0 400 250 1.5 600 250 3.0 1200 250 __________________________________________________________________________

EXAMPLE II

Following the procedure as given in Example I, except that a gold electroplating solution is used in place of the silver electroplating solution and the strip is advanced at a rate of about 2 feet per minute and a current density of about 750 amperes per square foot is used. The solution is circulated at about 8 ft./sec. A uniform deposit of about 0.00020 inch is achieved. Samples of the strip, when subjected to the blister and bend tests as in Example I, showed no blistering or flaking.

Claims

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

1. In a process for electroplating a metal pattern upon a portion of one side of a continuously advancing, electrically conductive substrate, the improvement comprising:

a. providing a potential difference between an anode and a cathode of a strip of continuously advancing electrically conductive material;

b. maintaining a current density at said cathode of at least about 300 amperes per square foot per foot per minute of advance of the strip; and

c. circulating an electroplating solution containing the metal to be deposited between said anode and the portion of said cathode to be electroplated at a velocity of at least 6.8 ft. per second.

2. A process according to claim 1 wherein silver is the metal deposited.

3. A process according to claim 2 wherein the rate of advance of said metal strip is from about 0.5 ft./min. to about 8.0 ft./min.

4. A process according to claim 3 wherein the rate of advance is from about 1 ft./min. to about 3 ft./min. and the current density is at least about 375 amperes per square ft. per ft./min. of advance and the velocity of said electroplating solution is from about 6.8 to about 10 ft. per second past the cathode.

5. A process according to claim 1 wherein gold is the metal deposited.

6. A process according to claim 5 wherein the rate of advance of said metal strip is from about 0.5 ft./min. to about 8.0 ft./min.

7. A process according to claim 6 wherein the rate of advance is from about 1 to about 5 ft./min. and the current density is from at least about 350 amperes per square foot per ft./min. of advance and the velocity of said electroplating solution is from about 6.8 to about 10 ft. per second past the cathode.