Method for selectively electroplating portions of articles

A plurality of articles are advanced in continuous sequence in spaced relation to each other through an electroplating bath to pass in sliding engagement with a pair of lands, thereby to move selected, laterally-extending strips of the articles along an anode surface located between the lands in selected, closely spaced, facing relation to the anode surface. Jets of the electroplating solution are directed through a plurality of openings in the anode surface to provide a continuous positive flow of electroplating solution in a direction from the anode surface against the selected strips of the articles moving past the anode surface and to permit the flow of electroplating solution to pass between the articles while the lands substantially restrict the flow of the electroplating solution in other directions. Electrical current is directed through the flowing electroplating solution between the anode surface and the article strips for plating the selected article strips to a desired thickness.

In providing electrical contact members formed of spring materials and the 
like, it is desirable to plate the members with a precious metal such as 
gold to improve the contact surface resistance properties of the members. 
Because of the high cost of the plating material, it is desirable to apply 
the gold plating only to those portions of the members which are to be 
actually engaged with a mating contact during opening and closing of a 
circuit, thereby to restrict the quantity of gold which is used. However, 
to achieve competitive pricing for such contact members, it is also 
necessary to manufacture the members with low unit manufacturing costs 
whether those costs constitute material costs or processing costs. Various 
methods and apparatus have been developed for selectively electroplating 
portions of the contact members and the like in attempting to reduce the 
amount of precious metal which is plated on the members. Frequently, 
however, the techniques which have been used in such selective 
electroplating have failed to achieve satisfactory savings in the amount 
of gold which is used or have involved processing costs which have tended 
to cancel out some of the material cost savings resulting from the 
selective electroplating. For example, some of the techniques used have 
involved intermittent advancing and individual masking of precisely 
predetermined portions of the articles to be plated and have involved 
excessive processing costs. Other techniques for selective plating have 
resulted in significant variation in the thickness of the plating formed 
on the members so that, when adequate tolerances have been provided to 
assure that the necessary minimum plating thicknesses are formed on 
selected parts of the articles to meet desired specifications, a 
substantial part of the material savings intended to be achieved by the 
selecting plating have been lost. 
It is an object of this invention to provide novel and improved methods and 
apparatus for selectively electroplating articles; to provide such methods 
and apparatus which are particularly adapted for electroplating at least a 
selected thickness of precious metal on selected laterally extending 
strips of a plurality of articles in a convenient and economical manner; 
to provide such methods and apparatus which are adapted to be employed 
with a high degree of uniformity and control for permitting use of 
relatively small thickness tolerances during such plating; and to provide 
such methods and apparatus which are adapted for use in selectively 
electroplating electrical contact members and the like with low unit 
processing costs. 
Briefly described, the novel and improved apparatus of this invention 
comprises a container for an electroplating bath, an anode having a 
longitudinally extending surface disposed in the bath and lands of 
electrically insulating material which extend longitudinally along the 
lateral edges of the anode surface. Means advance a plurality of articles 
in continuous sequence in spaced relation to each other so that portions 
of the articles including selected laterally extending strips of the 
articles are moved through the bath in sliding engagement with the lands, 
thereby to pass each of the selected laterally extending strips of the 
articles in closely spaced facing relation to the anode surface along the 
length of the anode surface. The anode and lands are preferably mounted on 
a conduit which extends through the electroplating bath. The conduit and 
anode have a plurality of openings therein and pump means direct 
electroplating solution into the conduit, whereby jets of the solution are 
directed through the openings to establish a continuous positive flow of 
the electroplating solution in a direction from the noted anode surface 
against the selected laterally extending strips of the articles moving 
past the anode surface and to permit the flow of the solution to pass 
between the articles being advanced while the lands substantially restrict 
the flow of the electroplating solution in other directions. Means direct 
electrical current through the flowing electroplating solution between all 
parts of the anode surface and the selected strips of the articles moving 
past the anode surface for electroplating the article strips. Preferably 
the anode surface has a configuration corresponding to that of the 
selected laterally extending strips of the articles moved past the anode 
surface so that each portion of each of the selected article strips is 
moved in the desired spaced relation to a corresponding portion of the 
anode surface. 
In this arrangement, the close spacing of the article strips to the anode 
surface as the strips are moved past the anode surface, and the 
maintenance of a continuous positive flow of the electroplating solution 
in the small space between the anode surface and the article strips moving 
past the anode surface, achieve rapid uniform plating of the article 
strips to the desired thickness without requiring excessive thickness 
tolerances such as would tend to waste the precious plating metal. On the 
other hand, the sliding engagement of the articles with the lands 
substantially restricts electroplating of other portions of the articles 
so that the selected laterally extending strips of the articles moving 
between the lands are plated in a substantially selective manner without 
resulting in plating of other portions of the articles to any excessive 
extent such as would tend to waste any excessive proportion of the plating 
metal. In this way, the combined benefits of low processing cost and 
limited use of the expensive plating material achieves the desired product 
quality with improved low unit manufacturing costs.

Referring to the drawings, 10 in FIGS. 1-3 indicates the novel and improved 
electroplating apparatus of this invention which is shown to include a 
tank or container 12 for a bath of an electroplating solution 14. The 
container is mounted on a frame 16 by supporting brackets 18 and is 
preferably divided into a central bath compartment 12.1 and overflow 
compartments 12.2, the overflow compartments being located at opposite 
ends of the central compartment as is best seen in FIG. 2. An inlet 
conduit 12.3 is preferably arranged to introduce electroplating solution 
into the central bath compartment 12.1 from a reservoir (not shown) as is 
diagrammatically indicated in FIGS. 1 and 3 by the arrow 14.1 while outlet 
conduits 12.4 from the overflow compartments return electroplating 
solution to the reservoir as is indicated by the arrows 14.2 in FIG. 1. 
The ends of the container 12 and the walls separating the container 
compartments are preferably provided with aligned wier-like slots 12.5. In 
this arrangement, the bath 14 of electroplating solution is maintained at 
a selected depth as indicated at 14a in FIG. 3 by the continuous 
introduction of the solution into the central container compartment 12.1 
through the inlet conduit 12.3, and by other means further described 
below, while the electroplating solution is also permitted to flow from 
the central bath compartment 12.1 into the overflow compartments 12.2 
through the wier-like slots 12.5 for return to the reservoir through the 
conduits 12.4. If desired, additional wier means of any conventional type 
are employed along the other sides of the central bath compartment for 
assisting in regulation of the depth of the electroplating bath 14. 
The frame 16 additionally mounts two work carrier rails 30 by means of 
supporting brackets 22.1 and 22.2 and a plurality of work carriers 24 
(only one of which is shown) are each provided with a plurality of grooved 
rollers 26 disposed in rolling engagement with the rails 20 as is best 
shown in FIGS. 1 and 3, whereby the work carriers are movable along the 
rails to pass along a selected path relative to the electroplating bath 
14. Typically, for example, the work carriers are interconnected by links 
29 or the like as partially shown in FIGS. 1 and 3, whereby the carriers 
are adapted to be advanced by any conventional means (not shown) in 
continuous sequence relative to the bath 14. Preferably each carrier 
includes a main plate 24.1 having a work-locating shoulder 24.2 and has a 
spring clamp 28 with one end 28.1 secured to the main plate, the clamp 
having its opposite end 28.2 resiliently engaging a work piece 30 for 
detachably holding the work piece in selected position on the carrier in 
electrically connected relation to the carrier. The carriers 24 or the 
work pieces 30 themselves are connected to electrical ground in any 
conventional manner as is diagrammatically illustrated at 31 in FIG. 2. 
The work piece or article 30 typically comprises a group of electrical 
contact members 30.1 (see FIG. 5) which are secured in selected spaced 
relation to each other by an integral web 30.2 of the same material, 
usually a beryllium copper material or the like. The work piece is 
inserted into the carrier 24 to abut the web 30.2 with the carrier 
shoulder 24.2 and the clamp is engaged with the web to locate the contact 
members is precisely predetermined position depending from the carrier. In 
this arrangement, by selected control of the depth of the bath 14, the 
carriers advance the contact members 30.1 through the wier-like slots 12.5 
in the ends and separating walls of the tank 12 into and through the 
plating bath 14 so that a selected portion of each contact member is 
immersed in the bath for a selected period of time as determined by the 
speed of advance of the carriers and by the length of the central bath 
compartment 12.1. In this way, the immersed portions of the contact 
members are passed through the bath in continuous sequence in selected 
spaced relation to each other to be selectively electroplated as is 
hereinafter described. If desired, the individual contact members 30.1, or 
selected groups of the contact members, are separated from the web 30.2 
after each electroplating. Alternately of course, smaller groups of the 
contact members, or even separate individual contact members or other 
articles are mounted in selected side-by-side spaced relation to each 
other in each of the work carriers to be passed through the bath 14 in the 
manner described. Of course, any other conventional means can also be 
employed in accordance with this invention for moving articles to be 
plated such as the contact members 30.1 through the bath 14 in the 
described spaced, sequential relation. 
In accordance with this invention, a conduit 32, preferably formed of a 
chemical-resistant, heat-resistant electrically insulating material such 
as a vinyl chloride copolymer or the like is positioned within the 
electroplating bath 14, the conduit being provided with inlets 32.1 32.2 
at its opposite ends as is best shown in FIG. 2. Preferably for example, 
the conduit includes a central, longitudinally extending tube portion 32.3 
which is bonded or otherwise secured to two end tube portions 32.4 along 
oblique lines of intersection 32.5 as shown in FIG. 2, the outer ends 32.6 
of the end tube portions shown in FIG. 2, the outer ends 32.6 of the end 
tube portions being closed with a plug or the like for a purpose 
hereinafter described. 
In accordance with this invention, the central tube 32.3 has a groove 32.7 
therein extending longitudinally along substantially the entire length of 
the central tube part 32.3. See FIGS. 4 and 6. The central tube also has a 
plurality of openings 32.8 communicating between the interior of the tube 
and the groove 32.7. Typically, for example, the central tube 32.3 has a 
length of about 40 inches, as interior diameter of about 1.0 inches, and a 
wall thickness of about 3/16 inches while the groove 32.7 is about 0.5 
inches wide and extends along the length of the central tube. The groove 
preferably has a central part 32.9 of a selected arcuate configuration or 
the like and has two lateral parts flared outwardly from the central part 
as shown in FIG. 4. Pairs of the openings 32.8 of about 1/32 inch diameter 
are then equally spaced about 1.0 inch apart along the length of the 
groove 32.7 in the central part of 32.9 of the groove. 
In accordance with this invention, an anode 34 is positioned within the 
groove 32.7 to extend longitudinally along the length of the groove, the 
anode also preferably having a center part 34.1 of a selected arcuate 
surface configuration or the like conformed to the center part 32.9 of the 
groove and has flared lateral parts conformed to the flared lateral parts 
of the groove. The anode also has openings 34.2 therein located in 
registry with the respective conduit openings 32.8, the anode openings 
extending through the center part of anode through the anode surface 34.3. 
Preferably the anode has a thin layer of platinum or the like 34.4 on the 
anode surface 34.3 while the greater part of the anode is formed of a 
layer of columbium or the like, the outer layer material 34.4 being 
selected with respect to the gold or other material to be plated while the 
material of the remainder of the anode is selected for its lower cost, for 
its electrical conductivity, and for its resistance to corrosion and the 
like during immersion in the electroplating bath 14. Typically, the anode 
is provided with leads 34.5 (see FIG. 2) which are electrically connected 
to a power source in any conventional manner as is diagrammatically 
illustrated at 35 in FIG. 2, the leads 34.5 and the electrical connection 
to the leads preferably being electrically insulated from the bath 14 in 
any conventional manner. 
In accordance with this invention, a pair of lands 36 of electrical 
insulating material are disposed along the lateral edges of the center 
part 34.1 of the anode in upstanding relation to the anode surface 34.3, 
whereby the outer edges 36.1 of the lands are precisely spaced from the 
anode surface 34.3. Preferably, as shown in FIGS. 3 and 4, the lands are 
formed of the same material as the conduit 32 and are bonded or otherwise 
secured in any conventional manner to the central tube 32.3 of the conduit 
and to the anode to extend over the lateral parts of the anode for 
securing the anode to the conduit 12. Preferably, as is best shown in FIG. 
2, the ends 36.2 of the lands are tapered down for a purpose to be 
described below. 
The conduit 32 as above described is connected by means of flexible tubes 
40 and 42 to the previously described reservoir of electroplating solution 
(not shown) and conventional pump means 44 are interposed in the tubes 40 
and 42 for circulating electroplating solution from the reservoir into the 
conduit to be directed in a series of jets or streams 46 through the 
openings 32.8 and 34.2 in the conduit and anode (as indicated at 46 in 
FIGS. 4 and 6) into the electroplating bath 14. Preferably the pump is 
selected to direct a sufficient flow into the conduit to achieve 
substantially uniform flow of the jets or streams 46 from the various 
openings 32.8 and 34.2 along the length of the conduit and anode as will 
be understood. 
In accordance with this invention, the conduit 32 is positioned within the 
bath 14, preferably by adjustable support means, so that the contact 
member 30.1 or the articles carried by the work carriers 24 are 
resiliently engaged with the lands 36 on the conduit as the articles are 
advanced in sequence through the bath 14. Typically for example the 
conduit is mounted on a support bracket 48 by means of clamps 48.1 while 
the bracket is suspended on support rods 48.2 from an adjusting mechanism 
50 secured to the frame 16. The adjusting mechanism includes a first plate 
50.1 having bosses 50.2 thereon which are threadedly engaged with studs 
50.3, the studs also being threaded into the support rods 48.2 and being 
rotatable by control knobs 50.4. The first plate is mounted on a second 
threaded stud 50.5 which is rotatable by a knob 50.6 to be advanced in 
bosses 50.7 on a second plate 50.8 secured to the frame 16. In this 
arrangement, rotation of the control knobs 50.4 and 50.6 adjusts the 
location of the conduit 32 relative to the path of the contact members 
30.1 through the bath as will be understood. Alternately, of course, any 
other conventional means are used for supporting the conduit 32 in the 
bath 14. 
In the method of this invention, an electroplating solution is introduced 
into the container 12 via the inlet 12.3 and through the conduit 32 so 
that jets of the solution are directed into the bath 14 through the holes 
32.8 and 34.2 in the conduit and anode. The work pieces 30, prepared for 
electroplating in any conventional manner as by degreasing and by 
preliminary full plating with a thin nickel strike or the like, are 
advanced through the bath in spaced sequential relation to each other as 
abovedescribed so that portions of the spaced contact members 30.1 are 
immersed in the bath and move in sliding engagement with the lands 36 on 
the conduit 32, thereby to pass selected laterally extending strips of the 
contact members (as indicated by the broken lines at 30.3 in FIG. 5) in 
closely spaced facing relation to the anode surface 34.3. The jets 46 of 
the electroplating solution directed through the openings 32.8 and 34.2 in 
the conduit and anode into the bath 14 provide a continuous positive flow 
of the electroplating solution in a direction from the anode surface 34.3 
toward the strips 30.3 of the contact members to permit the flowing 
electroplating solution to flow against the strips 30.3 and to pass 
between the contact members 30.1 while the lands 36 restrict the flow of 
the electroplating solution in other directions. That is, directing of the 
jets 46 into the small space defined between the anode face 34.3, the 
strips 30.3 and the lands 36 below the surface level 14a of the bath 
provides a uniform flow of the electroplating solution against each of the 
contact member strips 30.3 as the strips are advanced along the length of 
the anode face 34.3. At the same time, a potential differences is 
established between the contact members and the anode surface 34.3 to 
direct an electrical current between the anode surface and the members 
through the flowing electroplating solution. In this arrangement, the 
close spacing of the anode surface to the member strips 30.3 and the 
uniform positive flow of electroplating solution from the anode surface to 
the strips in the small space cooperate to achieve substantially uniform 
plating of all portions of each of the strips 30.3 as the strips are 
advanced along the anode face. Where the anode face 34.3 has a 
configuration corresponding to that of the member strips as shown, so that 
each portion of each strip is advanced along the anode surface in the same 
spaced relation to corresponding portions of the anode face, even further 
uniformity of the plating of the strip 30.3 is achieved. This arrangement 
is particularly advantageous where the strip 30.3 of the article to be 
plated has a bowed, or other thin flat, surface configuration as is shown 
in FIG. 6. That is, the thickness of the plating deposited on each strip 
30.3 between the lands 36 is highly uniform throughout all portions of the 
strip 30.3. Accordingly, the plating of the strips is controlled with 
small thickness tolerances by regulation of the applied potential, of the 
flow velocity and concentration of the electroplating solution, and of the 
speed of advance of the work pieces and the like in conventional manner 
with assurance that the plating formed on the strips 30.3 meets desired 
specifications. Some small thickness of plating does tend to be deposited 
on the contact members 30.1 outside the areas of the laterally extending 
strips 30.3 but because of the location of the lands 36 and the lesser 
current density between the anode surface 34.3 and those other portions of 
the contact members a relatively much lesser thickness of plating deposit 
is formed on those other surface areas. Further, the process is adapted 
for very fast operation so that the desired plating of the member strips 
30.3 is achieved with very low manufacturing costs even where the article 
to be plated is of a bowed configuration as shown. 
Typically for example, where the contact members 30.1 are formed of 
beryllium copper and are preliminarily plated over all of their surfaces 
with the thin nickel strike, a conventional acid-type cyanide gold plating 
solution is used in the bath 14 at a pH of 4.0, at a temperature of 
165.degree. F. (75.degree. C.) and with a specific gravity of at least 
about 18.degree. Baume; the solution having 4.0 troy ounces of gold per 
content per gallon. The work pieces 30 are then advanced at a speed of 
about 5 to 20 feet per minute along an anode 34 having a length of 40 
inches while a potential of about 4.0 volts d.c. is applied between the 
anode and the work pieces to achieve a current density of about 80 to 150 
amperes per square foot between the anode and work pieces. The 
electroplating solution is pumped into the conduit 32 at a rate of 40 
gallons per minute to achieve a positive flow of electroplating solution 
from the anode face 34.3 toward the contact member strips 30.3 of about 5 
gallons per minute. In this way each contact member is plated with gold of 
99.0 percent or greater purity to a thickness of between 120 and 140 
millionths of an inch as indicated at 52 in FIG. 6 while the other 
portions of the contact member immersed in the bath 14 are plated to a 
thickness of less than about 40 millionths of an inch as indicated at 54 
in FIG. 6, the remaining areas of the contact members which are not 
immersed in the bath being free of any plating as will be understood. In 
this way, substantial selectivity of plating of the contact member is 
achieved with assurance that the necessary thickness of plating is 
achieved in the more narrowly restricted areas of the laterally extending 
strips 30.3 of the member. Thus the yield of the plating process is high 
and the process is rapidly carried out so that unit costs are kept low. 
It should be understood that although preferred embodiments of the methods 
and apparatus of this invention have been described by way of illustrating 
the invention, the invention includes all modifications and equivalents of 
the described embodiments which fall within the scope of the appended 
claims.