Plating Interior Surfaces of Electrical Terminals

The present invention relates to selective plating; i.e., electroplating selectively, only the electrical contact surfaces of electrical terminals to the exclusion of other surfaces of the terminals. The terminals are stamped and formed from metal strip and are attached to a carrier strip which is useful for strip feeding the terminals through successive manufacturing operations. One necessary manufacturing operation involves plating; i.e., electroplating, the electrical contact surfaces of the strip fed terminals with precious metal or semi-precious metal. These metals are characterized by good electrical conductivity and little or no formation of oxides that reduce the conductivity. Therefore these metals, when applied as plating, will enhance conductivity of the terminals. The high cost of these metals has necessitated precision deposition on the contact surfaces of the terminals, and not on surfaces of the terminals on which plating is unnecessary.

Apparatus for plating is called a plating cell and includes an electrical anode, an electrical cathode comprised of the strip fed terminals, and a plating solution; i.e., an electrolyte of metal ions. The plating solution is fluidic and is placed in contact with the anode and the terminals. The apparatus operates by passing electrical current from the anode, through the plating solution to the terminals. The metal ions deposit, as metal plating on those terminal surfaces in contact with the plating solution.

There is disclosed in U.S. Pat. No. 3,951,761, plating apparatus in which strip fed terminals are plated by immersion in a plating solution. The carrier strip is masked; i.e., covered, by a nonconductive strip, that prevents deposition of plating onto the immersed carrier strip. However, masking requires another manufacturing operation. Some immersed surfaces are difficult to mask, particularly the surfaces of small size electrical terminals. The present invention accomplishes selective plating according to a rapid automatic process and apparatus without a need for masking immersed terminal surfaces on which plating is unnecessary. The present invention is particularly adapted for plating only interior surfaces of strip fed, receptacle type, terminals, and not the external surfaces, despite contact of the external surfaces with plating solution.

The present invention is characterized in that, a mandrel is rotated continuously as strip fed electrical terminals are strip fed continuously to the mandrel, and partially wrapped against the mandrel and exited from the mandrel, a conduit supplying plating fluid under pressure opens into a plurality of nozzles on the mandrel, anodes are mounted within the nozzles for reciprocation into and out of the interiors of the terminals that are against the mandrel, the conduit supplies plating solution under pressure to the nozzles, the nozzles inject plating solution into the interiors of those terminals in which the anodes are received, a source of electrical current supplies electrical current flowing from the anodes, through the plating solution and to the interiors of those terminals in which the anodes are received, and the anodes are constructed for withdrawal from the interiors of those terminals prior to those terminals exiting from the mandrel.

A better understanding of the invention is obtained by way of example from the following description and the accompanying drawings, wherein;

FIG. 1 is a perspective view of apparatus for continuous plating according to the invention with parts of the apparatus exploded;

FIG. 2 is a perspective view of the apparatus shown in FIG. 1 with parts assembled;

FIG. 2A is a schematic view of the apparatus shown in FIG. 2 combined with a belt mechanism;

FIG. 3 is an enlarged fragmentary perspective view of a portion of the apparatus shown in FIG. 2;

FIG. 4 is a view in section of a plating cell apparatus incorporating the apparatus of FIG. 2;

FIG. 5 is a fragmentary plan view, taken along the line 5--5 of FIG. 4, of a portion of the apparatus shown in FIG. 4, and illustrating an advanced anode;

FIG. 6 is a view similar to FIG. 5, illustrating a retracted anode;

FIG. 7 is a perspective view of a shaft of the apparatus shown in FIG. 2;

FIG. 8 is a section view of the shaft shown in FIG. 7;

FIG. 9 is a perspective view of a vacuum aspirator of the apparatus shown in FIG. 2;

FIG. 10 is an elevation view of an anode of the apparatus shown in FIG. 2;

FIG. 11 is an elevation view in section of a portion of an electrical receptacle that has been immersion plated; and

FIG. 12 is an elevation view in section of an electrical receptacle that has been plated according to the present invention.

FIGS. 1, 2, 4 illustrate a mandrel apparatus 1 according to the invention comprising an assembly of, an insulative disc flange 2, an insulative wheel shaped mandrel 3, an insulative nozzle plate 4, a conductive titanium, anode plate 5, a conductive copper-graphite bushing 6 that is attached to the anode plate 5, an insulative anode holder plate 7, an insulative hydraulic distributor plate 8, a shaft 9, an end cap 10 for fitting on the end of the shaft 9, a washer 11 and a sealing ring 12 compressed between the disc flange 2 and the end cap 10. The insulative parts 2, 3, 4, 7, 8 are advantageously machined from a high density polyvinylchloride, and are stacked together with the conductive parts 5, and 6. Bolts 13 are assembled through aligned bolt receiving holes 14 through each of the parts 2, 3, 4, 5, 7, 8. These parts are mounted for rotation on the shaft 9. A continuous length of strip fed electrical terminals 15 are integral with, and serially spaced along, a carrier strip 16. The terminals 15 are shown as electrical receptacles of barrel forms or sleeve forms. These forms are exemplary only, since many forms of electrical receptacles exist. The strip fed terminals 15 are shown in FIG. 2A as being looped over two idler pulleys 17 and onto a cylindrical alignment surface 18 of the mandrel 3.

FIG. 3 shows a series of radially projecting teeth 19 integral with and projecting from the alignment surface 18. The terminals 15 are nested in the spaces that form nests 20 between the teeth 19. The carrier strip 16 has pilot holes 21 in which are registered knobs 22 projecting from the mandrel 3. The flange 2 provides a rim projecting against and along the carrier strip 16. FIG. 2A illustrates a belt mechanism 23 comprising a continuous, insulative, flexible belt 24 looped over the pulleys 17 and also over two additional pulleys 25. The belt 24 also is held by the pulleys 25 against the terminals 15 that are nested in the nests 20, and the belt retains these terminals 15 against the alignment surface 18 of the mandrel 3. Thereby the stripped terminals 15 are between the belt 24 and the alignment surface 18, whereas the belt 24 is between the strip fed terminals and the pulleys 17.

FIG. 3 shows a nozzle wheel 4 that is turreted with a plurality of radially spaced orifices or nozzles 26. FIGS. 1, 4 show that the nozzles 26 are aligned with and open into the nests 20. These Figures also show the anode plate 5 that includes a plurality of radially spaced, anode receiving openings 27 that are aligned with and open into the nozzle openings 26. The anode holder plate 6 includes a plurality of anode receiving chambers 28 aligned with and communicating with the openings 27 in the anode plate 5.

FIG. 10 shows an anode 29 machined from a conductive metal such as titanium. The anode has an enlarged diameter body 30 and a reduced diameter, elongated probe 31 integral with the body 30. A section of the probe 31 is fabricated of a coil spring 31A which makes the probe flexible. A radially projecting, insulative collar 32 is mounted on the tip of the probe 31. One or more flat passageways 33 are recessed in the periphery of the body 30 and extend longitudinally from one end of the body to the other.

As shown in FIGS. 4, 5, 6 an anode body 30 is mounted for reciprocation in each chamber 28. The probe 31 of each anode body 30 projects into the openings 27, 26 that are aligned with the respective chamber 28. The aligned openings 27, 26, together with the chambers 28 cooperate to form anode passageways that mount the anodes 29 for reciprocation. The probe 31 of each anode 29 is mounted for advance into an interior of a terminal 15, as shown in FIG. 5, and also for retraction out of an interior of a terminal 15, as shown in FIG. 6. As each anode 29 is advanced into an interior of a terminal 15, the body 30 of the anode will impinge and stop against the anode plate 5, providing an electrical connection therebetween.

FIGS. 1, 4 show that the distributor plate 8 includes a central opening 34 communicating with a plurality of electrolyte passageways 35 that extend radially outward of the opening 34 and communicate with respective anode chambers 28.

FIGS. 7, 8 show the shaft 9 that is made of conductive stainless steel. The shaft 9 is provided with a central, stepped cylindrical, electrolyte conduit 36 extending entirely the length of the shaft. A plurality of electrolyte ports 37 connect the conduit 36 with a channel shaped, electrolyte inlet manifold 38 recessed in the cylindrical periphery of the shaft 9. A plurality of vacuum ports 39 connect the conduit with a channel shaped, vacuum manifold 40 that is recessed in the cylindrical periphery of the shaft 9, so that the central opening 34 of the plate 8 communicates with the manifolds 38, 40. The electrolyte passageways 35, that extend to the central opening 34, will communicate with the electrolyte inlet manifold 38, and then the vacuum manifold 40, in turn, as the distributor plate 8 is rotated relative to the shaft 9.

FIG. 9, taken with FIGS. 4 and 8, show a vacuum aspirator 41 machined from polyvinylchloride. The aspirator 41 is seated in the conduit 36 of the shaft 9. One or more longitudinal electrolyte passageways 42 are recessed in the periphery of the aspirator 41, and permit electrolyte flow along the conduit 36 into the ports 36 and the electrolyte inlet manifold 38. A longitudinal bore 43 through the aspirator 41 permits additional electrolyte flow through the aspirator 41, to the end of the conduit 36, through a passageway 44 through the end cap 10 and out a conduit 45 that is attached to the end cap 10 and communicates with the cap passageway 44. A series of vacuum ports 46 through the aspirator intercept the bore 43. The vacuum ports 46 communicate with the vacuum ports 39 and with the vacuum manifold 40. The electrolyte flow along the bore produces a vacuum in the vacuum ports 46 and also in the vacuum manifold 40. This phenomenon is well known in the art of hydraulic fluid devices.

FIG. 4 shows schematically a plating cell, including a source E of electrical potential applied across the strip 16 and the anode plate 5, a tank 47 containing a plating electrolyte 48 of precious or semi-precious metal ions and a supply hose 49 leading from the tank 47 through a pump 50 and into the conduit 36 of shaft 9. A drive sprocket with an axle bushing is secured on the distributor plate 8.

In operation, the sprocket is driven by a chain drive (not shown) to rotate the mandrel apparatus 1 and to feed the strip fed terminals 15 upon the mandrel 3. Electrolyte 48 is supplied under pressure from the hose 49 into the conduit 36 of the shaft 9. An electrical potential from the source E is applied between the anode plate 5 and the strip fed terminals 15 to produce a current l. The terminals 15 serve as a cathode onto which precious or semi-precious metal ions of the electrolyte 48 are to be plated. Upon rotation of the mandrel 3, each of the anode chambers 28, in turn, will communicate with the electrolyte manifold 38. The electrolyte will flow under pressure into the electrolyte manifold 38, and from there into several of the anode chambers 28 that communicate with the electrolyte manifold 38. The anodes 29 in these anode chambers 28 will be advanced to positions as shown in FIG. 5 by the electrolyte under pressure. Electrolyte will flow past the anodes 30 along the anode passageways 33, and be injected by the nozzles 26 into the interiors of the terminals 15, wetting the terminal interiors and the anode probes 31 which are in the terminal interiors. Sufficient ion density and current density are present for the ions to deposit as plating upon the surfaces of the terminal interiors. The proximity of the probes 31 to the terminal interiors assures that the surfaces of the terminal interiors are plated, to the exclusion of the other terminal surfaces. The collars 32 on the anodes are sized nearly to the diameters of the interiors of the terminals to position the anode probe precisely along the central axis of the terminal interiors during the plating operation.

As the mandrel apparatus 1 is further rotated, the anode chambers 28 will become disconnected from the electrolyte manifold 38, and will become connected with the vacuum manifold 40. The vacuum present in the vacuum manifold 40 will tend to draw out residual electrolyte in the several anode chambers 28 that communicate with the vacuum manifold 40. The vacuum also will retract the anodes 29 from their advanced positions, as shown in FIG. 5, to their retracted positions, shown in FIG. 6. Thereby, the probes 29 become withdrawn from the interiors of the terminals 15, plating deposition will cease, and the terminals become removed from the mandrel apparatus 1 as the strip 6 continues to be advanced.

The present invention relates additionally to an electrical receptacle that has an interior with a precious or semi-precious metal layer applied by the apparatus described in conjunction with FIGS. 1-10. The layer has observable characteristics that distinguish from characteristics of plating applied by apparatus and a process other than that described in conjunction with FIGS. 1-10. A standard requirement of the electrical industry is, that an electrical receptacle of base metal, copper or its alloy, should be plated first with nickel or its alloy, then have its interior plated with a precious or semi-precious metal such as cobalt-gold alloy that assures electrical conductivity. Further, the plating must equal or exceed a specified thickness, that allows for wear removal of the layer by abrasion. For example, one standard specification requires 15 microinches thickness of cobalt-gold plating extending from the end of the receptacle to a depth of 0.200 inches within the receptacle interior. The exterior surfaces of the receptacle are not subject to wear removal. Therefore, only a flash; i.e. five milliionths of an inch in thickness, of plating is required.

Heretofore, plating of electrical receptacles was accomplished by the prior processes of, plating over a strip of base metal prior to forming the strip into receptacle configurations, or by immersing fully formed electrical receptacles in plating electrolyte and plating all the surfaces of the receptacles. Each of these prior processes had disadvantages.

Forming a base metal strip subsequent to plating applies bending stresses in the plating. Observation by a microscope would reveal stress cracks in the surface of the outer plating layer. The cracks would be most prevalent in the areas of most severe bending. Severe bending also would cause localized separations of the outer plating layer from the metal underlying the outer plating layer. These separations called occlusions, would be observed by microscope observation of a cross-section of the outer plating layer and the underlying metal. These stress cracks and occlusions are defects that would permit corrosion of the underlying base metal and would be adverse to quality of the outer plating layer. Further, stamping of the plated base metal produces shears through the plating layers, exposing the base metal underlying the plating.

FIG. 11 depicts a cross-section of an electrical receptacle plated with a layer of nickel 51, and the immersion plated in cobalt-gold electrolyte, using an anode external to the receptacle during plating. Both the interior and the exterior of the receptacle receive plating deposit 52. The deposit on the interior rapidly tapers in thickness from the end of the receptacle toward the innermost depth of the receptacle. For example, the thickness varies from 0.200 microinches at the end of the receptacle to zero thickness at a depth of 0.140 inches from the end of the receptacle. This tapered characteristic results from the progressive, exponential decrease in charge density or current density due to distance from the external anode. So that thinner portions of the tapered deposit will meet the requirement for minimum thickness, other portions of the deposit must have excess thickness that wastefully consumes the plating ions of the electrolyte. Since the exterior of the receptacle is relatively near the external anode, the deposit is thicker than the deposit on the receptacle interior. For example, the deposit has a thickness of 43 microinches at a depth of 0.02 inches, and a thickness of 20 microinches at a depth of 0.14 inches. Deposit on the exterior of the receptacle is not subjected to wear removal. Therefore, any plating in excess of a flash, i.e., approximately five millionths of an inch in thickness, is wasted consumption. Masking, i.e. covering, the receptacle exterior during plating will eliminate the exterior deposit. However, masking requires an operation prior to plating and is not conducive to a mass production process. Further, masking does not eliminate wasteful consumption of a tapered deposit on the interior of the receptacle. Upon removal of the masking, an abrupt, not tapered, edge of the plating would be observed, where the plating had met the masking.

In the receptacle 15 of the present invention, shown in FIG. 12, the receptacle is stamped and formed from a base metal of copper or its alloy. A layer of nickel or its alloy is plated over all surfaces of the receptacle, including the sheared edges produced during the stamping and forming operations. The interior is plated with an outer layer of a precious or semi-precious metal, such as gold, platinum, palladium or silver, or the alloys thereof, such as cobalt-gold. For example, an outer layer of plating in the form of cobalt-gold of relatively even thickness is deposited along the length extending from the end of the receptacle to a distance of 0.200 inches toward the innermost depth of the interior. An abrupt and steep taper is at the edges of the plating. There is an absence of cobalt-gold, of equal or greater thickness, on the receptacle exterior. The even thickness and abrupt, tapered edges are characteristics of the plating deposit achieved by selective plating according to the invention. The length of the plating deposit substantially is equal to the length of the anode probe 31 that extends within the receptacle interior. At the terminal end of the probe 31, the charge and current densities abruptly cease, causing an abrupt, tapered edge of the plating deposit. The charge and current densities also cease at the chamfered end of the receptacle, causing an abrupt, tapered edge of the plating deposit. There is no need for masking the receptacle exterior, and the plating deposit does not have the nontapered edge that would result from masking. Further, the plating deposit is substantially free of stress cracks and occlusions, and has a grain structure characteristic of plating deposit.

The invention has been described by way of example, only. Other forms of the invention are to be covered by the spirit and scope of the claims. The receptacle 15 are only exemplary of the many forms of electrical receptacles, the internal surfaces of which are capable of being plated by the apparatus of the invention.