Sparger

Abstract

A machine for metal plating selected areas of a conductive workpiece and a sparger employed therein is disclosed. The machine includes a main frame having the sparger removably mounted therein and an hydraulic press for holding the workpiece securely against the sparger during a plating cycle. The sparger has an inlet port in a first chamber thereof removably connected to a source of electrolyte under pressure. A top plate of the first chamber has a pair of holes for each of the selected areas to be plated on the conducting workpiece. The total area of the holes in the top plate is small compared with the cross-sectional area of the first chamber. This provides a flow of electrolyte from the first chamber to a second chamber through the holes which is relatively uniform through each of the holes. An upper wall of the second chamber acts as a baffle plate being solid opposite to the holes in the upper wall of the first chamber and having cusps therethrough so that the fluid flows therearound into a third chamber. The third chamber has collimating holes in the upper wall thereof to provide a collimated stream of electrolyte to the workpiece to be plated. A source of electric current is connected to terminals on the sparger to provide positive and negative terminals during the plating cycle.

Description

FIELD OF THE INVENTION

This invention relates to a system for electroplating predetermined areas on conductive workpieces and particularly to a sparger used therein.

BACKGROUND OF THE INVENTION

There are numerous requirements in the electronic, industrial, and decorative fields for the selective plating of precious metal onto selected areas of a conductive workpiece. Presently most of the selective plating done uses an inert coating which is applied to the workpiece to mask the areas which are not to be plated. The coated workpiece is then inserted into a conventional plating bath as a cathode and electro-plated. The coating must then be removed after the plating has been completed to provide the finished selectively plated workpiece.

Many of the coatings used are organic. These coatings normally dissolve to a certain extent in the electroplating bath. The disolved organic matter contaminates the bath, requiring constant refining of the electro-plating bath.

Today, a workpiece which really needs to be plated only in a selected area with a precious metal, but will serve its intended function if the entire workpiece is plated is completely plated. This is because it has been found that the cost of applying and removing inert coating through the workpiece and refining the electro-plating baths is greater than the cost of precious metal applied to areas unnecessarily. This is true even when the cost of the additional precious metals is significant with respect to the cost of the entire workpiece.

A machine for plating selected areas of a workpiece is disclosed in a copending U.S. Pat. application of Albert M. Martini et al., Ser. No. 39,014, Filed--May 20, 1970, entitled "Machine for Selective Plating" in which the conductive workpiece to be plated is masked by a top plate of a manifold or sparger. It has been found that the above system satisfactorily masks the workpiece but when multiple areas are to be plated, the quantity of electrolyte provided to each area varies thereby providing different plating thicknesses on each of the preselected areas.

Therefore it is an object of this invention to provide an improved machine for electro-plating a conductive workpiece in preselected areas.

It is a further object of this invention to provide a machine for selectively plating preselected areas of a conductive workpiece with uniform thickness of plating on each of the preselected areas.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with this invention a system is provided for providing a uniform amount of electrolyte to a plurality of preselected areas on a conductive workpiece from a single stream of electrolyte. The system includes a plate for dividing the stream of electrolyte into equal volume paths at high velocity and a second plate for slowing down and shaping the flow of electrolyte in each path for application to the respective preselected areas.

In the preferred embodiment the slowing down and shaping is performed by a pair of plates, one of which forces the fluid to flow towards the periphery of the sparger and the second one collimates the fluid before it is applied to the workpiece.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional diagram partially in block diagram form and partially in section showing a system embodying the principles of this invention;

FIG. 2 is a sectional view through the line 2--2 of FIG. 1 showing a conductive workpiece having been plated in accordance with the teachings of this invention;

FIG. 3 is an exploded view showing three central plates and portions of anodes in a sparger used in the system of FIG. 1; and

FIG. 4 is a sectional view through the line 4--4 of FIG. 1 showing additional details of the sparger construction.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring first to the FIG. 2, we see a copper workpiece 10 having two small circular regions 11a and 11b which have been selectively gold plated thereon by a machine built in accordance with the teachings of this invention.

In FIG. 1, we see the workpiece 10, shown in half scale, mounted for plating in the apparatus of this invention. The apparatus includes a sparger 12, a tank of electrolyte from the tank 13, a pump system 14 for circulating electrolyte from the tank 13 through the sparger 12 onto the workpiece 10 and a hydraulic press 16 for holding the workpiece 10 against the sparger 12 during the plating operation.

The sparger 12 is mounted in a trough 17 which rests on a support 18. An outlet pipe 19 extends out from the bottom of the trough 17 and through the support 18. The sparger 12 is held above the bottom surface of the trough 17 by two supports 21 and 22. The trough 17 and the supports 21 and 22 are constructed from materials which are chemically inert in the electrolyte to be used in the plating process.

Referring now to FIGS. 1, 3 and 4 we see that the sparger 12 is formed from five horizontally arranged plates 23 through 27 forming four fluid receiving chambers 28 through 31 therein. A pair of anodes 32 and 33 are embedded in the sparger 12 to provide a source of ions for the plating operation.

The anodes 32 and 33 extend from the bottom plate 23 through to the second, third and fourth plates 24, 25 and 26 respectively, terminating slightly above the fourth plate 26. The anodes 32 and 33 completely seal the holes provided therefore in the bottom plate 23 rendering that plate fluid tight. In a like manner, the anodes 32 and 33 seal holes 34 and 36 through which they pass in the second plate 24. It should be noted that a pair of small holes 37 and 38 and 39 and 40 each having an equal area of opening flank the holes 34 and 36 respectively in the plate 24. These holes 37 through 40 are not blocked by the anodes 32 and 33.

The anodes 32 and 33 also pass through and seal holes 41 and 42 in the third plate 25. The holes 41 and 42 in the plate 25 are flanked by a pair of cusps 43 and 44 and 46 and 47 respectively. It should be noted that the holes 37 through 40 are arranged on a longitudinal axis of the sparger 12 while the cusps 43, 44, 46 and 47 are aligned with respect to a transverse axis thereof. As a result the portions of the plate 25 directly above the holes 37 through 40 are solid while the portions of the plate 24 below the cusps 43, 44, 46 and 47 are also solid. The holes 37 through 40 can be seen best in FIGS. 1 and 3 while the cusps 43, 44, 46 and 47 can best be seen in FIGS. 3 and 4. Finally, the anodes 32 and 33 pass through a pair of holes 48 and 49 in the fourth plate 26 with sufficient clearance to form an annulus of clearing therearound.

The sparger 12, as well as the plates 23 through 27, are made from inert nonconducting material. Therefore, the anodes 32 and 33 have been provided as a source of local current for the plating process. It should, of cource, be understood that anodes can be provided in other ways in which case in accordance with this invention the holes 34, 36, 41 and 42 would not be provided but an annulus would still be provided where the holes 48 and 49 are provided in this embodiment. The fifth plate 27 of the sparger 12 has a pair of holes 51 and 52 aligned with anodes 32 and 33. A mask 56 having beveled holes 57 and 58 therethrough is mounted in spaced relationship from the plate 27 with the holes 57 and 58 aligned with the holes 51 and 52.

In operation the workpiece 10 is held against the mask 56 by a ram 53 of the hydraulic press 16 having a neoprene layer 54 attached thereto. Electric power from a power source 54 is appropriately applied to the anodes 32 and 33 and the workpiece 10. The pump system 14 pumps electrolyte from the tank of electrolyte 13 through an inlet port 56 into the first chamber 28 of the sparger 12.

Since the cross-sectional area of the chamber 28 is large compared with the total area of the holes 37 through 40, energy supplied by the pumping system 14 to the electrolyte appears primarily as potential energy (i.e. pressure) rather than kinetic energy (i.e., velocity). In this way relatively equal velocity and therefore relatively equal volumes pass through each of the equal size holes 37 through 40 into the second chamber 29. It should be appreciated that if the cross-sectional area of the first chamber 28 was small compared to the total area of the holes 37 through 40, the pressure therein would not build up and a large portion of the energy in the electrolyte would be kinetic. As a result much greater variations would be present in the flow through the holes 37 through 40. This becomes particularly acute when long spargers are employed and also when the spacing between the anodes (for multi-anode operation) is unequal.

It is, of course, appreciated that the first plate 23 could be curved upward along its length to provide the equal flow without the necessity for the large cross-sectional area of the chamber 28. This approach, however, to equalization of flow through the holes 37 through 40 requires a far more expensive manufacturing process for the sparger 12.

The fluids flowing through the holes 37 through 40 are at a high but equal velocity. In most cases the velocity thereof is greater than required for proper plating. Therefore, the plate 25 blocks direct flow of the streams flowing through the holes 37 through 40. Rather, the second chamber 29 fills and flow is directed towards the outer walls of the sparger 12 through the scallops 43, 44, 46 and 47. The plate 25 acts in this way as a baffle.

The fluid flowing through the scallops 43, 44, 46 and 47 fills the third chamber 30 and flows through the annulus formed by the holes 48 and 49 and the anodes 32 and 33. The collimated stream therefrom flows through the holes 51 and 52 of the plate 27 and through the holes 57 and 58 of the mask 58 and then onto the workpiece 10 providing relatively equal volumes and velocities of electrolyte to each of the preselected areas 11a and 11b on the workpiece 10 for plating.

The bevels of the holes 57 and 58 are provided to carry electrolyte away from the sparger 12 after striking the workpiece 10. The fluid thus carried away is returned to the tank of electrolyte 13 after flowing to the bottom of the trough 17.

It should be understood that while this embodiment has been shown with two anodes and two preselected areas 11a and 11b to be plated, the principles taught in here are particularly applicable to long spargers in which multiple preselected areas are to be plated.

It should be obvious that the size of the preselected areas 11a and 11b of the workpiece 10 will require one of a set of relationships between the nominal diameter of the annulus, the diameter of the holes 51 and 52, the distance from the plate 27 to the mask 56 and the dimensions of the holes 57 and 58 in the mask 56.

It should be further noted that controls can be provided in series with each of the anodes 32 and 33 to adjust current densities to further insure equal thickness plating on each of the preselected areas 11a and 11b.

While this invention has been described with respect to a particular embodiment thereof, numerous others will become obvious to those or ordinary skill in the art in light thereof.

Claims

What is claimed is:

1. A system for providing a uniform amount of electrolyte per unit area to a first plurality of preselected areas on a conductive workpiece to be plated from a source of electrolyte; said source of electrolyte providing a single stream of electrolyte to said system; said system including:

first means for dividing said single stream of electrolyte into a second plurality of streams flowing at high velocity;

second means for slowing down and shaping said second plurality of streams into a third plurality of streams shaped to provide electrolyte to said first plurality of preselected areas; said first and third pluralities being equal;

each of said second plurality of streams has equal volume per unit flowing therein; and

means including a top plate for forming a first chamber having a preselected cross-sectional area; said top plate having holes therethrough equal in number to said second plurality for said third plurality of streams to flow therethrough; said holes having a total area; said preselected cross-sectional area being large compared with said total area.

2. The system as defined in claim 1 in which said second means includes:

a baffle plate for dispersing the flow of said second plurality of streams to provide dispersed streams; and

a collimating plate for collimating said dispersed streams into said third plurality of streams.

3. The system as defined in claim 2 in which said first chamber has an inlet opening therein for receiving said single stream of electrolyte; said system also including:

pumping means for supplying said single stream to said inlet opening under pressure.

4. The system as defined in claim 3 also including:

anode means mounted in spaced relationship from said workpiece and in the path of said second plurality of streams; and

an electric power source operably connected between said workpiece and said anode means.

5. The system as defined in claim 4 also including masking means for defining said first plurality of preselected areas.

6. The system as defined in claim 5 also including means for holding said workpiece against said masking means.