GB1600567A

GB1600567A - Plating apparatus

Info

Publication number: GB1600567A
Application number: GB21316/78A
Authority: GB
Original assignee: Oxy Metal Industries Corp
Current assignee: Oxy Metal Industries Corp
Priority date: 1978-05-23
Filing date: 1978-05-23
Publication date: 1981-10-21
Also published as: CA1126694A; JPS6037879B2; JPS54157740A

Description

(54) PLATING APPARATUS (71) We, OXY METAL INDUSTRIES CORPORATION, a Corporation organised under the laws of the State of California, United States of America, of 21441 Hoover Road, Warren, Michigan 48089, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method for plating a portion of a workpiece up to an accurately defined boundary without the need to mask the portion which is to be left unplated and to apparatus for carrying out the method.

According to the present invention a plating method comprises disposing a linear workpiece in a plating bath with the region to be plated immersed in the bath, causing a pair of flat thin input streams of electrolyte to be directed against both sides of the immersed portion simultaneously at substantially the same rate and withdrawing electrolyte downwardly from below the workpiece at a rate not in excess of the input rate, and passing an electric current through the workpiece as cathode and the solution and a pair of anodes disposed below the workpiece and on either side of it.

Preferably a shield is disposed between the anodes and the workpiece so that a straight line cannot be drawn between them.

Preferably the thin electrolyte streams are deflected upwardly at a small angle e.g. 10 to 200 to imp inge on the workpiece.

Preferably a small amount of electrolyte is allowed to drain from the plating bath and the rate of withdrawal of electrolyte and the rate of draining is slightly below the input rate so that the electrolyte just tends to overflow from the bath over the edges of the container therefor whereby the electrolyte level is kept substantially constant.

The invention also extends to apparatus for carrying out the method comprising an elongated electrolyte trough, a pair of electrolyte input spargers disposed near the top of the trough and parallel to and near the edges thereof with horizontally disposed input slots facing towards the centre line of the trough, a suction outlet sparger having an upwardly facing outlet slot disposed below the level of the said input slots and on the midline between the said input slots and means for feeding or mounting a workpiece or workpieces on the said midline, the top edges of the side walls of the trough defining the electrolyte solution level and the plating boundary for the workpiece, and means for collecting electrolyte displaced from the trough over the top edges thereof. The side walls of the trough are preferably each provided with one or more bleed orifices.The top edges of the side walls are preferably chamfered to assist drainage of electrolyte over the edges thereof with the minimum risk of ripples being formed.

Slot defining means are preferably provided above the outlet slot in the suction sparger leading from just below the bottom of the workpiece pass line to the said outlet slot.

Deflector means may also be provided to deflect the two opposed streams of electrolyte from the input spargers upwards at a small angle towards the workpiece.

Shield means may also be provided between the workpiece and the anodes so as to even out the distribution of current density over the surface of the workpiece.

The slot defining means, deflector means and shield means are preferably provided by a pair of triangular cross section members extending along the length of the trough and positioned back to back but spaced apart so as to define the slot, their outwardly and upwardly facing surfaces providing the deflecting means and their mass providing the shielding means.

Such deflector and shield means are preferably made of non conductive material e.g.

polymer such as polyethylene.

The input spargers are preferably provided with baffles so as to direct the electrolyte in a stream generally horizontally towards the inlets to the input slots which are preferably formed with a converging inlet and a narrow parallel sided outlet.

The outlet slot in the outlet sparger is preferably also provided with a converging inlet and a narrow parallel sided outlet and the outlet from the outlet sparger is preferably also baffled so as to direct the flow from the said outlet slot first to one side of the pass line and then back to the other side of the pass line before it passes into the outlet duct ofthe outlet sparger.

The present invention can be put into practice in various ways and two specific embodiments will be described by way of example to illustrate the invention with reference to the accompanying drawings in which: Figure 1 is a diagrammatic cross section of a first form ofplating apparatus in accordance with the present invention, Figure 2 is a cross section of a second form of plating apparatus in accordance with the present invention.

Figure 3 is an enlarged view of part of Figure 2.

The plating apparatus is designed to plate portions of workpieces from one edge inwardly to an accurately defined straight line boundary and to produce platings of even thickness from the edge up to the said boundary without the need for the region which is not to be plated to be masked by a layer of resist. The apparatus can be used to plate a strip which can be moved continuously through the apparatus or it can be used to plate an elongated article or a series of articles located in a stationary condition in the apparatus during the plating process.

The apparatus provides an elongated bath of plating composition, the articles to be plated are provided with current as the cathode and an anode or anodes are located in the bath. The problem is to ensure that fresh plating composition is continuously fed to the workpiece whilst the surface of the solution is kept nonturbulent and as nearly as possible at a constant level since it is this level which determines the boundary of the plating.

A subsidiary problem is to ensure that there are no extreme variations in current density over the area of the workpiece so that an even plating thickness is produced.

The apparatus consists of an elongated tank 10, defined by a bottom wall 11 having an inlet opening 12 and an outlet opening 13 and side walls 14 and 15 each having an outlet opening 16, and end walls 17 and 18 each containing an inlet opening 19. A plating trough 20 is located within the tank 10 and is defined by parallel weirs 21 and 22 extending along the length of the tank 10 and mounted on the bottom wall 11. The weirs 21 and 22 are adjustable in height and their top edges define the solution level and are provided with outwardly facing chamfers 23 over which excess solution can flow out (see arrows 26) into side drainage channels 24 afforded by the space between the walls 14 and 21 and 15 and 22.Each weir also has a bleed orifice 28 located in its lower half and arranged so that most of any excess of plating solution supplied to the trough drains out through the orifices 28 rather than flowing over the tops of the weirs 21 and 22.

The solution draining out through the orifices 28 passes into the channels 24 and thence out through the outlet openings 16.

The trough 20 contains a number of transverse beams 30 and 31 which extend from the lower portion of the upper half of each weir inwardly to a longitudinally extending conduit 33 or suction sparger. This has a slot shaped orifice 34 located in its upper face which is preferably planar, the sparger conveniently being of square box cross section. The slot 34 has upwardly and inwardly facing chamfers 35 so that it has a Y shaped cross section. A pair of deflectors 36 and 37 of right angled triangular cross section are mounted on the upper surface of the sparger 33 and the co-planar upper surfaces of the beams 31 and 32. The hypotenuses 38 of the deflectors face upwardly and outwardly, whilst they are spaced apart so that their short vertical sides form a longitudinally extending slot 39 leading down to the slot 34.

A pair of inwardly facing discharge spargers 41 and 42 are mounted on the upper surfaces of the beams 31 and 32 respectively parallel to the slot 34.

Each discharge sparger has an outlet slot 43 disposed in its inwardly disposed face just below the level of the tops of the weirs 21 and 22 i.e.

in use just below the surface of the plating solution.

These discharge spargers are arranged to direct an even thin solid stream of plating solution inwardly from each side towards the centre of the trough 20 and the suction sparger is arranged to withdraw liquid downwardly from the centre line ofthe surface of the trough evenly along the entire length of the trough whilst avoiding the formation of vorteces on the surface of the solution.

Each end wall 17 and 18 has a vertical inlet slot, 45 and 46 (not shown) respectively, preferably provided with an adjustable sliding seal, disposed on the centre line of the trough 20 in register with the slot 34.

The workpiece, or workpieces, is then fed sequentially through the end slot 45 along the trough 20 through the plating solution and out through the end slot 46.

An electrical sliding contact of conventional appropriate type is used to supply d.c. current to render the workpiece the cathode. A pair of anodes 50 and 51 of conventional appropriate type extend the length of the trough 20 and are mounted against the sides of the suction sparger 33 on the underneath faces of the beams 31 and 32.

The mode of operation is as follows.

The spargers 41 and 42 are provided with a pumped supply A of plating solution via the inlet 12 and connecting pipe work (not shown) and the suction sparger is provided with a pumped drain capacity B via the outlet 13 and connecting pipework (not shown). The drain C through the orifices 28 and over the weirs 21 and 22 is collected and may be held in a supply tank from which A is drawn and to which B is supplied. This supply tank may be subjected to appropriate filtration, monitoring, pH adjustment and component make up as necessary.

A is arranged to be slightly greater than B at all times.

The flow of plating solution travels inwardly from each outlet 43 and is deflected upwardly by the ramps 38 on to the immersed portion of the workpiece 56 and is then drawn down into the slot 39 and thence through the slot 34 by the suction sparger 33.

The plating current from the anodes is deflected and prevented from concentrating on the bottom edge of the workpiece by the deflectors 36 and 37.

This results in an even thickness of deposit.

Since fresh electrolyte solution is continuously supplied and the rate of supply can be varied high current densities can be used and good deposits achieved at the same time.

The apparatus has been found very suitable for gold plating conventional substrates such as brass strips.

We now turn to Figure 2 where the same reference numerals as in Figure 1 are used for the same parts.

The inlets and outlets to the spargers are modified as are the orifices 28 and the chamfers 23 on the weirs.

The orifices 28 are afforded by plugs 60 arranged to be removably located in bores in the weirs 21 and 22. This enables the orifices 28 to be changed by replacing the plugs 60 by other plugs having orifices of different size.

The chamfers 23 are reversed and face inwardly rather than outwardly. An exhaust hood 65 is also provided. The anodes 50 and 51 are provided with current via connectors 71 and 72.

The discharge spargers 41 and 42 are provided with a baffled arrangement to assist in producing a thin flat even stream of electrolyte solution.

The suction sparger 33 is alos provided with a baffled arrangement to assist in even withdrawal of electrolyte without the creation of vorteces on the surface of the solution. These arrangements are best seen in Figure 3.

The suction sparger 33 is formed with three longitudinally extending horizontal plates. The first 80 has the slot 34 located in it. The second 81 located below the first has a wider slot 82 located in it offset to one side of the centre line of the sparger and the bottom plate 83 has its outlet opening offset to the other side of the centre line.

Each discharge sparger 41 and 42 isconstructed in the same manner, having three longitudinally extending strip shaped horizontally disposed chambers 85, 86 and 87 defined by four plates 88, 89,90 and 91. The lowest plate 88 has its inlet opening disposed on the outer side of its centre line. The next plate 89 has a longitudinally extending slot 92 disposed on the other side of the centre line of the sparger. The next plate 90 has a narrower longitudinally extending slot 93 disposed on the other side of the centre line of the sparger and opposite it in the upper outer corner of the top chamber 87 there is a triangular fillet 94 providing an inclined downwardly and inwardly facing surface 95.This deflects the liquid crossing through the slot 93 inwardly towards the inside face of the sparger, through which extends the horizontal slot 43 having a converging inlet 96 and a parallel sided outlet 97.

This outlet 97 is opposite the lower end of the surface 38 of the deflectors 36 and 37 so that the incoming electrolyte is directed up the inclined surface to impinge against the immersed portion 55 of the workpiece 56.

The upper and lower edges of the vertical walls of the deflectors 36 and 37 which form the slot 39 are provided with a slight chamfer 98 and 99 to assist smooth flow of electrolyte.

WHAT WE CLAIM IS: 1. A plating method which comprise disposing a linear workpiece in a plating bath with the region to be plated immersed in the bath, causing a pair of flat thin input streams of electrolyte to be directed against both sides of the immersed portion simultaneously at sub tank tially the same rate and withdrawing electrolyte downwardly from below the workpiece at a rate not in excess of the input rate, and passing an electric current through the workpiece as cathode and the solution to a pair of anodes disposed below the workpiece and on either side of it.

2. A method as claimed in Claim 1 in which a shield is disposed between the anodes and the workpiece so that a straight line cannot be drawn between them.

3. A method as claimed in Claim 1 or Claim 2 in which the thin electrolyte streams are deflected upwardly at a small angle to impinge on the workpiece.

4. A method as claimed in Claim 3 in which the small angle is 10 to 20 .

5. A method as claimed in any one of Claims 1 to 4 in which a small amount of electrolyte is allowed to drain from the plating bath and therate of withdrawal of electrolyte and the rate of draining is slightly below the input rate so that the electrolyte just tends to overflow from the bath over the edges of the container therefore whereby the electrolyte level is kept sub tank tially constant.

6. A method as claimed in Claim 1 substantially as specifically described herein with reference to Figure 1 or Figure 2 and Figure 3 of the accompanying drawings.

7. Plating apparatus comprising an elongated electrolyte trough, a pair of electrolyte input spargers disposed near the top of the trough and parallel to and near the edges thereof with longitudinally disposed input slots facing towards the centre line of the trough, a suction outlet sparger having an upwardly facing outlet slot disposed below the level of the said input slots and on the mid line between the said input slots and means for feeding along or mounting a workpiece or workpieces on the said mid line,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. appropriate filtration, monitoring, pH adjustment and component make up as necessary. A is arranged to be slightly greater than B at all times. The flow of plating solution travels inwardly from each outlet 43 and is deflected upwardly by the ramps 38 on to the immersed portion of the workpiece 56 and is then drawn down into the slot 39 and thence through the slot 34 by the suction sparger 33. The plating current from the anodes is deflected and prevented from concentrating on the bottom edge of the workpiece by the deflectors 36 and 37. This results in an even thickness of deposit. Since fresh electrolyte solution is continuously supplied and the rate of supply can be varied high current densities can be used and good deposits achieved at the same time. The apparatus has been found very suitable for gold plating conventional substrates such as brass strips. We now turn to Figure 2 where the same reference numerals as in Figure 1 are used for the same parts. The inlets and outlets to the spargers are modified as are the orifices 28 and the chamfers 23 on the weirs. The orifices 28 are afforded by plugs 60 arranged to be removably located in bores in the weirs 21 and 22. This enables the orifices 28 to be changed by replacing the plugs 60 by other plugs having orifices of different size. The chamfers 23 are reversed and face inwardly rather than outwardly. An exhaust hood 65 is also provided. The anodes 50 and 51 are provided with current via connectors 71 and 72. The discharge spargers 41 and 42 are provided with a baffled arrangement to assist in producing a thin flat even stream of electrolyte solution. The suction sparger 33 is alos provided with a baffled arrangement to assist in even withdrawal of electrolyte without the creation of vorteces on the surface of the solution. These arrangements are best seen in Figure 3. The suction sparger 33 is formed with three longitudinally extending horizontal plates. The first 80 has the slot 34 located in it. The second 81 located below the first has a wider slot 82 located in it offset to one side of the centre line of the sparger and the bottom plate 83 has its outlet opening offset to the other side of the centre line. Each discharge sparger 41 and 42 isconstructed in the same manner, having three longitudinally extending strip shaped horizontally disposed chambers 85, 86 and 87 defined by four plates 88, 89,90 and 91. The lowest plate 88 has its inlet opening disposed on the outer side of its centre line. The next plate 89 has a longitudinally extending slot 92 disposed on the other side of the centre line of the sparger. The next plate 90 has a narrower longitudinally extending slot 93 disposed on the other side of the centre line of the sparger and opposite it in the upper outer corner of the top chamber 87 there is a triangular fillet 94 providing an inclined downwardly and inwardly facing surface 95.This deflects the liquid crossing through the slot 93 inwardly towards the inside face of the sparger, through which extends the horizontal slot 43 having a converging inlet 96 and a parallel sided outlet 97. This outlet 97 is opposite the lower end of the surface 38 of the deflectors 36 and 37 so that the incoming electrolyte is directed up the inclined surface to impinge against the immersed portion 55 of the workpiece 56. The upper and lower edges of the vertical walls of the deflectors 36 and 37 which form the slot 39 are provided with a slight chamfer 98 and 99 to assist smooth flow of electrolyte. WHAT WE CLAIM IS:

1. A plating method which comprise disposing a linear workpiece in a plating bath with the region to be plated immersed in the bath, causing a pair of flat thin input streams of electrolyte to be directed against both sides of the immersed portion simultaneously at sub tank tially the same rate and withdrawing electrolyte downwardly from below the workpiece at a rate not in excess of the input rate, and passing an electric current through the workpiece as cathode and the solution to a pair of anodes disposed below the workpiece and on either side of it.

4. A method as claimed in Claim 3 in which the small angle is 10 to 20 .

the top edges of the side walls of the trough defining the electrolyte solution level and the plating boundary for the workpiece, and means for collecting electrolyte displaced from the trough over the top edges thereof.

8. Apparatus as claimed in Claim 7 in which the side walls of the trough are each provided with one or more bleed orifices.

9. Apparatus as claimed in Claim 7 or Claim 8 in which the top edges of the side walls are chamfered to assist drainage of electrolyte over the edges thereof with the minimum risk of ripples being formed.

10. Apparatus as claimed in Claim 7,8 or 9 in which slot means are provided above the outlet slot in the suction sparger leading from just below the bottom of the workpiece pass line to the said outlet slot.

11. Apparatus as claimed in any one of Claims 7 to 10 in which deflector means are also provided to deflect the two opposed streams of electrolyte from the input spargers upwards at a small angle towards the workpiece.

12. Apparatus as claimed in any one of Claims 7 to 11 in which shield means are also provided between the workpiece and the anodes so as to even out the distribution of current density over the surface of the workpiece.

13. Apparatus as claimed in any one of Claims 7 to 12 in which the slot defining means, deflector means and shield means are provided by a pair of triangular cross section members extending along the length of the trough and positioned back to back but spaced apart so as to define the slot, their outwardly and upwardly facing surfaces providing the deflecting means and their mass providing the shielding means.

14. Apparatus as claimed in any one of Claims 7 to 13 in which the input spargers are provided with baffles so as to direct the electrolyte in a stream generally horizontally towards the inlets to the input slots.

15. Apparatus as claimed in Claim 14 in which the input slots are formed with a converging inlet and a narrow parallel sided outlet.

16. Apparatus as claimed in any one of Claims 7 to 15 in which the outlet slot in the outlet sparger is also provided with a converging inlet and a narrow parallel sided outlet.

17. Apparatus as claimed in any one of Claims 7 to 16 in which the outlet from the outlet sparger is baffled so as to direct the flow from the said outlet slot first to one side of the pass line and then back to the otherside of the pass line before it passes into the outlet duct of the outlet sparger.

18. Apparatus as claimed in Claim 7 substantially as specifically described herein with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings.