EP1523589A2

EP1523589A2 - Electrolytic reactor

Info

Publication number: EP1523589A2
Application number: EP03750816A
Authority: EP
Inventors: David Henry; Christel Dieppedale; Thierry Terrier; Gérard Barrois
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2002-07-19
Filing date: 2003-07-17
Publication date: 2005-04-20
Also published as: WO2004009877A2; US20050247556A1; FR2842536B1; FR2842536A1; US7361256B2; WO2004009877A3

Abstract

The invention concerns an electrolytic reactor (2) comprising a tapered recess consisting of removable slabs (13) through which the electrolyte flows towards a component (31) to be coated under the action of a pump ensuring forced circulation. The component is cathode-polarized, opposite a coaxial anode (20) in the recess (13). Said configuration produces a good flow of the electrolyte in front of the component conducive to an accelerated deposition as well as uniform thickness of the coating material, and the dimensions of the reactor can be increased.

Description

ELECTROLYTIC REACTOR DESCRIPTION

Here, an electrolytic reactor will be treated, in particular in an application for coating the surface of a part taken as an electrode.

The coating of parts by electrolytic means is a well-known technique which has the advantage of being inexpensive while allowing thick deposits of a few tens of microns to be produced in certain cases, for example for copper. In addition, the implementation of this technique is simple. It is therefore preferred to others, in particular to spray or evaporation deposits, in applications where competition exists between them, such as the manufacture of parts in microelectronics and micromechanics.

However, satisfactory formation of the electrolytic coating is not always guaranteed. The defects which can be observed are an unevenness of thickness on the surface or an excessive slowness of the growth of the electrolytically deposited material. In addition, providing a suitable process, that is to say the parameters of which give a satisfactory and reproducible result for the intended application, is difficult, and these parameters vary greatly with the application, which is particularly regrettable for micro-systems, which require very dissimilar deposits. Finally, it is sometimes desired to subject the coating to a magnetic field to achieve a particular deposit with a preferential magnetic orientation of the material. This involves placing a magnet around the cathode or around the reactor, and therefore limiting the size thereof and in practice making the cathode stationary to avoid alteration of the corresponding magnetic characteristics of the material.

We were thus led to discern the following parameters as essential for obtaining a deposit of uniform thickness: the electrolyte, and in particular its conductivity; the density of the current in continuous mode or the parameters of its pulsations in pulsed mode; the geometrical constitution of the reactor, in particular its size and its shape, and the positions and the relative sizes of the electrodes; finally, the conditions of agitation and circulation of the electrolyte near the part to be coated.

The movements of chemical species in the electrolyte take place by migration, by diffusion or by convection, which depend respectively on the difference in potential applied between the electrodes, on the differences in concentration in the electrolyte and on the agitation of the bath. But the predominant phenomenon instead of coating is diffusion. A homogeneous concentration of the material composing the coating in the electrolyte is therefore necessary in front of the surface to be coated.

A known method for promoting the circulation of the electrolyte and its renewal in front of the surface to be coated consists in moving a pallet in front of the surface to be coated in order to agitate the electrolyte. Another method consists in circulating the electrolyte in a circuit by means of a pump, this circuit passing in front of the surface. Document US 5,516,412 - A illustrates them. These processes often give suitable results but, rather promoting turbulent agitation of the bath, they are not suitable for all situations and improvements are desired.

The fundamental object of the invention is to regulate the flow of the electrolyte, in particular in front of the part to be coated, and the electrical polarization to increase the uniformity and the speed of deposition of the coating.

In its most general form, the invention thus relates to an electrolytic reactor, characterized in that it comprises a conical chamber open at two opposite ends, a support for a part to be coated (cathode) and a counter electrode

(anode) arranged in the chamber or optionally at its outlet, respectively towards the wide end and the narrow end, and a means of circulation of electrolyte through the chamber from the narrow end to the wide end.

The progressive development, and started well upstream thereof, of the flow towards the part to be coated contributes to this object.

The chamber is made up of stacked sections and an armature for holding and clamping the sections, which gives the reactor modularity properties which are very useful when applied to other parts having different dimensions and requiring different geometric deposit parameters. The flow is in fact more regular in the conical chamber than at its exit, which makes it preferable to place the part to be coated there rather than at said exit, even if suitable results can still be obtained then. Slices with openings largely containing the part to be coated and its support are provided. This modularity is increased if at least one of the sections contains an imprint for accommodating the anode or its support, because it becomes possible to adjust the position of the anode or to change the shape of the latter. It is preferable that a large number of the slices have this property. The modularity can be exploited to adapt the device to a part to be coated having a determined shape or surface, or to modify the distribution of the current lines leading to the part (what is called the "diaphragm effect" described more far). In the first case, we add or remove slices 7 upstream of the room; in the second case, downstream.

It is recommended that the conical chamber have an opening angle of less than 20 ° and regular, and even less than 14 °; that the circulation of the electrolyte is coaxial with the conical chamber in a tank containing said chamber, and that the device comprises an electrolyte circuit looping on the tank; and again that the electrolyte circuit is connected to the narrow end of the chamber by a nozzle having a conical opening extending the bedroom ; all provisions also contributing to the regularity of the flow.

Another improvement concerns the cathode (the part to be coated) and its support, since it is desired that the means for fixing the part on the support only slightly disturb the flow and in particular do not form significant reliefs. The arrangement which is proposed for this purpose consists in securing the part by the same electrical contacts which polarize it: then, the support of the part to be coated comprises electrical contacts for cathodic polarization of the part which are arranged around the support and which comprise a free end pressed on the workpiece, and a connection end extending on a face of the support opposite the workpiece. A clever embodiment is characterized in that the connection ends of the electrical contacts are connected to flexible branches of a star connector, joined to the support by a variable-spacing mechanism, in that the support comprises stops on which the branches flex, and the electrical contacts are in the form of curved hooks standing on the branches.

At this point, the flow is further improved if the part to be coated and its support form a common smooth surface, that is to say that the workpiece support comprises a perimeter and depth housing adjusted to the workpiece.

Finally, the modularity is further improved if it also relates to the cathode holder, ie the workpiece support is removably mounted on a frame delimiting the conical chamber.

An essential aspect of the invention remains that the conical chamber, the support of the part to be coated, the part itself, the anode, and also preferably the connections of the circuit for circulating the electrolyte through the chamber, are coaxial to most easily achieve the desired objectives; the electrodes, anode and cathode, therefore being suspended in the center of the chamber.

The invention will now be described more fully in conjunction with the figures:

- Figure 1 is an overall view of the reactor; - Figure 2 illustrates a section delimiting the reactor chamber, and adj acent parts;

- Figures 3 and 4 illustrating two states of the cathode holder; - Figure 5 illustrates another section;

- Figure 6 illustrates a detail of this section;

- Figure 7 illustrates a complementary means of manipulation; - Figure 8 illustrates a disassembly slide; and

- Figure 9 illustrates the use of this slide.

Let us now pass to the complete description of the invention by the figures. The invention comprises a tank 1 filled with electrolyte and containing also a structure which constitutes the reactor 2 proper, that is to say the place where electrolysis takes place and the coating is formed. A pump 3 ensures circulation of the electrolyte through a looped conduit 4, the ends of which connect to opposite orifices of the tank 1 by establishing a circulation through the reactor 2. The tank 1 comprises feet 5 allowing it to be placed on a table or other surface. The feet 5 also make it possible to tilt the tank 1 to carry out emptying or maintenance operations. The reactor 2 is composed of a series of sections 7 stacked one on or against the other, whose outer edges are uniform. The sections 7, all include a conical central recess, and these recesses taken in extension themselves draw a conical recess 13 overall (chamber) s' reducing on one side where the reactor 2 is adjacent to a side of the tank 1 and flourishing towards the opposite side of the tank 1, without however reaching it. This second side 8 carries an orifice 9 through which the electrolyte is sucked into the conduit 4, while the side 10 which has been discussed above carries an injection nozzle 11 through which the electrolyte is sent to the reactor 2 ; the nozzle 11 also includes a conical recess 12 fitting to the conical recess 13 of the reactor 2.

The sections 7 are substantially square while including a few notches as shown in the one which is shown completely in FIG. 2. One of these notches is triangular, bears the reference 18 and allows the technician to place suitably the slices 7 in the tank 1, by adjusting the notch 18 on a slide 21 placed on the bottom of the tank 1. Two other notches 19 affect the opposite sides of the slices 7 and allow them to slide on racks 22 fixed to the walls of the tank 1 and on which slides, by meshing, a blocking carriage 23 which compresses the stack of sections 7 of the reactor 2. The section 7 shown here is intended for fixing an anode 20 of which only the silhouette is represented here and which can be a disc, a crown, a grid or any other structure according to the distributions of the lines of electric current and flow of the electrolyte which one wants to see being established. An anode 20 can fully reduce the excess flow to the center, and an anode 20 in the crown can ^focus' the deposition material before it, that is to say near the periphery of the part to be coated. An interesting arrangement could then consist of a plurality of concentric anodes 20, extending to different radii and placed on various sections 7 of the reactor 2, as illustrated in FIG. 1. If several anodes 20 are used at the same time , they can be polarized independently in order to apply different currents to each of them and thus compensate for any edge effects on the cathode.

The capture of the bubbles possibly present in the electrolyte (as hydrogen generated by the electrochemical reaction) - can be obtained with a diffusion grid 24 without electrical properties placed in front of the cathode. Whatever the configuration chosen, the anode 20 is housed in the section 7 which is assigned to it by arms 25 driven into opposite vertical notches 26 of the section 7. The upper arm 25 contains an electrical conductor 61 and ends on a connector 27 inserted in a hollow 28 of the wafer 7. The wafer 7 also comprises holes 29 at mid-height, of horizontal direction and which receive pins 60 preventing the anode 20 from pivoting. The connector 27 receives a wire 61 leading to the positive terminal of a DC generator 62 illustrated in FIG. 1; the wire 61 is sheathed for its entire length immersed in the tank, except at the end engaged in the connector 27. Referring to FIG. 3, details of the cathode holder 30 (support of the part) appear. We know that it is the part itself, the surface of which is to be coated, which acts as a cathode in the electrolytic coating processes. The part here is a thin plate 31 placed on a substrate 32 which comprises an anterior housing 33 whose extent and depth are adapted to that of the plate 31, so that it can be housed therein substantially without play and without form protrusions or depressions. Such an arrangement equalizes the flow of the electrolyte in front of the cathode holder 30 and the plate 31. The substrate 32 also includes a posterior housing 34 with circular step 35 in which extends a mechanical star 36, formed of a hub central from which radiating arms 37 stand out, the ends of which rest on the step 35. The arms 37 carry contacts electrical 38, sheathed to ensure electrical insulation from the electrolyte, and which extend obliquely first through notches 39 formed at the periphery of the substrate 32, then forward to bend in a half-turn and finish with electrically insulating end pieces 40, preferably in the form of a suction cup and making it possible to electrically isolate the current supply of the electrolyte on the wafer 31. Thus, the electrical contacts 38 ensure not only an electrical connection with the plate 31 but a mechanical fixing by keeping it in the housing 33.

The star 36 carries a screw 41 which is retained there at a constant position and whose rotation in a thread 42 of the rear face of the substrate 32 produces an elevation or a depression of the head and therefore a bending of the star 36 by the support of the arms 37 on the step 35. This bending is made possible by weakening 43 of the section of the arms 37 which form points of articulation. The arrangement is such that, as shown in FIG. 4, the driving in of the screw 41 and the bending of the arms 37 of the star 36 produces a tilting of the electrical contacts 38 which lifts the ends 40 of the plate 31 and the moves outwards, away from the plate 31 which can therefore be removed or replaced.

The electrical contacts 38 can be adjustable in number if they are embedded in the arms 37 by separable connections and in particular 'elastic. They can thus include a deformable button 44 pressed through holes in the arms 37 to get there. maintain a constant position while establishing electrical contact with electrical wires 46 embedded in the arms 37. The electrical wires 46 are connected by a conductive wheel 47 to a common connection wire 63 leading to the negative terminal of the generator 62. The modification of the number of electrical contacts 38 also makes it possible to adjust the circulation of the electric current and the flow of the electrolyte in and in front of the plate 31. The cathode holder 30 is retained in a frame 64 by arms 65 similar to those (25) of the anode 20.

The electrical contacts 38 are, like the electrical wires 61 and 63, sheathed where the electrolyte bathes them.

By the freedom of development which it allows, especially with the division of the reactor 2 into sections 7, the device proposed here makes it possible to finely adjust the hydrodynamic and electrical characteristics of the process and therefore to more easily achieve a satisfactory coating on the plate 31. It is possible not only to easily modify the number and the arrangement of the electrodes, but also the length and the section of the conical recess 13 by choosing only part of all the slices 7 available. A more or less pronounced "diaphragm" effect can be created at the cathode level, by removing or adding the desired number of sections 7. This effect is characterized by the fact that it is possible to limit the current lines on the edges of the cathode and concentrate them in its central part.

It will be all the more pronounced as the ratio between the diameter at the outlet of the cone and the diameter of the substrate to be coated (the wafer 31) will decrease. This ratio is varied by removing or adding slices 7.

Naturally and in most cases, the electrolytic deposit is in the form of a bowl with more material on the edges than in the center. Creating a material defect at the edges makes it possible to flatten the profile and to tend towards a flat profile and therefore to improve the uniformity of the deposit.

When the device has a given configuration for a given size of substrate to be coated, to treat a substrate of smaller size, the cathode holder 30 is adapted and slices 7 can be removed until the desired effect is obtained:

- diaphragm effect with small cone opening;

- normal flow with large opening of the cone.

Similarly, to obtain a diaphragm effect on a larger substrate, slices are added. The compression of the stack is maintained by the carriage 23 movable on the racks 22.

The small opening (about 20 ° or less, and preferably about 14 ° or less) of conicity of the recess 13 allows a great regularity of the flow, which is further increased if the geometric irregularities are reduced and especially if the surface of the recess 13 is smooth: the turbulence of the flow is then almost nonexistent. It should be added that attachment of the wafer 31 by suction on the cathode holder 30 remains possible.

Finally, magnets 66 for magnetic polarization of the wafer 31 can easily be accommodated in the armature 64, in the cathode holder 30 or around the reactor 2 provided that they are placed in such a way that they magnetically orient the deposited material. on the plate 31.

It is suitable to replace the unitary nozzle 11 with a stack of removable sections 7 making up an adjustable nozzle.

By varying the speed of injection of the electrolyte, the flow conditions are modified as well as the flow of ¹ electrolyte on the wafer 31.

Those skilled in the art will choose the tank 1, the reactor 2, etc. electrical insulating materials, chemically inert, hydrophilic and having good mechanical strength. An electrolyte retention tank can be placed on the conduit 4 downstream of the pump to adjust the level of the electrolyte in the tank 1, especially when the reactor 2 is changed by adding or removing sections 7, to drain the tank 1 or fill it again. Valves leading to the nozzle 11 and the retention tank are switched to allow the electrolyte to flow freely in the tank 1, or to discharge the electrolyte into the tank, or to allow normal flow in a closed circuit in the conduit 4. Certain improvements to the preceding embodiments are given in the last figures. FIG. 5 illustrates a section 70 different from the previous one by the presence of three notches 71 replacing the two notches 26 and now placed 120 from one another, radiating towards the center in order to receive an anode, not shown, which would be provided three radiating arms 25 instead of two as in the previous embodiment. This device alone would prevent accidental rotation of the anode, and in a better way than by pins 60, which are here omitted.

Above all, the edge 70 has grooves 72 at its top, and a portion 73 of the grooves 72 is free and another portion 74 is shaped with a hook imprint, as shown in Figure 6 which is a section through this portion. The grooves 72 make it possible to insert a handle 75 (FIG. 7) comprising a pair of vertical edges 76 penetrating into the portions 73 and a pair of pins 77 in alignment penetrating into the portions 74. When the handle 75 is engaged in the grooves 72 and raised, it extracts the edge 70.

It has been found that this extraction poses serious practical problems because of the propensity of the slices 7 or 70 to stick when they have been wet. The device described above allows extract the slices more easily, but does not itself allow them to be separated, so that it is still possible to extract several at the same time. The device of FIG. 8 is then used: it is a slide 78 provided with two wings 79 and 80, the second of which is divided by a slot 81. The wing 79 carries a thumb wheel 82 and the two halves of the wing 80 each carry a pawn 83.

The reactor here comprises (FIG. 9) side walls 84 each having a pair of grooves 85 and 86 near their upper edges. When a wafer 70 must be extracted, the upper face of the tank is removed and the slides 78 are installed on the side walls 84 so that their pins 83 enter the groove 85 inside and the knobs 82 of the groove 86 outside. It is then possible to move the slides 78 along the stack of slices 70, to stop them in front of the slice 70 to be extracted and to retain them by a rotation of the wheel 82 which makes it rub against the walls 84. The handle 75 is then slid into the grooves 72 of the section concerned, which is extracted by passing through the slots 81. The slides 78 retain the neighboring sections.

Claims

1) Electrolytic reactor, comprising a conical chamber (13) open at two opposite ends, a support (30) of a part to be coated and an anode (20) arranged in the chamber, respectively towards the wide end and the end narrow, and an electrolyte circulation means through the chamber from the narrow end to the wide end, characterized in that the chamber is composed of stacked and removable sections (7) and of a frame (22, 23 ) holding and tightening the edges.

2) Electrolytic reactor according to claim 1, characterized in that at least one of the wafers contains an imprint (26, 28, 29) at least housing the support portions, of the anode.

3) Electrolytic reactor according to any one of claims 1 to 2, characterized in that the conical chamber at an opening angle less than 20 ° and regular.

4) Electrolytic reactor according to claim 3, characterized in that the circulation of one electrolyte is coaxial with the conical chamber in a tank (1) containing said chamber, and in that it comprises an electrolyte circuit looping on tank.

5) Electrolytic reactor according to claim 4, characterized in that the electrolyte circuit is connected to the narrow end of the chamber by a nozzle (11) having a conical opening extending the chamber. 6) Electrolytic reactor according to any one of claims 1 to 5, characterized in that the support (30) of the part to be coated comprises electrical contacts (38) of cathodic polarization of the part which are arranged around the support, comprise a free end (40) pressed on the part (31), and a connection end (44) extending on a face of the support opposite to the part.

7) Electrolytic reactor according to claim 6, characterized in that the connection ends of the electrical contacts are connected to flexible branches (37) of a star connector (36), united to the support (30) by a mechanism (41 ) with variable spacing, in that the support comprises stops (35) on which the branches flex, and the electrical contacts are in the form of curved hooks standing on the branches.

8) Electrolytic reactor according to any one of the preceding claims, characterized in that the support (30) of part (31) comprises a perimeter and depth housing adjusted to the part (31).

9) Electrolytic reactor according to any one of the preceding claims, characterized in that the support of the part is removably mounted on a frame (64) delimiting the conical chamber.

10) Electrolytic reactor according to any one of the preceding claims, characterized in that the conical chamber, the support of the part to be coated, the part itself and the anode are coaxial. 11) Electrolytic reactor according to claim 5, characterized in that the nozzle (11) is also composed of stacked and removable sections.

12) Electrolytic reactor according to any one of the preceding claims, characterized in that the wafers (70) are provided with individual extraction means (74).

13) Electrolytic reactor according to claim 12, characterized in that it comprises slides (78) movable in grooves (85, 86) of side walls (84) of the tank (1) and hollowed out (81) above a slice (70) to be extracted.

14) Electrolytic reactor according to claim 2, characterized in that said wafer (70) comprises at least three imprints (71) of radiating arms supporting the anode.