DEVICE FOR METALIZING SUBSTRATES

Abstract

A wet-chemical treatment system for electrochemically coating flat substrates with coating material, has having a basin for receiving an electrolyte, a transporting means, by means of which the flat substrates can be transported through the electrolyte horizontally, and at least one contact element which comprises a shaft having an axis of rotation and a cylindrical circumferential surface suitable for rolling on the substrate, wherein the circumferential surface comprises at least one electrically insulated segment and at least one electrically conductive segment which can be connected to a current source in such a way that the polarity can be reversed, wherein the axis of rotation of the contact element is positioned above the surface of the electrolyte, and wherein the contact element is designed as a consumable electrode.

Description

The invention relates to a device for metalizing substrates. In particular, the invention relates to the field of contact elements used to electroplate solar cells in the context of a wet-chemical continuous (in-line) treatment system.

STATE OF THE ART AND DRAWBACKS

In the context of producing electronic elements such as e.g. solar cells, substrates made of semiconductor materials such as e.g. silicon require an at least one sided coating with conductive materials such as e.g. copper. For this, wet-chemical continuous systems (“inline systems”) are used amongst others, by the means of which the substrates laying on transporting rolls are transported. During transport, the substrates are in contact with an electrolyte. For precipitation of the metal contained therein, the substrates are set cathodic.

For producing the electric contact between a current source and the substrate, contact wheels are known that roll off on the substrate. For example, DE 44 13 149 and DE 198 40 471 A1 disclose electroplating systems which use such contact wheels.

It is problematic in this context that not only the substrate but also the conductive part of the contact wheel is metalized. Therefore, both of the aforementioned documents suggest to design the contact wheel in a segmented manner and to de-metalize the contact segment after it has left the surface of the substrate by switching the polarity. An improved solution for this is known from the letters of patent DE 10 2007 055 338. It is suggested to use pairs of contact wheels each mounted on a shaft and triggered in different phases in order to ensure a continuous coating of the substrate. The contact wheels and the mandatory consumable electrodes are completely nested in the electrolyte. In order to protect the contact wheels from coating, it is suggested to use shielding hoods of insulating material which are each to be mounted between contact wheel and consumable electrode.

An alternative solution is e.g. disclosed in EP 0 678 699 B1. However, the sectorless contact rolls as shown therein require auxiliary cathodes and semipermeable membranes to achieve the desired effect thus rendering the construction complicated; in addition, the necessity for often changing the auxiliary cathodes is a disadvantage.

In practice, realizing durably functioning contact wheels proved to be difficult.

Another problem is caused by the high floor space requirement of the known contact wheels resulting in correspondingly voluminous systems. Furthermore, contact wheels that are completely immersed in the electrolyte require costly solutions for driving the substrates in and out of the system, respectively, because the easily breakable substrates have to surmount significant height differences.

Also the maintenance of the known systems with the contact wheels as used therein is costly due to the high number of parts.

Finally, practice has also shown that the coating result often is not sufficiently homogenous.

OBJECT OF THE INVENTION AND SOLUTION

The object of the invention is thus to avoid the drawbacks mentioned above. The invention shall enable a robust and durably functioning electric contacting of substrates to be metalized in wet-chemical continuous systems with low maintenance requirements. A system designed according to the invention shall be smaller than known systems. The maintenance shall be simplified and the coating result, if possible, shall be improved.

The problem is solved by providing a treatment system according to claim 1. Further advantageous embodiments are to be taken from the subclaims, the description and the figures.

DESCRIPTION

A wet-chemical treatment system for the electrochemical coating of flat substrates with coating material that is suitable for carrying out the invention has a basin for receiving an electrolyte and transporting means by the means of which the flat substrates can be transported through the electrolyte horizontally. As transporting means, particularly roller-shaped transporting means on which the substrates lay upon, come into consideration. But also clamps at which hanging substrates are transported, or string-attached bars onto which the substrates lay, are useful as transporting means.

The treatment system further comprises at least a contact element which comprises a shaft having an axis of rotation and a cylindrical circumferential surface suitable to roll on the substrate, wherein the circumferential surface comprises at least one electrically insolated segment and at least one electrically conducting segment that can be connected with a current source in a manner such that the polarity can be reversed. Accordingly, the contact element serves to electrically contact a substrate for its electrochemical treatment (coating). The electric contact between the current source and the substrate is only established when the latter is touched by the electrically conductive segment. Since the circumferential surface during the continuous transport of the substrate rolls off on the same, the conductive and the insolated segment interchange with respect to each other.

The central angle of the electrically conductive segment preferably is between 90° and 270°, with an angle of 180° being particularly preferred. The remaining part of the circumferential angle is attributed to the electrically insolated segment.

While the conductive segment during its contact with the substrate is switched cathodic and thus enables a coating of the substrate, it is switched anodic upon non-contacting the substrate resulting in a de-metallization (“de-coating”) of the segment. In this manner, the thickness of a possible layer of coating material undesirably precipitated onto the segment is reduced rather than enlarged with a net precipitation of coating material being zero. With central angles of the electrically conductive segment deviating from 180°, it is advantageous to optimize the de-coating performance by adapting e.g. the current strength or the speed of rotation.

According to the invention, the axis of rotation of the contact element is positioned above the surface of the electrolyte. This means, that at least half of the circumferential surface of the contact element is outside the electrolyte. Contrary to what is known from the state of the art, the contact element is not completely immersed in the electrolyte. Nevertheless, a de-coating is possible because the circumferential surface upon rotation drags some electrolyte and does not dry out quickly such that the anodic switch of the electrically conductive segment results in delivering of the coating material, which e.g. is copper, to the electrolyte.

Preferably, the distance between the axis of rotation and the substrate side to be contacted running in parallel thereto is 80% to 100% of the radius of the circumferential surface. This means, that only a small part of the circumferential surface is positioned within the electrolyte, with only a line touching between circumferential surface and surface of the electrolyte being possible in boarder case conditions (100%). In this case, the substrate must be transported immediately along the surface of the electrolyte, while in other cases it may lay correspondingly lower. Particularly preferred, the said distance is dimensioned such that at least the shaft and possibly its bearings are positioned outside the electrolyte, if they are not arranged beyond the basin wall, because in such a case there is no danger of damage from aggressive media anyway.

Such a treatment system has the advantage that, due to the arrangement of the typically plurality of present contact elements essentially outside of the electrolyte, it is more robust and durably functioning and requires less maintenance. The reason for this lies in the avoidance of problems encountered with systems of the art with regard to the bearing and sealing of the contact elements within the electrolyte. The mostly aggressive media do no longer or only to a minor extent come into contact with the bearings, resulting in an improved operational life span and a simpler construction of the same.

A further advantage is that a substrate, irrespective of the diameter of the contact element being present there above, has to be guided to a lesser extent below the surface of the electrolyte.

According to the invention, the contact element is furthermore designed as a consumable electrode. This means, that it is at least partly made of coating material such that upon corresponding polarity it continuously delivers coating material to the electrolyte which then deposits onto the substrate.

The advantage of a contact element designed as consumable electrode is that a system comprising such contact elements can be configured significantly smaller because parts are left out.

As soon as the consumable electrode has delivered the major part of its coating material to the electrolyte, it may either be replaced or it may be regenerated by cathodic polarity while simultaneously feeding new coating material which e.g. is introduced into the system or transported through the same in the form of substrate-shaped plates.

By permanently coating and de-coating the consumable electrode, i.e. the electrically conductive parts of the contact element, an oxidation of the same is/are avoided effectively such that a stable process with uniform deposition is achieved.

According to a preferred embodiment, the contact element is designed as a pipe or rod made of coating material, e.g. of copper, and has an electric insulation layer along at least one longitudinal section of its circumferential surface destined for contacting the substrate. However, this insulating layer may also extend to longitudinal sections not destined to contact the substrate, if this is constructively advantageous.

Constructively, this embodiment may be realized particularly easy and cost-effective.

According to another embodiment, the contact element is designed as one or several discs being arranged on the shaft which is designed as pipe or rod.

In the case of an essentially pipe- or rod-shaped contact element it is preferred that the insulating layer is designed as plastic part which can be attached to the circumferential surface and partly covers the same. The attachment may be effected along the longitudinal axis (sliding on) or it can be clipped-on laterally. If the central angle of the insulating segment is smaller than ca. 190°, it is clear that measures are needed to hold the insulating layer at the pipe or rod because otherwise it would fall off. Such measures may e.g. be sections with enlarged central angle which are then located at positions being outside of the substrate track. But also plastic pins which interact with corresponding holes being introduced in the pipe- or rod-shaped shaft may serve to fasten. Preferably, the insulating layer may be used again.

According to a further embodiment, the shaft of the contact element at a free longitudinal or end section not destined for contacting the substrate has a wiper contact surface that rotates with the shaft in order to provide a connection to the current source whose polarity can be switched/reversed. This wiper contact surface interacts with correspondingly positioned, preferably fixed pins or the like which themselves are connected with the poles of the current source and are preferably arranged outside the electrolyte.

The wiper contact surface preferably is designed disc-shaped having two arc-shaped contact strips which are configured to correspond to the segments arranged at the circumferential surface. This means, that their angle of the arc correspond to the two central angles of the segments and are arranged such that a reverse of the polarity just happens when there is a segment change at the substrate surface. It is clear, that both contact strips are connected with the electrically conductive segment.

It is particularly preferred that the wiper contact surface is arranged completely outside the electrolyte. This can e.g. be achieved by providing a corresponding passage in the wall of the basin through which the shaft can be guided. Thus, no problems caused by aggressive media occur at the wiper contact surface. If the shaft has a significantly smaller diameter than the circumferential surface, it is also possible to guide the shaft above the rim of the basin to the outside of the basin, or there is enough place between the lowest point of the wiper contact surface and the surface of the electrolyte such that one has not to fear any liquid contact.

According to a further embodiment, the contact element is also a holding-down means to avoid floating of the substrates. In other words, the contact element is designed and arranged in such a manner that it avoids the flat substrate to float and leave the transportation track. Holding-down means are known in the art but they are exclusively used to guide the substrates, not for electric contacting.

In this way, components can again be omitted resulting in a smaller and more cost-effective construction.

According to another embodiment that can be combined with the above embodiments, the contact element is also a roller-shaped transportation means. In other words, the substrate lays on additional contact elements which then are positioned underneath the same in the electrolyte and which upon rotation provide a continuous transport of the substrate through the basin.

Also by this, mounting parts, particularly separate transporting rolls, can be omitted also resulting in a smaller and more cost-effective construction.

In certain cases the exchange of the electrolyte in the region underneath the substrate—in particular when contact elements are present there—may not be completely satisfying such that a non-sufficiently homogenous coating develops at the substrate underside. Accordingly, a further embodiment provides flush nozzles arranged within the electrolyte for continuously streaming the electrolyte against those parts of the contact element that are also arranged within the electrolyte.

In other cases it may occur that the wetting of the contact element during the phase in which the electrically conductive segment is outside the electrolyte as mentioned above is not completely satisfying. Therefore, a further and preferred embodiment provides flush nozzles which are arranged outside the electrolyte, i.e. above its surface, in order to continuously wet those parts of the contact element with the electrolyte which are also outside the electrolyte. In other words, the flush nozzles eject the electrolyte from the basin and/or e.g. from a separate reservoir in direction of the contact elements such that these are to a large extent completely wetted. In this manner, the construction can be kept simple as described above without questioning the success in de-metallization.

The present invention solves the problems known in the art in a simple and effective manner. It provides a robust and durably functioning electric contacting of substrates to be metalized in wet-chemical continuous systems with low maintenance requirements. A system according to the invention is smaller than known systems. Maintenance is simplified and the preferred embodiment of the invention improves the coating result.

DESCRIPTION OF THE FIGURES

In FIG. 1 the invention is exemplified schematically.

A flat substrate 1 in the form of a solar cell is arranged in an electrolyte (not shown). Its upper side is touched by a contact element 2, i.e. by an electrically conductive segment 3A of the same. The circumferential surface of the contact element 2 as shown serving to touch the substrate 1 is disc-shaped, although it can also be cylindrical according to an embodiment not shown.

Opposite to the electrically conductive segment 3A, an electrically insulated segment 3B is arranged.

The contact element 2 has a shaft 4 with an axis of rotation 5 around which the contact element 2 and in particular the circumferential surface can rotate (arrow 7). The conductive components being in contact with the electrolyte (conductive segment 3A, shaft 4) consist at least partly of a material that is suitable for consumption and thus represent a consumable electrode. As shown, an additional consumable electrode 12 that is separate from the device according to the invention and electrically connected with the current source 6 is arranged in the electrolyte, although it can be omitted advantageously according to a preferred embodiment not shown.

At an end section 8 not destined for contacting the substrate 1 the contact element 2 has a wiper contact surface 9 which rotates with the shaft 4 to generate a connection with the current source 6 in such a manner that the polarity can be reversed. This wiper contact surface 9 is preferably completely, but at least partly arranged outside of the electrolyte, and interacts with correspondingly arranged wiper contacts 10 which themselves are connected with the poles of the current source 6.

The wiper contact surface 9 as shown is designed disc-shaped and has two arc-shaped contact strips 11A, 11B which are designed in correspondence with the segments 3A, 3B being arranged at the circumferential surface. This means that their angles of the arc correspond to the two central angles of the segments 3A, 3B and are arranged such that a switching of polarity just happens when there is a segment change at the substrate surface. It is clear, that both contact strips are connected with the electrically conductive segment 3A which, as shown, can be achieved via the shaft 4.

The contact strip 11A thus provides the contact region for the de-coating of the contact element, and the contact strip 11B serves as contact region for the coating of the substrate. Not shown are electrical connections from the contact strips to the conductive part of the circumferential surface or to the shaft, respectively.

REFERENCE LIST

• 1 Substrate
• 2 Contact element
• 3A Electrically conducting segment
• 3B Electrically insolated segment
• 4 Shaft
• 5 Axis of rotation
• 6 Current source
• 7 Arrow
• 8 Longitudinal or end section not destined for contacting
• 9 Wiper contact surface
• 10 Wiper contact
• 11A Contact strip
• 11B Contact strip
• 12 Consumable electrode

Claims

1. A wet-chemical treatment system for electrochemically coating flat substrates (1) with coating material, with a basin for receiving an electrolyte, a transporting means, by means of which the flat substrate (1) can be transported horizontally through the electrolyte, and with at least one contact element (2) which comprises a shaft (4) having an axis of rotation (5) and a cylindrical circumferential surface suitable for rolling on the substrate (1), wherein the circumferential surface comprises at least one electrically insolated segment (3B) and at least one electrically conductive segment (3A) which can be connected to a current source (6) in such a way that the polarity can be reversed, wherein the axis of rotation (5) of the contact element (2) is positioned above the surface of the electrolyte, and wherein the contact element (2) is designed as a consumable electrode.

2. The treatment system according to claim 1, wherein the contact element (2) is designed as a pipe or rod of coating material and has an electrically insolating layer along at least one longitudinal section of its circumferential surface destined for contacting the substrate (1).

3. The treatment system according to claim 2, wherein the insolating layer is designed as a plastic piece which can be mounted on the circumferential surface.

4. The treatment system according to claim 1, wherein the shaft (4) of the contact element (2) at a longitudinal or end section (8) not being destined for contacting the substrate (1) has a wiper contact surface (9) for its commutatable connection to the current source (6).

5. The treatment system according to claim 4, wherein the wiper contact surface (9) is positioned completely outside of the electrolyte.

6. The treatment system according to claim 1, wherein the contact element (2) is a holding-down means to avoid the substrates (1) to float.

7. The treatment system according to claim 1, wherein the contact element (2) is a cylindrical transporting means.

8. The treatment system according to claim 1, wherein flush nozzles are positioned within the electrolyte for the continuous flow of the electrolyte against those parts of the contact element (2) which are also positioned within the electrolyte.

9. The treatment system according to claim 1, wherein flush nozzles are positioned outside the electrolyte for the continuous wetting of those parts of the contact element (2) with the electrolyte which are also positioned outside the electrolyte.