Apparatus and method for reducing oxides on workpiece surfaces

Abstract

The invention relates to an apparatus (50, 150) for reducing oxides on workpiece surfaces, having a treatment tunnel (52) which runs from an inlet opening (54) to an outlet opening (56), having a reaction region (82) arranged inside the treatment tunnel (52), with a plasma nozzle (2, 84) which is designed to generate an atmospheric plasma jet (28, 88), having a reducing gas supply (74) which is designed to introduce a reducing gas (23) into the reaction region (82), and having a transport apparatus (58) which is designed to transport workpieces (80) through the treatment tunnel (52), wherein the plasma nozzle (2, 84) is arranged and designed so as to introduce the atmospheric plasma jet (28, 88) into the reaction region (82) during operation. The invention further relates to the use of the apparatus (50, 150) and to a method for reducing oxides on workpiece surfaces.

Description

[0001] Device and method for reducing oxides on

[0002] Workpiece surfaces

[0003] The present invention relates to a device and a method for reducing oxides on workpiece surfaces. Furthermore, the invention relates to the use of such a device.

[0004] It is known from the prior art to reduce oxides on metallic workpiece surfaces using low-pressure plasma. For example, oxides on workpiece surfaces are reduced to achieve better wettability of the workpiece surfaces or to create an electrically conductive connection, for example, a soldered connection. This is particularly advantageous for subsequent process steps on the workpieces, such as bonding or soldering to other workpieces. A method for removing oxides using low-pressure plasma treatment is described, for example, in WO 00 / 29642 A1. However, due to the required in- and out-feed processes, such low-pressure processes have the disadvantage that they can only be integrated into continuous production operations with considerable technical effort.

[0005] Attempts have also been made to use atmospheric plasma to reduce metal surfaces. However, these experiments have not always been successful.

[0006] Against this background, the object of the present invention is to provide an improved device and an improved method for reducing oxides on workpiece surfaces, which are particularly suitable for inline use.This object is achieved according to the invention by a device for reducing oxides on workpiece surfaces, comprising a treatment tunnel which runs from an inlet opening to an outlet opening, a reaction region arranged within the treatment tunnel, a plasma nozzle which is designed to generate an atmospheric plasma jet, a reducing gas supply which is designed to introduce a reducing gas into the reaction region, and a transport device which is designed to transport workpieces through the treatment tunnel, wherein the plasma nozzle is arranged and designed to introduce the atmospheric plasma jet into the reaction region during operation.

[0007] By introducing the plasma jet into the reaction area, the gas volume in the reaction area can be excited or activated so that oxides on the workpiece surface of workpieces transported through the reaction area are reduced.

[0008] Preferably, the plasma nozzle is also arranged and configured to expose workpieces transported through the treatment tunnel with the transport device in the reaction zone to the atmospheric plasma jet. By directing the atmospheric plasma jet onto the workpieces during operation, the effect of the plasma jet on the workpiece surface can be intensified, resulting in more effective oxide reduction.

[0009] In addition, by applying the plasma jet to the workpieces, the heat input into the workpieces during reduction can be increased, thereby accelerating the reduction treatment.

[0010] It was recognized that a problem with the reduction of metal surfaces using plasma in inline operation is that plasma-reduced

[0011] Workpiece surfaces are particularly prone to reoxidation immediately after plasma treatment, thus reducing the effects of the prior reduction. In particular, experiments have shown that exposing a metal surface to an atmospheric plasma jet to reduce oxides leads to significant heating of the metal surface, which promotes subsequent reoxidation in an oxygen-containing atmosphere. Furthermore, the interaction of the atmospheric plasma with the metal surface can lead to a modification, particularly activation, of the metal surface, which promotes reoxidation.

[0012] By arranging the reaction zone, into which an atmospheric plasma jet is introduced, in particular in which preferably a workpiece surface is exposed to an atmospheric plasma jet to reduce oxides, within a treatment tunnel through which the workpiece is transported by means of a transport device, a device for reducing oxides on workpiece surfaces using plasma is provided that can be easily integrated into a continuously operating inline process, in particular a manufacturing process. In particular, the workpieces to be treated can be moved one after the other through the reaction zone in a controlled manner and subjected to the reduction treatment there. Secondly, the reaction zone is shielded from the direct influence of the environment by the treatment tunnel.In this way, the environmental conditions acting on a treated workpiece in the reaction zone and in the part of the treatment tunnel adjacent to the reaction zone can be better controlled, thus reducing reoxidation processes. In particular, a reducing and oxygen-poor or oxygen-free atmosphere can be more easily maintained in the reaction zone and the adjacent part of the treatment tunnel to reduce or prevent reoxidation of the workpiece surface immediately after the reduction treatment.

[0013] The device can, in particular, comprise a housing, for example a metal housing, which forms the treatment tunnel. During operation, the workpieces to be treated enter the treatment tunnel through the inlet opening and exit the tunnel through the outlet opening after treatment in the reaction area. Compared to vacuum- or low-pressure-based

[0014] Treatment devices eliminate the need for in- and out-feed processes, making the device ideal for inline operation. The inlet and / or outlet openings can be designed as simple openings through which the workpieces to be treated can enter and exit the treatment tunnel. To further separate the atmosphere in the treatment tunnel from the surroundings, a curtain, such as a strip curtain, can optionally be provided at the inlet and / or outlet openings.

[0015] In particular, the treatment tunnel is essentially at atmospheric pressure. In order to reduce or prevent the penetration of oxygen-containing air from the environment into the treatment tunnel, a slight overpressure compared to the ambient pressure can also prevail in the treatment tunnel. The overpressure can be achieved, for example, via the reducing gas supply or via a separate gas supply, e.g. a purge gas supply. The treatment tunnel preferably has at least a predetermined minimum length between the inlet opening and the reaction region and / or between the reaction region and the outlet opening, which can be, for example, 5 cm, preferably 10 cm, more preferably 20 cm. For example, the distance between the inlet opening and the reaction region and / or between the reaction region and the outlet opening can be in the range of 5 to 50 cm.In this way, the influence of the ambient atmosphere on the workpiece during or shortly after the reduction treatment is reduced. Preferably, the minimum length is greater than the height of the treatment tunnel. The treatment tunnel can, for example, have a width of a few centimeters, for example, 10 cm, up to several meters, for example, 3 m, and / or a height of a few centimeters, for example, 5 cm, up to several tens of centimeters, for example, 20 cm. In particular, the dimensions of the treatment tunnel can be adapted to the dimensions of the workpieces to be treated.

[0016] Between the inlet opening and the reaction area and / or between the reaction area and the outlet opening, the treatment tunnel preferably has a cross-section that is reduced compared to the reaction area.

[0017] In this way, the influence of the ambient atmosphere on the workpiece can be further reduced during or shortly after the reduction treatment.

[0018] The plasma nozzle is designed to generate an atmospheric plasma jet. For this purpose, the plasma nozzle preferably has a

[0019] Working gas supply for supplying the plasma nozzle with a working gas as well as a nozzle opening from which the plasma jet emerges during operation. The atmospheric plasma jet operates in the atmospheric pressure range, in particular at ambient pressure or a slight overpressure. In this way, complex negative pressure environments are unnecessary. In order to expose workpieces transported through the treatment tunnel in the reaction area with the atmospheric plasma jet during operation with the transport device, the plasma nozzle can preferably be arranged in or on the reaction area. For example, the housing of the device in the reaction area can have a receptacle into which the plasma nozzle is inserted. Furthermore, the treatment tunnel can be

[0020] The reaction area can have a plasma jet inlet opening which is connected to a nozzle opening of the plasma nozzle so that the plasma jet reaches the reaction area during operation. The plasma jet inlet opening and / or the nozzle opening of the plasma nozzle are preferably arranged such that the plasma jet is directed during operation onto an area of ​​the transport device in which workpieces are transported through the reaction area. The transport device is particularly designed to transport workpieces to be treated from the inlet opening through the treatment tunnel to the outlet opening. For example, the transport device can be designed as a conveyor belt on which the workpieces to be treated can be transported from the inlet opening through the treatment tunnel to the outlet opening. The transport device can be part of a larger transport system of an inline process with multiple stations.For example, it is conceivable that a conveyor belt is provided with which workpieces are transported through various processing and / or treatment stations, one of which is the device described here for reducing oxides on workpiece surfaces.

[0021] The transport device preferably has a drive with an adjustable conveying speed. In this way, the treatment time of the workpieces in the reaction zone can be specifically adjusted. Good reduction results on workpiece surfaces have been achieved, for example, at a conveying speed in the range of 0.1–10 m / min, in particular in the range of 0.3–0.6 m / min. The transport device can be configured to transport the workpieces through the treatment tunnel at a constant speed. Alternatively, the transport device can be configured to slow down the transport of the workpieces in certain areas of the treatment tunnel, for example in the reaction zone, or to pause it for a certain period of time. In this way, the reduction treatment on the workpieces can be influenced.

[0022] The reducing gas supply is configured to introduce a reducing gas into the reaction zone. For this purpose, the reducing gas supply can, in particular, comprise a reducing gas source for providing a reducing gas, for example, a gas cylinder containing a reducing gas, as well as a reducing gas line through which the reducing gas is introduced from the reducing gas source into the reaction zone. The reducing gas supply can be configured to introduce the reducing gas into the reaction zone at a predetermined or predeterminable gas supply rate. For this purpose, the reducing gas supply can, for example, comprise an adjustable valve. In this way, the gas supply rate can be specifically adjusted, for example, to suit the material of the workpieces to be treated and / or depending on the speed of the transport device.Suitable gas feed rates can be, for example, in a range of 5-50 1 / min, preferably 20-40 1 / min, particularly preferably about 35 1 / min, so that sufficient reducing gas can be made available for the reduction and at the same time reoxidation can be prevented.

[0023] The reducing gas is preferably a hydrogen-containing gas, for example a mixture of hydrogen and an inert gas such as nitrogen or argon.

[0024] It has been found that when dissociated hydrogen is applied to an oxidized metal surface through a plasma process, the reduction of metals can be carried out at relatively low temperatures. In this way, workpiece surfaces made of metals with a low melting point, such as tin with a melting point of approximately 230 °C, can be effectively reduced.

[0025] A hydrogen content of the reducing gas of 1 to 10 vol.%, preferably 2 to 5 vol.%, has proven particularly advantageous for the effective reduction of oxides on workpiece surfaces, especially metallic workpiece surfaces. Further components of the working gas can be, in particular, nitrogen and argon. Inert gases are particularly advantageous as working gases because they participate only with difficulty in chemical reactions and are therefore well suited as carrier gases, for example for hydrogen as a reducing gas. A possible reducing gas is forming gas, for example with a hydrogen content (H2) of 5 vol.% and a nitrogen content (N2) of 95

[0026] Vol%.

[0027] The reducing gas is in particular oxygen-free or has an oxygen content of less than 1 vol.%, in particular less than 0.3 vol.%.

[0028] Furthermore, the above-mentioned object is achieved according to the invention by the use of the previously described device or an embodiment thereof for the reduction of oxides on workpiece surfaces, in particular metallic workpiece surfaces.

[0029] The above-mentioned object is further achieved according to the invention by a method for reducing oxides on workpiece surfaces using the device described above or an embodiment thereof, in which one or more workpieces are transported through the treatment tunnel using the transport device, in which an atmospheric plasma jet is generated using the plasma nozzle, in which a reducing gas is introduced into the reaction area, and in which the atmospheric plasma jet is introduced into the reaction area.

[0030] Preferably, the one or more workpieces transported through the treatment tunnel are exposed to the atmospheric plasma jet in the reaction area.

[0031] In particular, the device and the method serve to reduce oxides on at least partially metallic workpiece surfaces of a workpiece that consists at least partially of metal or a metal alloy. The metal can be, for example, aluminum, copper, silver, iron, nickel, titanium, chromium or tin. More preferably, the device is used in an inline process in which the treated workpiece surface is subsequently subjected to a soldering process. It has been found that the use of the device according to the invention or the method according to the invention for reducing oxides on workpiece surfaces to be soldered achieves improved wetting of the workpiece surface with solder, so that less flux needs to be used or can even be dispensed with entirely. This allows for more environmentally friendly, less hazardous to health and more cost-effective soldering processes.

[0032] Various embodiments of the device, its use, and the method are described below. Each of the individual embodiments applies independently to the device, its use, and the method. Furthermore, the individual embodiments can be combined with one another.

[0033] In one embodiment, the plasma nozzle is configured to generate an atmospheric plasma jet by means of a high-frequency, high-voltage discharge, in particular between at least two electrodes. In particular, the plasma nozzle can be configured to generate the plasma jet by means of a high-frequency arc-like discharge in a working gas. A plasma jet generated in this way is easy to align and has proven very effective in reducing oxides on metallic surfaces.

[0034] To generate the arc-like electrical discharge, at least two electrodes can be provided, as well as a voltage source for applying a high-frequency high voltage to the electrodes. The high-frequency high voltage for generating a high-frequency arc-like discharge has, in particular, a voltage in the range of 1-100 kV, preferably 1-50 kV, more preferably 10-50 kV, and a frequency of 1-300 kHz, in particular 1-100 kHz, preferably 10-100 kHz, more preferably 10-50 kHz. Furthermore, the plasma nozzle can be configured to generate the atmospheric plasma jet by means of direct barrier discharges (DBD). Due to the low temperature of the plasma jet generated by DBD, this type of discharge is particularly suitable for applying to temperature-sensitive surfaces.To generate the dielectrically impeded discharge, at least two electrodes and a dielectric arranged therebetween can be provided, which prevents a direct electrical discharge between the two electrodes. Preferably, one of the electrodes is grounded. Furthermore, a voltage source is provided, in particular, to apply a high-frequency high voltage to the electrodes, for example, with a voltage intensity in the range of 5 to 15 kV and a voltage frequency in the range of 7.5 to 25 kHz, in particular 13 to 14 kHz.

[0035] In a further embodiment of the device, the reducing gas supply is designed to supply the reducing gas to the plasma nozzle as a working gas. In a corresponding embodiment of the method, the reducing gas is introduced into the plasma nozzle as a working gas. In this way, the reducing gas can be introduced directly through the plasma nozzle into the reaction zone, eliminating the need for a reducing gas inlet opening separate from the plasma nozzle into the reaction zone. However, it is equally conceivable for the reducing gas supply to have a reducing gas inlet opening separate from the plasma nozzle in order to introduce the reducing gas into the reaction zone. By supplying the reducing gas to the plasma nozzle as a working gas, the reducing gas in the plasma nozzle is strongly excited, thereby achieving a strong reduction effect.In a further embodiment of the device, the reducing gas supply is configured to introduce the reducing gas into the reaction zone through a reducing gas inlet opening separate from the plasma nozzle. In a corresponding embodiment of the method, the reducing gas is introduced into the reaction zone through a reducing gas inlet opening separate from the plasma nozzle. In this way, the reducing gas flow can be adjusted independently of the working gas flow of the plasma nozzle. Furthermore, the working gas of the plasma nozzle can be freely selected in this way. For example, an inert gas can be used as the working gas of the plasma nozzle in order to extend the service life of the plasma nozzle.However, it is also conceivable that the reducing gas supply is designed to supply the reactive gas both to the plasma nozzle as a working gas and to introduce it into the reaction area via a reducing gas inlet opening separate from the plasma nozzle.

[0036] The reducing gas supply is preferably configured to introduce the reducing gas into the reaction zone at atmospheric pressure or under overpressure. In this way, the reaction zone can be effectively filled with reducing gas, so that, in particular, the workpieces transported through the reaction zone during operation are surrounded by the gas to be reduced.

[0037] In a further embodiment, a purge gas supply is provided which is designed to introduce a purge gas into the treatment tunnel, in particular into the reaction region. The purge gas supply is preferably designed to introduce the purge gas into the treatment tunnel, in particular into the reaction region, under atmospheric pressure or under overpressure. The treatment tunnel, in particular the reaction region, can be purged by the purge gas before, during and / or after operation in order to reduce the oxygen content in the treatment tunnel. For this purpose, in particular an oxygen-free purge gas is used or a purge gas whose oxygen content is less than 1 vol.%, preferably less than 0.3 vol.%. An inert gas, for example argon or nitrogen, is preferably used as the purge gas.By introducing a purge gas into the treatment tunnel, especially into the reaction zone, reoxidation of the reduced workpiece surfaces can be reduced or even prevented, allowing the device to achieve an overall improved reduction of oxides on workpiece surfaces. Suitable gas supply rates for purge gases are, for example, in the range of 1-30 rpm, preferably 5-15 rpm.

[0038] The purge gas supply can in particular comprise a purge gas source for providing a purge gas, for example a gas cylinder with a purge gas, as well as a purge gas line through which the purge gas is introduced from the purge gas source into the reaction area.

[0039] Particularly advantageously, the purge gas supply can be configured to introduce purge gas into the treatment tunnel, in particular into the reaction zone, even before the plasma nozzle is operated. Thus, the treatment tunnel, in particular the reaction zone, is purged, in particular substantially freed of oxygen, even before the workpiece surfaces are exposed to the atmospheric plasma jet, so that reoxidation of the reduced workpiece surfaces is further reduced.

[0040] The purge gas supply can be configured to introduce the purge gas into the treatment tunnel, in particular into the reaction zone, through a separate purge gas supply. The purge gas supply can also be configured to introduce the purge gas into the reaction zone through a provided reducing gas inlet opening. In this way, reducing gas and purge gas can be introduced into the reaction zone simultaneously or sequentially through the same reducing gas inlet opening. In particular, the reducing gas supply and the purge gas supply can be combined with one another, so that, for example, a gas supply is provided that is configured to introduce a reducing gas and / or a purge gas into the reaction zone.

[0041] In a further embodiment, the plasma nozzle has a nozzle head from which the plasma jet emerges during operation and which rotates about a rotational axis during operation. The plasma jet emerges from the nozzle head, in particular at an oblique angle to the rotational axis. In this way, a larger area can be effectively covered by the plasma jet, so that a larger gas volume can be excited by the plasma jet, and in particular, larger portions of the workpiece surfaces of the workpieces transported through the reaction zone can be exposed to the plasma jet. In this way, a larger area of ​​workpiece surfaces can be subjected to reduction treatment in a shorter time.

[0042] In a further embodiment, a heating element and / or a cooling element are provided which are designed to heat and / or cool the workpieces transported through the treatment tunnel.

[0043] By providing a heating element, particularly in an area of ​​the treatment tunnel between the entrance opening and the reaction zone, the workpiece can be preheated for the reduction treatment in the treatment chamber, thereby enhancing the reduction effect. Furthermore, heating the workpiece can achieve an improved depth of reduction of oxides on the workpiece surfaces, since the depth of reduction depends, among other things, on the diffusion of atomic hydrogen into the workpiece surface, which is favored at higher temperatures.

[0044] By providing a cooling element, particularly in a region of the treatment tunnel between the reaction region and the exit opening, the heat energy introduced by the plasma treatment can be at least partially removed from the workpiece. In this way, the workpiece has a lower temperature when it comes into contact with oxygen again, whereby reoxidation of the workpiece surfaces can be effectively reduced or even largely avoided. In particular, a lower workpiece surface temperature results in a lower oxidation rate of the workpiece surface. The heating element and / or cooling element can be designed as active or passive elements. Furthermore, temperature control can be provided, in particular a controlled heating element and / or a controlled cooling element can be used.With controlled elements, the temperature of the heating elements can be adjusted depending on the workpiece materials so that the melting point is not exceeded and degradation of the workpieces is prevented. This is particularly advantageous when reducing metal surfaces with a low melting point, such as tin.

[0045] In a further embodiment, the plasma nozzle or an optionally provided separate coating plasma nozzle is configured to apply a protective layer by means of plasma coating to workpieces transported through the reaction zone during operation and exposed to the atmospheric plasma jet in the reaction zone. For this purpose, a precursor feed is provided, in particular, which is configured to introduce a precursor into the plasma jet generated by the plasma nozzle or the coating plasma nozzle.

[0046] In this way, after the reduction of oxides on the workpiece surface by means of plasma coating through the plasma nozzle or the optionally provided coating plasma nozzle, the workpieces can be provided with a protective layer in order to protect the reduced workpiece surface from further oxidation.

[0047] The protective layer can, for example, be an organic layer, for example a hydrocarbon-containing layer, in particular a plastic layer. The protective layer is preferably an organosilicon protective layer. By covering the workpiece surface with an organic protective layer, oxygen can be kept away from the workpiece surface, thus preventing the formation of metal oxides with metal atoms on the workpiece surface. The protective layer can also be an inorganic layer, in particular a silane layer or a metal or semiconductor oxide layer such as a TiO2 or SiO2 layer. It has been found that oxidation of the metal on the workpiece surface can also be prevented by such a protective layer. In particular, it has been found that the amount of oxygen contained in the metal or...The oxygen contained in the oxide layer of a semiconductor oxide layer does not tend to bond with the metal on the workpiece surface. Furthermore, a metal or semiconductor oxide layer can provide good oxidation protection for the workpiece surface even with a very thin layer thickness.

[0048] To prevent oxidation of the workpiece surface during the deposition of a metal or semiconductor oxide layer as a protective layer, the plasma nozzle or the optionally provided coating plasma nozzle can be configured to generate the plasma jet generated by the plasma nozzle or the coating plasma nozzle using an oxygen-free working gas. An oxygen-containing precursor can then be used to form the metal or semiconductor oxide layer, which is, for example, introduced into the plasma jet generated by the plasma nozzle or the coating plasma nozzle. It has been found that the formation of the metal or semiconductor oxide layer from the precursor occurs so quickly that oxidation of the workpiece surface by the oxygen contained in the precursor practically does not occur.

[0049] The protective layer can be removed before a subsequent processing step or alternatively remain on the workpiece surface.

[0050] The application of a layer by means of plasma coating, in particular plasma polymerization, is generally known and therefore need not be described in detail here. To produce an organic, in particular organosilicon, protective layer, an organic or organosilicon precursor is preferably used as the precursor. Suitable precursors include, for example, hexamethyldisiloxane (HMDSO), tetraethylorthosilicate (TEOS), 3-trimethoxysilylpropyl methacrylate (MEMO), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (Ds), dodecamethylcyclohexasiloxane (D6), and generally aminosilanes, triethoxysilanes, organosilanes, organosilanols, siloxanes, polysilazanes, and carbosilanesilanes.

[0051] Other possible precursors are, in particular, functionalized organosilicon compounds with epoxy groups such as 3-glycidoxypropyltrimethoxysilane, with acrylate groups such as γ-methacryloxypropyltrimethoxysilane, with amino groups such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane or [3-(2-aminoethyl)aminopropyl]trimethoxysilane, with vinyl groups such as vinyltrimethoxysilane or 1,3-divinyltetramethyldisiloxane, with thiol groups such as (3-mercaptopropyl)trimethoxysilane or sulfane groups such as bis [3-

[0052] (triethoxysilyl)propyl]tetrasulfide. Furthermore, purely organic, i.e., aliphatic, cyclic, and aromatic precursors can also be used, such as heptane, 1-hexene, 1-octene, 1-heptyne, 1,7-octadiene, 1,5-hexadiene, 1,5-cyclooctadiene, toluene, acetylene, and xylenes.

[0053] Furthermore, a Si-based precursor comprising chemical Si-O bonds in combination with a) an organically polar chain, in particular a hydroxyl, amino, carboxylic acid, imido, anhydrite, ester, or epoxy chain, and / or b) an organically apolar chain, in particular a methyl, ethyl, propyl, vinyl, or butyl chain, can be used as a precursor. Furthermore, metal alkoxides, in particular a Si, Ti, Zn, Al, Zr, or Sr alkoxide, can be used as precursors, in particular for plasma coating with a metal oxide protective layer.

[0054] The application of a protective coating can, for example, take place in the reaction zone. For this purpose, the plasma nozzle and the coating plasma nozzle can be operated alternately, for example. If the reduction treatment and the coating with a protective coating are carried out using a plasma nozzle, the precursor supply can, for example, be switched on and off alternately with the precursor supply. The transport device can, for example, be configured to stop the transport of the workpieces in the reaction zone so that a reduction treatment and a plasma coating can take place there one after the other.

[0055] Furthermore, the application of a protective coating can also take place in a separate coating area. For this purpose, in a further embodiment, a coating area is arranged between the reaction area and the exit opening, and the coating plasma nozzle is configured to apply a protective coating to workpieces transported through the coating area by means of plasma coating during operation with the transport device. This enables, in particular, a continuous reduction treatment in the reduction area and a continuous plasma coating in the coating area without the two treatments interfering with each other.

[0056] By providing a coating plasma nozzle in the coating area, the device can be configured to simultaneously and independently perform a reduction treatment on workpieces and a plasma coating on workpieces that have already undergone a reduction treatment. This enables, in particular, continuous transport of workpieces through the treatment tunnel, preferably at a constant speed, and thus facilitates easier inline installation of the device. Furthermore, contamination of the reaction area with precursor can be reduced in this way.

[0057] To further decouple the reduction treatment and the plasma coating, the reaction zone and the coating zone are preferably spaced apart from each other. The treatment tunnel preferably has a reduced cross-section in the area between the reaction zone and the coating zone compared to the reaction zone and / or the coating zone.

[0058] In a further embodiment, the device comprises a control device for controlling the device. In particular, the control device can be configured to control the operation of the plasma nozzle and / or the optional coating plasma nozzle, the reducing gas supply and / or the optional purge gas supply, the transport device, and / or the optional cooling and / or heating elements. In this way, the device and the method can be automated, simplifying handling and standardizing the reduction of oxides on workpiece surfaces.Furthermore, this method allows for automatic adjustment of process parameters, such as gas feed rates into the treatment tunnel, especially into the reaction zone, the transport speed of the workpieces through the reaction and / or coating zone, and / or the control of the heating and / or cooling elements on workpiece surfaces of different materials, as well as the use of different gas mixtures. Overall, this method allows for effective reduction of oxides on workpiece surfaces of different materials.

[0059] Further features and advantages of the device, the use and the method will become apparent from the following description of exemplary embodiments, with reference to the accompanying drawings.

[0060] Fig. 1 a plasma nozzle for generating an atmospheric plasma jet with a nozzle head that rotates around a rotation axis during operation,

[0061] Fig. 2 shows a first embodiment of the device and method for reducing oxides on workpiece surfaces and

[0062] Fig. 3 shows a second embodiment of the device and method for reducing oxides on workpiece surfaces.

[0063] Before discussing a first embodiment of the device described here, the basic structure and functional principle of a plasma nozzle suitable for the device described here will first be explained using the plasma nozzle shown in Fig. 1.

[0064] Fig. 1 shows a schematic sectional view of a plasma nozzle for generating a plasma jet by means of a high-frequency high-voltage discharge in the form of an arc-like discharge.

[0065] The plasma nozzle 2 comprises a tubular housing 10, which is enlarged in diameter in its upper region (in the drawing) and is rotatably mounted on a fixed support tube 14 by means of a bearing 12. The upper part of a nozzle channel 16 is formed inside the housing 10, which leads from the working gas supply 25 to a nozzle opening 18.

[0066] An electrically insulating ceramic tube 20 is inserted into the support tube 14. A working gas 23, for example a reducing gas, is fed through the working gas supply 25 and through the support tube 14 and the ceramic tube 20 into the nozzle channel 16. With the aid of a swirl device 22 inserted into the ceramic tube 20, the working gas 23 is wired such that it flows in a vortex pattern through the nozzle channel 16 toward the nozzle opening 18, as symbolized in the drawing by a helical arrow 40. This creates a vortex core in the nozzle channel 16 that runs along the axis A of the housing 10.

[0067] Mounted on the swirl device 22 is a pin-shaped inner electrode 24, which projects coaxially into the upper part of the nozzle channel 16 and to which a high-frequency high voltage is applied by means of a high-voltage generator 26. The high-frequency high voltage can have a voltage in the range of 1-100 kV, preferably 1-50 kV, more preferably 1-10 kV, and a frequency of 1-300 kHz, in particular 1-100 kHz, preferably 10-100 kHz, more preferably 10-50 kHz. The high-frequency high voltage can be a high-frequency alternating voltage, but also a pulsed direct voltage, or a superposition of both voltage forms.

[0068] The metal housing 10 is grounded via the bearing 12 and the support tube 14 and serves as a counter electrode so that an electrical discharge 42 can be generated between the inner electrode 24 and the housing 10.

[0069] The inner electrode 24 arranged within the housing 10 is preferably aligned parallel to the axis A, in particular the axis A can run through the inner electrode 24.

[0070] The nozzle opening 18 of the nozzle channel is formed by a metal nozzle head 30, which is screwed into a threaded bore 32 of the housing 10 and in which a channel 34 is formed that tapers towards the nozzle opening 18 and is arc-shaped and runs obliquely with respect to the axis A, forming the lower part of the nozzle channel 16 up to the nozzle opening 18. In this way, the plasma jet 28 emerging from the nozzle opening 18 forms an angle with the axis A of the housing, which in the example shown is approximately 45°. This angle can be varied as required by replacing the nozzle head 30. The nozzle head 30 is thus arranged at the end of the discharge path of the high-frequency arc discharge 42 and is grounded via the metallic contact with the housing 10. The nozzle head 30 thus channels the outflowing gas and plasma jet 28, wherein the direction of the nozzle opening 18 runs at a predetermined angle to the axis A.

[0071] Since the nozzle head 30 is connected to the housing 10 in a rotationally fixed manner, and since the housing 10 is in turn rotatably mounted relative to the support tube 14 via the bearing 12, the nozzle head 30 can rotate relatively about the axis A. In this embodiment, the axis of rotation therefore coincides with the housing axis A. A gear 36 is arranged on the extended upper part of the housing 10, which is drive-connected to a rotary drive 38, such as a motor, for example, via a toothed belt or a pinion 37.

[0072] During operation of the plasma nozzle 2 by the high-frequency high voltage, an arc discharge 42 is generated between the inner electrode 24 and the housing 10 due to the high frequency of the voltage. The arc of this high-frequency arc discharge is entrained by the incoming working gas 23 and channeled in the core of the vortex-shaped gas flow, so that the arc 42 then runs almost straight from the tip of the inner electrode 24 along the axis A and only branches radially onto the housing wall or the wall of the nozzle head 30 in the region of the lower end of the housing 10 or in the region of the channel 34. In this way, a plasma jet 28 is generated, which exits through the nozzle opening 18.

[0073] The terms "arc" and "arc discharge" are used here as a phenomenological description of the discharge, since the discharge occurs in the form of an arc. The term "arc" is also used elsewhere as a discharge form for DC discharges with essentially constant voltage values. In this case, however, it is a high-frequency discharge in the form of an arc, i.e., a high-frequency arc discharge.

[0074] During operation, the housing 10 rotates at high speed about the axis A, so that the plasma jet 28 describes a conical surface that sweeps over the surface of a workpiece (not shown) to be treated. When a workpiece is then moved along the plasma nozzle 2, a relatively uniform treatment of the workpiece surface is achieved along a strip whose width corresponds to the diameter of the cone described by the plasma jet 28 on the workpiece surface. By varying the distance between the nozzle head 30 and the workpiece, the width of the pre-treated area can be influenced. The plasma jet 28, which is itself wired and impinges on the workpiece surface at an angle, achieves an intensive effect of the plasma on the workpiece surface. The direction of swirl of the plasma jet can be the same or opposite to the direction of rotation of the housing 10.The intensity of the plasma treatment by the rotating plasma jet 28 depends on the distance of the nozzle opening 18 to the surface and the angle of incidence of the plasma jet 28 on the surface to be treated as well as on the relative speed between the workpiece and the plasma nozzle 2.

[0075] Figure 2 shows a first embodiment of the device and the method for reducing oxides on workpiece surfaces in a schematic view.

[0076] The device 50 comprises a housing 51, for example made of metal, which surrounds a treatment tunnel 52 having an inlet opening 54 and an outlet opening 56 for the introduction and removal of workpieces 80. Furthermore, a transport device 58 is provided for transporting workpieces 80. In the present example, the transport device is in the form of a conveyor belt 62 that runs over drive rollers 60 driven by a motor 61. A reaction region 82 is provided in the treatment tunnel 52, spaced apart from the inlet opening 54 and the outlet opening 56, in which the treatment tunnel 52 has an enlarged cross-section. A plasma nozzle 84 is inserted into the housing 51 in the reaction region 82.The plasma nozzle 84 is arranged and configured such that, during operation, an atmospheric plasma jet 88 generated by the plasma nozzle 84 is introduced into the reaction region 82, in particular, workpieces 80 transported through the reaction region 82 are exposed to the atmospheric plasma jet 88 generated by the plasma nozzle 84. The plasma nozzle 84 can, for example, be designed like the plasma nozzle 2 from Fig. 1. Alternatively, the plasma nozzle 84 can also be designed as a non-rotating plasma nozzle, wherein the plasma jet can, for example, exit from the nozzle opening in the longitudinal direction of the plasma nozzle. The plasma nozzle 84 has a working gas supply 75 (corresponding to the working gas supply 25 from Fig. 1) for supplying the plasma nozzle 84 with working gas.

[0077] The device 50 further comprises a reducing gas supply 74, which is configured to introduce a reducing gas, for example, forming gas, into the reaction region 82. For this purpose, the reducing gas supply 74 comprises a reducing gas source 76, which in the present example is designed as a gas cylinder.

[0078] The reducing gas supply 74 can be configured to supply the reducing gas to the plasma nozzle 84 as the working gas. For this purpose, a reducing gas line 77 can be provided, which conducts the reducing gas from the reducing gas source 76 to the working gas supply 75. For example, a controllable valve for controlling the gas supply rate can be integrated into the reducing gas line 77.

[0079] In one possible variant of the exemplary embodiment, the reducing gas supply 74 is configured to introduce the reducing gas into the reaction zone through a reducing gas inlet opening 92 separate from the plasma nozzle 84. For this purpose, a reducing gas line 94 can be provided, which conducts the reducing gas from the reducing gas source 76 to the reducing gas inlet opening 92. For example, a controllable valve for controlling the gas supply rate can be integrated into the reducing gas line 94. In this variant, the working gas supply 75 can also be connected to the reducing gas source 76 or, alternatively, via a working gas line 72 to a working gas source 70 for providing a working gas, for example, nitrogen or argon.

[0080] Furthermore, the device 50 can have a purge gas supply 96 configured to introduce a purge gas into the treatment tunnel 52. For this purpose, the purge gas supply 96 has, in particular, a purge gas source 98 for providing an oxygen-free purge gas, for example, nitrogen or argon, as well as a purge gas line 99, by which the purge gas is guided from the purge gas source 98 to a purge gas inlet opening 100 in the treatment tunnel 52. For example, a controllable valve for controlling the gas supply rate can be integrated into the purge gas line 99.

[0081] If the reducing gas supply 74 has a separate reducing gas inlet opening 92, this separate reducing gas inlet opening 92 can, for example, be used simultaneously as a purge gas inlet opening 100, as shown in Fig. 2. However, separate inlet openings are also conceivable.

[0082] If the reducing gas supply 74 does not have a separate reducing gas inlet opening 92, the inlet opening shown in Fig. 2 can be used alone as the purge gas inlet opening 100.

[0083] Furthermore, a heating element 64 is provided between the inlet opening 54 and the reaction area 82, and thus upstream of the reaction area 82 in the transport direction 106 of the transport device 58, in order to preheat workpieces transported by the transport device 58 before they enter the reaction area 82. Furthermore, a cooling element 104 is arranged between the reaction area 82 and the outlet opening 56, and thus downstream of the reaction area 82 in the transport direction 106, in order to cool workpieces transported by the transport device 58 after the reduction treatment in the reaction area 82. Furthermore, a heating and / or cooling element 102 can also be provided in the reaction area 82 itself.

[0084] The device 50 further comprises a control device 66 for its control, which is connected via communication connections 68 (for the sake of clarity, not all connections are shown) to the plasma nozzle 84, to the gas sources 70, 76, 98 or to valves integrated into the gas lines 72, 77, 94, 99, and to the motor 61 of the transport device 58. The control device 66 is preferably configured to regulate gas supply rates at the gas supplies 74, 96, the operation of the plasma nozzle 84, in particular the electrical power used for its operation, the speed of the transport device 58, and optionally the temperature of the heating and cooling elements 64, 102, 104.

[0085] The operation of the device 50 is described below.

[0086] Before the reduction treatment begins with the device 50, a purge gas, for example nitrogen, is first introduced into the treatment tunnel 52 via the purge gas supply 96, for example via the purge gas inlet opening 100, so that any oxygen-containing atmosphere present there is purged out through the inlet or outlet openings 54, 56. Alternatively, the treatment tunnel 52 can also be purged with reducing gas, which can be introduced into the reaction area 82 via the reducing gas supply 74.

[0087] Subsequently, the plasma nozzle 84 is activated, and an atmospheric plasma jet 88 is generated, which is introduced into the reaction area 82. A reducing gas is introduced into the reaction area 82 using the reducing gas supply 74, for example, via the plasma nozzle 84 itself or via the optional reducing gas inlet opening 92. In this way, a reactive reducing atmosphere is created in the reaction area 82.

[0088] The transport device 58 transports workpieces 80 through the treatment tunnel 52, optionally preheated by the optional heating element 64, and transports them through the reaction zone 82, where the reactive atmosphere created by the reducing gas provided in the reaction zone 82 via the reducing gas supply 74 and the plasma jet 88 acts on the workpiece surface, resulting in a reduction of oxides on the workpiece surface. Preferably, the plasma nozzle 84 is aligned with the transport device 58 such that the workpieces 80 in the reaction zone 82 are exposed to the plasma jet 88, thereby achieving an even more intensive reduction of oxides on the workpiece surface of the workpieces 80.

[0089] The workpieces 80 can be transported by the transport device 58 at a constant speed through the reaction area 82. Alternatively, the transport device 58 can be configured to interrupt the transport for specific treatment periods when a workpiece 80 is located in the reaction area 82.

[0090] By transporting the workpieces further through the treatment tunnel 52 behind the reaction area 82 and optionally cooling them there by the optional cooling element 104, reoxidation of the workpiece surface can be reduced or completely prevented.

[0091] In an optional variant of the exemplary embodiment, the plasma nozzle 84 can be configured to provide the workpieces 80 with a protective layer. For this purpose, a precursor supply line can be provided, for example, in the region of the nozzle head 86 or at the working gas supply 75, via which a precursor can be introduced into the plasma jet 88. The plasma nozzle 84 can further be configured to operate alternately in reduction mode and in coating mode, so that a workpiece 80 transported through the reaction region 82 is first subjected to a reduction treatment in reduction mode and then provided with a protective layer in coating mode by adding a precursor.

[0092] Figure 3 shows a second embodiment of the device and the method for reducing oxides on workpiece surfaces in a schematic view.

[0093] The device 150 has a similar structure to the device 50. Corresponding components are provided with the same reference numerals, and reference is made to the above explanations regarding Fig. 2. The device 150 differs from the device 50 in that a coating region 182, spaced from the reaction region 82, is provided between the reaction region 82 and the exit opening 56. In the coating region 182, a coating plasma nozzle 184 is integrated into the housing 51. This coating plasma nozzle is designed to apply a protective layer by means of plasma coating to workpieces 80 transported through the coating region 182 by the transport device 58 during operation. For this purpose, a precursor feed 214 is provided, with which a precursor can be introduced into the atmospheric plasma jet 188 generated by the coating plasma nozzle 184 during operation.Furthermore, a purge gas line 212 is provided, by means of which the purge gas is guided from the purge gas source 98 to a purge gas inlet opening 200 in the treatment tunnel 52, in particular into the coating area 182.

[0094] The coating plasma nozzle 184 can, in particular, have a similar structure to the plasma nozzle 2 from Fig. 1, to which reference is made here. Alternatively, the plasma nozzle 84 can also be designed as a non-rotating plasma nozzle, wherein the plasma jet can exit from the nozzle opening, for example, in the longitudinal direction of the plasma nozzle.

[0095] In the present example, the precursor feed 214 is configured to introduce the precursor, together with the purge gas provided by the purge gas source 98 via the purge gas line 212, into the region of the nozzle head 186 of the coating plasma nozzle 184 by means of the purge gas inlet opening 200. Alternatively, a precursor feed 215 separate from the purge gas inlet opening 200 can also be provided, which, for example, introduces the precursor directly at or into the coating plasma nozzle 184, preferably near its nozzle opening on the nozzle head 186. When using a non-rotating coating plasma nozzle, this can, for example, have a precursor feed that guides the precursor laterally into the nozzle head 186. In the embodiment shown in Fig. 3, the plasma nozzle 84 is supplied with a reducing gas as the working gas via the working gas supply 75. The coating plasma nozzle 184 is supplied with a reducing gas as the working gas in the embodiment shown in Fig.3, the working gas supply 190 is supplied with a working gas, for example nitrogen and / or argon, provided by a working gas source 192 via a working gas line 194.

[0096] Tests were conducted to compare the effectiveness of reducing oxides on metal workpiece surfaces under various process conditions using a device 50 according to the embodiment in Fig. 2. The working gas used was a reducing gas containing nitrogen and hydrogen, which was supplied to the plasma nozzle 84 through the working gas supply 75 and thus introduced into the reaction region 82. Nitrogen and argon were used as purge gases, with the purge gas being introduced into the reaction region 82 via the purge gas inlet opening 100. In the tests, the proportion of the metal workpiece surface present in oxidized form and the proportion present in metallic form of metal workpieces were measured before and after treatment with the device 50.It was found that treatment with device 50 effectively reduced the portion of the metal workpiece surface present in oxidized form and effectively increased the portion of the metal workpiece surface present in metallic form. List of reference symbols.

[0097] 2, 84 plasma nozzle

[0098] 10 housings

[0099] 12 camps

[0100] 14 Support tube

[0101] 16 nozzle channel

[0102] 18 Nozzle opening

[0103] 20 ceramic tubes

[0104] 22 Swirl device

[0105] 23 Working gas

[0106] 24 Internal electrode

[0107] 25, 75, 190 Working gas supply

[0108] 26 high-voltage generators

[0109] 28, 88, 188 Plasma beam

[0110] 30, 86, 186 nozzle head

[0111] 32 threaded hole

[0112] 34 channels

[0113] 36 gear

[0114] 37 pinions

[0115] 38 rotary drive

[0116] 40 arrow 42 arc-like discharge 50, 150 device

[0117] 51 housings

[0118] 52 treatment tunnels

[0119] 54 Entrance opening

[0120] 56 Exit opening

[0121] 58 Transport device

[0122] 60 drive roller

[0123] 61 engine

[0124] 62 Conveyor belt

[0125] 64 heating element

[0126] 66 Control device

[0127] 68 Communication connections 70, 192 Working gas source 72, 194 Working gas line

[0128] 74 Reducing gas supply

[0129] 76 reducing gas source 77, 94 reducing gas line

[0130] 80 workpiece

[0131] 82 Reaction area

[0132] 92 Reducing gas inlet opening

[0133] 96 Purge gas supply

[0134] 98 Purge gas source 99, 212 Purge gas line 100 , 200 Purge gas inlet opening 102 , 104 Cooling element

[0135] 106 Transport direction

[0136] 182 coating area

[0137] 184 Coating plasma nozzle 214 , 215 Precursor feed

Claims

Patent claims 1. Device (50, 150) for reducing oxides on workpiece surfaces, comprising a treatment tunnel (52) extending from an inlet opening (54) to an outlet opening (56), a reaction chamber (82) arranged within the treatment tunnel (52), a plasma nozzle (2, 84) configured to generate an atmospheric plasma jet (28, 88), a reducing gas supply (74) configured to introduce a reducing gas (23) into the reaction chamber (82), and a transport device (58) configured to transport workpieces (80) through the treatment tunnel (52), wherein the plasma nozzle (2, 84) is arranged and configured to introduce the atmospheric plasma jet (28, 88) into the reaction chamber (82) during operation. 2.Device according to claim 1, characterized in that the plasma nozzle (2, 84) is arranged and configured to impart the atmospheric plasma jet (28, 88) to workpieces (80) transported through the treatment tunnel (52) in the reaction zone (82) during operation with the transport device (58).

3. Device according to claim 1 or 2, characterized in that the reducing gas supply (74) is configured to supply the reducing gas to the plasma nozzle (2, 84) as the working gas.

4. Device according to claim 1 or 2. characterized in that the reducing gas supply (74) is designed to introduce the reducing gas into the reaction area (82) through a reducing gas inlet opening (92) separate from the plasma nozzle (2, 84).

5. . Device according to one of claims 1 to 4, characterized in that a purge gas supply (100) is provided which is configured to introduce a purge gas into the treatment tunnel (52), in particular into the reaction area (82).

6. Device according to one of claims 1 to 5, characterized in that the plasma nozzle (2, 84) has a nozzle head (30, 86) from which the plasma jet (28, 88) emerges during operation and which rotates about an axis of rotation (A) during operation.

7. Device according to one of claims 1 to 6, characterized in that a heating element (64) and / or a cooling element (102, 104) are provided which are configured to heat and / or cool the workpieces (80) transported through the treatment tunnel (52).

8. Device according to one of claims 1 to 7, characterized in that the plasma nozzle (2, 84) or an optionally provided separate coating plasma nozzle (2, 184) is configured to provide workpieces (80) transported through the treatment tunnel (52) during operation and exposed to the atmospheric plasma jet (88, 188) in the reaction area (82) with a protective layer by means of plasma coating.

9. Device according to claim 8, characterized in that a coating area (182) is arranged between the reaction area (82) and the outlet opening (56), and the The coating plasma nozzle (2, 184) is designed to provide workpieces (80) transported through the treatment tunnel (52) with a protective layer in the coating area (182) by means of plasma coating during operation with the transport device (58).

10. Use of a device (50, 150) according to one of claims 1 to 9 for reducing oxides on workpiece surfaces.

11. Method for reducing oxides on workpiece surfaces with a device (50, 150) according to one of claims 1 to 9, in which one or more workpieces (80) are transported through the treatment tunnel (52) with the transport device (58), in which an atmospheric plasma jet (28, 88) is generated with the plasma nozzle (2, 84), in which a reducing gas is introduced into the reaction area (82) and in which the atmospheric plasma jet (28, 88) is introduced into the reaction area (82).

12. Method according to claim 11, characterized in that the one or more workpieces (80) transported through the treatment tunnel (52) are exposed to the atmospheric plasma jet (28, 88) in the reaction area (82).

13. Method according to claim 11 or 12, characterized in that the reducing gas is introduced as working gas (23) into the plasma nozzle (28, 88).

14. Method according to claim 11 or 12, characterized in that the reducing gas passes through a [missing information] Plasma nozzle (2, 84) separate reducing gas inlet opening (92) is introduced into the reaction area (82).

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