Screen printing unit, screen printing device and screen printing process

Abstract

The invention relates to a screen printing unit for applying a screen printing paste to an object, in particular to a semiconductor substrate, comprising a screen printing form which has a screen printing frame and a screen printing mesh arranged on the screen printing frame. Essentially, the screen printing unit has a tensioning device with a plurality of actuators, the screen printing unit is designed such that the mesh extends in a frame plane within the screen printing frame without action from the actuators, and the actuators of the tensioning device are designed to interact with the screen printing mesh so that tensioning areas of the screen printing mesh can be arranged outside the frame plane by means of the actuators, wherein the tensioning areas are arranged within the screen printing frame, in particular in an area of ​​the screen printing mesh delimited by the screen printing frame.

Description

[0001] Screen printing is used in many different applications to apply a screen printing paste to an object. In particular, screen printing is used industrially on a large scale for applying screen printing paste to a semiconductor substrate, and especially for the production of solar cells.

[0002] For screen printing, a screen printing stencil is used, which has a screen printing frame and a screen printing mesh attached to the frame. Screen printing paste is applied to one side of the screen printing mesh using the squeegee, and the object to be printed is positioned at a distance from the screen printing mesh on the opposite printing side of the screen printing mesh.

[0003] Using a squeegee positioned against the squeegee side of the screen printing mesh, the mesh is pressed onto the object, and screen printing paste is applied through the mesh to the object. The screen printing mesh is clamped in the screen printing frame, so that as the squeegee is moved, the mesh is released from the object.

[0004] For the printing process and an accurate print image, a defined and homogeneous screen tension is necessary. Over the course of printing cycles, the screen tension of the screen mesh decreases due to wear. Insufficient screen tension leads to an inaccurate print image, which can be broken down into mesh distortion and screen drag. Mesh distortion results from a heterogeneous screen tension distribution, caused primarily by uneven mesh wear. Screen drag originates from insufficient buoyancy of the screen printing mesh, resulting in either no or uneven release of the screen printing mesh from the object after printing.

[0005] A reduction in screen printing tension, and in particular an inhomogeneous screen printing tension, therefore leads to a deterioration of the printed image, making a costly replacement of the screen printing form necessary.

[0006] In previously known screen printing frames, the screen printing mesh extends within a frame plane inside the screen printing frame. Screen printing frames are known that have tensioning devices. The screen printing mesh is arranged on the tensioning devices, and the tensioning devices can be moved parallel to the frame plane by means of screws to increase the tension of the screen printing mesh. Such screen printing frames are known from US 5,220,867 and US 5,136,797. With the previously known screen printing frames with tensioning devices, stretching the screen printing mesh onto the screen printing frame is more complex, since the screen printing mesh must be attached to the tensioning devices or individual elements of the tensioning devices. This makes the manufacture of the screen printing frame more expensive.Furthermore, such screen printing frames are less stable and, in particular due to misalignments of the screw connections, are not suitable for screen printing processes with high accuracy and a high throughput rate in industrial applications.

[0007] The present invention is therefore based on the objective of providing a screen printing unit, a screen printing device and a screen printing process, so that an increase in the service life of the screen printing frames used is made possible with uncomplicated production of the screen printing frames.

[0008] This problem is solved by a screen printing unit for applying a screen printing paste to an object according to claim 1, by a screen printing device for applying a screen printing paste to an object according to claim 10, and by a screen printing method for applying a screen printing paste to an object according to claim 13. Advantageous embodiments are found in the dependent subclaims.

[0009] The screen printing device is preferably designed for use with a screen printing unit according to the invention, in particular a preferred embodiment thereof. The screen printing process is preferably designed for use with a screen printing device and / or a screen printing unit according to the invention, in particular preferred embodiments thereof. The screen printing unit and the screen printing device according to the invention are preferably designed for carrying out the screen printing process according to the invention, in particular a preferred embodiment thereof.

[0010] The screen printing unit according to the invention for applying a screen printing paste to an object, in particular to a semiconductor substrate, comprises a screen printing mold. The screen printing mold includes a screen printing frame and a screen printing mesh arranged on the screen printing frame.

[0011] It is essential that the screen printing unit has a tensioning device with a plurality of actuators, that the screen printing unit is designed such that the fabric extends in a frame plane within the screen printing frame without action of the actuators, that the actuators of the tensioning device are designed to interact with the screen printing fabric, so that tensioning areas of the screen printing fabric can be arranged outside the frame plane by means of the actuators, wherein the tensioning areas are arranged within the screen printing frame, in particular in an area of ​​the screen printing fabric delimited by the screen printing frame.

[0012] The screen printing unit according to the invention thus enables the use of screen printing forms known per se with a screen printing frame on which the screen printing mesh is arranged. This allows the use of known, robust and cost-effective screen printing forms.

[0013] Additionally, the screen printing unit has a tensioning device with a plurality of actuators. Without the actuators acting on the screen printing mesh, the mesh extends in a frame plane as known from the prior art; in particular, the screen printing mesh preferably forms a flat surface within the screen printing frame as the frame plane.

[0014] The actuators of the tensioning device of the screen printing unit according to the invention are designed to interact with the screen printing mesh, such that tensioning areas of the screen printing mesh can be arranged outside the frame plane by means of the actuators. Thus, the tension of the screen printing mesh can be increased by means of the actuators, whereas, unlike the prior art, the area of ​​the screen printing mesh within a frame is not increased by means of tensioning devices in order to increase the screen tension. In the screen printing unit according to the invention, the tensioning areas are arranged outside the frame plane by means of the actuators, thereby increasing the tension of the screen printing mesh. Thus, partial areas of the screen printing mesh – the tensioning areas – are moved by means of the actuators to achieve a tensioning effect.

[0015] The tensioning areas are arranged within the screen printing frame, in particular in an area of ​​the screen printing mesh delimited by the screen printing frame. This allows the use of screen printing stencils known per se. If the screen tension of the screen printing mesh decreases, the screen tension can be increased again in the screen printing unit according to the invention, even when using screen printing stencils known per se with screen printing mesh arranged on the screen printing frame, particularly by means of gluing. In particular, by providing a plurality of actuators, it is possible to increase the screen tension of the screen printing mesh to varying degrees in different sub-areas of the screen printing mesh.

[0016] The present invention thus enables the use of previously known, cost-effective adjustable screen printing molds and increases the service life of these molds. Furthermore, the clamping device, or at least parts of the clamping device, in particular the actuators or parts of the actuators, can be reused, so that even when a screen printing mold is replaced, the full cost of a screen printing unit is not incurred again.

[0017] The aforementioned problem is further solved by a screen printing device according to claim 10.

[0018] The screen printing device according to the invention for applying a screen printing paste to an object, in particular to a semiconductor substrate, comprises a squeegee unit, which includes a squeegee and a squeegee movement unit. The screen printing device includes a screen printing unit, wherein the screen printing unit comprises a screen printing form with a screen printing frame and a screen printing mesh arranged on the screen printing frame.

[0019] The squeegee movement unit is designed to work in conjunction with the screen printing unit in order to move the squeegee on one side of the screen printing mesh and to move the screen printing mesh in an object direction towards the object to be printed.

[0020] It is essential that the screen printing unit has a clamping device with a plurality of actuators and that the actuators of the clamping device are designed to move clamping areas of the screen printing fabric against the direction of the object.

[0021] In the screen printing device according to the invention, the screen printing mesh can thus be moved towards the object to be printed by means of the squeegee in a manner known per se, in particular to come into contact with the object. By means of the actuators of the tensioning device, tensioned areas of the screen printing mesh can be moved against the direction of the object, i.e., away from the object. By means of the actuators, the operating tension of the screen printing mesh, in particular the screen tension between the tensioned areas and the area of ​​the screen printing mesh against which the squeegee rests, can thus be increased.

[0022] The screen printing device according to the invention thus also achieves the advantages mentioned for the screen printing unit according to the invention.

[0023] In particular, it is advantageous that the screen printing unit of the screen printing device according to the invention is designed as a screen printing unit according to the invention, in particular of a preferred embodiment thereof. In this advantageous embodiment, moving the clamping areas of the screen printing fabric by means of the actuators against the object direction corresponds to arranging the clamping areas outside the frame plane of the screen printing unit.

[0024] The aforementioned problem is further solved by a screen printing process according to claim 13. The screen printing process according to the invention for applying a screen printing paste to an object, in particular a semiconductor substrate, comprises the following process steps: A. Providing a screen printing form with a screen printing frame and a screen printing mesh arranged on the screen printing frame; B. Arranging the object to be printed on one side of the screen printing mesh, with the object being spaced away from the screen printing mesh, and applying printing paste to a squeegee side of the screen printing mesh opposite the side of the object; C. Applying the printing paste to the object, wherein the printing paste is applied to the object through the screen printing mesh using a squeegee, and wherein the screen printing mesh is moved in one direction towards the object using the squeegee.

[0025] The essential point is that, by means of a number of actuators, tension areas of the screen printing fabric are moved relative to the screen printing frame against the direction of the object in order to increase the tension of the screen printing fabric at least in certain areas during process step C.

[0026] In the methods according to the invention, the screen printing fabric is moved towards the object by means of the squeegee, whereby tension areas of the screen printing fabric are moved away from the object by means of the actuators, so that the screen tension of the screen printing fabric is increased, in particular between the tension areas and the place where the squeegee is applied to the screen printing fabric.

[0027] The method according to the invention thus also achieves the advantages mentioned for the screen printing unit according to the invention.

[0028] It is known that screen printing stencils have a printing area for forming a printed image, wherein the printing area is only permeable to the screen printing paste in certain sections, and these sections are designed to achieve the desired printed image. For this purpose, the printing area can include a mask applied to and / or the screen printing mesh with openings for the desired printed image.

[0029] To avoid interference with the printing process by the actuators and / or interference with the working area of ​​a squeegee by the actuators, it is advantageous that the clamping areas are arranged outside the printing area, so that there is a spatial separation between the printed image and the working area of ​​the squeegee during screen printing.

[0030] In an advantageous embodiment, the screen printing fabric therefore has a printing area for forming a printed image on the object to be printed, wherein the printing area is arranged at a distance from the screen printing frame and the clamping areas are arranged between the printing area and the screen printing frame.

[0031] In particular, it is advantageous that within the screen printing frame a perimeter edge of the screen printing fabric is excluded from the printing area and the tensioning areas of the screen printing fabric are arranged within this perimeter edge.

[0032] Accordingly, in the screen printing device according to the invention, the screen printing fabric preferably has a printing area for forming a printed image on the object to be printed, wherein the printing area is arranged at a distance from the screen printing frame and the clamping areas are arranged between the printing area and the screen printing frame.

[0033] Similarly, in the screen printing process according to the invention, a screen printing fabric is preferably used which has a printing area for forming a printed image on the object to be printed, wherein the printing area is arranged at a distance from the screen printing frame and the clamping areas are arranged between the printing area and the screen printing frame.

[0034] In typical screen printing devices, the object to be printed is positioned below the screen printing mesh and at a distance from it. The screen printing device according to the invention is therefore preferably designed for positioning the object to be printed below the screen printing unit, preferably below the screen printing mesh, and particularly preferably at a distance from it. It is designed such that the screen printing mesh can be moved downwards by means of the squeegee and the squeegee movement unit, and the tensioning areas of the screen printing mesh can be moved upwards by means of the actuators.

[0035] Accordingly, the screen printing process according to the invention is preferably designed such that the object to be printed is arranged under the screen printing mesh and the screen printing mesh is moved downwards by means of the squeegee and the tension areas of the screen printing mesh are moved upwards by means of the actuators.

[0036] To achieve efficient clamping action when moving the clamping areas by means of the actuators, it is advantageous that the actuators of the screen printing unit are designed to move the clamping areas in a direction of movement which forms an angle with the frame plane in the range of 70° to 120°, preferably 80° to 110°, and particularly 85° to 95°. It is particularly advantageous that the direction of movement is perpendicular to the frame plane.

[0037] To achieve a material-friendly clamping action on the screen printing mesh, it is advantageous for the actuators to be designed to exert a force on the mesh at the tensioning points, preferably several force applications of varying strengths. Different force applications allow for the selective application of varying tension to different areas of the screen printing mesh. This is particularly advantageous in cases of uneven wear of the screen printing mesh.

[0038] It is advantageous that the actuators are designed to generate the force effect by means of a magnetic field, preferably by means of electromagnetic interaction.

[0039] In particular, it is advantageous that the actuators each have at least one magnetic layer, preferably a ferromagnetic layer, which is arranged on one of the clamping areas of the screen printing fabric and have at least one magnet, preferably an electromagnet, which is arranged at a distance from the magnetic layer of the actuator.

[0040] In this advantageous embodiment, the actuators are designed with at least two parts. One actuator has a magnetic element with a magnetic layer, which is arranged on a clamping area of ​​the screen printing fabric. Furthermore, the actuator has at least one magnet, preferably an electromagnet, which is arranged at a distance from the magnetic layer. This allows for a fabric-friendly force to be applied to the clamping areas. By using a magnet, the force applied to the magnetic layer, and thus the clamping effect, can also be adjusted by changing the distance of the magnet from the frame plane. In the advantageous embodiment of the magnet as an electromagnet, the force can be controlled particularly easily via the current strength of the electromagnet.

[0041] In an advantageous embodiment, the actuators each have at least one movable, preferably linearly movable, clamping element, with each clamping element being arranged on one of the clamping areas of the screen-printed fabric. In this advantageous embodiment, the clamping effect can thus be achieved in a technically unobtrusive manner by moving the clamping element. It is advantageous that the clamping elements of the actuators are pneumatically and / or electrically movable, preferably by means of an electric motor. For this purpose, commercially available pneumatic or electric linear actuators can be used.

[0042] As previously explained, due to the multiple actuators, different clamping areas can be moved differently or not moved at all, so that an inhomogeneous clamping effect can be formed.

[0043] The screen printing unit, the screen printing device and the screen printing process according to the invention thus make it possible to selectively increase the tension in partial areas of the screen printing fabric.

[0044] According to the applicant's findings, the use of screen printing fabric often results in inhomogeneous stress changes, in particular an inhomogeneous stress drop in the screen printing fabric. This is primarily due to uneven, heterogeneous fabric wear.

[0045] In an advantageous embodiment of the method according to the invention, a spatially resolved measurement of the fabric tension of the screen printing fabric is therefore carried out and, depending on the measurement, a selective increase of the tension of the screen printing fabric is carried out depending on the tension loss resulting from the measurement data.

[0046] In particular, for the formation of selective, spatially inhomogeneous tension effects, it is advantageous that in an advantageous embodiment of the screen printing unit according to the invention, the tensioning unit has several pairs of actuators, wherein the two actuators of each pair of actuators are arranged on opposite edge regions of the screen printing fabric.

[0047] In this way, the tension of the screen printing fabric can be increased, particularly in the area of ​​the screen printing fabric located between the two actuators, by means of a pair of actuators.

[0048] It is advantageous that at least two actuators and two clamping areas are arranged on each side of the screen printing unit's frame. This allows for the selective application of a clamping effect.

[0049] In an advantageous embodiment of the screen printing device according to the invention, the screen printing unit of the screen printing device has a control device and the actuators of the clamping unit are designed to cooperate with the control device in order to control the force exerted on the clamping areas by means of the actuators.

[0050] This makes it possible to automate the tensioning of screen printing fabric, in particular the selective application of a tensioning effect to the screen printing fabric using the actuators.

[0051] The actuators allow the tension to be changed during the screen printing process.

[0052] Investigations by the applicant show that it is advantageous to establish a tension effect that is as homogeneous as possible before the start of the printing process and to maintain this tension effect during the printing process. In an advantageous embodiment of the method according to the invention, a force is therefore applied to the tension areas of the screen printing fabric by means of the actuators before process step C, and this force is maintained during process step C.

[0053] The screen printing unit, the screen printing device and the screen printing method according to the invention are particularly suitable for applying screen printing paste to a semiconductor substrate, since high accuracy is of particular importance in such applications.

[0054] The use of screen printing frames is particularly advantageous in the production of solar cells, especially photovoltaic solar cells, and especially for the formation of metallic contact structures. In such applications, a precise print image is of paramount importance for achieving high quality and, in particular, high efficiency of the solar cell. Furthermore, solar cells have a lower value density compared to the production of integrated circuits such as processors, meaning that the cost of the screen printing frames and, consequently, their lifespan in the manufacturing process significantly impact the overall cost of solar cell production.

[0055] Further advantageous designs and features are described below with reference to exemplary embodiments and the figures. These show: Fig. 1 a top view of a screen printing mold and clamping devices of a first embodiment of a screen printing unit according to the invention; Fig. 2 to Fig. 4 sectional views of the screen printing unit according to the first embodiment in different processing steps and Fig. 5 a sectional view of a second embodiment of a screen printing unit according to the invention.

[0056] All figures are schematic representations, not to scale. Identical reference symbols within the figures denote identical or equivalent elements.

[0057] In the Fig. Figures 1 to 4 show a first embodiment of a screen printing unit according to the invention for applying a screen printing paste to an object.

[0058] In Fig. Figure 1 is a schematic top view of a screen printing mold and a clamping device of the screen printing unit.

[0059] The screen printing form has a screen printing frame 1, which in this case is square. A screen printing mesh 2 is arranged on the screen printing frame 1, completely filling the inner area of ​​the screen printing frame. The screen printing unit serves to apply a metal particle-containing paste in the form of several parallel lines onto an object 3 designed as a semiconductor substrate, in this case as a precursor of a solar cell, in order to form a metallic contact structure on the object by means of subsequent treatment steps, in particular heating. A mask 4 is therefore arranged on the screen printing mesh 2, which has several parallel, straight openings.

[0060] The screen printing unit further comprises a clamping device with a plurality of actuators. In this case, the actuators are designed as electromagnets, which are arranged circumferentially around the screen printing frame. The screen printing unit according to the first embodiment has nine actuators, with three actuators arranged on each of the four sides of the screen printing frame.

[0061] In plan view according to Fig. Figure 1 shows a holder 5a and an electromagnet 5b represented as a circle for each actuator 5.

[0062] These elements are shown as an example on the upper left actuator, marked with reference symbols.

[0063] In Fig. Figure 2 shows a cross-sectional view of the screen printing unit, with the cutting plane in Fig. 1 is perpendicular to the drawing plane and approximately centered by the dashed line. Fig. is marked with 1.

[0064] As in Fig. As can be seen in Figure 2, each actuator also has a ferromagnetic layer 5c. In this case, the ferromagnetic layer is formed as an iron layer and is bonded to the top surface of the screen printing fabric by means of adhesive bonding. Fig. Figure 2 shows the state with electromagnets 5b switched off, i.e., without the action of the actuators. As is known per se, the screen-printed fabric 2 forms a straight, flat surface without the action of the actuators, as shown in the illustration. Fig. 2. A horizontally extending surface, perpendicular to the drawing plane, which extends within the screen printing frame 1. If an electric current is now passed through the electromagnets 5b of the actuators 5, an attractive effect results on the ferromagnetic layers 5c, so that in the representation according to Fig. 2. A force is exerted upwards on the ferromagnetic layers 5c. The area covered by the ferromagnetic layers 5c on the screen printing fabric thus represents the area of ​​direct force action and therefore forms the clamping areas.

[0065] The ferromagnetic layers 5c are also circular, with a slightly smaller diameter than the electromagnets 5b. Electromagnets 5b and ferromagnetic layers 5c are arranged concentrically.

[0066] In plan view according to Fig. 1 thus each electromagnet 5b covers one in the representation according to Fig. 2 ferromagnetic layer 5c arranged under the electromagnet 5b on the screen printing fabric.

[0067] The screen printing device further comprises a squeegee unit with a squeegee movement unit 6a and a squeegee 6b. The squeegee can be moved by means of the squeegee movement unit 6a as shown in the illustration. Fig. 2. The squeegee can be moved vertically up and down to press the screen printing mesh onto the object 3. Furthermore, the squeegee can be positioned as shown in the illustration. Fig. 2 to the right and left in order to apply screen printing paste applied to the mask 4 through the openings of the mask 4 to the object 3 in a manner known per se.

[0068] In one embodiment of a method according to the invention, in process step 1 the screen printing form with the screen printing frame 1 and the screen printing mesh 2 arranged on the screen printing frame is provided. In process step B the object 3 to be printed is arranged on one side of the screen printing mesh 2. The object side of the screen printing mesh 2 is the side shown in the Fig. 2 to 5 bottom side of the screen printing mesh 2. The object 3 is positioned at a distance from the screen printing mesh 2, as shown in Fig. 2 is evident.

[0069] Furthermore, the previously described metal particle-containing printing paste is applied to a squeegee side of the screen printing mesh opposite the object side, i.e., to the side in the Fig. 2 to 5 upper side of the screen printing fabric 2, whereby the printing paste is applied to the mask 4.

[0070] In process step C, the printing paste is applied to the object 3, whereby the screen printing mesh 2 is moved in the direction of the object, i.e. in the direction of the object, by means of the squeegee 6b. Fig. 2 to 5 downwards in the direction of the object.

[0071] Before process step C, in the present embodiment of the method according to the invention, clamping areas of the screen printing fabric 2 are moved relative to the screen printing frame 1 against the direction of the object by means of the nine actuators 5. As described above, the clamping areas are defined by the surfaces of the screen printing fabric covered by the ferromagnetic layers 5c.

[0072] This condition is in Fig. Figure 3 shows: The force generated by the electromagnets 5b causes the ferromagnetic layers 5c to be lifted upwards, thus increasing the tension of the screen printing fabric 2.

[0073] In Fig. Figure 4 shows the printing process in which the screen printing mesh 2 is pressed onto the object 3 using the squeegee 6b. The squeegee is then moved laterally so that the screen printing paste applied to the mask 4 is transferred to the object 3 through the openings of the mask 4 to form straight, parallel lines corresponding to the openings of the mask 4. As shown in Fig. As can be seen in section 4, the tension of the screen printing fabric 2 is increased again.

[0074] In Fig. Figure 5 shows a second embodiment of a screen printing unit according to the invention. The basic structure is the same as in the first embodiment. In contrast to the first embodiment, the actuators are designed as linear actuators 7. In this embodiment, the linear actuators are designed as pneumatically actuated linear actuators, each of which has a piston for pneumatic actuation as shown in the illustration. Fig. 5. to move the screen printing fabric upwards. The linear actuators are accordingly arranged below the screen printing fabric 2, so that by extending the pistons upwards in the contact area between the piston and the screen printing fabric, clamping areas are formed accordingly, and the tensile tension of the screen printing fabric is increased by moving the clamping areas upwards. In an alternative embodiment, the linear actuators are designed as electrically operated linear actuators, with each linear actuator having an electric motor. Reference symbol list 1 screen printing frame 2 screen printing fabrics 3 objects 4 Mask 5 Actuator 5a bracket 5b Electromagnet 5c ferromagnetic layer 6 squeegee units 6a Squeegee movement unit 6b Squeegee 7 linear actuators

Claims

[1] Screen printing unit for applying a screen printing paste to an object, in particular to a semiconductor substrate, with a screen printing form which has a screen printing frame (1) and a screen printing mesh (2) arranged on the screen printing frame (1), characterized by , that the screen printing unit has a clamping device with a plurality of actuators (5), that the screen printing unit is designed such that the fabric extends in a frame plane within the screen printing frame (1) without the action of the actuators (5), that the actuators (5) of the tensioning device are designed to interact with the screen printing fabric (2) so that tensioning areas of the screen printing fabric (2) can be arranged outside the frame plane by means of the actuators (5), wherein the tensioning areas are arranged within the screen printing frame (1), in particular in an area of ​​the screen printing fabric (2) delimited by the screen printing frame (1). [2] Screen printing unit according to claim 1, characterized by , that the screen printing fabric (2) has a printing area for forming a printed image on the object to be printed, wherein the printing area is arranged at a distance from the screen printing frame (1) and the clamping areas are arranged between the printing area and the screen printing frame (1). [3] Screen printing unit according to any of the preceding claims, characterized by , that the actuators (5) are designed to move the clamping areas in a direction of movement which forms an angle with the frame plane in the range of 70° to 120°, preferably 80° to 110°, in particular 85° to 95°. [4] Screen printing unit according to any of the preceding claims, characterized by , that the actuators (5) are designed to exert a force on the screen printing fabric (2) at the clamping areas of the screen printing fabric (2), preferably several force effects of different strengths. [5] Screen printing unit according to claim 4, characterized by , that the actuators (5) are designed to generate the force effect by means of a magnetic field, preferably by means of electromagnetic interaction. [6] Screen printing unit according to claim 5, characterized by that the actuators (5) each have at least one magnetic layer, preferably a ferromagnetic layer (5c), which is arranged on one of the clamping areas of the screen printing fabric (2) and have at least one magnet, preferably an electromagnet (5b), which is arranged spaced apart from the magnetic layer of the actuator (5). [7] Screen printing unit according to any one of claims 1 to 4, characterized by . that the actuators (5) each have at least one displaceable, preferably linearly displaceable, clamping element, wherein each clamping element is arranged on one of the clamping areas of the screen printing fabric (2), in particular, that the clamping elements of the actuators (5) are pneumatically and / or electrically displaceable, preferably by means of an electric motor. [8] Screen printing unit according to any of the preceding claims, characterized by , that the tensioning unit has several pairs of actuators (5), wherein the two actuators (5) of each pair of actuators (5) are arranged at opposite edge regions of the screen printing fabric (2). [9] Screen printing unit according to any of the preceding claims, characterized by that at least two actuators (5) and two clamping areas are arranged on each side of the frame. [10] Screen printing device for applying a screen printing paste to an object (3), in particular to a semiconductor substrate, with a doctor blade unit (6) comprising a doctor blade (6b) and a doctor blade movement unit (6a) and with a screen printing unit, preferably according to one of the preceding claims, wherein the screen printing unit comprises a screen printing form with a screen printing frame (1) and a screen printing mesh (2) arranged on the screen printing frame (1), wherein the squeegee movement unit (6a) is designed to interact with the screen printing unit in order to move the squeegee (6b) on a squeegee side of the screen printing fabric (2) and to move the screen printing fabric (2) in an object direction towards the object (3) to be printed by means of the squeegee (6b), characterized by , that the screen printing unit has a clamping device with a plurality of actuators (5) and the actuators (5) of the clamping device are designed to move clamping areas of the screen printing fabric (2) against the direction of the object. [11] Screen printing device according to claim 10, wherein the screen printing fabric (2) has a printing area for forming a printed image on the object (3) to be printed, wherein the printing area is arranged at a distance from the screen printing frame (1) and the clamping areas are arranged between the printing area and the screen printing frame (1). [12] Screen printing device according to any one of claims 10 to 11, characterized by , that the screen printing unit has a control device and the actuators (5) of the clamping unit are designed to interact with the control device in order to control the force exerted on the clamping areas by means of the actuators (5). [13] Screen printing method for applying a screen printing paste to an object (3), in particular to a semiconductor substrate, with the process steps A. Providing a screen printing form with a screen printing frame (1) and a screen printing mesh (2) arranged on the screen printing frame (1); B. Arranging the object to be printed (3) on an object side of the screen printing mesh (2), wherein the object is spaced away from the screen printing mesh (2) and applying printing paste to a squeegee side of the screen printing mesh (2) opposite the object side; C. Applying the printing paste to the object (3), wherein the printing paste is applied to the object (3) through the screen printing mesh (2) by means of a squeegee (6b) and wherein the screen printing mesh (2) is moved in an object direction towards the object (3) by means of the squeegee (6b); characterized by , that by means of a plurality of actuators (5) tension areas of the screen printing fabric (2) are moved relative to the screen printing frame (1) against the direction of the object in order to increase the tension of the screen printing fabric (2) at least in certain areas during process step C. [14] Method according to claim 13, characterized by, that the screen printing fabric (2) which has a printing area is used to form a printed image on the object to be printed (3), wherein the printing area is arranged at a distance from the screen printing frame (1) and the clamping areas are arranged between the printing area and the screen printing frame (1). [15] Method according to any one of claims 13 to 14, characterized by , that by means of the actuators (5) a force is exerted on the clamping areas of the screen printing fabric (2) before process step C and the force is maintained during process step C.

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