Printing plate for producing electronic components, in particular photovoltaic solar cell structures, and method for producing said printing plate

Abstract

The present invention relates to a printing plate for producing electronic components, in particular structures of photovoltaic solar cells, comprising a screen frame and a screen formed as a planar fabric having a plurality of elongated screen elements arranged within the screen frame, the screen having at least one printing area through which the printing paste can pass and at least one blocking area through which the printing paste cannot pass, characterized in that the elongated screen elements are made of glass fibers, carbon fibers and / or carbon nanotubes.

Description

Technical field

[0001] The invention relates to a printing plate for producing the structure of an electronic component, in particular a photovoltaic solar cell, according to the preamble of claim 1, and to a method for producing such a printing plate according to the preamble of claim 9. Furthermore, the invention relates to a method for applying a printing paste using a printing plate to the surface of an electronic component, in particular a photovoltaic solar cell, according to the preamble of claim 14. [Background technology]

[0002] For example, in the production of electronic components such as semiconductor components and printed circuit boards, and in particular the production of photovoltaic solar cells, printing pastes are often applied to predetermined, typically linear, especially linear structures. Necessary in the manufacturing process.

[0003] The printing paste may contain metal particles to form metal wire conductive structures and / or contact structures of the part. Alternatively or additionally, the printing paste may have doping elements for forming doping regions in the respective substances for processing semiconductors, in particular in the semiconductor material of said component.

[0004] To form the aforementioned structures, it is known to use screen printing to apply a printing paste to one or more localized areas on the surface of the component. In this case, a printing plate consisting of a screen frame and a screen is used. The screen is formed as a planar fabric. A stencil is disposed relative to the screen, the stencil defining a printing area through which the printing paste can pass, with each aperture or area omitted from the stencil being further covered by the stencil. , defining a blocking area through which the printing paste cannot pass. The screen, which is formed as a planar fabric, has a plurality of elongated screen elements, each generally spaced apart and extending either parallel to each other or perpendicular to each other.

[0005] To apply the printing paste to the surface of the electronic component, the printing paste is applied at least to the printing area of ​​the printing plate. When the printing paste is applied to the printing plate, the screen prevents the printing paste from immediately penetrating the printing plate. Generally, the printing paste is passed through the printing plate in the printing area only after an additional force is applied using a squeegee, in particular passing through the screen to apply the printing paste onto the surface of the part. be done. [Summary of the invention] [Problem to be solved by the invention]

[0006] There is an ever-increasing demand for forming linear structures with narrower widths. Therefore, each channel defined by the printing area to form a linear structure needs to have a narrow width corresponding to this requirement.

[0007] A disadvantage of hitherto known printing plates is that due to the structure of the printing plate itself it is not possible to go below a minimum channel width, which would otherwise result in the linear structure of the printing paste being applied unevenly or non-continuously. This is for the purpose of

[0008] The invention is therefore based on the problem of providing a printing plate which allows the formation of narrow linear areas of printing paste. [Means to solve the problem]

[0009] The object is solved by a printing plate according to claim 1, a method for manufacturing a printing plate according to claim 9 and a method for applying a printing paste according to claim 14. Advantageous embodiments result from the respective dependent claims.

[0010] The printing plate according to the invention is preferably produced by a method for producing a printing plate according to the invention, in particular a preferred embodiment of the method. The method for producing a printing plate according to the invention is preferably applied for producing a printing plate according to the invention, particularly preferably an advantageous embodiment of the printing plate.

[0011] The printing plate according to the invention for producing the structure of electronic components, in particular photovoltaic solar cells, has a screen frame and a screen that is designed as a planar fabric with a plurality of elongated screen elements.

[0012] The screen is preferably placed in the screen frame under tensile stress.

[0013] The screen has at least one printing area through which the printing paste can pass and at least one blocking area through which the printing paste cannot pass.

[0014] Importantly, the elongate screen elements are formed as glass fibers, carbon fibers and / or carbon nanotubes.

[0015] The invention is based on the applicant's finding that the tensile stress at which the elongated screen element is placed in the screen frame is an important parameter for the minimum channel width that can be the printing area of ​​the printing plate. It is something. By using a material that allows particularly high tensile stresses in the elongated screen elements, it is therefore possible to form linear elements with particularly narrow widths.

[0016] By experiment and calculation, the applicant has adapted the material of manufacture of each of said screen elements to obtain a high tensile stress inherent in the material, and has determined that the number of screen elements per line (generally the number of each screen element per inch) ) and the diameter of the screen element.

[0017] According to the applicant's studies, the fact that the elongated screen elements are formed as glass fibers, carbon fibers and / or carbon nanotubes increases the maximum fabric tension of the screen, especially when it is formed as a planar fabric. It has been shown that the printing quality of coated structures with concomitantly narrow channel widths is improved.

[0018] Using screen elements made of glass and carbon fibers, it is possible to obtain tensile stresses in the range of 4,900 megapascals. By forming the elongated screen elements as carbon nanotubes, it is possible to obtain a tensile stress of 63,000 megapascals.

[0019] The screen, which is formed as a planar fabric, is thus placed in the screen frame at a tensile stress of greater than 15 N / cm, preferably greater than 20 N / cm and most preferably greater than 25 N / cm.

[0020] Studies by the applicant have shown that by increasing the tensile stress through material selection of each screen element in the printing plate of the present invention, the diameter of each screen element can be significantly reduced. This is surprising considering that the diameter of each screen element is a parameter that allows even greater tensile stresses to be achieved by increasing the diameter. Previously known printing plates have desirably increased the fabric tension, ie the tensile stress of the elongated screen elements, by increasing the diameter of each of the screen elements. On the other hand, the printing plate of the present invention makes it possible to obtain high fabric tension despite having a small diameter by selecting materials.

[0021] Applicant's studies have shown that it is preferable for the printing plate to be formed with the following tensile tensions and respective diameters of the elongated screen elements:

[0022]

table 1

[0023] The preferred ranges for each of the aforementioned parameters make it possible to achieve narrow channel widths and, accordingly, to reduce the width of linear structures formed using the printing paste.

[0024] According to studies by the applicant, when the elongated screen elements are formed using glass fiber and / or carbon, the screen elements range from 50 screen elements per inch to 3000 screen elements per inch. It has been shown that it is preferable to have a density of . When the elongated screen elements are formed using carbon nanotubes, they are arranged in a range of 50 screen elements per inch to 10,000 screen elements per inch.

[0025] In particular, when the elongated screen elements are formed using glass fiber or carbon, from 280 screen elements per inch to 950 screen elements per inch, and when each elongated screen element is formed using carbon nanotubes. , it is advantageous to arrange from 70 screen elements per inch to 2025 screen elements per inch.

[0026] The above-mentioned densities of each of the screen elements are preferably formed at least in the printing area of ​​the printing plate, and further preferably in the printing area and the blocking area.

[0027] As mentioned above, the printing plate according to the invention is particularly suitable for producing elongated linear structures of printing paste. The printed area is therefore at least partially elongated as an elongated channel opening, in particular a linear channel opening, preferably a straight channel opening, preferably extending in the longitudinal direction and having a channel width (b). is advantageously formed at Said channel width (b) is preferably smaller than 40 μm, more preferably smaller than 20 μm, particularly preferably smaller than 10 μm.

[0028] Preferably, said screen formed as a planar fabric has at least a first group of elongated screen elements, said elongated screen elements of said group being parallel to each other and more preferably equidistant to each other. placed at intervals. If at least one linear channel opening is provided in the printing area, it is preferred that the channel opening is arranged at an angle not equal to 0° to the longitudinal axis of the channel opening.

[0029] It is particularly advantageous to provide the angles and maximum channel widths described in DE 10 2019 122 126.9. This document is hereby incorporated by reference in its entirety. In particular, said at least one linear channel of said printing area and a screen element of said printing area form an angle with a tolerance of ±0.1°, said angle being 11.31°, 14.04°, 18.44°, 26.57°, 45°. , 33.69°, in particular from the group consisting of 11.31°, 14.04°, 18.44°, 26.57°, 33.69°.

[0030] This makes it possible, as known from DE 10 2019 122 126.9, to advantageously reduce the knots of the screen elements in the channel openings.

[0031] Advantageously, the screen formed as a planar fabric of the printing plate has at least a second group of elongate screen elements, the elongate screen elements of the second group being parallel to and parallel to each other. Preferably they are equally spaced apart from each other.

[0032] In particular, each of said screen elements of said first group and said second group has an angle in the range from 30° to 150°, preferably from 60° to 120°, particularly preferably from 85° to 95°, preferably from 90°. It is advantageous to

[0033] It is particularly advantageous if the elongate screen elements of the printing form are completely assigned to the first and second groups mentioned above. Accordingly, the elongated screen elements are preferably arranged parallel or perpendicular to each other in pairs.

[0034] According to studies by the applicant, an area ratio SUI calculated from the ratio of the area covered by the elongated screen element to the area of ​​the printing area is preferably larger than 0.5 in the printing area. It has been shown that a value greater than 0.75, especially greater than 1, is preferred. This provides an advantageous aperture ratio for applying the printing paste at an advantageously low pressure through the screen, in particular using a squeegee, to the surface of the component.

[0035] As mentioned above, the printing plate according to the invention has a plurality of elongated screen elements. It is within the scope of the invention for the screen elements to be connected to one another and in particular to be formed by folding one or more elongated, flexible screen elements-basic elements in the area of ​​the screen frame.

[0036] The aforementioned problem is further solved by a printing plate having a screen frame, a planar screen having a plurality of elongated screen elements, at least one printing area through which the printing paste can pass, and a blocking area through which the printing paste cannot pass. The problem is solved by a method for manufacturing.

[0037] Importantly, said elongated screen elements are formed in the form of glass fibers and / or carbon fibers and / or carbon nanotubes and are bonded to a flexible planar fabric, in particular a woven or non-crimped fabric, in a bonding step. That is. The planar fabric is placed on the screen frame in the edge region in a tensioning step and joined to the screen frame, preferably under tensile stress.

[0038] This results in the advantages mentioned for the printing plate according to the invention. In particular, as mentioned above, it is advantageous for the fabric to be placed in the screen frame with a tensile stress of greater than 15 N / cm, preferably greater than 20 N / cm, most preferably greater than 25 N / cm.

[0039] The tensile stress of the fabric is particularly preferably applied after the elongated screen element has been placed in a screen frame used for manufacturing under the application of a tensile stress, particularly preferably with the material used to form the blocking area. Preferably, it is obtained by being fixed. In this advantageous embodiment, therefore, the tensile stress of the fabric need not necessarily be imparted by tensioning it in a frame, for example the screen frame of the printing plate. Fixation using a fixing material, in particular the material of the stencil defining the blocking area, makes it possible to fix the tensile stresses in the fabric without using an external frame.

[0040] In another preferred embodiment, the tensile stress of the fabric is obtained by placing the screen in the frame and fixing it to the frame under tensile stress.

[0041] In another advantageous embodiment, the creation of a tensile stress in the fabric comprises tensioning the fabric in the screen frame of the printing plate and using a material, preferably a material used to form the blocking area, in particular It is performed by combining the fastening of the fabric with the material of the stencil that defines the blocking area.

[0042] Advantageously, in the coating step, the screen is provided with a barrier layer through which the printing paste cannot pass, preferably comprising ethylene-propylene-diene rubber.

[0043] Preferably, in the structuring step, openings, particularly preferably elongated channel openings, for the printing areas in the barrier layer are formed. Preferably, the opening is formed using a laser, in particular using laser ablation. This allows for accurate and inexpensive formation of the printing area or areas.

[0044] The opening thus forms a printing area through which the printing paste can pass.

[0045] Advantageously, at least one channel opening is formed in the printing stencil, said channel opening being formed linearly, particularly preferably linearly, and smaller than 40 μm, preferably smaller than 20 μm. , most preferably with a channel width of less than 10 μm.

[0046] Advantageously, in the opening step, a stencil blank, in particular a thin metal plate, is processed into a printing stencil using a laser, wherein elongated channel openings, preferably straight channels, are formed in said stencil blank. The openings are removed and the printed stencil is placed on the screen in an assembly step.

[0047] Therefore, in this advantageous embodiment the definition of the printing area on the printing stencil is performed before the printing stencil is placed on the screen. This prevents damage to the screen when forming one or more of the printing areas.

[0048] The above-mentioned problem is further solved by a method for applying a printing paste to the surface of an electronic component, in particular a photovoltaic solar cell, by means of a printing plate, the printing paste being passed through said printing plate by means of a squeegee. and coated on the substrate of the electronic component. What is important is that a printing plate according to the invention, in particular a preferred embodiment of the printing plate, is used. As a result, narrow linear structures of printing paste can advantageously be applied onto the surface of the electronic component. [Brief explanation of drawings]

[0049]

Figure 1

Figure 2

[0050] Further advantageous features and preferred embodiments are explained below using the embodiments and the figures. Figures 1 to 4 are schematic and show figures not true to scale. Identical reference numerals in the drawings indicate elements that are identical or have identical functions.

[0051] In FIG. 1 a first embodiment of a screen printing apparatus is shown in side view. The apparatus is configured to carry out flatbed screen printing.

[0052] The apparatus has a first embodiment of a printing plate according to the invention, configured as a screen printing plate 1, which printing plate is configured as a flatbed screen printing plate. The screen printing plate 1 is formed in such a way that the screen printing paste 2 can pass through it in parts and in parts through which the screen printing paste 2 cannot pass, in order to form a predetermined structure. This will be explained in detail later using FIGS. 3 and 4.

[0053] Printing paste 2 here is a printing paste containing metal particles, which after heat treatment is applied with metal contacts in the form of contact grids, which are known per se, on the front side of an electronic component formed as a photovoltaic solar cell. Used to form structures.

[0054] The device includes a squeegee 3, which is movable along a direction indicated by an arrow above the squeegee using electric means (not shown). This causes a screen printing paste 2 to be applied onto the screen printing plate 1, and a structure 4 of screen printing paste is applied onto the substrate 5 in order to penetrate the screen printing plate 1 at each passable point.

[0055] The substrate 5 here is formed as a silicon wafer, which already has p-doped regions and n-doped regions for forming the emitter and the base. Therefore, the substrate 5 constitutes a precursor of a solar cell, and it is further necessary to arrange a metal contact structure on the front side of the semiconductor substrate 5 to complete the solar cell.

[0056] The apparatus has a supply unit for supplying and discharging semiconductor substrates, the supply unit having a conveyor belt (not shown), on which a plurality of shuttles are arranged. FIG. 1 shows an example of a shuttle 6 on which a substrate 5 is disposed.

[0057] In FIG. 2, a second printing device with a second embodiment of a printing form according to the invention, designed as a screen printing form 1', is shown as an alternative embodiment. The printing device is configured to carry out a rotary screen printing method.

[0058] As is clear from a comparison with FIGS. 1 and 2, some elements are constructed and arranged identically. However, it is important that in the second embodiment according to FIG. 2 the screen printing plate 1' is designed as a cylindrical screen with a cylindrical shape.

[0059] The squeegee 3 is placed inside the screen printing plate 1' formed into a cylindrical shape, so that the printing paste 2 is placed inside the screen printing plate 1' in order to form the structure 4 made of printing paste on the substrate 5. It is then pushed outward through a screen printing plate.

[0060] Therefore, the screen printing plate 1' formed as a cylindrical screen has a rotating shaft 1a and can be rotated in the direction indicated by the arcuate arrow using each motor means. Therefore, the rotation axis 1a is arranged perpendicular to the drawing plane in FIG. 2.

[0061] At the same time, the semiconductor substrate 5 is shuttled so that the relative velocity between the substrate 5 and the outer surface of the screen printing plate 1' is zero or at least negligibly low at the point of contact between the screen printing plate 1' and the substrate 5. 6 to move in the direction indicated by the straight arrow.

[0062] On the other hand, since the squeegee 3 does not rotate, the printing paste 2 inside the screen printing plate 1' is pressed against the squeegee 3 by the rotating motion of the screen printing plate 1', and the screen is pressed using the squeegee. It passes through a printing plate and is applied onto the substrate 5.

[0063] Each screen printing plate 1 and 1' has basically the same structure, but the screen printing plate 1 has a flat rectangular shape whereas the shape of the screen printing plate 1' corresponds to the outer surface of a cylinder.

[0064] Accordingly, each screen printing plate 1 and 1' respectively represents a respective embodiment of a printing plate according to the invention, said printing plate having a screen frame and formed as a screen printing fabric within said screen frame. A flat woven fabric is placed as a screen under tensile stress.

[0065] In the case of the screen printing plate according to FIG. 1, the screen frame and the screen are rectangularly formed.

[0066] In the case of the screen printing plate according to FIG. 2, the screen is designed as the outer surface of a cylinder. The screen frame has ring-shaped elements arranged on both edges of the screen having an outer shape. Preferably, the fabric is joined to each of the ring-shaped elements.

[0067] In the case of the screen-printing plate according to FIG. 1, the tensile stresses are created substantially by tensioning the screen in the screen frame. In the case of the screen-printing plate according to FIG. 2, the tensile stress is substantially formed by fixing the screen-printing fabric by the stencil. In an alternative embodiment, additional webs are provided between the ring-shaped elements so that the tensile stress is obtained by stretching the screen.

[0068] In the case of both of these screen printing plates, a plurality of elongated, linear, here rectangular openings are formed with a stencil so that each opening defines a printing area through which the printing paste can pass. whereas the stencil itself forms a blocking area through which the printing paste cannot pass.

[0069] In FIG. 3 a cross section through the screen printing plate 1 of the device of FIG. 1 is illustrated.

[0070] The screen printing plate 1 has a rectangular frame 1a, in which a planar fabric formed as a screen printing fabric 1b is stretched.

[0071] The screen printing fabric 1b has elongated screen elements formed as a plurality of fabric elements, the screen elements being arranged in a first element direction and in an element direction which is perpendicular. Said first element direction is the direction perpendicular to the drawing plane in FIG. 3 and correspondingly the second element direction is the direction parallel to the drawing plane in FIG.

[0072] In the screen-printing fabric 1b, stencils 1c are formed from an emulsion and placed in a manner known per se.

[0073] The stencil 1c has a plurality of openings, each formed as a straight elongated channel 1d. The channels of the screen printing plate 1 run parallel to each other and perpendicular to the drawing plane of FIG. 3 and here have the same width. Three channels 1d are exemplarily illustrated in FIG.

[0074] Here, in FIG. 3, when the screen printing paste is pressed against the screen printing plate 1 using the squeegee from above, the screen printing paste can pass through the screen printing plate only in the region of each channel 1d. A structure of screen printing paste corresponding to the positive mold of is formed on the substrate at the bottom of FIG. The structure consists of a corresponding plurality of lines of screen printing paste arranged parallel to each other and adjacent to each other.

[0075] FIG. 4 shows a rear view of the screen printing plate 1 of FIG. 3 as seen from below. Because each textile element of the screen printing fabric 1b extends below each channel 1d, the screen printing plate is not completely opened in the area of ​​each opening of the stencil 1c, i.e. in the area of ​​each channel 1d. It is schematically illustrated that the

[0076] For the printing plate shown in FIG. 1, the elongated screen elements are formed from glass fibers with a fiber diameter of 5 μm and a fiber density of 1500 fibers per inch. The tensile stress is 4000 megapascals.

[0077] In another implementation of this embodiment, the elongated screen elements are formed from carbon fibers having the aforementioned parameters.

[0078] The printing plate of Figure 2 has elongated screen elements formed by carbon nanotubes. The diameter of each screen element is 0.5 μm and the fiber density is 5000 screen elements per inch. Each screen element is placed in a screen frame with a tensile stress of 40,000 megapascals.

[0079] This has the advantage that a narrow channel width can be achieved. The channel width here is 10 μm in the first embodiment and 5 μm in the second embodiment. [Description of symbols]

[0080] 1 screen printing plate 1’ screen printing plate 1a frame 1b screen printing woven fabric 1c stencil 1d channel 2 printing paste 3 Squeegee 4 Structure 5 Substrate (semiconductor substrate) 6 Shuttle

Claims

1. A printing plate for producing a structure of an electronic component, comprising: A printing plate comprising a screen frame and a screen formed as a planar woven fabric having a plurality of elongated screen elements, the screen being disposed within the screen frame, the screen having at least one printing area through which printing paste can pass and at least one blocking area through which printing paste cannot pass, the elongated screen elements are formed from carbon nanotubes having a diameter between 50 nm and 2 μm; The printing plate is characterized in that the fabric is placed in the screen frame at a tensile stress of 6,001 to 63,000 megapascals.

2. 2. The printing plate of claim 1, wherein the fabric is disposed within the screen frame at a tensile stress greater than 15 N / cm.

3. 3. The printing plate according to claim 1, wherein the diameter of the screen elements is less than 10 [mu]m.

4. The printing plate according to any one of claims 1 to 3, characterized in that the screen frame is configured to have a bonding area in an edge region that at least partially joins the stretched fabric to the screen frame.

5. 5. A printing plate according to claim 1, wherein the printing areas are configured at least in part as elongated channel openings having a longitudinal axis and a channel width (w), the channel width (w) being smaller than 40 μm.

6. 6. The printing plate of claim 5, wherein at least one of the screen elements is disposed at an angle unequal to 0[deg.] relative to the longitudinal axis of the channel opening.

7. 7. The printing plate according to claim 1, wherein the printing area has an area ratio SUI calculated from the ratio of the exposed area of ​​the printing area to the area of ​​the printing area covered by the elongated screen elements, the area ratio being greater than 0.

5.

8. 8. The printing plate according to claim 1, wherein the elongated screen elements are arranged in pairs parallel or perpendicular to each other.

9. 1. A method for producing a printing plate having a screen frame and a planar screen having a plurality of elongated screen elements, at least one printing area through which printing paste can pass, and a blocking area through which printing paste cannot pass, comprising: said elongated screen elements in the form of carbon nanotubes having a diameter of between 50 nm and 2 μm are bonded to a flexible planar fabric in a bonding step; The flat fabric is placed on the screen frame at an edge region in a stretching step and joined to the screen frame; The method of claim 1, wherein the fabric is placed within the screen frame at a tensile stress of between 6,001 and 63,000 megapascals.

10. 10. The method of claim 9, wherein the fabric is placed in the screen frame at a tensile stress greater than 15 N / cm.

11. a barrier layer that is impermeable to the printing paste in the coating step is disposed on the screen; 11. A method according to claim 9 or 10, characterized in that elongated channel openings are formed in the barrier layer to form printing areas through which printing paste can pass in the structuring step.

12. 12. The method of claim 11, wherein the channel opening has a channel width, the channel width being less than 40 μm.

13. In the opening step, a stencil blank is processed into a printing stencil using a laser to form elongated channel openings in the stencil blank; 13. The method of claim 12, wherein the assembling step includes placing the printing stencil in the printing area of ​​the screen.

14. A method for applying a printing paste to a surface of an electronic component using a printing plate, the method comprising: passing the printing paste through the printing plate using a squeegee and applying it onto a substrate of the electronic component; 9. A method, characterized in that a printing plate according to any one of claims 1 to 8 is used.

15. The printing plate of claim 1, wherein the electronic component is a photovoltaic solar cell.

16. A printing plate as described in claim 2, characterized in that the tensile stress is greater than 20 N / cm.

17. A printing plate as described in claim 2, characterized in that the tensile stress is greater than 25 N / cm.

18. A printing plate as described in claim 3, characterized in that the diameter of the screen elements is smaller than 6 μm.

19. A printing plate as described in claim 3, characterized in that the diameter of the screen elements is smaller than 2 μm.

20. A printing plate as described in claim 5, characterized in that the channel width (w) is smaller than 20 μm.

21. A printing plate as described in claim 5, characterized in that the channel width (w) is smaller than 10 μm.

22. A printing plate as described in claim 7, characterized in that the SUI is greater than 0.

75.

23. The printing plate of claim 7, wherein the SUI is greater than 1.

24. The method of claim 9, wherein the flexible planar fabric is a woven fabric or a non-crimp fabric.

25. The method of claim 10, wherein the tensile stress is greater than 20 N / cm.

26. The method of claim 10, wherein the tensile stress is greater than 25 N / cm.

27. The method of claim 11, wherein in the coating step, the barrier layer comprises ethylene-propylene-diene rubber.

28. The method of claim 11, wherein in the structuring step, the elongated channel openings are formed using a laser.

29. The method of claim 12, wherein the channel width is less than 20 μm.

30. The method of claim 12, wherein the channel width is less than 10 μm.

31. The method described in claim 13, wherein in the opening step the stencil blank is a thin metal plate.

32. The method described in claim 14, wherein the electronic component is a photovoltaic solar cell.

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