Photovoltaic cell silk screen printing plate and processing method thereof

Abstract

The invention discloses a photovoltaic cell silk screen printing plate and a processing method thereof.The screen printing plate is of a composite silk screen structure formed by weaving warps and wefts in a differentiated mode, the diameter (6-11 micrometers) of the warps is smaller than the diameter (7-13 micrometers) of the wefts, the weaving mesh number (500-600 meshes) of the warps is higher than the weaving mesh number (430-500 meshes) of the wefts, by optimizing silk screen tension distribution and opening uniformity, the mesh number of the warps is increased, and the mesh number of the wefts is increased. Printing deformation is reduced; and slurry conveying efficiency is improved. The processing method comprises the steps of straightening, pressing stress releasing, three-dimensional scanning positioning and PI laser drawing, specifically, a coordinate system is established with the latitude line as the reference, after the grid line grooving position is scanned, the grid line of an original screen printing plate is accurately matched with scanning bending grooving through positioning points at the four corners, and finally, laser grooving (5-15 micrometers in width) is adopted. The technology solves the problem of pattern offset caused by uneven tension of a traditional screen printing plate, and when the screen printing plate is applied to photovoltaic cell auxiliary grid printing, the consistency of electrode line width can be improved, virtual printing line breakage is reduced, and silver paste consumption is reduced.

Description

Technical Field

[0001] This application relates to the technical field of screen printing, and in particular to a screen for photovoltaic cells and a processing method thereof. Background Art

[0002] Photovoltaic cells are manufactured by means of semiconductor wafers, and this manufacturing requires the formation of electrical conductors on the surface of the wafers. The electrical conductors include wide parallel main grid conductors and narrow parallel sub-grid conductors. The function of the sub-grid conductors is to collect electrons generated in silicon by light; the main grid conductors are oriented in a direction perpendicular to the sub-grid conductors, and their function is to conduct higher charges from the photovoltaic cell to the photovoltaic cell. The main grid conductors are usually connected to a metal strip that extends over the entire length.

[0003] The methods of the prior art use screen printing twice to print the main grid conductors and the sub-grid conductors respectively. Specifically, conductive paste is deposited on the semiconductor wafer by screen printing to form these electrical conductors. For this purpose, the method consists in making the conductive paste penetrate a screen composed of a screen mesh. This screen mesh is covered with a sealing layer outside the printing area (except at the positions where the paste should penetrate the screen mesh). This penetration is obtained by means of a squeegee that presses the paste through the mesh fabric. However, the mesh wires of the screen mesh cause interference in this operation, resulting in the impossibility of obtaining electrical conductors with an ideal geometry. In particular, it is limited by the height of the deposited paste layer, resulting in the inability of this method to form electrical conductors with sufficiently good performance. In fact, the electrical conductivity of these electrical conductors is very sensitive to their geometry, especially to the height / width ratio, where the height is measured in the vertical direction perpendicular to the semiconductor wafer and the width is measured in the horizontal direction across the electrical conductor.

[0004] Therefore, this application provides a screen for photovoltaic cells and a processing method thereof, aiming to make the printed electrical conductors as close as possible to their ideal geometry. Summary of the Invention

[0005] In order to solve the deficiencies of the prior art, the purpose of this application is to provide a screen for photovoltaic cells and a processing method thereof, which can reduce the thickness of the pressure nodes at the screen openings to reduce the screen thickness, and reduce the height of the deposited paste layer to optimize the ink permeability of the screen, so as to make the printed electrical conductors as close as possible to their ideal geometry, thereby improving the electrical conductivity of the electrical conductors of the photovoltaic cells.

[0006] To achieve the above purpose, this application adopts the following technical solutions: The present application provides a screen stencil for a photovoltaic cell. The screen stencil for the photovoltaic cell includes a screen frame and a composite screen structure disposed within the screen frame. The composite screen structure is formed by laminating a first screen and a second screen. It is characterized in that the first screen is woven by crossing warp threads and weft threads, and the wire diameter of the warp threads is smaller than that of the weft threads, and the weaving count of the warp threads is greater than that of the weft threads.

[0007] As a preferred technical solution, the wire diameter of the weft threads is 7 - 13 μm, and the weaving count of the weft threads is 430 - 500 meshes; the wire diameter of the warp threads is 6 - 11 μm, and the weaving count of the warp threads is 500 - 600 meshes.

[0008] As a preferred technical solution, the distance between adjacent weft threads of the first screen is increased by 15% - 30% compared to the distance between adjacent warp threads, and the weaving count of the warp threads is 10% - 20% higher than that of the weft threads.

[0009] As a preferred technical solution, the screen stencil for the photovoltaic cell is used for printing the auxiliary grid conductors of the semiconductor wafer of the photovoltaic cell.

[0010] The present application also provides a processing method for the above-mentioned screen stencil for the photovoltaic cell. The processing method includes the following steps: S1. Straightening: The screen stencil is leveled through a top frame machine and an electronic imager to adjust the straightness; S2. Pressing and ironing: The leveled screen stencil is pressed and ironed at a preset temperature and pressure, and left standing for several hours to release the internal stress; S3. Three-dimensional scanning: The pressed and ironed screen stencil is placed in a three-dimensional scanner, and a coordinate system is established based on the first weft thread to scan the grooving positions of the grid lines; S4. Wire clamping and synthesis: A grid line distribution map is generated based on the scanning data, so that each grid line of the original drawing of the screen stencil coincides with the grooving position in the scanned image; S5. PI laser mapping: The synthesized drawing is imported into a PI machine, and by checking whether the fine grid lines of the battery pattern of the entire original drawing of the screen stencil are within the grid of the screen stencil, laser grooving processing is performed.

[0011] As a preferred technical solution, in step 3, positioning points are added at the four corners of the screen stencil during the scanning process for positioning in the subsequent wire clamping and synthesis process; in step 4, the method of wire clamping and synthesis is: taking the scanned image in step 3 as the bottom layer, the grid lines of the scanned image of the bottom layer are in an irregular curved shape. According to the four added positioning points, the battery pattern on the original drawing of the screen stencil is placed in the bottom layer scanned image in the warp direction, and each grid line on the original drawing of the screen stencil is respectively placed into its grid line according to the curved shape of the bottom layer scanned image to obtain a synthesized image with wire clamping completed, thus completing the drawing.

[0012] As a preferred technical solution, in step S5, the grooving width is 5 - 15 μm.

[0013] Compared with the prior art, the beneficial effects of the present application are as follows: (1) This application can reduce the thickness of the knotted points at the screen openings to decrease the screen thickness, and lower the height of the deposited paste layer to optimize the ink permeability of the screen, so that the printed electrical conductor can be as close as possible to its ideal geometric shape, thereby improving the conductivity of the electrical conductor of the photovoltaic cell.

[0014] (2) Since the distance between adjacent latitudes of the screen printing stencil of this application is increased, it is easier to find the slotting position, which is more suitable for the wire clamping process of the sub-grid stencil. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic structural diagram of the screen printing stencil of the photovoltaic cell of this application; Figure 2 is a side view of the screen printing stencil of the photovoltaic cell of this application; Figure 3 is a schematic structural diagram of the opening node of a traditional screen printing stencil; Figure 4 is a schematic structural diagram of the opening node of the screen printing stencil of the photovoltaic cell of this application; Wherein: 11, warp threads; 12, weft threads. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In order to enable those skilled in the art to better understand the solution of this application, the technical solutions in the specific embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application.

[0017] This application provides a screen printing stencil for a photovoltaic cell, which is used to transfer ink or paste through the mesh holes to the substrate by screen printing to form patterns or texts.

[0018] As Figure 1 and Figure 2 shown, the screen printing stencil includes a screen frame, and a screen formed by laminating a first screen and a second screen through a screen lamination process is provided inside the screen frame. In this application, the first screen is made of tungsten steel wires woven, and the second screen is made of nylon wires woven.

[0019] Among them, the first screen includes: a plurality of warp threads 11 and a plurality of weft threads 12 arranged in a crosswise pattern.

[0020] Specifically, the wire diameter of the warp 11 is smaller than that of the weft 12, and the knitting count of the warp 11 is larger than that of the weft 12. The warp 11 uses a thin wire with a higher count, so it has higher precision and can print finer grid lines. The weft 12 uses a thick wire, which can provide higher structural strength in the non-printing area, improve the overall tension and stress of the screen printing plate, and is not easily relaxed under the pressure of the squeegee during use, thus extending the service life of the screen printing plate. More specifically, the wire diameter of the weft 12 is 7 - 13um, and the count is 430 - 500; the wire diameter of the warp 11 is 6 - 11um, and the count is 500 - 600; the thickness of the first screen is 10 - 20um. More specifically, the distance between adjacent wefts 12 of the first screen is 15% - 30% larger than the distance between adjacent warps 11, and the knitting count of the warp 11 is 10% - 20% higher than that of the weft 12.

[0021] As Figure 3 shown, in a traditional screen printing plate, the wire diameter of the screen warp 11 is equal to that of the weft 12, and the knitting count of the warp 11 is equal to that of the weft 12. Therefore, the distance between adjacent warps 11 is equal to the distance between adjacent wefts 12, and its opening is a square opening with a relatively large opening node.

[0022] As Figure 4 shown, in the screen printing plate of the present application, the wire diameter of the first screen warp 11 is smaller than that of the weft 12, and the knitting count of the warp 11 is larger than that of the weft 12. By increasing the knitting count of the warp 11 and decreasing the knitting count of the weft 12, the overall tension and stress of the screen printing plate can be maintained. Since the knitting count of the weft 12 decreases, the distance between adjacent wefts 12 increases. The opening of the first screen of the present application is a rectangular opening, and the opening node is significantly smaller than that of the traditional screen printing plate. Therefore, the present application can reduce the size of the screen opening stamping node, reduce the slurry blockage at the opening node to optimize the ink permeability of the screen, so that the printed electrical conductor is as close as possible to its ideal geometric shape, and thus improve the conductivity of the electrical conductor of the photovoltaic cell.

[0023] For the screen printing plate of the present application, without changing the wire diameter of the weft 12, the wire diameter of the warp 11 is reduced, and the overall tension and stress of the screen printing plate are maintained by increasing the knitting count of the warp 11. The screen thickness is equal to the thickness of the screen opening stamping node, and the thickness of the screen opening stamping node is equal to the sum of the wire diameters of the warp 11 and the weft 12. Assuming that in a traditional screen printing plate, the wire diameters of both the screen warp 11 and the weft 12 are 9um, then the thickness of the screen opening stamping node is equal to 18um; while for the screen printing plate of the present application, the wire diameter of the weft 12 remains 9um unchanged, and the wire diameter of the warp 11 is reduced to, for example, 7um, then the thickness of the screen opening stamping node of the present application is equal to 16um. Therefore, the present application can reduce the thickness of the screen opening stamping node to reduce the screen thickness, reduce the height of the deposited slurry layer to optimize the ink permeability of the screen, so that the printed electrical conductor is as close as possible to its ideal geometric shape, and thus improve the conductivity of the electrical conductor of the photovoltaic cell.

[0024] The screen screen of the present application can maintain the tension and stress of the screen as a whole by increasing the number of weaving meshes of the warp threads 11 and reducing the number of weaving meshes of the weft threads 12. Since the number of weaving meshes of the weft threads 12 is reduced, the spacing between adjacent weft threads 12 is increased, so the screen screen of the present application can be equipped with a wire clamping process suitable for manufacturing the screen screen sub-grid.

[0025] Furthermore, the photovoltaic cell screen is used to print the secondary grid conductor of the photovoltaic cell semiconductor wafer.

[0026] It should be noted that, according to the main grid conductor and the secondary grid conductor of the photovoltaic cell, the silk screen screen is also divided into the main grid screen and the secondary grid screen. The length direction of the secondary grid conductor is consistent with the direction of the latitude 12, and the length direction of the main grid conductor is consistent with the direction of the warp 11. Since the main grid conductor is much thicker than the secondary grid conductor, the manufacturing precision of the secondary grid screen is higher than that of the main grid screen. The silk screen screen of this application mainly refers to the secondary grid screen.

[0027] The wire mesh screen of the present application is more suitable for the wire clamping process of the secondary grid screen. The wire clamping process of the secondary grid screen refers to making grooves on the warp 11, and then clamping the secondary grid wires into the grooves of the warp 11. Since the number of grooves on the main grid screen is much less than that on the secondary grid screen (generally, the main grid screen has 16-20 grooves, and the secondary grid screen has about 200 grooves), the wire mesh screen of the present application is more suitable for the wire clamping process of the secondary grid screen. Since the spacing between adjacent weft lines 12 of the wire mesh screen of the present application is increased, it is easier to find the groove position.

[0028] The present application also provides a method for processing the above-mentioned photovoltaic cell silk screen, which includes the following steps: S1. Straightening: The silk screen is leveled by a top frame machine and an electronic imager to adjust the straightness; S2. Pressing: The leveled silk screen is pressed at a preset temperature and pressure, and left to stand for several hours to release internal stress; S3. Three-dimensional scanning: The pressed silk screen is placed on a three-dimensional scanner, a coordinate system is established with the first latitude line 12 as a reference, and the grid line slot positions are scanned; S4. Line synthesis: A grid line distribution map is generated based on the scanning data, so that each grid line of the silk screen original image coincides with the slot position in the scanned image; S5. PI laser mapping: The synthesized drawing is imported into the PI machine, and the laser is used to perform slotting processing by checking whether the fine grid lines of the battery pattern of the entire silk screen original image are within the grid of the silk screen.

[0029] Further, in step 3, positioning points are added at the four corners of the silk screen stencil during the scanning process for positioning in the subsequent wire clamping synthesis process; in step 4, the method of wire clamping synthesis is as follows: taking the scanned image in step 3 as the bottom layer, the raster lines of the scanned image of the bottom layer are irregularly curved. According to the four added positioning points, the battery patterns on the original silk screen stencil are placed on the bottom layer scanned image in the direction of warp 11, and each grid line on the original silk screen stencil is placed into its grid line respectively according to the curvature of the bottom layer scanned image to obtain the synthesized image with wire clamping completed, thus completing the drawing.

[0030] Further, in step S5, the slot width is 5 - 15um.

[0031] Specifically, first, manually place the silk screen stencil to be produced in the top frame machine, and use the electronic imager therein to level the straightness of the wire mesh, so that the wire mesh maintains tension. Subsequently, manually place the well-positioned silk screen stencil on the positioning holes of the laser cutting machine, set the number of drawn wires per root to 3, and the drawn wire spacing to 360 - 410 meshes. After setting, start the laser cutting machine to draw wires on the upper and lower wire meshes of the silk screen stencil, with a total of 6 drawn wires, avoiding the long time in the existing wire drawing process and the easy displacement of the silk screen stencil during the wire drawing process, resulting in low efficiency and problems with the quality of the silk screen stencil; after the laser cutting of the upper and lower lines is completed, perform the hot pressing process on the silk screen stencil through the hot press according to the SOP. Subsequently, place the silk screen stencil after hot pressing in a clean, cool, dry and well-ventilated environment for static placement, avoiding direct sunlight and excessive humidity during the process, so as to prevent the silk screen stencil from deforming in size due to environmental factors. It should be noted that the static placement time is controlled within 9 - 10h. If the static placement time is too short, the tension of the silk screen stencil will be unstable, affecting the subsequent printing effect of the stencil; if the static placement time is too long, the silk screen stencil will absorb dust and impurities in the air, resulting in residue in the mesh holes and affecting the smooth passage during subsequent printing; Subsequently, manually place the static silk screen stencil on the 3D scanner, and start scanning with the first wire drawn during the above wire drawing process as the starting point of the scanned image. After the scanning is completed, obtain the scanned image and the original stencil image, and start drawing through the computer. Place each thin grid line of the battery pattern on the original silk screen stencil completely into the grid lines of the scanned image, thus completing the drawing to obtain the synthesized image with wire clamping. In this way, without drawing wires on each wire mesh of the stencil, the thin grid lines of the battery pattern can be placed into the intervals of warp 11 of the wire mesh, greatly reducing the cost of manufacturing the silk screen stencil. At the same time, because the number of steel wires cut by laser is small and the stencil shape is small, the phenomena of burst stencil and cracking are avoided, and at the same time, the problem of secondary high-temperature hot pressing caused by rework due to the quality decline caused by wire drawing is also reduced; Subsequently, the card line synthesis drawing is manually imported into the PI machine, and a grid line is arbitrarily selected for preview observation to ensure the quality of the card line synthesis and avoid the problem of quality degradation caused by direct laser mapping. After confirmation, PI laser mapping can be started to obtain the finished silk screen screen and complete the silk screen screen production of the card line process. The finished silk screen screen of the card line process is closer to the mesh knots on both sides in terms of the grid line distance, so that the slope of the grid line edge is increased and the mesh is supported. In subsequent printing, the scraper is closer to the mesh knot during the walking process, which will make the printed lines high and the line shape good, and reduce the problem of virtual printing.

[0032] In the traditional silk screen drawing process, one yarn is drawn out on each side of the slot. Compared with the silk drawing process, the positioning process has one less step of drawing, and the yarns of the silk screen are intact, which does not affect the mechanical properties of the silk screen. Since the silk drawing process draws out several yarns, the total number of yarns is reduced, resulting in a smaller tension that the silk screen can withstand, making it easier to break when the scraper is pressed down for printing.

[0033] It should be noted that the main force-bearing line of the silk screen is the weft 12, and drawing the wire is to draw out the weft 12. The wire-carding process leaves more weft 12 than the drawing process, so the silk screen has better mechanical properties, can withstand more times of scraper pressure during printing, and has a longer lifespan.

[0034] It should be noted that the words "first", "second" and similar words used in the specification and claims of this application do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "a" do not indicate a quantitative limitation, but indicate the existence of at least one. "Multiple" or "several" means at least two. Unless otherwise specified, words such as "front", "back", "left", "right", "bottom" and / or "top" are only for the convenience of description and are not limited to one position or one spatial orientation. Words such as "include" or "comprise" mean that the elements or objects appearing before "include" or "comprise" include the elements or objects listed after "include" or "comprise" and their equivalents, and do not exclude other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, and may include electrical connections, whether direct or indirect.

[0035] The singular forms "a", "said" and "the" used in this specification and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0036] It should be understood that those of ordinary skill in the art can make improvements or modifications based on the above description, and all such improvements and modifications shall fall within the protection scope of the appended claims of this application.

Claims

1. A screen printing stencil for a photovoltaic cell, the screen printing stencil for the photovoltaic cell comprising a screen frame and a composite screen structure disposed within the screen frame, the composite screen structure being formed by laminating a first screen and a second screen, characterized in that, The first wire mesh is woven by the cross arrangement of warp and weft threads, and the wire diameter of the warp thread is smaller than that of the weft thread, and the weaving count of the warp thread is larger than that of the weft thread.

2. The screen printing stencil for a photovoltaic cell according to claim 1, characterized in that, The wire diameter of the weft thread is 7 - 13 μm, and the weaving count of the weft thread is 430 - 500 meshes; the wire diameter of the warp thread is 6 - 11 μm, and the weaving count of the warp thread is 500 - 600 meshes.

3. The screen printing stencil for a photovoltaic cell according to claim 1, characterized in that, The adjacent weft thread spacing of the first wire mesh is increased by 15% - 30% compared with the adjacent warp thread spacing, and the weaving count of the warp thread is 10% - 20% higher than that of the weft thread.

4. The screen printing stencil for a photovoltaic cell according to claim 1 or 2 or 3, characterized in that, The wire mesh screen plate of the photovoltaic cell is used for printing the auxiliary grid conductor of the semiconductor wafer of the photovoltaic cell.

5. A method for processing a screen printing stencil of a photovoltaic cell according to any one of claims 1-4, characterized in that, The processing method includes the following steps: S1. Straightening: Level the wire mesh screen plate through a top frame machine and an electronic imager to adjust the straightness. S2. Pressing and ironing: Press and iron the leveled wire mesh screen plate at a preset temperature and pressure, and let it stand for several hours to release the internal stress. S3. Three - dimensional scanning: Place the pressed and ironed wire mesh screen plate on a three - dimensional scanner, establish a coordinate system with the first weft thread as the reference, and scan the grooving positions of the grid lines. S4. Wire clamping and synthesis: Generate a grid line distribution map based on the scanning data, and make each grid line of the original drawing of the wire mesh screen plate coincide with the grooving position in the scanned image. S5. PI laser mapping: Import the synthesized drawing into a PI machine, check whether all the fine grid lines of the battery pattern in the original drawing of the entire wire mesh screen plate are within the grid of the wire mesh screen plate, and perform grooving processing using a laser.

6. The processing method of the wire mesh screen plate of the photovoltaic cell according to claim 5, wherein in step 3, positioning points are added at the four corners of the wire mesh screen plate during the scanning process for positioning in the subsequent wire clamping and synthesis process. in step 4, the method of wire clamping and synthesis is as follows: Take the scanned image in step 3 as the bottom layer. The grid lines of the scanned image of the bottom layer are in an irregular curved shape. According to the four added positioning points, place the battery pattern on the original drawing of the wire mesh screen plate in the warp direction on the bottom - layer scanned image, and place each grid line on the original drawing of the wire mesh screen plate into its grid line according to the curved shape of the bottom - layer scanned image to obtain a synthesized image with wire clamping completed, thus completing the drawing.

7. The method for processing a screen printing stencil for a photovoltaic cell according to claim 5, wherein In step S5, the grooving width is 5 - 15 μm.

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