PRINTING MOLD FOR PRODUCE OF A STRUCTURE OF AN ELECTRONIC COMPONENT, IN PARTICULAR A PHOTOVOLTAIC SOLAR CELL AND METHOD FOR PRODUCEING SUCH A PRINTING MOLD

Description

[0001] The invention relates to a printing mold for producing a 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 mold according to the preamble of claim 7. The invention further relates to 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 mold according to the preamble of claim 11.

[0002] In the manufacture of electronic components such as semiconductor devices or printed circuit boards, and especially in the production of photovoltaic solar cells, many manufacturing processes require the application of a printing paste in a predefined, typically linear, and particularly rectilinear structure. The printing paste may contain metallic particles to form a metallic conduction and / or contact structure of the component. Additionally or alternatively, the printing paste may also contain substances for treating the semiconductor, in particular dopants for forming doping regions in the semiconductor material of the component.

[0003] It is known to apply a printing paste to one or more local areas of a component's surface using screen printing to create the aforementioned structure. A printing form is used, comprising a screen frame and a screen. The screen is designed as a sheet-like textile. A stencil is arranged on the screen, defining a printing area permeable to the printing paste through openings or areas cut out by the stencil, and a barrier area impermeable to the printing paste, which is covered by the stencil. The sheet-like textile screen has several elongated screen elements, which typically run parallel and spaced apart from each other or perpendicular to each other.

[0004] To apply the printing paste to the surface of the electronic component, the paste is applied at least within the printing area of ​​the mold. The screen prevents the paste from immediately penetrating the mold upon application. Only by applying additional force, typically with a squeegee, is the paste forced through the mold and thus, in particular, through the screen onto the surface of the component.

[0005] There is an increasing need to create line-like structures with progressively smaller widths. The channels defined by the printing area for forming these line-like structures must therefore have a correspondingly small width to meet this requirement. A disadvantage of existing printing forms is that the design of the printing form itself prevents a minimum channel width from being undercut, as otherwise irregular or even discontinuous line-like structures of the printing paste would be applied.

[0006] JP2017091741A discloses a method for creating fine membrane line patterns on a substrate using screen printing. First, a resist layer with inverted patterns is applied. Then, using a second screen printing plate, the membrane is applied to the uncovered areas. Finally, the desired membrane line pattern is formed by removing the resist layer.

[0007] US20170001430A1 proposes a printing stencil with a uniform thickness for precise printing and a rough surface for improved separation from the printing medium, as well as a manufacturing process. The process involves preparing a substrate with a printing pattern and an organic surface, followed by dry etching on the printed surface.

[0008] US Patent 2015 / 352830A1 discloses a screen printing plate consisting of at least two woven fibers, including polymer fibers or inorganic fibers. At least one of these fibers is soluble, e.g., in an organic solvent. The screen printing plate exhibits a distinct mesh pattern resulting from the dissolution of the woven fiber(s).

[0009] JPH10315647A also proposes a screen printing plate for printing fine patterns on thick material. This screen printing plate comprises at least one frame mesh and a stencil, the mesh consisting of two or more meshes. The meshes are arranged such that the spaces between at least two meshes lie at a symmetrical angle to the printing direction, and the two meshes are fixed by a film or coating.

[0010] In DE29708329U1, a screen printing stencil is disclosed which combines the flexibility and adaptability of a screen with the stability of open openings of a metal stencil. A stencil consisting of two different materials for the top and bottom is proposed.

[0011] EP3000612A1 proposes a structure for screen printing which increases the wettability of a squeegee-coated surface and forms a water / oil-repellent layer.

[0012] The present invention is therefore based on the objective of providing a printing form which enables the formation of narrow, linear structures from printing paste.

[0013] This problem is solved by a printing form according to claim 1, a method for producing a printing form according to claim 7 and a method for applying a printing paste according to claim 11. Advantageous embodiments are found in the dependent claims.

[0014] The printing form according to the invention for producing a structure of an electronic component, in particular a photovoltaic solar cell, comprises a screen frame and a screen designed as a planar textile with a plurality of elongated screen elements. The screen is arranged in the screen frame, preferably under tensile tension. The screen has at least one printing area permeable to the printing paste and at least one barrier area impermeable to the printing paste.

[0015] It is essential that the elongated sieve elements are designed as carbon nanotubes and that the textile is arranged in the sieve frame with a tensile stress in the range of 6001 N / mm 2< (Megapascal) to 63000 N / mm 2< (Megapascal).

[0016] The invention is based on the applicant's finding that the tensile stress with which the elongated sieve elements are arranged in the sieve frame is an essential parameter for the minimum possible channel width of a printing area of ​​the printing form.

[0017] Therefore, if a material with particularly high tensile strength is used for the elongated sieve elements, linear elements with a particularly narrow width can be produced. Through experiments and calculations, the applicant has succeeded in reducing the number of sieve elements per unit length (typically specified in sieve elements per inch) as well as the diameter of the sieve elements by adapting the material from which the sieve elements are manufactured to such an extent that a material-specific high tensile strength is present.

[0018] Investigations by the applicant show that, in particular, the maximum fabric tension of the screen formed as a planar textile and thus also the print quality of applied structures with a small channel width is increased by forming the elongated screen elements as carbon nanotubes.

[0019] When the elongated sieve elements are formed as carbon nanotubes, tensile stresses of 63,000 N / mm² (megapascal) can be achieved.

[0020] Investigations by the applicant show that increasing the tensile stress by selecting the material of the sieve elements in the printing form according to the invention enables a significant reduction in the diameter of the sieve elements.

[0021] This is surprising because the diameter of the sieve elements is a parameter whose increase allows for greater tensile stresses. With previously known printing dies, a desired increase in fabric tension, i.e., the tensile stress of the elongated sieve elements, was achieved by increasing the diameter of the sieve elements. In contrast, the material selection for the printing die according to the invention makes it possible to achieve high fabric tensions with still small diameters.

[0022] According to the invention, the printing form is designed with the following tensile stresses and diameters of the elongated sieve elements: Material of the elongated sieve elements Diameter of the sieve elements Tensile stress Carbon nanotubes 50 nm to 2 µm 6001 N / mm 2< (megapascal) to 63000 N / mm 2< (megapascal)

[0023] The aforementioned preferred areas for the parameters mentioned above enable small channel widths and thus small widths of the line-like structures formed by means of the printing paste.

[0024] Investigations by the applicant show that in the design of the elongated sieve elements made of carbon nanotubes, preferably in the range of 1968 sieve elements per m (50 sieve elements per inch) to 393700 sieve elements per m (10,000 sieve elements per inch) are arranged.

[0025] In particular, it is advantageous to arrange between 2755 sieve elements per m (70 sieve elements per inch) and 79724 sieve elements per m (2025 sieve elements per inch) when forming the elongated sieve elements from carbon nanotubes.

[0026] The aforementioned densities for the sieve elements are preferably formed at least in the pressure area of ​​the printing form, and more preferably in the pressure area and barrier area.

[0027] As previously described, the printing form according to the invention is particularly suitable for producing elongated, linear structures from printing paste. Advantageously, the printing area is therefore at least partially designed as an elongated channel opening, in particular a linear channel opening, preferably a straight channel opening, preferably with a longitudinal extent and a channel width (b). The channel width (b) is preferably less than 40 µm, preferably less than 20 µm, and particularly preferably less than 10 µm.

[0028] The sieve, designed as a sheet-like textile, preferably comprises at least a first group of elongated sieve elements, wherein the elongated sieve elements of this group are arranged parallel to one another and, more preferably, equidistant from one another. Preferably, if at least one straight channel opening is provided in the printing area, the channel opening is arranged at an angle other than 0° to the longitudinal axis of the channel opening. In particular, it is advantageous to provide an angle and a maximum channel width as described in DE 10 2019 122 126.9. In particular, it is advantageous that the previously described at least one straight channel of the printing area includes an angle with a sieve element of the printing area with a tolerance of + / - 0.1°, wherein the angle is selected from the group 11.31°, 14.04°, 18.44°, 26.57°, 45°, 33.69°, in particular 11.31°, 14.04°, 18.44°, 26.57°, 33.69°.

[0029] This allows for an advantageous reduction in the number of nodes of sieve elements within the channel opening, as known from DE 10 2019 122 126.9.

[0030] Advantageously, the screen of the printing form, which is designed as a planar textile, has at least a second group of elongated screen elements, wherein the elongated screen elements of the second group are arranged parallel to each other and preferably equidistantly. In particular, it is advantageous that the screen elements of the first and second groups enclose an angle in the range of 30° to 150°, preferably 60° to 120°, more preferably 85° to 95°, more preferably 90°.

[0031] In particular, it is advantageous that the elongated sieve elements of the printing form are completely assigned to the aforementioned first and second groups.

[0032] The elongated sieve elements are therefore preferably arranged in pairs parallel or perpendicular to each other.

[0033] Investigations by the applicant have shown that, preferably, in the printing area, the area ratio SUI, which results from the ratio of the free area in the printing area to the area covered by the elongated sieve elements in the printing area, is greater than 0.5, before preferably greater than 0.75, and in particular greater than 1. This achieves an advantageous opening ratio for applying printing paste through the sieve onto the surface of the component at an advantageously low pressure, in particular by means of a squeegee.

[0034] As described above, the printing form according to the invention has a plurality of elongated sieve elements. It is within the scope of the invention that the sieve elements are connected to one another and, in particular, are formed from one or more elongated, flexible sieve element base elements by means of deflection in the area of ​​the sieve frame.

[0035] The aforementioned problem is further solved by a method for producing a printing form with a screen frame and a planar screen with a plurality of elongated screen elements and at least one printing area suitable for printing and a barrier area impermeable to printing paste.

[0036] Essentially, the elongated sieve elements are formed in the form of carbon nanotubes and joined in a single bonding step to form a flexible, planar textile, in particular a woven or non-woven fabric. In a tensioning step, the planar textile is positioned with its edge region against the sieve frame and connected to the sieve frame, preferably by applying tensile stress.

[0037] This results in the advantages mentioned for the printing form according to the invention. It is essential that the textile is arranged in the screen frame with a tensile stress in the range of 6001 N / mm² to 63000 N / mm².

[0038] The tensile tension of the textile is preferably achieved by arranging the elongated screen elements under tension, particularly within a screen frame used for manufacturing, and then fixing them, preferably by means of the material that forms the barrier area. In this advantageous embodiment, the tensile tension of the textile does not necessarily have to be achieved by clamping it in a frame such as the screen frame of the printing form. By fixing it with the fixing material, in particular the material of a template that defines the barrier area, the tensile tension of the textile can also be achieved without an external frame.

[0039] In an alternative preferred embodiment, the tensile tension of the textile is achieved by arranging the sieve under tensile tension in the frame and fixing it to the frame.

[0040] In a further advantageous embodiment, the tensile stress of the textile is created by a combination of clamping the textile in the screen frame of the printing form and fixing the textile with a material, preferably by means of the material by means of which the barrier area is formed, in particular the material of a template which defines the barrier area.

[0041] Advantageously, in a coating step, a barrier layer impermeable to printing paste, preferably containing ethylene propylene diene monomer rubber, is applied to the screen. In the structuring step, an opening for the printing area is preferably formed in the barrier layer, particularly preferably an elongated channel opening. The opening is preferably formed using a laser, especially by laser ablation. This enables precise and cost-effective formation of the printing area(s).

[0042] This opening thus forms a pressure area permeable to the printing paste.

[0043] Advantageously, at least one channel opening is formed in the printing stencil, which is linear, in particular preferably straight, and has a channel width which is less than 40 µm, preferably less than 20 µm, most preferably less than 10 µm.

[0044] Advantageously, in one opening step a template blank, in particular a thin-walled sheet, is processed into a printing template by means of a laser, wherein an elongated channel opening, preferably a straight channel opening, is eliminated in the template blank, and in one assembly step the printing template is arranged on the screen.

[0045] In this advantageous embodiment, the printing area is defined in the printing stencil before the printing stencil is positioned on the screen. This prevents damage to the screen during the formation of the printing area(s).

[0046] The aforementioned 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 mold, wherein a squeegee is used to apply the printing paste through the printing mold onto a substrate of the electronic component. It is essential that a printing mold according to the invention, in particular a preferred embodiment thereof, is used.

[0047] This allows for the advantageous application of narrow, linear structures of printing paste to the surface of the electronic component.

[0048] Further advantageous features and preferred embodiments are explained below with reference to exemplary embodiments and the figures. Figure 1 shows an illustrative example of a screen printing device with an illustrative example of a printing form for flatbed screen printing; Figure 2 shows a second embodiment of a screen printing device with an exemplary embodiment of a printing form according to the invention for rotary screen printing; Figure 3 shows a sectional view of the illustrative example of a printing form of the screen printing device according to the invention. Figure 1 Figure 4 shows a top view of the printing form according to Figure 3 .

[0049] The figures are schematic representations, not to scale. Identical reference symbols within the figures denote identical or equivalent elements.

[0050] In Figure 1 Figure 1 is an illustrative example of a screen printing device shown in side view. The device is designed to perform a flatbed screen printing process.

[0051] The device includes an illustrative example of a printing form designed as a screen printing mold 1, which is configured as a flatbed screen printing mold. The screen printing mold 1 is partially permeable to a screen printing paste 2 and partially impermeable to the screen printing paste 2 in order to form a predetermined structure. This will be explained below using the Figures 3 and 4 explained in more detail.

[0052] The printing paste 2 is a printing paste containing metal particles, which serves to form a metallic contact structure in the form of a known contact grid on the front side of an electronic component designed as a photovoltaic solar cell after thermal treatment.

[0053] The device includes a squeegee 3 which can be moved along the direction indicated by the arrow above the squeegee by means of a motor (not shown). This spreads the screen printing paste 2 over the screen printing form 1, where it penetrates the form at the permeable areas, thus applying the screen printing paste structure 4 to a substrate 5.

[0054] The substrate 5 is configured as a silicon wafer, which already has p- and n-doped regions for forming the emitter and base. The substrate 5 thus represents a solar cell precursor; to complete the solar cell, the metallic contact structure still needs to be arranged on the front face of the semiconductor substrate 5.

[0055] The device includes a feeding unit for supplying and removing semiconductor substrates, which has a conveyor belt (not shown) on which several shuttles are arranged. An example is shown in Figure 1 A shuttle 6 with substrate 5 lying on it is shown.

[0056] In Figure 2 As an alternative embodiment, a second printing device is shown, comprising an embodiment of a printing form according to the invention designed as a screen printing mold 1'. This printing device is designed for carrying out a rotary screen printing process. As a comparison of Figures 1 and 2 shows, some elements are identically designed and arranged. However, it is essential that in the second embodiment according to Figure 2The screen printing form 1' is designed as a round screen with a cylindrical shape. The squeegee 3 is arranged inside the cylindrical screen printing form 1', so that the printing paste 2 is forced from inside the screen printing form 1' through the screen printing form to the outside in order to form the structure 4 of printing paste on the substrate 5.

[0057] For this purpose, the screen printing form 1', designed as a rotary screen, has a rotation axis 1a and can be rotated by means of a motor in the direction indicated by the circular arc arrow. The rotation axis 1a is thus oriented in Figure 2 perpendicular to the drawing plane.

[0058] At the same time, the semiconductor substrate 5 is moved by means of the shuttle 6 in the direction shown as a straight arrow, such that the relative velocity between substrate 5 and the lateral surface of the screen printing mold 1' at the point of contact between screen printing mold 1' and substrate 5 is zero or at least negligibly small.

[0059] The squeegee 3, however, does not perform a rotational movement, so that the printing paste 2 inside the screen printing form 1' is pressed against the squeegee 3 due to the rotational movement of the screen printing form 1' and is applied to the substrate 5 through the screen printing form by means of the squeegee.

[0060] Screen printing forms 1 and 1' are basically constructed the same, except that screen printing form 1 has a flat, rectangular shape, whereas the shape of screen printing form 1' corresponds to the lateral surface of a cylinder.

[0061] The screen printing form 1' thus represents an embodiment of a printing form according to the invention, which has a screen frame in which a planar textile designed as screen printing fabric is arranged as a screen under tension. In the case of the screen printing form according to Figure 1 The screen frame and the screen itself are rectangular. In the case of the screen printing form according to Figure 2The screen is designed as the lateral surface of a cylinder. The screen frame has ring-shaped elements arranged at both edges of the lateral surface of the screen. The fabric is preferably glued to these ring-shaped elements. In the screen printing form according to... Figure 1 The tensile stress is essentially created by clamping the screen in the screen frame. In the screen printing mold according to... Figure 2 The tensile tension is essentially created by fixing the screen printing mesh to the stencil. In an alternative design, additional webs are provided between the ring-shaped elements, so that the tensile tension is achieved by clamping the screen.

[0062] In both screen printing forms, a stencil is used to create a plurality of elongated, straight, in this case rectangular openings, so that these openings form a printing area permeable to printing paste, whereas the stencil itself forms a barrier area impermeable to the printing paste.

[0063] In Figure 3 is a cross-section through the screen printing mold 1 of the device according to Figure 1 The screen printing form 1 has the rectangular frame 1a in which the planar textile, designed as screen printing fabric 1b, is stretched. The screen printing fabric 1b has a plurality of elongated screen elements designed as woven elements, which are arranged in a first element direction and a perpendicular element direction. The first element direction is as follows: Figure 3 perpendicular to the drawing plane and accordingly the second element direction lies according to the representation in Figure 3parallel to the drawing plane.

[0064] The stencil 1c, which is formed as an emulsion in a manner known per se, is arranged on the screen printing mesh 1b. The stencil 1c has a plurality of openings, each formed as a straight, elongated channel 1d. The channels of the screen printing form 1 run parallel to each other and perpendicular to the drawing plane according to Figure 3 and exhibit identical widths. Examples are shown in Figure 3 three channels labeled 1d.

[0065] Will now in Figure 3 When screen printing paste is pressed onto the screen printing form 1 from above using the squeegee, the screen printing paste can only penetrate the screen printing form in the area of ​​the channels 1d, so that a structure of screen printing paste corresponding to the positive shape of the channels is formed on a surface below the Figure 3 A substrate is created lying on the ground, which consists of a corresponding number of parallel lines of screen printing paste arranged next to each other.

[0066] In Figure 4 is a rear view from below of screen printing form 1 according to Figure 3 The schematic diagram shows that in the area of ​​the openings of the stencil 1c, i.e. in the area of ​​the channels 1d, the screen printing form is not fully open, since fabric elements of the screen printing fabric 1b run below the channels 1d.

[0067] In the case of the in Figure 1 In the depicted printing form, the elongated sieve elements are made of glass fiber with a fiber diameter of 5 µm and a fiber density of 59,055 wires per m (1,500 wires per inch). The tensile stress is 4,000 N / mm² (megapascals). In an alternative embodiment of this exemplary design, the elongated sieve elements are made of carbon fibers with the aforementioned parameters.

[0068] The printing form according to Figure 2The device features elongated sieve elements made of carbon nanotubes. The sieve elements have a diameter of 0.5 µm and a fiber density of 196,850 per m³ (5,000 sieve elements per inch). The sieve elements are arranged on the sieve frame with a tensile stress of 40,000 N / mm² (megapascals).

[0069] This offers the advantage of enabling the use of narrow channel widths. In the present example, the channel width is 10 µm, and in the embodiment, it is 5 µm.

Claims

1. Printing stencil for producing a structure (4) of an electronic structural element, having a sieve frame and a sieve which is in the form of a sheet-like textile having a large number of elongate sieve elements, wherein the sieve is arranged in the sieve frame and the sieve has at least one pressure region which is permeable for a printing paste and at least one barrier region which is impermeable for the printing paste, characterized in that the elongate sieve elements are in the form of carbon nanotubes having a diameter of from 50 nm to 2 µm and in that the textile having a tensile stress in the range from 6001 N / mm2 (Megapascal) to 63,000 N / mm2 (Megapascal) is arranged in the sieve frame.

2. Printing stencil according to any one of the preceding claims, characterized in that the sieve frame has a joint region which is configured to at least partially connect the tensioned textile in the edge region to the sieve frame in a materially engaging manner.

3. Printing stencil according to any one of the preceding claims, characterized in that the printing region is at least partially in the form of an elongate channel opening having a longitudinal axis and a channel width (w), wherein the channel width (w) is less than 40 µm.

4. Printing stencil according to claim 3, characterized in that at least one sieve element is arranged at an angle not equal to 0° with respect to the longitudinal axis of the channel opening.

5. Printing stencil according to any one of the preceding claims, characterized in that in the printing region a surface ratio SUI which is produced from the ratio of the free surface-area in the printing region to the surface-area covered by the elongate sieve elements in the printing region is greater than 0.5.

6. Printing stencil according to any one of the preceding claims, characterized in that the elongate sieve elements are arranged in pairs parallel with or perpendicular to each other.

7. Method for producing a printing stencil having a sieve frame and a planar sieve having a large number of elongate sieve elements and at least one printing region which is permeable for printing paste (2) and a barrier region which is non-permeable for printing paste (2), characterized in that the elongate sieve elements in the form of carbon nanotubes having a diameter of from 50 nm to 2 µm are joined in a binding step to form a flexible planar textile, in particular a woven fabric or a web, wherein the planar textile in a clamping step is arranged with the edge region on the sieve frame and is connected to the sieve frame, in that the textile with a tensile stress in the range from 6001 N / mm2 (Megapascal) to 63,000 N / mm2 (Megapascal) is arranged in the sieve frame.

8. Method according to claim 7, characterized in that in a coating step a barrier layer which is non-permeable for printing paste is arranged on the sieve and in a structuring step an elongate channel opening is configured in the barrier layer in order to form a printing region which is permeable for printing paste (2).

9. Method according to claim 8, characterized in that the channel opening has a longitudinal axis and a channel width and the channel width is less than 40 µm.

10. Method according to claim 9, characterized in that in a separation step a template blank, in particular a thin-walled metal sheet, is processed by means of a laser to form a printing template (1c), wherein an elongate channel opening is formed in the template blank, in an assembly step the printing template (1c) is arranged in the printing region of the sieve.

11. Method for applying a printing paste (2) to the surface of an electronic structural element, in particular a photovoltaic solar cell, by means of a printing stencil, wherein by means of a doctor blade (3) printing paste (2) is applied by the printing stencil to a substrate (5) of the electronic structural element, characterized in that a printing stencil according to any one of claims 1 to 6 is used.