Screen version

Abstract

The present invention provides a screen plate that can suppress the breakage of linear electrodes in printed solar cells. [Solution] The screen plate 100 comprises a metal mask 10, a screen mesh 20, and a frame member 30. The metal mask 10 has a first surface facing the space partitioned by the frame member 30 and a second surface opposite to the first surface, and has a pattern portion 11 for forming linear electrodes inside the outer peripheral portion 12 of the metal mask 10. The pattern portion 11 has a plurality of through holes 15 arranged in a row in the stretching direction, which is the direction in which the linear electrode to be formed extends, and rib portions that separate adjacent through holes 15 in the stretching direction on at least the second surface.

Description

Technical Field

[0001] The present disclosure relates to a screen plate used for forming electrodes of a solar cell by screen printing.

Background Art

[0002] Generally, on the light-receiving surface of a silicon-based solar cell, a bus bar electrode extending linearly and a large number of thin grid electrodes extending orthogonally to the bus bar electrode are arranged. Conventionally, screen printing has been used to form these electrodes. In screen printing, a screen mask in which an emulsion or the like is coated on a screen mesh made of synthetic fibers or metal fibers is used. This coating layer has openings corresponding to the pattern of the electrode to be formed. In the printing process, a conductive paste is pressed against the screen mask by a squeegee, and the conductive paste moves onto the light-receiving surface through the openings. Thereby, an electrode made of the conductive paste is formed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, fibers constituting the screen mesh pass through the openings in the above-described screen mask. Therefore, in the portion where the fibers are located, particularly in the portion corresponding to the intersections of the mesh, the resistance to the passage of the conductive paste increases, so that a part of the printed pattern may be missing and the electrode may be disconnected.

[0005] On the other hand, in solar cells, in order to improve output, there is a demand for thinner electrodes to reduce the obstruction of incident light by the electrodes at the light-receiving surface. The demand for thinner electrodes is particularly high for grid electrodes. Since there is a limit to how much the wire diameter of the screen mesh can be reduced, the smaller the wire width of the electrodes, the greater the influence of the mesh within the aperture, and the higher the risk of electrode breakage. Therefore, measures to reduce the risk of breakage are needed. [Means for solving the problem]

[0006] The following describes various aspects of the screen version designed to address the above issues. [Aspect 1] A screen printing screen used for forming linear electrodes of a solar cell, comprising a metal mask, a screen mesh supporting the outer periphery of the metal mask, and a frame member supporting the outer periphery of the screen mesh, wherein the metal mask has a first surface facing a space partitioned by the frame member and a second surface opposite to the first surface, and the metal mask has a pattern portion for forming the linear electrodes on the inside of the outer periphery, the pattern portion having a plurality of through holes arranged in a row in the stretching direction which corresponds to the direction in which the linear electrodes to be formed extend, and rib portions that separate adjacent through holes in the stretching direction on at least the second surface, the screen printing screen.

[0007] According to the above configuration, the passage of conductive paste is not obstructed throughout the width direction in the region for forming linear electrodes on the metal mask, thus suppressing the occurrence of breaks in the printed linear electrodes. In addition, since the amount of conductive paste passing through the through holes is increased, it is suitably possible to form linear electrodes with a high aspect ratio. Furthermore, because the through holes and rib portions are arranged alternately, good strength of the pattern portion against the tension applied to the metal mask is obtained.

[0008] [Aspect 2] The screen plate according to [Aspect 1], wherein the rib portion separates the through holes adjacent in the extension direction over the entire area between the first surface and the second surface. With the above configuration, the strength of the rib section is increased, and therefore the strength of the pattern section is also increased.

[0009] [Aspect 3] The screen plate according to [Aspect 1] or [Aspect 2], wherein the through hole has a shape in which a first hole portion that opens on the first surface and tapers toward the second surface from the first surface and a second hole portion that opens on the second surface and tapers toward the first surface are connected, and the opening of the first hole portion on the first surface is larger than the opening of the second hole portion on the second surface.

[0010] According to the above configuration, even if the conductive paste has properties that make it more likely to adhere to the inner wall of the through-hole than to the printed object, it is possible to suppress the amount of conductive paste remaining in the through-hole and form a thick linear electrode. Furthermore, even if the conductive paste has properties that make it easy to pass through the through-hole, the width of the linear electrode will not widen significantly. In addition, the filling of the conductive paste into the through-hole can proceed smoothly.

[0011] [Aspect 4] The screen plate according to [Aspect 3], wherein in the stretching direction, the length of the rib portion on the second surface is less than the length of the opening of the second hole portion on the second surface, and is 10 μm or more and 30 μm or less.

[0012] With the above configuration, sufficient strength of the rib portion can be obtained against the tension applied to the metal mask, and conductive paste can easily spread to the area located below the rib portion during the printing process.

[0013] [Aspect 5] The screen plate according to [Aspect 3] or [Aspect 4], wherein the direction perpendicular to the stretching direction is the width direction, and the length of the opening of the second hole on the second surface along the width direction is 15 μm or more and 35 μm or less. According to the above configuration, the precision of forming the second hole can be improved, and a fine, wire-shaped linear electrode can be suitably formed.

[0014] [Aspect 6] The screen plate according to [Aspect 5], wherein the length of the opening of the second hole along the extension direction is equal to the length of the opening along the width direction. According to the above configuration, the design of the through-holes is simplified, and the length of the opening in the second hole along the extension direction is suppressed, resulting in good strength of the patterned portion.

[0015] [Aspect 7] A screen plate according to any one of [Aspect 3] to [Aspect 6], wherein, in a cross section of the metal mask along the thickness direction of the through hole, the angle made between the tangent line drawn from the end of the opening of the first hole on the first surface to the connection between the first hole and the second hole, with respect to a plane parallel to the first surface, is 30° or more and 60° or less. According to the above configuration, good ease of filling the through-holes with conductive paste and ease of transferring the conductive paste from the through-holes to the printing target can be obtained.

[0016] [Aspect 8] The screen plate according to any one of [Aspect 3] to [Aspect 7], wherein the period of the arrangement of the openings of the second hole portion on the second surface in the stretching direction is 60 μm or less. According to the above configuration, the length of the opening of the second hole along the extension direction is suppressed, thus good strength of the patterned portion can be obtained.

[0017] [Aspect 9] The screen plate according to any one of [Aspect 3] to [Aspect 8], wherein the thickness of the metal mask is 20 μm or more and 40 μm or less.

[0018] According to the above configuration, good strength of the metal mask can be obtained, and the width and thickness of the formed linear electrodes can be suitably secured. [Effects of the Invention]

[0019] According to this disclosure, it is possible to suppress the breakage of linear electrodes in printed solar cells. [Brief explanation of the drawing]

[0020] [Figure 1] FIG. 1 is a diagram showing the configuration of an electrode of a solar cell to be formed by a screen plate according to an embodiment. [Figure 2] FIG. 2 is a diagram showing the planar structure of a screen plate according to an embodiment. [Figure 3] FIG. 3 is a diagram showing the cross-sectional structure taken along line III-III of the screen plate in FIG. 2. [Figure 4] FIG. 4 is a diagram showing a part of the cross-sectional structure of a metal mask according to an embodiment. [Figure 5] FIG. 5 is a diagram showing a part of the planar structure of a metal mask on the first surface according to an embodiment. [Figure 6] FIG. 6 is a diagram showing a part of the planar structure of a metal mask on the second surface according to an embodiment. [Figure 7] FIG. 7 is a diagram showing the manufacturing process of a metal mask according to an embodiment. [Figure 8] FIG. 8 is a diagram showing the manufacturing process of a metal mask according to an embodiment. [Figure 9] FIG. 9 is a diagram showing the manufacturing process of a metal mask according to an embodiment. [Figure 10] FIG. 10 is a diagram showing the manufacturing process of a metal mask according to an embodiment. [Figure 11] FIG. 11 is a diagram showing the manufacturing process of a metal mask according to an embodiment. [Figure 12] FIG. 12 is a diagram showing the manufacturing process of a metal mask according to an embodiment. [Figure 13] FIG. 13 is a diagram showing the manufacturing process of a screen plate according to an embodiment. [Figure 14] FIG. 14 is a diagram showing the manufacturing process of a screen plate according to an embodiment. [Figure 15] FIG. 15 is a diagram showing the manufacturing process of a screen plate according to an embodiment. [Figure 16] FIG. 16 is a diagram showing the manufacturing process of an electrode of a solar cell using a screen plate according to an embodiment.

MODE FOR CARRYING OUT THE INVENTION

[0021] Referring to the drawings, one embodiment of a screen plate used for forming electrodes of a solar cell will be described. [Solar cell electrode configuration] Referring to Figure 1, the configuration of the electrodes of the solar cell to be formed will be explained. A solar cell 110, which is one cell of a crystalline silicon solar cell, comprises a solar cell substrate 120 including a pn junction and a light-receiving surface electrode 130 located on the light-receiving surface of the solar cell substrate 120. The light-receiving surface of the solar cell substrate 120 is the surface of the solar cell substrate 120 that receives light.

[0022] The light-receiving surface electrode 130 has a busbar electrode 131 for collecting current and a grid electrode 132 for collecting the generated carriers toward the busbar electrode 131. Each of the busbar electrode 131 and the grid electrode 132 is linear, and the line width of the grid electrode 132 is smaller than the line width of the busbar electrode 131. The grid electrode 132 intersects the busbar electrode 131, for example, perpendicular to the busbar electrode 131. The light-receiving surface electrode 130 has, for example, several busbar electrodes 131 and a number of grid electrodes 132.

[0023] The line width of the busbar electrode 131 is, for example, 0.5 mm to 2.0 mm. The line width of the grid electrode 132 is, for example, 30 μm to 100 μm. To increase the light-receiving area on the light-receiving surface, it is preferable that the line width of the grid electrode 132 be 40 μm or less. The length of each of the busbar electrode 131 and the grid electrode 132 may be a length corresponding to the size of the cell, for example, 150 mm to 160 mm.

[0024] The electrodes formed using the screen plate of this embodiment are linear electrodes of a solar cell, and specifically, they may be at least one of a busbar electrode 131 and a grid electrode 132. As described above, since thinning of the grid electrode 132 is desirable, the screen plate of this embodiment can be suitably used for forming the grid electrode 132. Furthermore, the structure of the solar cell is not limited to the structure described above, and the linear electrodes to be formed may be electrodes located on the back surface of the solar cell substrate, depending on the structure of the solar cell.

[0025] [Screen Version Configuration] The configuration of the screen version of this embodiment will be described with reference to Figures 2 and 3. As shown in Figures 2 and 3, the screen plate 100 comprises a metal mask 10, a screen mesh 20, and a frame member 30. Of these, the metal mask 10 located in the center of the screen plate 100 has a pattern portion 11 for forming linear electrodes.

[0026] The frame member 30 has a rectangular frame shape and functions to support the metal mask 10 and the screen mesh 20. The frame member 30 is formed from a metal material such as aluminum.

[0027] The screen mesh 20 is a mesh made of synthetic fibers. The screen mesh 20 is attached to the lower surface of the frame member 30. The lower surface of the frame member 30 is the surface facing the side on which the object to be printed is placed relative to the frame member 30. The screen mesh 20 has the function of applying isotropic tension to the metal mask 10 by utilizing the elasticity generated by the expansion and contraction of the mesh.

[0028] The metal mask 10 is a thin metal sheet having a rectangular shape. The metal mask 10 is attached to the lower or upper surface of the screen mesh 20. When viewed from a position opposite the upper surface, the metal mask 10 has the pattern portion 11 described above and an outer peripheral portion 12 surrounding the pattern portion 11. The screen mesh 20 has an opening in the region that overlaps with the pattern portion 11, and the pattern portion 11 is exposed through this opening. The outer peripheral portion 12 of the metal mask 10 is bonded to the screen mesh 20.

[0029] In other words, the screen mesh 20 has a frame shape that follows the frame member 30 and supports the outer periphery 12 of the metal mask 10. The outer periphery of the screen mesh 20 is supported by the frame member 30.

[0030] In the above configuration, the pattern portion 11 of the metal mask 10 faces the partitioned space which is the space partitioned by the frame member 30, and the screen mesh 20 faces the partitioned space on the outside of the pattern portion 11. Thus, the screen plate 100 of this embodiment is a combination mask comprising a metal mask 10 and a screen mesh 20.

[0031] The metal mask 10 has a first surface S1 and a second surface S2. The first surface S1 is the surface facing the partitioned space of the frame member 30 and is the squeegee surface against which the squeegee is pressed during the printing process. The second surface S2 is the surface opposite to the first surface S1 and is the printing surface that faces the object to be printed during the printing process.

[0032] The pattern portion 11 of the metal mask 10 has through holes 15 arranged to correspond to the linear electrodes to be formed. In the region corresponding to a single linear electrode, multiple through holes 15 are arranged in a single row along the direction corresponding to the direction in which the linear electrode extends. Figure 2 shows an example in which multiple rows of through holes 15 are arranged for the formation of multiple linear electrodes. The through holes 15 function as passages for conductive paste during the printing process.

[0033] For example, the metal mask 10 can be made of copper plate, nickel plate, rolled stainless steel plate, etc. The material of the metal mask 10 may be an iron-containing alloy such as an iron-nickel alloy, an iron-nickel-cobalt alloy, or an iron-chromium-nickel alloy. An example of an iron-nickel alloy is Invar material, i.e., an iron alloy containing 34% to 38% by mass of nickel. An example of an iron-nickel-cobalt alloy is Super Invar material, i.e., an iron alloy containing 30% to 34% by mass of nickel and cobalt. An example of an iron-chromium-nickel alloy is chromium-nickel stainless steel such as SUS304 and SUS430.

[0034] The fibers constituting the screen mesh 20 may be, for example, polyester or polyamide synthetic fibers. The screen mesh 20 may be a mesh made of a plain weave or twill weave structure. The wire diameter of the screen mesh 20 is not particularly limited, but from the viewpoint of obtaining good elastic recovery, it is preferably 20 μm or more, and more preferably 25 μm or more and 120 μm or less.

[0035] For bonding the frame member 30 to the screen mesh 20, and for bonding the screen mesh 20 to the metal mask 10, it is preferable to use a fast-drying adhesive such as a cyanoacrylate adhesive.

[0036] [Metal Mask Configuration] The configuration of the through-holes 15 in the metal mask 10 will be further explained with reference to Figures 4 to 6. Figure 4 is a diagram showing the cross-sectional structure of a part of the pattern portion 11 in the metal mask 10, Figure 5 is a diagram showing the planar structure of a part of the pattern portion 11 as seen from a position opposite the first surface S1, and Figure 6 is a diagram showing the planar structure of a part of the pattern portion 11 as seen from a position opposite the second surface S2.

[0037] As shown in Figure 4, the through hole 15 penetrates between the first surface S1 and the second surface S2. The through hole 15 includes a first hole portion 16 that opens into the first surface S1 and a second hole portion 17 that opens into the second surface S2, and these holes 16 and 17 are connected in shape.

[0038] The first hole 16 has a shape that tapers from the first surface S1 towards the second surface S2. The second hole 17 has a shape that tapers from the second surface S2 towards the first surface S1. The ends of the first hole 16 and the ends of the second hole 17 are connected in the thickness direction Dz of the metal mask 10.

[0039] In other words, in a cross-section perpendicular to the thickness direction Dz, the area of ​​the first hole 16 decreases monotonically along the direction from the first surface S1 to the second surface S2, and the area of ​​the second hole 17 decreases monotonically along the direction from the second surface S2 to the first surface S1. Furthermore, the area of ​​the through hole 15 in a cross-section perpendicular to the thickness direction Dz is smallest at the connection between the first hole 16 and the second hole 17.

[0040] In other words, the through hole 15 has a shape that is constricted in the middle of the thickness direction Dz. This constricted portion, that is, the portion that protrudes inward from the through hole 15 at the connection point between the first hole portion 16 and the second hole portion 17, is the protruding portion 18.

[0041] As shown in Figures 5 and 6, the opening of the first surface S1 in the first hole 16 is larger than the opening of the second surface S2 in the second hole 17. The shape of the opening of the first surface S1 in the first hole 16 and the shape of the opening of the second surface S2 in the second hole 17 can be a polygon such as a circle, ellipse, or rectangle. Polygons also include shapes composed of curves such that the corners have curvature. The shape of the opening of the first hole 16 and the shape of the opening of the second hole 17 may be different. It is preferable that these opening shapes, especially the opening shape of the second hole 17, be rectangular, as this makes it easier to form a uniform width for the linear electrode.

[0042] Multiple through-holes 15 are arranged in a row along the stretching direction Dx, which corresponds to the direction in which the linear electrode to be formed extends. The width direction Dy, which is perpendicular to the stretching direction Dx and the thickness direction Dz, corresponds to the width direction of the linear electrode to be formed. In the region for forming a single linear electrode, one through-hole 15 is located in the width direction Dy, and a number of through-holes 15 corresponding to the length of the linear electrode to be formed are located in the stretching direction Dx.

[0043] As shown in Figures 4 to 6, rib portions 19 are located between adjacent through holes 15, separating these through holes 15. In other words, the through holes 15 and rib portions 19 are arranged alternately along the extension direction Dx.

[0044] On the second surface S2, the rib portion 19 is a planar region; that is, adjacent second holes 17 are separated from each other. On the first surface S1, the rib portion 19 may be a planar region or a linear region extending along the width direction Dy; that is, adjacent first holes 16 may be separated from each other or may be close together via a linear boundary. Alternatively, the first surface S1 may not include the rib portion 19, and adjacent first holes 16 may be connected. In this case, the length of the rib portion 19 in the thickness direction Dz is smaller than the thickness T of the metal mask 10.

[0045] Thus, the rib portion 19 only needs to separate adjacent through holes 15 on at least the second surface S2, or in other words, the rib portion 19 only needs to separate adjacent second hole portions 17. It is preferable that the rib portion 19 separates adjacent through holes 15 throughout the entire area between the first surface S1 and the second surface S2, that is, that the length of the rib portion 19 matches the thickness T of the metal mask 10, because this increases the strength of the rib portion 19.

[0046] The second opening length X2, which is the length of the second hole 17 on the second surface S2 in the stretching direction Dx, and the second opening width Y2, which is the length of the second hole 17 on the second surface S2 in the width direction Dy, are preferably 15 μm or more and 35 μm or less. The second opening length X2 and the second opening width Y2 may be the same or they may be different. If the second opening length X2 and the second opening width Y2 are the same, the design of the through-hole pattern 15 is easier. If the length of the second hole 17 is not constant, the second opening length X2 and the second opening width Y2 are the maximum lengths in each direction.

[0047] If both the second aperture length X2 and the second aperture width Y2 are 15 μm or more, the accuracy of the formation of the second hole 17 can be obtained with high precision. Since the line width of the formed linear electrode will be about 5 μm wider than the second aperture width Y2, it is preferable that the second aperture width Y2 be about 5 μm smaller than the desired line width. If the second aperture width Y2 is 35 μm or less, it is possible to accurately set the line width of the linear electrode to 40 μm or less, and a fine linear electrode can be suitably formed.

[0048] The rib width W, which is the length of the rib portion 19 on the second surface S2 in the stretching direction Dx, is smaller than the second opening length X2. The rib width W is preferably 10 μm or more and 30 μm or less. If the rib width W is 10 μm or more, sufficient strength of the rib portion 19 can be obtained against the tension applied to the metal mask 10. If the rib width W is 30 μm or less, the conductive paste can sufficiently flow into the area located below the rib portion 19 during the printing process. If the length of the rib portion 19 is not constant, the rib width W is the length of the rib portion 19 at the center of the width direction Dy.

[0049] The pitch P, which indicates the period of the arrangement of through holes 15 in the stretching direction Dx, is preferably 60 μm or less. The pitch P may correspond to the combined length of the second opening length X2 and the rib width W. The pitch P is also the period of the arrangement of the first holes 16 and the period of the arrangement of the second holes 17.

[0050] As shown in Figure 4, in a cross-section along the thickness direction Dz passing through the center of the through hole 15 in the extension direction Dx and width direction Dy, the tangent line drawn from one end of the first hole portion 16 on the first surface S1 to the protruding portion 18 protruding from that end is the straight line A. The acute angle that the straight line A makes with a plane parallel to the first surface S1 is the taper angle θ. The taper angle θ is preferably 30° or more and 60° or less.

[0051] The cross-section that determines the taper angle θ may be a cross-section along the extension direction Dx or a cross-section along the width direction Dy, as long as the end of the first hole 16 on the first surface S1, i.e., the edge of the opening of the first hole 16, is visible. In either cross-section, the taper angle is constant.

[0052] In the thickness direction Dz, the depth of the first hole 16 is greater than the depth of the second hole 17. In other words, the depth of the second hole 17, i.e., the step height H which is the length between the tip of the protrusion 18 and the second surface S2 in the thickness direction Dz, is less than half the thickness T of the metal mask 10. The thickness T is the length between the first surface S1 and the second surface S2 along the thickness direction Dz. From the viewpoint of facilitating the processing of the through hole 15, the thickness T is preferably 20 μm or more and 40 μm or less. Furthermore, if the thickness T is 20 μm or more, good strength of the metal mask 10 can be obtained, and if the thickness T is 40 μm or less, it is easier to keep the width and thickness of the linear electrode within a suitable range.

[0053] The first opening length X1, which is the length of the first hole 16 on the first surface S1 in the extension direction Dx, and the first opening width Y1, which is the length of the first hole 16 on the first surface S1 in the width direction Dy, can each be determined according to the desired second opening length X2, second opening width Y2, step height H, and taper angle θ.

[0054] In the screen plate 100 of this embodiment, since one through-hole 15 is located in the width direction of the region corresponding to one linear electrode, the passage of conductive paste is not obstructed throughout the entire width direction. Therefore, compared to the case where a pattern is provided on the screen mesh, that is, when a part of the width direction within the opening through which the conductive paste passes is blocked by the mesh, the occurrence of breaks in the printed linear electrodes is suppressed.

[0055] Furthermore, when reducing the line width of the linear electrode, it is preferable to increase the thickness of the linear electrode in order to suppress the increase in resistance. By using the screen plate 100 of this embodiment, the amount of conductive paste passing through the through-hole 15 increases because it is not obstructed by the mesh, so the linear electrode can be formed thicker. In other words, it is suitably possible to form a linear electrode with a high aspect ratio, which is the thickness relative to the line width.

[0056] In the pattern portion 11 of the metal mask 10, if the region corresponding to a single linear electrode is composed of a single through-hole with an elongated planar shape, the strength of the pattern portion 11 cannot be sufficiently obtained, and the metal mask 10 is prone to breaking when tension is applied to it. In contrast, in this embodiment, the region corresponding to a single linear electrode is composed of multiple through-holes 15 arranged on either side of the rib portion 19, so that the strength of the pattern portion 11 can be sufficiently obtained.

[0057] Furthermore, in this embodiment, the through-hole 15 has a shape in which the first hole portion 16 and the second hole portion 17 are connected. With this configuration, even if the conductive paste has properties that make it more likely to adhere to the inner wall of the through-hole 15 than to the object to be printed, the conductive paste is easily transferred to the object to be printed because the second hole portion 17 extends toward the second surface S2. In addition, because the through-hole 15 is constricted at the connection between the first hole portion 16 and the second hole portion 17, the force that pulls the conductive paste from the inner wall of the first hole portion 16 does not easily act on the conductive paste in the second hole portion 17. Therefore, it is possible to suppress the amount of conductive paste remaining in the through-hole 15 and form a thicker linear electrode.

[0058] On the other hand, even if the conductive paste has properties that allow it to easily pass through the through-hole 15, the through-hole 15 is constricted at the connection point between the first hole 16 and the second hole 17, which prevents the conductive paste from rapidly and in large quantities coming out of the through-hole 15 and greatly widening the width of the linear electrode.

[0059] Furthermore, since the first hole 16 widens toward the first surface S1, the filling of conductive paste into the through hole 15 proceeds smoothly. Also, because the opening of the first hole 16 is larger than the opening of the second hole 17, the filling of conductive paste into the through hole 15 proceeds smoothly. Therefore, even if the squeegee moves at a high speed, the conductive paste is accurately filled into the through hole 15. If the taper angle θ is between 30° and 60°, a good balance can be obtained between the ease of filling the through hole 15 with conductive paste and the ease of transferring the conductive paste from the through hole 15 to the printing target.

[0060] The metal mask 10 may also have a water-repellent coating covering the inner wall of the through-hole 15. The presence of this water-repellent coating makes it easier for the conductive paste that enters the through-hole 15 to pass through during the printing process.

[0061] [Method for manufacturing metal masks] A method for manufacturing a metal mask 10 having through holes 15 will be described with reference to Figures 7 to 12. For illustrative purposes, Figures 7 to 12 show the process of forming one through hole 15.

[0062] As shown in Figure 7, a first resist layer 51R is formed on the surface that will become the first surface S1 of the substrate 50, which is a metal plate used to form the metal mask 10, and a second resist layer 52R is formed on the surface that will become the second surface S2. The resist layers 51R and 52R are formed from, for example, a negative-type resist. The resist layers 51R and 52R may also be formed from a positive-type resist. Furthermore, the resist layers 51R and 52R may be dry film resists or coated resists.

[0063] As shown in Figure 8, exposure and development of the resist layers 51R and 52R form a first resist pattern 51M from the first resist layer 51R and a second resist pattern 52M from the second resist layer 52R. For developing the resist layers 51R and 52R, a developer such as an aqueous sodium carbonate solution is used.

[0064] The first resist pattern 51M has first resist holes 51H corresponding to the position and opening shape of the first hole portion 16 to be formed. The second resist pattern 52M has second resist holes 52H corresponding to the position and opening shape of the second hole portion 17 to be formed.

[0065] As shown in Figure 9, a first protective layer 53 is formed on the surface of the first resist pattern 51M. This blocks the first resist pores 51H, preventing the etching solution from reaching the substrate 50 through the first resist pores 51H. Next, the substrate 50 is etched using the second resist pattern 52M. For etching the substrate 50, an etching solution containing chloride ions, for example, may be used. A specific example of the etching solution is ferric chloride solution. This forms a second pore portion 17 that opens onto the second surface S2.

[0066] As shown in Figure 10, the first protective layer 53 is removed from the surface of the first resist pattern 51M. Also, the second resist pattern 52M is removed from the second surface S2 of the substrate 50, and the second surface S2 of the substrate 50 is covered with the second protective layer 54. At this time, the second protective layer 54 is formed such that a portion of the second protective layer 54 fills the inside of the second hole 17.

[0067] As shown in Figure 11, the substrate 50 is etched using the first resist pattern 51M. For etching, the same etching solution as that used for forming the second hole 17 may be used. This forms the first hole 16 that opens into the first surface S1. The first hole 16 is formed so as to reach a part of the second protective layer 54 filled in the second hole 17, thereby connecting the first hole 16 to the second hole 17.

[0068] As shown in Figure 12, the first resist pattern 51M is removed from the first surface S1 of the substrate 50. Also, the second protective layer 54 is removed from the second surface S2. This results in a metal mask 10 having through holes 15. Furthermore, the method for manufacturing the metal mask 10 may differ from the method described above, as long as it is possible to form through holes 15 consisting of the first hole portion 16 and the second hole portion 17.

[0069] [Manufacturing method for screen printing plates] The manufacturing method of the screen plate 100 will be described with reference to Figures 13 to 15. The manufacturing method of the screen plate 100 includes a temporary fixing step, a tensioning step, a permanent fixing step, and a cutting step.

[0070] As shown in Figure 13, in the temporary fixing process, the screen mesh 20 is bonded to the lower surface of the frame member 30 while tension is applied to the screen mesh 20. At this time, the screen mesh 20 has no openings, and on the lower surface side of the frame member 30, the screen mesh 20 covers the entire opening of the frame member 30. Tension is applied to the screen mesh 20 isotropically in the direction along each side of the frame member 30.

[0071] Furthermore, in the temporary fixing process, as shown in Figure 14, the metal mask 10 is temporarily fixed to the center of the screen mesh 20. Specifically, a temporary fixing area, which is part of the outer periphery 12 of the metal mask 10, is bonded to the screen mesh 20. The temporary fixing area is an extremely small area, such as a point-like region, and for example, the corners of the outer periphery 12 and the points that equally divide the space between the corners are designated as temporary fixing areas. A fast-drying adhesive such as a cyanoacrylate adhesive may be used to bond the temporary fixing areas.

[0072] Next, in the tensioning process, tension is applied to the screen mesh 20. This applies isotropic tension to the metal mask 10, which is temporarily fixed to the screen mesh 20, through the screen mesh 20. Therefore, even if there are wrinkles or sagging in the metal mask 10, these will be eliminated by applying tension.

[0073] Next, in the final fixing process, the metal mask 10 is permanently fixed to the screen mesh 20. Specifically, the entire outer periphery 12 is bonded to the screen mesh 20. Since the screen mesh 20 has a mesh structure, the application of the adhesive for final fixing can be performed from the side opposite to the metal mask 10 relative to the screen mesh 20. Because the final fixing is performed after any wrinkles or sagging of the metal mask 10 have been eliminated in the tensioning process, a good bonding area can be ensured. Therefore, fixing defects caused by wrinkles or sagging are suppressed, and peeling of the metal mask 10 from the screen mesh 20 during printing is effectively prevented.

[0074] As shown in Figure 15, in the cutting process, the central portion 21 of the screen mesh 20 that overlaps with the pattern portion 11 of the metal mask 10 is cut and removed. The central portion 21 is located inside the fixing point between the screen mesh 20 and the metal mask 10. This results in the obtained screen plate 100.

[0075] A laser cutter is preferably used to cut the screen mesh 20. The output of the laser cutter is adjusted so that only the screen mesh 20 is cut in the laminate of the screen mesh 20 and the metal mask 10. The type of laser used in the laser cutter is not particularly limited as long as the output can be adjusted, but for example, a carbon dioxide laser can be used.

[0076] By using a laser cutter with adjustable output, it is possible to cut only the screen mesh 20 without scratching or damaging the metal mask 10, even with thin workpieces such as a laminate of screen mesh 20 and metal mask 10, where controlling the cutting thickness with a blade is difficult. Furthermore, since the cutting thickness can be changed by adjusting the output, a high degree of versatility and flexibility in the cutting process can be obtained.

[0077] Furthermore, if it is possible to manufacture a screen plate 100 comprising the metal mask 10, screen mesh 20, and frame member 30 as described above, the method for manufacturing the screen plate 100 may differ from the method described above, and may include other steps in addition to the steps described above.

[0078] [How to use the screen version] Referring to Figure 16, the method of using the screen plate 100, that is, the method of manufacturing linear electrodes for solar cells by screen printing using the screen plate 100, will be explained.

[0079] As shown in Figure 16, the screen plate 100 and the solar cell substrate 120 are positioned such that the surface on which the linear electrodes are formed on the solar cell substrate 120, which is the object to be printed, faces the second surface S2 of the metal mask 10. In the initial state, there is a gap between the screen plate 100 and the solar cell substrate 120.

[0080] Then, conductive paste 60 is supplied onto the first surface S1 of the metal mask 10 within the partitioned space of the frame member 30, and the squeegee 70 presses the conductive paste 60 onto the metal mask 10 while moving along one direction.

[0081] The pressing force from the squeegee 70 presses the metal mask 10 against the solar cell substrate 120, and the conductive paste 60 fills the through-holes 15 of the metal mask 10. As a result, the conductive paste 60 adheres to the solar cell substrate 120 through the openings of the second holes 17 on the second surface S2 of the metal mask 10. The conductive paste 60 may also spread slightly around the openings of the second holes 17 and may wrap around to the underside of the rib portion 19.

[0082] When the squeegee 70 passes over the through-hole 15 and the pressure is released, the tension of the screen mesh 20 causes the through-hole 15 to separate from the solar cell substrate 120. At this time, the conductive paste 60 that was filled in the through-hole 15 comes out through the opening of the second hole 17 and remains on the solar cell substrate 120.

[0083] As a result, a pattern consisting of conductive paste 60 supplied through a row of through-holes 15 is printed onto the solar cell substrate 120. This pattern has irregularities in the areas where the through-holes 15 were located and in the areas where the rib portions 19 were located. Subsequently, a leveling process is performed to smooth out the irregularities and form linear electrodes.

[0084] Any known paste can be used as the conductive paste 60. For example, the conductive paste 60 may be a paste containing conductive particles made of metal, glass frit, an organic binder, a solvent, and other additives.

[0085] For the squeegee 70, any known squeegee that has been conventionally used in screen printing may be used. The material of the squeegee 70 can be, for example, a rubber composition such as urethane rubber or silicone rubber, or a metal material.

[0086] Printing conditions such as the attack angle, which is the angle at which the squeegee 70 contacts the metal mask 10, and the movement speed of the squeegee 70, should be set according to the properties of the conductive paste 60 and the configuration of the metal mask 10, such as the size of the through-holes 15. In off-contact screen printing, as the squeegee 70 moves, that is, immediately after the conductive paste 60 adheres to the solar cell substrate 120, the through-holes 15 of the metal mask 10 separate from the solar cell substrate 120 and the conductive paste 60 is transferred to the solar cell substrate 120. Therefore, fast printing is possible with a squeegee speed of about 100 mm / second to 300 mm / second.

[0087] As described above, the following effects can be obtained with the screen version 100 of the above embodiment. (1) The metal mask 10 is provided with a pattern portion 11 for forming linear electrodes, and the pattern portion 11 has a plurality of through holes 15 arranged in a row in the stretching direction Dx, and rib portions 19 that separate adjacent through holes 15 in the stretching direction Dx. With this configuration, the passage of conductive paste is not obstructed throughout the width direction Dy, so that breaks in the printed linear electrodes are suppressed. In addition, since the amount of conductive paste passing through the through holes 15 is increased, it is possible to suitably form linear electrodes with a high aspect ratio.

[0088] (2) The alternating arrangement of the through holes 15 and the rib portions 19 provides good strength to the pattern portion 11 against the tension applied to the metal mask 10. In particular, if the rib portions 19 divide adjacent through holes 15 in the stretching direction Dx across the entire area between the first surface S1 and the second surface S2, the strength of the pattern portion 11 can be increased.

[0089] (3) The through-hole 15 has a shape in which the first hole portion 16 and the second hole portion 17 are connected. This makes it possible to form a thick linear electrode by suppressing the amount of conductive paste remaining in the through-hole 15, even if the conductive paste has properties that make it easier to adhere to the inner wall of the through-hole 15 than the object to be printed. Also, even if the conductive paste has properties that make it easy to pass through the through-hole 15, the width of the linear electrode does not widen significantly. Furthermore, the filling of the conductive paste into the through-hole 15 proceeds smoothly.

[0090] (4) The rib width W is smaller than the second opening length X2 of the second hole 17, and is between 10 μm and 30 μm. With this configuration, sufficient strength of the rib portion 19 can be obtained against the tension applied to the metal mask 10, and conductive paste can easily flow into the area located below the rib portion 19 during the printing process.

[0091] (5) The second opening width Y2 of the second hole 17 is 15 μm or more and 35 μm or less. With this configuration, the precision of forming the second hole 17 can be improved, and a fine wire-shaped linear electrode can be suitably formed.

[0092] (6) In the second hole 17, the second opening length X2 and the second opening width Y2 are equal. With this configuration, the design of the through hole 15 is easy, and the second opening length X2 does not become too large, so that good strength of the pattern portion 11 can be obtained.

[0093] (7) The taper angle θ of the through hole 15 is 30° or more and 60° or less. With this configuration, a good balance can be obtained between the ease of filling the through hole 15 with conductive paste and the ease of transferring the conductive paste from the through hole 15 to the printing target.

[0094] (8) The pitch P, which is the period of the arrangement of the second holes 17, is 60 μm or less. With this configuration, the second opening length X2 does not become large, and the strength of the pattern portion 11 is obtained.

[0095] (9) The thickness of the metal mask 10 is 20 μm or more and 40 μm or less. With this configuration, good strength of the metal mask 10 can be obtained, and the width and thickness of the formed linear electrodes can be suitably secured.

[0096] [Examples] The screen version of the above embodiment and its usage method will be explained using specific examples.

[0097] A metal mask with multiple through-holes was formed by etching a stainless steel metal plate. The thickness T of the metal mask was 20 μm, the second opening length X2 and second opening width Y2 of the second hole portion of the through-holes were each 24 μm, and the pitch P was 65 μm or less.

[0098] A screen plate was fabricated using the above-mentioned metal mask, a screen mesh made of polyester fabric, and a frame member. The screen mesh had a mesh count of 200 threads / inch and a wire diameter of 50 μm. The outer dimensions of the frame member were a square with sides of 450 mm, and the pattern area of ​​the metal mask was a square with sides of 180 mm.

[0099] Screen printing was performed using the above-mentioned screen plate with conductive paste. The viscosity of the conductive paste at a rotation speed of 10 rpm was 300 Pa·s. The squeegee was made of silicone rubber with a hardness of 70°. Printing was performed under the following conditions: squeegee attack angle of 70°, squeegee movement speed of 200 mm / second, and printing pressure of 0.2 Pa.

[0100] The dimensions of each part of a linear electrode made of printed conductive paste were measured using an image measurement system (NEXIV VMR-12072, Nikon). The results showed that the linear electrode had a line width of 30 μm, an average height of 20 μm, and an aspect ratio of 0.67 (height to line width). No breaks in the wire were observed. Therefore, it was confirmed that linear electrodes with a line width of 40 μm or less can be suitably formed.

[0101] [Differentiation] The above embodiment may be implemented with the following modifications. The through-hole 15 is composed only of a first hole portion 16, and the first hole portion 16 may also open to the second surface S2. That is, the through-hole 15 may have a shape in which the area of ​​the cross section perpendicular to the thickness direction Dz decreases monotonically from the first surface S1 to the second surface S2. If the pattern portion 11 has through-holes 15 and rib portions 19 arranged in a single row in the stretching direction Dx, the effect of suppressing disconnection of the formed linear electrodes can be obtained. [Explanation of Symbols]

[0102] 10…Metal Mask 11...Pattern section 12…Outer perimeter 15…Through hole 16...First hole 17...Second hole 19... Rib section 20…Screen Mesh 30… Frame members 100... Screen version

Claims

1. A screen plate used for forming linear electrodes of solar cells by screen printing, Metal mask and, A screen mesh supporting the outer periphery of the metal mask, The system comprises a frame member that supports the outer periphery of the screen mesh, The metal mask has a first surface facing the space partitioned by the frame member and a second surface opposite to the first surface, and the inner side of the outer periphery of the metal mask is provided with a pattern portion for forming the linear electrode. The pattern portion has a plurality of through holes arranged in a row in the stretching direction, which is the direction in which the linear electrode to be formed extends, and a rib portion that separates adjacent through holes in the stretching direction on at least the second surface. Screen version.

2. The rib portion, throughout the entire area between the first and second surfaces, separates the through holes adjacent to each other in the extension direction. The screen plate according to claim 1.

3. The through hole has a shape in which a first hole portion that opens to the first surface and tapers toward the second surface is connected to a second hole portion that opens to the second surface and tapers toward the first surface. The opening of the first hole on the first surface is larger than the opening of the second hole on the second surface. The screen plate according to claim 1.

4. In the stretching direction, the length of the rib portion on the second surface is less than the length of the opening of the second hole portion on the second surface, and is between 10 μm and 30 μm. The screen plate according to claim 3.

5. The direction perpendicular to the stretching direction is the width direction, and the length of the opening of the second hole in the second surface along the width direction is 15 μm or more and 35 μm or less. The screen plate according to claim 3.

6. In the second surface, the length of the opening of the second hole along the extending direction is equal to the length of the opening along the width direction. The screen plate according to claim 5.

7. In a cross-section of the through-hole along the thickness direction of the metal mask, the angle between the tangent line drawn from the end of the opening of the first hole on the first surface to the connection between the first hole and the second hole, and the plane parallel to the first surface, is 30° or more and 60° or less. The screen plate according to claim 3.

8. The period of the arrangement of the openings of the second hole portion on the second surface in the stretching direction is 60 μm or less. The screen plate according to claim 3.

9. The thickness of the metal mask is 20 μm or more and 40 μm or less. The screen plate according to claim 3.

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