Printing metal mask

Abstract

To provide a printing metal mask capable of forming a printing layer with high accuracy and high quality, by further improving printing accuracy when printing and forming a printing layer.SOLUTION: The printing metal mask of the present invention comprises a mask body 7 having a back surface 9 facing the object 2 to be printed, and a plurality of through-holes 10 that penetrate the mask body 7 from front to back and are filled with the print material 4. The through-hole 10 has a first hole portion 13 opening on the surface 8 of the mask body 7, and a second hole portion 14 that is continuous with the first hole portion 13 and opens on the back surface 9 of the mask body 7. The second hole portion 14 consists of a straight hole, and the first hole portion 13 has an inner cross-sectional shape formed in an R-shape. When the hole depth of the first hole portion 13 is defined as H1 and half of the enlarged dimension of the first hole portion 13 is defined as D5, the first hole portion 13 is formed so as to satisfy the inequality (H1<D5).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for improving printing defects such as bleeding and fading of a printed layer in a metal mask. An example of the metal mask of the present invention is a printing metal mask used when printing a layer of flux (printing paste) for temporarily adhering solder balls onto a substrate by screen printing. [Background technology]

[0002] The present applicant previously proposed a technology for improving the printing accuracy of metal masks for printing (Patent Document 1). In Patent Document 1, the cross-sectional shape of the through-holes formed in a metal mask produced by electroforming is tapered, with the hole diameter on the electroformed surface side being smaller and the hole diameter on the electroformed matrix surface being larger. During printing, the electroformed surface side becomes the front side, i.e., the squeegee surface side, and the electroformed matrix surface side becomes the back side, i.e., the printed material (target) side. To form a layer of ink paste (printing paste), the printed material side of the metal mask is first placed in close contact with the printed material. Then, the ink paste is placed on the squeegee surface of the metal mask, and the ink paste on the squeegee surface is spread with the squeegee to fill the through-holes. After the ink paste has filled the through-holes, the metal mask is separated from the printed material, allowing the ink paste printing layer corresponding to the through-holes to be printed on the printed material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-305670 Summary of the Invention [Problem to be solved by the invention]

[0004] In the metal mask of Patent Document 1, the through-holes are tapered to widen toward the back side, improving the ink paste's releasability. This prevents some of the ink paste from being removed when the metal mask is separated from the substrate, thereby preventing print defects such as bleeding and fading. However, with the metal mask of Patent Document 1, the ink paste contacts the entire inner surface of the through-holes, so the ink paste filled inside the through-holes still adheres to the inner surface of the through-holes, and the metal mask may be separated from the substrate with some of the ink paste still attached, resulting in print defects such as distorted print shapes or fading. Furthermore, the ink paste does not adhere uniformly to each through-hole, resulting in print defects such as uneven amounts of ink paste in each printing layer.

[0005] An object of the present invention is to provide a metal mask for printing that further improves the printing accuracy when printing a print layer, and that can form a high-precision, high-quality print layer. [Means for solving the problem]

[0006] The printing metal mask of the present invention comprises a mask body 7 made of a thin metal plate with a back surface 9 facing the printing object 2, and a large number of through holes 10 which penetrate the mask body 7 from front to back and are round holes which are filled with printing paste 4. The through holes 10 are characterized by comprising first hole portions 13 which are straight holes opening on the front surface 8 of the mask body 7, and second hole portions 14 which have an R-shaped inner cross section, are smoothly continuous with the first hole portions 13, and expand as they open on the back surface 9 of the mask body 7.

[0007] A configuration can be adopted in which the first hole portion 13 is configured as a straight circular hole, and the second hole portion 14 is configured as a bell-mouth hole.

[0008] When the thickness T of the mask body 7 is 1, H1 defined by the hole depth of the first hole portion 13 is preferably set to 0.2 or more and 0.6 or less.

[0009] More preferably, when the thickness T of the mask body 7 is set to 1, H1 defined by the hole depth of the first hole portion 13 is preferably set to 0.2 or more and less than 0.5.

[0010] When the hole depth of the second hole portion 14 is defined as H2 and half of the enlarged dimension of the second hole portion 14 is defined as D3, a form in which the second hole portion 14 is formed can be adopted so as to satisfy the inequality (H2 < D3).

[0011] When the opening dimension of the first hole portion 13 on the front surface 8 of the mask body 7 is defined as D1 and the opening dimension of the second hole portion 14 on the back surface 9 of the mask body 7 is defined as D2, a form in which the opening dimension D2 is set to 1.5 times or more of the opening dimension D1 can be adopted.

[0012] The thickness T of the mask body 7 is preferably set to 25 μm or less.

[0013] A coating layer 17 for suppressing the adhesion of the printing paste 4 is formed on the inner surface of the through hole 10 and the back surface 9 of the mask body 7. When the layer thickness of the coating layer 17 in the first hole portion 13 is defined as C1, the layer thickness of the coating layer 17 in the second hole portion 14 is defined as C2, and the layer thickness of the coating layer 17 on the back surface 9 of the mask body 7 is defined as C3, the coating layer 17 is formed so as to satisfy the inequality (C1 ≤ C2 ≤ C3).

Advantages of the Invention

[0014] In the printing metal mask of the present invention, the through holes 10 penetrating the mask body 7 from front to back are composed of first hole portions 13 consisting of straight holes opening on the front surface 8 of the mask body 7, and second hole portions 14 whose inner surface has an R-shaped cross section, smoothly continues with the first hole portions 13, and widens as they open on the back surface 9 of the mask body 7. In this way, when the first hole portions 13 opening on the front surface 8 of the mask body 7 are composed of straight holes, the flow direction of the printing paste 4 when filling the through holes 10 can be guided by the inner surface of the first hole portions 13 extending in the vertical direction, and the printing paste 4 can be reliably dropped into the through holes 10 in the thickness direction (vertical direction) of the mask body 7. Furthermore, if the second hole portions 14 connected to the first hole portions 13 have an R-shaped inner cross section, are smoothly continuous with the first hole portions 13, and expand as they open to the back surface 9 of the mask body 7, when the printing paste 4 is guided by the inner surfaces of the first hole portions 13 and reaches the vicinity of the boundary between the two hole portions 13 and 14, the printing paste 4 can be peeled off from the inner surfaces of the second hole portions 14 near the boundary. Furthermore, after being peeled off from the inner surfaces of the second hole portions 14, the printing paste 4 can be led to the back surface 9 of the mask body 7 of the second hole portions 14. Thus, according to the printing metal mask of the present invention, the printing paste 4 can be peeled off from the inner surfaces of the second hole portions 14 near the boundary between the two hole portions 13 and 14. Therefore, compared to conventional metal masks, the contact area between the inner surfaces of the through holes 10 and the printing paste 4 can be reduced, and the amount of printing paste 4 that adheres to the mask and is removed from the printing object 2 when the mask is separated from the printing object 2 can be reduced. As described above, the printing metal mask of the present invention can suppress printing defects such as distortion of the printing shape of the printing layer on the printing object 2 or faint printing, thereby improving the printing accuracy when printing the printing layer, and enabling a high-precision, high-quality printing layer to be formed on the printing object 2.

[0015] When the first hole portion 13 is formed of a straight round hole and the second hole portion 14 is formed of a bellmouth-shaped hole, compared with a form in which the first hole portion 13 and the second hole portion 14 are formed of a polygonal hole having corners, the inner surface shape of the through hole 10 can be made into a smooth inner surface shape without corners. Therefore, it is possible to further suppress the occurrence of printing defects such as the printing paste 4 adhering to the corners and the printing shape of the printed layer on the printing target 2 being distorted or the printing being blurred.

[0016] When the thickness T of the mask body 7 is set to 1, it is preferable that H1 defined by the hole depth of the first hole portion 13 is set to 0.2 or more and 0.6 or less. This is based on the fact that when the hole depth H1 is less than 0.2 or when the hole depth H1 exceeds 0.6, printing defects occur. More specifically, when the hole depth H1 is less than 0.2, the guiding effect of the printing paste 4 by the inner surface of the hole of the first hole portion 13 becomes insufficient, and the printing paste 4 is filled in an unintended direction during printing, resulting in the shape of the printed layer being distorted or the printed layer being blurred, and as a result, printing defects occur. Further, when the hole depth H1 exceeds 0.6, the printing paste 4 adheres to the inner surface of the hole of the first hole portion 13, and a part thereof is removed together with the metal mask, resulting in the shape of the printed layer being distorted or the printed layer being blurred, and as a result, printing defects occur.

[0017] When the thickness T of the mask body 7 is set to 1, it is more preferable that H1 defined by the hole depth of the first hole portion 13 is set to 0.2 or more and less than 0.5. Thereby, the occurrence of the above-mentioned printing defects can be suppressed, and a printed layer with a generally good thickness can be obtained.

[0018] When the hole depth of the second hole portion 14 is defined as H2 and half of the enlarged dimension of the second hole portion 14 is defined as D3, when the second hole portion 14 is formed so as to satisfy the inequality (H2 < D3), the curvature of the cross-sectional shape constituting the inner surface of the hole of the second hole portion 14 formed of the bellmouth-shaped hole can be increased. Therefore, the peeling of the printing paste 4 in the second hole portion 14 can be promoted.

[0019] When the opening dimension of the first hole portion 13 on the front surface 8 of the mask body 7 is defined as D1 and the opening dimension of the second hole portion 14 on the back surface 9 of the mask body 7 is defined as D2, if the opening dimension D2 is set to be 1.5 times or more the opening dimension D1, as described above, the curvature of the cross-sectional shape constituting the inner surface of the second hole portion 14, which is a bell-mouth-shaped hole, can be made large, thereby promoting the peeling of the printing paste 4 in the second hole portion 14.

[0020] It is preferable that the thickness T of the mask body 7 is set to 25 μm or less. This is because, as the definition of printing metal masks increases, the opening dimension D1 of the first hole portion 13 also becomes smaller, but if the thickness T of the mask body 7 exceeds 25 μm, the hole depth of the through-hole 10 becomes large relative to the opening dimension D1, and there is a risk that the squeegee will not be able to sufficiently fill the printing paste 4 into the through-hole 10.

[0021] If a coating layer 17 that suppresses adhesion of the printing paste 4 is formed on the inner surface of the through hole 10 and the back surface 9 of the mask body 7, the printing paste 4 can be guided through the first hole 13 and smoothly peeled off through the second hole 14. Furthermore, when the thickness of the coating layer 17 formed on the first hole 13 is defined as C1, the thickness of the coating layer 17 formed on the second hole 14 is defined as C2, and the thickness of the coating layer 17 formed on the back surface 9 of the mask body 7 is defined as C3, the coating layer 17 can be formed so as to satisfy the inequality (C1≦C2≦C3). In this configuration, by minimizing the thickness C1 of the coating layer 17, the change in the opening diameter D1 of the first hole 13, which determines the shape of the printing layer, can be minimized. In this configuration, by making the thickness C3 of the coating layer 17 larger than the thicknesses C1 and C2 of the coating layer 17, the effect of the coating layer 17, which gradually wears away due to contact with the printing object 2, can be maintained for a longer period of time. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a longitudinal sectional front view showing a main part of a printing metal mask according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing the entire printing metal mask. [Figure 3] FIG. 1 is a vertical cross-sectional side view showing an example of how a printing metal mask is used. [Figure 4] 1A to 1C are explanatory diagrams showing the manufacturing process of a printing metal mask. [Figure 5] 1A and 1B show a main part of a metal mask for printing according to a second embodiment of the present invention, where (a) is a longitudinal front view and (b) is a bottom view. [Figure 6] FIG. 10 is a vertical cross-sectional side view showing an example of how the printing metal mask according to the third embodiment of the present invention is used. DETAILED DESCRIPTION OF THE INVENTION

[0023] (First embodiment) Figures 1 to 4 show a first embodiment of a printing metal mask according to the present invention. Note that the dimensions such as thickness and width in each figure are shown schematically and not indicative of the actual state. A printing metal mask (hereinafter simply referred to as a mask) 1 is used to print and form a printing layer made of flux (printing paste) 4 for temporarily adhering solder balls on electrodes 3 formed on the surface of a circuit board (printing target) 2, as shown in Figure 3, by screen printing.

[0024] In FIG. 2, the mask 1 is based on a mask body 7, a thin metal plate formed by electroforming using an electrodeposited metal such as nickel, copper, or a nickel alloy such as nickel-cobalt. The mask body 7 has numerous circular through-holes 10 that penetrate the surface from the front surface 8 to the back surface 9. The mask 1 is formed in a square shape with sides of 250 mm. When the mask 1 is divided into four quadrants, a pattern formation region M is defined in each quadrant. The through-holes 10 are provided within the pattern formation region M in a manner that corresponds to the electrode pattern corresponding to the electrodes 3 of the circuit board 2. Surrounding the pattern formation region M is a cut mark formation region C, which is used to print cut marks used to cut the circuit board 2 into a specified shape in a process after screen printing. The mask 1 is attached to the mask fixing unit of the screen printing machine either alone or with a frame attached to its four edges.

[0025] As shown in Figure 1, the through hole 10 is composed of a first hole portion 13 that opens to the front surface 8 of the mask body 7 and a second hole portion 14 that opens to the back surface 9 of the mask body 7. The first hole portion 13 is a straight circular hole that extends in the thickness direction of the mask body 7, and the second hole portion 14 is a bell-mouth hole that is smoothly continuous with the first hole portion 13 and widens downward.

[0026] The thickness T of the mask body 7 is preferably 25 μm or less, and more preferably 18 μm or less In this embodiment, the thickness T of the mask body 7 is set to 18 μm.

[0027] The hole depth H1 of the first hole portion 13 (see FIG. 1) is set to 0.2 or more and less than 0.5 when the thickness T of the mask body 7 is 1. In this embodiment, the hole depth H1 is set to 3.6 μm, and when the thickness T of the mask body 7 is 1, the hole depth H1 is 0.2 (3.6 / 18=0.2).

[0028] The opening dimension of the first hole portion 13, that is, the opening diameter (diameter) D1 (see FIG. 1) is set to be the same as the diameter dimension of the layer of the flux 4 to be formed on the electrode 3. The diameter dimension of the layer of the general flux 4 is set to be 20 μm to 50 μm. From this, the opening diameter D1 of the present embodiment is set to 40 μm. The opening diameter D1 of the first hole portion 13 defines the planar shape of the printed layer to be printed. On the electrode 3, a circular printed layer is formed in a plan view.

[0029] The hole depth H2 of the second hole portion 14 (see FIG. 1) is the dimension obtained by subtracting the hole depth H1 of the first hole portion 13 from the thickness T of the mask body 7, and is set to 14.4 μm in the present embodiment. As described above, when the thickness T of the mask body 7 is taken as 1, the hole depth H1 of the first hole portion 13 is set to be less than 0.5. Therefore, the relationship between the hole depth H1 of the first hole portion 13 and the hole depth H2 of the second hole portion 14 is set to satisfy the inequality (H1 < H2).

[0030] The opening dimension of the second hole portion 14, that is, the opening diameter (diameter) D2 (see FIG. 1) is set to be larger than the opening diameter D1. In the present embodiment, the opening diameter D2 is set to be 1.5 times or more of the opening diameter D1. In addition, the diameter expansion dimension (half of the opening expansion dimension) D3 of the radius of the second hole portion 14 is set to be larger than the hole depth H2 (H2 < D3). The diameter expansion dimension D3 in FIG. 1 means half of the value obtained by subtracting the opening diameter D1 from the opening diameter D2 ((D2 - D1) / 2). The opening diameter (diameter) D2 is preferably set to be 50 μm to 100 μm, and the opening diameter D2 of the present embodiment is set to 80 μm. Accordingly, the diameter expansion dimension D3 is set to 20 μm. In the present embodiment, in order to set the relationship between the diameter expansion dimension D3 and the hole depth H2 to satisfy the inequality (H2 < D3), the cross-sectional shape of the inner surface of the second hole portion 14 is formed in a quarter-elliptical arc shape having a minor axis in the thickness direction of the mask body 7. Further, the opening end of the second hole portion z and the back surface 9 of the mask body 7 are smoothly continuous.

[0031] The electrode 3 of this embodiment is formed in a circular shape. When the diameter of the electrode 3 is D4, the opening diameter D1 of the first hole 13 is formed smaller than the diameter D4, and the opening diameter D2 of the second hole 14 is formed larger than the diameter D4. In other words, the opening diameters D1 and D2 are formed so as to satisfy the inequality (D1 < D4 < D2) (see FIG. 1).

[0032] As shown in FIG. 1, a coating layer 17 is formed on the inner surface of the through hole 10 and the back surface 9 of the mask body 7. The coating layer 17 suppresses the adhesion of the flux 4 to the inner surface of the through hole 10 and the back surface 9 of the mask body 7. The layer thickness C1 of the coating layer 17 in the first hole portion 13, the layer thickness C2 of the coating layer 17 in the second hole portion 14, and the layer thickness C3 of the coating layer 17 on the back surface 9 of the mask body 7 are set so as to satisfy the inequality (C1 ≤ C2 ≤ C3). Further, since the inner surface of the first hole portion 13 defines the shape of the printing layer, the layer thickness C1 of the coating layer 17 in this portion is formed thinner than other portions, so that the shape change of the opening diameter D1 can be reduced. Since the back surface 9 of the mask body 7 contacts the circuit board 2 when the printing metal mask 1 is used, the layer thickness C3 of the coating layer 17 in this portion is formed thicker than other portions, thereby improving its durability. Therefore, the respective layer thicknesses C1, C2, and C3 of the coating layer 17 are set so as to satisfy the inequality (C1 ≤ C2 ≤ C3) and further satisfy the formula (C1 ≠ C3).

[0033] The layer thickness C1 in this embodiment is set to 0.5 μm, the layer thickness C2 is 0.5 μm at the adjacent portion to the first hole portion 13 and is set to 1.0 μm at the adjacent portion to the back surface 9 of the mask body 7, and the layer thickness C3 is set to 1.0 μm. The layer thickness C2 of the coating layer 17 in the second hole portion 14 is formed to gradually increase from the side of the first hole portion 13 toward the side of the back surface 9 of the mask body 7, and the coating layer 17 is a smooth one without a stepped portion. The coating layer 17 can be formed by dip formation or spraying. Although the coating layer 17 of this embodiment is formed on the order of μm, it is also possible to form the coating layer 17 on the order of nm.

[0034] Also, the coating layer 17 can be set to satisfy the inequality (C1 < C2 < C3). Specifically, when the layer thickness C3 is set to 1, the layer thickness C1 is set to less than 0.5, and the layer thickness C2 is set to more than 0.5 and less than 1.

[0035] The surface 8 of the mask body 7 constitutes a squeegee surface. When forming a printed layer made of the flux 4, the back surface 9 of the mask body 7 is made to face the surface of the circuit board 2, and with the electrodes 3 and the through holes 10 aligned, the two (the mask 1 and the circuit board 2) are brought into close contact. Printing is performed by squeegeeing the flux 4 placed on the squeegee surface (surface 8) with the squeegee S, so that the through holes 10 and the openings for the cut marks are filled with the flux 4, and a printed layer made of the flux 4 that matches the through holes 10 and the cut marks is formed on the surface of the circuit board 2. The squeegee S forms the printed layer while moving from the front side (lower side toward FIG. 2) to the back side (upper side toward FIG. 2) of the mask 1 in a state where its tip is in contact with the squeegee surface (the surface 8 of the mask body 7).

[0036] During printing, the flux 4 is filled from the surface 8 of the mask body 7 into the inside of the first hole portion 13. The flux 4 that has entered the through hole 10 is guided by the inner surface of the hole of the first hole portion 13 and enters in a state where the filling direction is dropped toward the thickness direction of the mask body 7, that is, the direction toward the electrode 3. The flux 4 that has entered the inside of the through hole 10 is peeled off from the second hole portion 14 at the boundary portion between the first hole portion 13 and the second hole portion 14 and heads toward the electrode 3. The flux 4 that has reached the back surface 9 of the mask body 7 contacts the electrode 3, and a printed layer made of the flux 4 as shown in FIG. 3 is formed.

[0037] FIG. 4 shows a method for manufacturing the mask 1 according to the embodiment. (Patterning process) As shown in FIG. 4(a), a photoresist layer 22 of a predetermined thickness is formed over the entire surface of a conductive matrix 21 made of, for example, stainless steel or brass. Then, a pattern film 23 consisting of a glass mask with circular light-transmitting holes corresponding to the through holes 10 and linear light-transmitting holes corresponding to the cut marks is adhered to the matrix. In this state, the matrix is ​​exposed to ultraviolet light, and then developed and dried. The photoresist layer 22 is formed by laminating one or more sheets of negative-type photosensitive dry film resist using thermocompression bonding to achieve the desired thickness. Next, the unexposed portions of the photoresist layer 22 are dissolved and removed to obtain a pattern resist 25 having resist bodies 24 corresponding to the through holes 10 and the cut marks, as shown in FIG. 4(b).

[0038] (Electroforming process) The matrix 21 on which the pattern resist 25 has been formed is placed in a prepared electroforming tank, and as shown in Figure 4(c), an electroformed metal is electrodeposited in an area that does not extend beyond the upper edge of the resist body 24 to form an electroformed layer 26, i.e., a layer that will become the mask body 7. At this time, the edge of the growth tip of the electroformed metal grows in the shape of a quarter ellipse, so that the bell-mouth-shaped second hole 14 can be formed simply by electrodepositing the electroformed metal on the matrix 21.

[0039] (peeling process) As shown in Fig. 4(d), the electroformed layer 26 and the pattern resist 25 are peeled off from the matrix 21, and then the pattern resist 25 is dissolved and removed to obtain the mask 1 shown in Fig. 3. Note that a frame may be adhered to the outer periphery of the obtained mask body 7 with an adhesive, so that the mask body 7 and the frame are inseparably joined to form the mask 1 with a frame.

[0040] As described above, in the mask 1 of this embodiment, the first hole portions 13 opening on the front surface 8 of the mask body 7 are configured as straight holes. Therefore, the flow direction of the flux 4 when filling the through holes 10 is guided by the vertically extending inner surfaces of the first hole portions 13, thereby reliably dropping the flux 4 in the thickness direction (vertical direction) of the mask body 7. Furthermore, the second hole portions 14 are configured as bell-mouth holes whose inner cross-sectional surfaces are rounded, smoothly connected to the first hole portions 13, and widen in diameter as they open on the back surface 9 of the mask body 7. Therefore, when the flux 4 is guided by the inner surfaces of the first hole portions 13 and reaches the vicinity of the boundary between the first hole portions 13 and 14, the flux 4 can be peeled off from the inner surfaces of the second hole portions 14 near the boundary. Furthermore, the flux 4 can reach the second hole portions 14 on the back surface 9 side of the mask body 7 after being peeled off from the inner surfaces of the second hole portions 14. As described above, the mask 1 of this embodiment can peel off the flux 4 from the inner surface of the second hole portion 14 near the boundary between the hole portions 13 and 14, thereby reducing the contact area between the inner surface of the through hole 10 and the flux 4 compared to conventional metal masks, and reducing the amount of flux 4 that adheres to the mask 1 and is removed from the circuit board 2 when the mask 1 is separated from the circuit board 2. As described above, the mask 1 of this embodiment can suppress printing defects such as distortion of the printed shape of the printed layer on the circuit board 2 and faint printing, thereby improving the printing accuracy when printing the printed layer and allowing a high-precision, high-quality printed layer to be formed on the circuit board 2.

[0041] Furthermore, since the through hole 10 is composed of the first hole portion 13 which is a straight round hole and the second hole portion 14 which is a bell-mouth hole, the inner surface shape of the through hole 10 can be made smooth without corners, which further reduces the occurrence of printing defects such as flux 4 adhering to the corners and causing distortion of the printing shape of the printing layer on the circuit board 2 or fading of the print.

[0042] When the thickness T of the mask body 7 is taken as 1, it is preferable to set H1 defined by the hole depth of the first hole portion 13 to be 0.2 or more and 0.6 or less. This is based on the fact that when the hole depth H1 is less than 0.2 or when the hole depth H1 exceeds 0.6, printing defects occur. More specifically, when the hole depth H1 is less than 0.2, the guiding effect of the flux 4 by the inner surface of the hole of the first hole portion 13 becomes insufficient, and the flux 4 is filled in an unintended direction during printing, resulting in the distortion of the shape of the printing layer or the fading of the printing layer, and as a result, printing defects occur. Also, when the hole depth H1 exceeds 0.6, the flux 4 adheres to the inner surface of the hole of the first hole portion 13, and a part of it is removed together with the metal mask, resulting in the distortion of the shape of the printing layer or the fading of the printing layer, and as a result, printing defects occur.

[0043] Furthermore, when the thickness T of the mask body 7 is taken as 1, it is more preferable to set H1 defined by the hole depth of the first hole portion 13 to be 0.2 or more and less than 0.5. Thereby, the occurrence of the previous printing defects can be suppressed, and a printing layer with a generally good thickness can be obtained.

[0044] Since the second hole portion 14 is formed such that the hole depth H2 of the second hole portion 14 and the diameter expansion dimension D3 of the radius of the second hole portion 14 satisfy the inequality (H2 < D3), the curvature of the cross-sectional shape constituting the inner surface of the hole of the second hole portion 14 formed of a bell-mouth-shaped hole can be increased, and the peeling of the flux 4 in the second hole portion 14 can be promoted.

[0045] Since the opening diameter D2 of the second hole portion 14 is set to be 1.5 times or more the opening diameter D1 of the first hole portion 13, similarly to the above, the curvature of the cross-sectional shape constituting the inner surface of the hole of the second hole portion 14 formed of a bell-mouth-shaped hole can be increased, and the peeling of the flux 4 in the second hole portion 14 can be promoted.

[0046] As the definition of the mask 1 increases, the opening diameter D1 of the first hole portion 13 becomes smaller, but if the thickness T of the mask body 7 increases, the hole depth of the through hole 10 becomes larger relative to the opening diameter D1, which may result in insufficient filling of the flux 4 into the through hole 10 by the squeegee. In this embodiment, the thickness T of the mask body 7 is set to 25 μm or less (18 μm), so the above problem does not occur and it is possible to avoid insufficient filling of the flux 4 into the through hole 10 by the squeegee.

[0047] Coating layer 17, which inhibits adhesion of flux 4, is formed on the inner surface of through-hole 10 and on back surface 9 of mask body 7, allowing for smooth guiding of flux 4 through first hole 13 and smooth removal of flux 4 through second hole 14. Furthermore, while thicknesses C1, C2, and C3 of coating layer 17 satisfy the inequality (C1≦C2≦C3), thickness C1 is set to the smallest, minimizing change in the opening diameter D1 of first hole 13, which determines the shape of the printing layer. Furthermore, thickness C3 is set to the largest, allowing for the long-term maintenance of the effectiveness of coating layer 17, which gradually wears away due to contact with circuit board 2.

[0048] For these reasons, the printing metal mask according to this embodiment can contribute to Goal 9 (Industry, innovation and infrastructure - Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation) and Goal 12 (Responsible consumption and production - Ensure sustainable consumption and production patterns) of the Sustainable Development Goals (SDGs) advocated by the United Nations.

[0049] Second Embodiment Figure 5 shows a second embodiment of a printing metal mask according to the present invention. In this embodiment, the shape of the through holes 10 differs from that of the first embodiment. Note that the coating layer 17 is omitted in Figure 5, and the line of the rounded rectangle immediately outside the rectangle indicating the first hole portion 13 in Figure 5(b) is a line indicating the opening end of the second hole portion 14 that opens on the back surface 9 side of the mask body 7.

[0050] The through hole 10 is configured such that the first hole portion 13 opening to the front surface 8 of the mask body 7 is a straight square hole (rectangular hole), and the second hole portion 14 has an inner cross section formed in an R-shape, smoothly continuing to the first hole portion 13, and expanding to open to the back surface 9 of the mask body 7. The inner cross section of the second hole portion 14 is formed in a quadrant elliptical arc shape with a minor axis in the thickness direction of the mask body 7, including the quadrant-shaped regions at the four corners of the second hole portion 14 when viewed from the bottom. As such, the through hole 10 may be rectangular or polygonal, and the corners of the rectangular or polygonal through hole 10 may be rounded. The through hole 10 may also be formed in an elliptical shape.

[0051] In this embodiment, the length of one side of the square holes constituting the first hole portions 13 is defined as the opening dimension D1 of the first hole portions 13, and this opening dimension D1 is the same as the opening diameter D1 of the first hole portions 13 in the first embodiment. Under these conditions, the opening area of ​​the first hole portions 13 opening on the surface 8 of the mask body 7 is approximately 1.3 times larger in this embodiment than in the first embodiment. Therefore, in a printing metal mask 1 in which it is difficult to form a large opening diameter (opening dimension) D1, first hole portions 13 with an opening shape such as that of this embodiment are effective when it is desired to print a larger amount of flux 4 on the electrode 3. This is also effective when the electrode 3 is configured in a quadrangular (rectangular, polygonal) shape.

[0052] (Third embodiment) Figure 6 shows a third embodiment of the printing metal mask according to the present invention. In this embodiment, the configuration of the through holes 10 differs from that of the first embodiment. Specifically, in this embodiment, the second hole portions in the first embodiment are on the front side of the mask body, and the first hole portions are on the back side of the mask body. Note that the coating layer 17 is omitted from Figure 6.

[0053] In this embodiment, the through holes 10 are composed of first hole portions 13 that open to the front surface (squeegee surface) 8 of the mask body 7 and second hole portions 14 that open to the back surface (circuit board-facing surface) 9 of the mask body 7. The second hole portions 14 are straight circular holes that extend in the thickness direction of the mask body 7, and the first hole portions 13 are bell-mouth holes that have an R-shaped inner cross section that smoothly connects to the second hole portions 14 and widens upward. In this way, when the first hole portions 13 that open to the front surface 8 of the mask body 7 are composed of bell-mouth holes, the printing paste 4 can be guided by the inner surface of the R-shaped first hole portions 13 when filling the through holes 10, and the printing paste 4 can be guided into the through holes 10. Furthermore, if the second hole portions 14 connected to the first hole portions 13 are formed in a straight shape and open smoothly continuous with the first hole portions 13 on the back surface 9 of the mask body 7, the printing paste 4 is guided by the inner surfaces of the first hole portions 13, reaches the vicinity of the boundary between the two hole portions 13 and 14, and is guided and filled into the second hole portions 14, allowing the printing paste 4 to reach the back surface 9 side of the mask body 7 of the second hole portions 14. Thus, according to the printing metal mask of this embodiment, the printing paste 4 guided by the first hole portions 13 is gathered near the boundary between the two hole portions 13 and 14 and can be guided into the second hole portions 14. Therefore, even if the printing paste 4 comes into contact with the inner surfaces of the through-holes 10, it can be guided to the printing object 2. As described above, the printing metal mask of this embodiment can suppress printing defects such as distortion of the printing shape of the printing layer on the printing object 2 or faint printing, thereby improving the printing accuracy when printing the printing layer, and enabling a high-precision, high-quality printing layer to be formed on the printing object 2.

[0054] In the printing metal mask of the present invention, when a coating layer 17 is formed, it is preferably formed on the back surface (circuit board-facing surface) 9 of the mask body 7. Furthermore, when forming the coating layer 17 on the inner surface of the through-holes 10, it is preferably formed only on the inner surface of the second hole portions 14. This is because if the coating layer 17 is formed on the front surface (squeegee surface) 8 of the mask body 7 or the inner surface of the first hole portions 13, the printing paste 4 may not be rolled when squeegeeing it with the squeegee S, which may result in poor printing (guiding and filling into the through-holes 10). Furthermore, when forming the coating layer 17 on the back surface 9 of the mask body 7 and the inner surface of the second hole portions 14, it is preferably formed so that the thickness of the coating layer 17 on the back surface 9 of the mask body 7 is equal to or greater than the thickness of the coating layer 17 on the inner surface of the second hole portions 14. Furthermore, in the printing metal mask of the first embodiment, the opening dimension (opening diameter) D1 of the first hole portion 13 is formed smaller than the length dimension (diameter) D4 of the electrode 3, and the opening dimension (opening diameter) D2 of the second hole portion 14 is formed larger than the length dimension (diameter) D4 of the electrode 3. With this configuration, the shape of the printing layer printed on the printing object 2 is formed as a columnar body having the same dimensions as the opening dimension (opening diameter) D1 of the first hole portion 13 from the top side to the bottom side, or as a cross-sectional mountain-shaped shape whose top side dimensions are the same as the opening dimension (opening diameter) D1 of the first hole portion 13 and whose dimensions increase toward the bottom side (toward the printing object 2). On the other hand, in this embodiment, the printing metal mask is formed so that the opening dimension (opening diameter) D1 of the first hole portion 13 is larger than the length dimension (diameter) D4 of the electrode 3, and the opening dimension (opening diameter) D2 of the second hole portion 14 is smaller than the length dimension (diameter) D4 of the electrode 3.With this configuration, the shape of the printing layer printed on the printing object 2 is such that the printing paste 4 is filled into the through hole 10 and formed into a columnar body having the same dimensions from the top side to the bottom side as the opening dimension (opening diameter) D2 of the second hole portion 14.In this way, the printing metal mask of this embodiment has second hole portions 14 that open on the back surface 9 of the mask formed in a straight shape, so that even if printing paste 4 is filled into the through holes 10 and the printing paste 4 comes into contact with the entire inner surface of the through holes 10, when the printing metal mask is separated from the printing object 2, the printing paste 4 located on the inner surface of the second hole portions 14 can be printed on the printing object 2, and the amount of printing paste 4 that adheres to the inner surface of the through holes 10 and is removed from the printing object 2 can be reduced compared to a metal mask with an R-shaped cross-sectional shape of the inner surface of the through holes. Therefore, the printing metal mask of this embodiment can print and form a printing layer with a uniform thickness on the printing object 2 and high reproducibility.

[0055] In the above embodiment, the cross-sectional shape of the inner surface of the second hole portion 14 is formed as a quarter elliptical arc with a minor axis in the thickness direction of the mask body 7. However, it can also be formed as a quarter elliptical arc with a major axis in the thickness direction of the mask body 7, or as a circular arc. Essentially, the cross-sectional shape of the inner surface of the second hole portion 14 may be an R-shape that bulges toward the center of the hole. For example, the cross-sectional shape of the inner surface of the second hole portion 14 may be an R-shape in which the curvature changes between the first hole portion 13 and the back surface 9 of the mask body 7, such as an R-shape in which the curvature is large near the first hole portion 13 and near the back surface 9 of the mask body 7 and becomes smaller in the middle portion. Furthermore, in the above embodiment, contact printing is performed in which the printing metal mask 1 is placed directly on the printing target 2 for printing. However, off-contact printing may also be performed in which a gap is provided between the printing target 2 and the printing metal mask 1 for printing. The technology of the present invention is not limited to printing metal masks, but can also be applied to metal masks such as evaporation masks, solder ball array masks, and solder ball attraction masks. [Explanation of symbols]

[0056] 1 Metal mask for printing 2 Printing target (circuit board) 4 Printed materials (flux, paste) 7 Mask body 8. Surface of the mask body 9 Back of the mask body 10 through hole 13 First hole 14 2nd hole 17 Coating Layer D1 First hole opening size (opening diameter) D2 Second hole opening size (opening diameter) D3 Half the expansion dimension of the opening of the second hole (expansion dimension of the radius) D4 Electrode length (diameter) D5 Half the expansion dimension of the opening of the first hole (expansion dimension of the radius) H1 Hole depth of first hole H2 Depth of the second hole T Mask body thickness

Claims

1. The mask comprises a mask body (7) having a back surface (9) facing the printing object (2), and a large number of through holes (10) that penetrate the mask body (7) from front to back and are filled with a printed matter (4), The through hole (10) has a first hole portion (13) that opens to the front surface (8) of the mask body (7) and a second hole portion (14) that is continuous with the first hole portion (13) and opens to the back surface (9) of the mask body (7), The second hole portion (14) is a straight hole, and the first hole portion (13) has an inner cross section formed in an R-shape, A printing metal mask characterized in that, when the hole depth of the first hole portion (13) is defined as (H1) and half the enlarged dimension of the first hole portion (13) is defined as (D5), the first hole portion (13) is formed so as to satisfy the inequality (H1<D5).

2. 2. The printing metal mask according to claim 1, wherein the second hole portion (14) is a straight hole, and the first hole portion (13) is a bell-mouth hole.

3. 3. The printing metal mask according to claim 1, wherein when the thickness (T) of the mask body (7) is 1, the value (H2) defined by the hole depth of the second hole portion (14) is set to be 0.2 or more and 0.6 or less.

4. 3. The printing metal mask according to claim 1, wherein when the thickness (T) of the mask body (7) is 1, the hole depth (H2) of the second hole portion (14) is set to be 0.2 or more and less than 0.

5.

5. 5. The printing metal mask according to claim 1, wherein the opening dimension (D1) of the first hole portion (13) on the front surface (8) of the mask body (7) is defined as (D1), and the opening dimension (D2) of the second hole portion (14) on the back surface (9) of the mask body (7) is defined as (D2), and the opening dimension (D1) is set to be 1.5 times or more the opening dimension (D2).

6. 6. The printing metal mask according to claim 1, wherein the thickness (T) of the mask body (7) is set to 25 μm or less.

7. 7. A printing metal mask according to claim 1, characterized in that a coating layer (17) for suppressing adhesion of the printed matter (4) is formed on the back surface (9) of the mask body (7) and on the inner surface of the second hole portion (14).

8. The mask comprises a mask body (7) having a back surface (9) facing the printing object (2), and a large number of through holes (10) that penetrate the mask body (7) from front to back and are filled with a printed matter (4), The through hole (10) has a first hole portion (13) that opens to the front surface (8) of the mask body (7) and a second hole portion (14) that is continuous with the first hole portion (13) and opens to the back surface (9) of the mask body (7), The first hole portion (13) is a straight hole, and the second hole portion (14) has an inner cross section formed in an R-shape, A printing metal mask characterized in that, when the hole depth of the second hole portion (14) is defined as (H2) and half the enlarged dimension of the second hole portion (14) is defined as (D3), the second hole portion (14) is formed so as to satisfy the inequality (H2<D3).

9. 9. The printing metal mask according to claim 8, wherein the first hole portion (13) is configured as a straight hole, and the second hole portion (14) is configured as a bell-mouth hole.

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