Metal mask for printing

Abstract

To provide a metal mask for printing that enables improved printing accuracy in printing and forming a printed layer so as to form a high-accuracy and high-quality printed layer.SOLUTION: A metal mask for printing includes a mask body 7 that is composed of a metal sheet with its back side 9 facing a printing object 2, and multiple through-holes 10 that penetrate the mask body 7 from the front to rear and are filled with printing paste 4. Each of the through-holes 10 is constituted by a first hole part 13 that opens in a surface 8 of the mask body 7 and is composed of a straight hole and a second hole part 14 that has an inner-surface cross-sectional shape formed in an R shape, is smoothly continuous with the first hole part 13, and opens in the back side 9 of the mask body 7 while expanding.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for improving printing defects such as bleeding and smearing of a printing layer in a printing metal mask. Examples of the printing metal mask of the present invention include a printing metal mask used when forming a layer of flux (printing paste) for temporarily adhering solder balls on a substrate by screen printing.

Background Art

[0002] As a technique for improving the printing accuracy of a printing metal mask, the applicant has previously proposed Patent Document 1. In Patent Document 1, the cross-sectional shape of the through holes formed in the metal mask manufactured by the electroforming method is formed in a tapered shape in which the hole diameter on the electroformed surface side is small and the hole diameter on the electroforming master surface side is large. During printing, the electroformed surface side becomes the front surface side, that is, the squeegee surface side, and the electroforming master surface side becomes the back surface side, that is, the printed object (printing target) side. When forming a layer of ink paste (printing paste) (printing layer), first, the printed object side of the metal mask is brought into close contact with the printed object, and then the ink paste is placed on the squeegee surface of the metal mask, and the ink paste on the squeegee surface is extended with a squeegee while being filled into the through holes. After the filling of the ink paste into the through holes is completed, by separating the metal mask from the printed object, a printing layer of the ink paste corresponding to the through holes can be printed and formed on the printed object.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the metal mask of Patent Document 1, the through-holes are tapered holes that widen towards the back side, resulting in good ink / paste penetration. Therefore, when separating the metal mask from the substrate, it is possible to suppress the removal of some of the ink / paste along with the separation of the metal mask, thus preventing printing defects such as bleeding and smudging. However, in the metal mask of Patent Document 1, since the ink / paste is in contact with the entire inner surface of the through-holes, some of the ink / paste filling inside the through-holes still adheres to the inner surface of the through-holes. This can result in some ink / paste remaining attached when the metal mask is separated from the substrate, causing printing defects such as distorted print shapes or smudging. Furthermore, because the adhesion of the ink / paste is not uniform in each through-hole, printing defects such as uneven amounts of ink / paste in each printing layer also occur.

[0005] The present invention aims to provide a metal mask for printing that can further improve the printing accuracy when forming a printed layer, and can form a highly accurate and high-quality printed 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 sheet, with its back surface 9 facing the object to be printed 2, and a number of through holes 10 that penetrate the mask body 7 from front to back and are made of circular holes filled with printing paste 4. . General hole 10 teeth On the surface 8 of the mask body 7 In a perfect circle Open, Uniform inner radius straight Circle The first hole portion 13 consists of holes, and the inner surface cross-sectional shape is formed in an R shape, smoothly continuing with the first hole portion 13 and expanding to the back surface 9 of the mask body 7. In a perfect circle Open Bellmouth shape It is composed of a second hole 14 The cross-sectional shape of the inner surface of the bell-mouth-shaped second hole 14 is configured such that the radius of curvature is small at the upper end portion continuous with the first hole 13, and increases as it goes downwards. At the upper end of the second hole 14, the tangent to the upper end of the arc formed by the radius of curvature defining the cross-sectional shape of the inner surface of the upper end coincides with the straight line defining the cross-sectional shape of the inner surface of the straight first hole 13. It is characterized by having this feature.

[0007] When the thickness T of the mask body 7 is 1, it is preferable that H1, which is defined by the hole depth of the first hole portion 13, be set to 0.2 or more and 0.6 or less.

[0008] 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.

[0009] 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).

[0010] 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.

[0011] The thickness T of the mask body 7 is preferably set to 25 μm or less.

[0012] 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).

Effect of the Invention

[0013] In the metal mask for printing of the present invention, the through-hole 10 that penetrates the mask body 7 from front to back is composed of a first hole portion 13, which is a straight hole that opens into the surface 8 of the mask body 7, and a second hole portion 14, which has an R-shaped cross-sectional shape on its inner surface, is smoothly continuous with the first hole portion 13, and opens into the back surface 9 of the mask body 7 while expanding. In this way, since the first hole portion 13 that opens into the surface 8 of the mask body 7 is composed of a straight hole, the flow direction of the printing paste 4 when filling the through-hole 10 can be guided by the inner surface of the hole portion 13 that extends vertically, so that the printing paste 4 can be reliably dropped into the through-hole 10 in the thickness direction (vertical direction) of the mask body 7. Furthermore, if the second hole 14 connected to the first hole 13 has an inner cross-sectional shape that is rounded, smoothly continuous with the first hole 13, and opens to the back surface 9 of the mask body 7 while expanding, the printing paste 4 is guided along the inner surface of the first hole 13, and when it reaches the vicinity of the boundary between the two holes 13 and 14, the printing paste 4 can be peeled off from the inner surface of the second hole 14 near that boundary. Also, in the state where it has been peeled off from the inner surface of the second hole 14, the printing paste 4 can be brought to the back surface 9 of the mask body 7 of the second hole 14. Thus, with the printing metal mask of the present invention, the printing paste 4 can be peeled off from the inner surface of the second hole 14 near the boundary between the two holes 13 and 14, so that the contact area between the inner surface of the through hole 10 and the printing paste 4 can be reduced compared to conventional metal masks, and the amount of printing paste 4 that adheres to the mask and is removed from the printing target 2 when the mask is separated from the printing target 2 can be reduced. As described above, the printing metal mask of the present invention can suppress the occurrence of printing defects such as distortion of the printed shape of the printed layer on the printing target 2 and blurring of the print. Therefore, it is possible to improve the printing accuracy when forming the printed layer and to form a highly accurate and high-quality printed layer on the printing target 2.

[0014] When the first hole portion 13 is formed of a straight circular hole and the second hole portion 14 is formed of a bell mouth-shaped hole, compared with the 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 printing layer on the printing target 2 being distorted or the printing being blurred.

[0015] When the thickness T of the mask body 7 is taken as 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 printing layer being distorted or the printing layer being blurred, and as a result, printing defects occur. Also, 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 of it is removed together with the metal mask, resulting in the shape of the printing layer being distorted or the printing layer being blurred, and as a result, printing defects occur.

[0016] When the thickness T of the mask body 7 is taken as 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 printing layer with a generally good thickness can be obtained.

[0017] 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 a bell mouth-shaped hole can be made large. Therefore, the peeling of the printing paste 4 in the second hole portion 14 can be promoted.

[0018] When defining the opening dimension of the first hole 13 on the front surface 8 of the mask body 7 as D1 and the opening dimension of the second hole 14 on the back surface 9 of the mask body 7 as D2, if the opening dimension D2 is set to be 1.5 times or more of the opening dimension D1, similar to the above, the curvature of the cross-sectional shape constituting the inner surface of the second hole 14 formed by the bell-mouse-shaped hole can be increased, so that the peeling of the printing paste 4 in the second hole 14 can be promoted.

[0019] It is preferable that the thickness T of the mask body 7 is set to 25 μm or less. As the high definition of the printing metal mask progresses, the opening dimension D1 of the first hole 13 is also miniaturized. However, if the thickness T of the mask body 7 exceeds 25 μm, the hole depth of the through hole 10 becomes larger with respect to the opening dimension D1, so that the filling of the printing paste 4 into the through hole 10 by the squeegee may become insufficient.

[0020] When 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, the guiding of the printing paste 4 by the first hole 13 and the peeling of the printing paste 4 in the second hole 14 can be performed smoothly. Also, when defining the layer thickness of the coating layer 17 formed in the first hole 13 as C1, the layer thickness of the coating layer 17 formed in the second hole 14 as C2, and the layer thickness of the coating layer 17 formed on the back surface 9 of the mask body 7 as C3, a form in which the coating layer 17 is formed can be adopted so as to satisfy the inequality (C1 ≤ C2 ≤ C3). In such a form, by setting the layer thickness C1 of the coating layer 17 to be the smallest, the change in the shape of the opening diameter D1 of the first hole 13 that defines the shape of the printing layer can be reduced. Also, in such a form, by forming the layer thickness C3 of the coating layer 17 larger than the layer thicknesses C1 and C2 of the coating layer 17, the effect of the coating layer 17 that gradually wears due to contact with the printing object 2 can be maintained for a longer period.

Brief Description of the Drawings

[0021] [Figure 1] [6]]A longitudinal front view showing the main part of the printing metal mask according to the first embodiment of the present invention. [Figure 2] It is a plan view showing the whole of a metal mask for printing. [Figure 3] It is a longitudinal sectional side view showing an example of the usage mode of a metal mask for printing. [Figure 4] It is an explanatory view showing the manufacturing process of a metal mask for printing. [Figure 5] The main part of the metal mask for printing according to the second embodiment of the present invention is shown. (a) is a longitudinal front view, and (b) is a bottom view.

Mode for Carrying Out the Invention

[0022] (First Embodiment) FIGS. 1 to 4 show the first embodiment of a metal mask for printing according to the present invention. Note that the dimensions such as thickness and width in each figure do not show the actual state but are schematically shown. A metal mask for printing (hereinafter simply referred to as a mask) 1 is used to print and form a printing layer made of a flux (printing paste) 4 for temporarily adhering solder balls on an electrode 3 formed on the surface of a circuit board (printing target) 2 by a screen printing method as shown in FIG. 3.

[0023] In FIG. 2, the mask 1 is based on a mask body 7 made of a thin metal plate formed by electroforming using an electrodeposited metal such as a nickel alloy such as nickel, copper, or nickel - cobalt as a material. A large number of through - holes 10 formed of round holes penetrating the board surface from the front surface 8 to the back surface 9 are opened in the mask body 7. The mask 1 is formed in a square shape with a side length of 250 mm. When the mask 1 is divided into four quadrants, a pattern - forming region M is defined in each of the quadrants. The through - holes 10 are provided in the pattern - forming region M in a state arranged in an electrode pattern corresponding to the electrode 3 of the circuit board 2. Around the pattern - forming region M, a cut - mark forming region C for printing cut marks used when cutting the circuit board 2 into a specified shape in a process after screen printing is defined so as to surround the region M. The mask 1 is mounted on the mask fixing part of a screen printing device either alone or in a state where a frame body is fixed to its four peripheral edges.

[0024] As shown in FIG. 1, the through hole 10 is composed of a first hole portion 13 that opens on the surface 8 of the mask body 7 and a second hole portion 14 that opens on the back surface 9 of the mask body 7. The first hole portion 13 is a straight circular hole extending in the thickness direction of the mask body 7, and the second hole portion 14 is a bell mouth-shaped hole that smoothly continues with the first hole portion 13 and expands downward.

[0025] 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.

[0026] The hole depth H1 of the first hole portion 13 (see FIG. 1) is set to be 0.2 or more and less than 0.5 when the thickness T of the mask body 7 is taken as 1. The hole depth H1 of this embodiment is set to 3.6 μm, and the hole depth H1 when the thickness T of the mask body 7 is taken as 1 is 0.2 (3.6 / 18 = 0.2).

[0027] 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 a general flux 4 is set to be 20 μm to 50 μm. From this, the opening diameter D1 of this 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, and a circular printed layer is formed on the electrode 3 in a plan view.

[0028] 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 this embodiment. As described above, since the hole depth H1 when the thickness T of the mask body 7 is taken as 1 is set to be less than 0.5, 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).

[0029] 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 the opening diameter D1. In addition, the diameter expansion dimension (half of the opening expansion dimension) D3 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 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 short axis in the thickness direction of the mask body 7. Further, the opening end of the second hole portion 14 and the back surface 9 of the mask body 7 are smoothly continuous.

[0030] The electrode 3 of the present embodiment is formed in a circular shape. When the diameter of the electrode 3 is D4, the opening diameter D1 of the first hole portion 13 is formed to be smaller than the diameter D4, and the opening diameter D2 of the second hole portion 14 is formed to be larger than the diameter D4. In other words, the opening diameter D1 and the opening diameter D2 are formed to satisfy the inequality (D1 < D4 < D2) (see FIG. 1).

[0031] 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 can be made thinner than other portions to reduce the shape change of the opening diameter D1. 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 can be made thicker than other portions to improve 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 equation (C1≠C3).

[0032] In this embodiment, the layer thickness C1 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 so as 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 step portion. The coating layer 17 can be formed by dip formation or coating by spraying. Although the coating layer 17 of this embodiment is formed in the order of μm, it is also possible to form the coating layer 17 in the order of nm.

[0033] Also, the coating layer 17 can be set so as 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.

[0034] The surface 8 of the mask body 7 constitutes the squeegee surface. When forming the printing layer made of flux 4, the back surface 9 of the mask body 7 is positioned directly opposite the surface of the circuit board 2, and the electrodes 3 and through holes 10 are aligned, bringing the two (mask 1 and circuit board 2) into close contact. Printing is performed by squeegeeing the flux 4 placed on the squeegee surface (surface 8) with the squeegee S. This fills the through holes 10 and the openings for cut marks with flux 4, forming a printing layer made of flux 4 that matches the through holes 10 and cut marks on the surface of the circuit board 2. The squeegee S moves from the front side (bottom side in Figure 2) to the back side (top side in Figure 2) of the mask 1 with its tip in contact with the squeegee surface (surface 8 of the mask body 7), forming the printing layer.

[0035] During printing, the flux 4 is filled from the surface 8 of the mask body 7 into the interior of the first hole 13. The flux 4 that enters the through hole 10 is guided by the inner surface of the first hole 13 and enters in a manner in which the filling direction is in the thickness direction of the mask body 7, that is, toward the electrode 3. The flux 4 that enters the interior of the through hole 10 is peeled off from the second hole 14 at the boundary between the first hole 13 and the second hole 14 and moves toward the electrode 3, and the flux 4 that reaches the back surface 9 of the mask body 7 comes into contact with the electrode 3, forming a printed layer of flux 4 as shown in Figure 3.

[0036] Figure 4 shows a method for manufacturing the mask 1 according to an embodiment. (Patterning process) As shown in Figure 4(a), a photoresist layer 22 of a predetermined thickness is formed on the entire surface of a conductive matrix 21 made of, for example, stainless steel or brass. Then, a pattern film 23 made of a glass mask having circular light-transmitting holes corresponding to the through-holes 10 and linear light-transmitting holes corresponding to the cut marks is pressed into contact with the matrix. In this state, exposure is performed by irradiating with ultraviolet light, followed by development and drying. The photoresist layer 22 here is formed by laminating one or more negative-type sheet-shaped photosensitive dry film resists and bonding them together to a predetermined thickness. Next, the unexposed portion of the photoresist layer 22 is dissolved and removed to obtain a pattern resist 25 having resist bodies 24 corresponding to the through-holes 10 and cut marks, as shown in Figure 4(b).

[0037] (Electroforming process) The mold 21 on which the pattern resist 25 described above is formed is placed in a prepared electroforming bath, and as shown in Figure 4(c), the electrodeposited metal is deposited within a range that does not exceed the upper edge of the resist body 24 to form the electroformed layer 26, i.e., the layer that will become the mask body 7. At this time, the edge of the growth tip of the electroformed metal grows in a quarter-elliptical arc shape, so the bell-mouth-shaped second hole 14 can be formed simply by electrodepositing the electrodeposited metal onto the mold 21.

[0038] (Peeling process) As shown in Figure 4(d), the electroformed layer 26 and the pattern resist 25 are peeled off from the master mold 21, and the pattern resist 25 is dissolved and removed to obtain the mask 1 shown in Figure 3. Alternatively, a frame can be attached to the outer edge of the obtained mask body 7 with an adhesive, so that the mask body 7 and the frame are joined together inseparably, resulting in a mask 1 with a frame.

[0039] As described above, in the mask 1 of this embodiment, the first hole 13 opening to the surface 8 of the mask body 7 is configured as a straight hole, so that the flow direction of the flux 4 when filling the through hole 10 is guided by the inner surface of the first hole 13 which extends vertically, and the flux 4 can be reliably dropped into the thickness direction (vertical direction) of the mask body 7. Furthermore, the second hole 14 is configured as a bell-mouth-shaped hole with an R-shaped inner cross-sectional shape, which is smoothly continuous with the first hole 13 and opens to the back surface 9 of the mask body 7 while expanding in diameter, so that the flux 4 is guided by the inner surface of the first hole 13 and when it reaches the vicinity of the boundary between the two holes 13 and 14, the flux 4 can be peeled off from the inner surface of the second hole 14 near that boundary. In addition, the flux 4 can be brought to the back surface 9 side of the mask body 7 of the second hole 14 in the state where it has been peeled off from the inner surface of the second hole 14. Thus, with the mask 1 of this embodiment, the flux 4 can be peeled off from the inner surface of the second hole 14 near the boundary between the two holes 13 and 14. Compared to conventional metal masks, this reduces the contact area between the inner surface of the through-hole 10 and the flux 4, thereby 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 a result, the mask 1 of this embodiment can suppress the occurrence of printing defects such as distortion of the printed shape of the printed layer on the circuit board 2 and blurring of the print. This improves the printing accuracy when forming the printed layer, enabling the formation of a high-precision and high-quality printed layer on the circuit board 2.

[0040] Furthermore, with a through-hole 10 consisting of a first hole portion 13 made of a straight circular hole and a second hole portion 14 made of a bell-mouth-shaped hole, the inner surface shape of the through-hole 10 can be made smooth without corners. This further suppresses the occurrence of printing defects such as flux 4 adhering to corners, which can distort the printed shape of the printed layer on the circuit board 2 or cause the print to become blurred.

[0041] 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 because 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 distortion of the shape of the printed layer or fading of the printed 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 distortion of the shape of the printed layer or fading of the printed layer, and as a result, printing defects occur.

[0042] Furthermore, 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. By doing so, the occurrence of the above-mentioned printing defects can be suppressed, and a printed layer with a generally good thickness can be obtained.

[0043] 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 having a bell-mouth shape can be increased, and the peeling of the flux 4 in the second hole portion 14 can be promoted.

[0044] Since the opening diameter D2 of the second hole portion 14 is set to 1.5 times or more of the opening diameter D1 of the first hole portion 13, the curvature of the cross-sectional shape constituting the inner surface of the hole of the second hole portion 14 having a bell-mouth shape can be increased as described above, and the peeling of the flux 4 in the second hole portion 14 can be promoted.

[0045] As the resolution of the mask 1 increases, the opening diameter D1 of the first hole 13 is reduced. However, 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 through hole 10 with flux 4 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 insufficient filling of the through hole 10 with flux 4 by the squeegee can be avoided.

[0046] Since a coating layer 17 that suppresses the adhesion of flux 4 is formed on the inner surface of the through-hole 10 and the back surface 9 of the mask body 7, the guidance of flux 4 by the first hole 13 and the peeling of flux 4 at the second hole 14 can be performed smoothly. Furthermore, since the layer thickness C1 is set to the smallest while the layer thicknesses C1, C2, and C3 of the coating layer 17 satisfy the inequality (C1 ≤ C2 ≤ C3), the shape change of the opening diameter D1 of the first hole 13 that defines the shape of the printed layer can be reduced. In addition, since the layer thickness C3 is formed to the largest extent, the effect of the coating layer 17, which gradually wears down due to contact with the circuit board 2, can be maintained over a long period of time.

[0047] Based on the above, the printing metal mask according to this embodiment can contribute to Goal 9 (Build resilient infrastructure, promote inclusive and sustainable industrialization and expand technological innovation) and Goal 12 (Responsible consumption and production patterns) of the United Nations' Sustainable Development Goals (SDGs).

[0048] (Second Embodiment) Figure 5 shows a second embodiment of the printing metal mask according to the present invention. In this embodiment, the shape of the through-hole 10 differs from that of the first embodiment. Note that in Figure 5, the coating layer 17 is omitted from the illustration, and in Figure 5(b), the line of the rounded rectangle just outside the rectangle showing the first hole 13 is a line that indicates the opening end of the second hole 14 that opens to the back surface 9 side of the mask body 7.

[0049] The through-hole 10 has a first hole 13 that opens onto the surface 8 of the mask body 7, which is a straight square hole (rectangular hole), and a second hole 14 that has an inner cross-sectional shape that is rounded, smoothly continuous with the first hole 13, and opens onto the back surface 9 of the mask body 7 while expanding. The inner cross-sectional shape of the second hole 14 is formed as a quarter-elliptical arc with a minor axis in the thickness direction of the mask body 7, including the quarter-circular regions at the four corners of the second hole 14 when viewed from the bottom. Thus, the through-hole 10 may be rectangular or polygonal, and the corners of the through-hole 10, which consists of a rectangular or polygonal hole, may be rounded. The through-hole 10 can also be formed in an elliptical shape.

[0050] In this embodiment, the length of one side of the square hole constituting the first hole portion 13 is defined as the opening dimension D1 of the first hole portion 13, and this opening dimension D1 is the same as the opening diameter D1 of the first hole portion 13 in the first embodiment. Under these conditions, the opening area of ​​the first hole portion 13 opening into the surface 8 of the mask body 7 is approximately 1.3 times larger in this embodiment compared to the first embodiment. Therefore, in a printing metal mask 1 where it is difficult to form a large opening diameter (opening dimension) D1, a first hole portion 13 with an opening shape like that of this embodiment is effective when it is desired to print more flux 4 on the electrode 3. It is also effective when the electrode 3 is configured in a square shape (rectangular, polygonal).

[0051] In the above embodiment, the cross-sectional shape of the inner surface of the second hole 14 is formed as a quarter-elliptical arc with a minor axis in the thickness direction of the mask body 7, but it can also be formed as a quarter-elliptical arc or a circular arc with a major axis in the thickness direction of the mask body 7. In short, the cross-sectional shape of the inner surface of the second hole 14 can be any R shape that bulges toward the center of the hole. For example, the cross-sectional shape of the inner surface of the second hole 14 may be an R shape in which the curvature changes between the first hole 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 13 and near the back surface 9 of the mask body 7, and the curvature is small in the intermediate part. The technology of the present invention can be applied not only to metal masks for printing, but also to metal masks such as masks for vapor deposition, masks for solder ball arrangement, and masks for solder ball adsorption. [Explanation of symbols]

[0052] 1. Metal mask for printing 2. Printing target (circuit board) 4. Printing paste (flux) 7. Mask body 8. Surface of the mask body 9. The back of the mask itself 10 through hole 13 First hole 14 2nd hole 17 Coating layer D1 Opening dimensions (opening diameter) of the first hole D2 Opening dimensions (opening diameter) of the second hole D3 Half the enlarged dimension of the opening of the second hole (enlarged radius dimension) H1 Hole depth of the first hole H2 Hole depth of the second hole Thickness of the T mask body

Claims

1. The mask body (7) is made of a thin metal plate and its back surface (9) faces the object to be printed (2), The mask body (7) has numerous through holes (10) that penetrate from front to back and are filled with printing paste (4) Equipped with, The through-hole (10) consists of a first hole (13) which is a straight, circular hole with a uniform inner radius that opens in a perfect circle on the surface (8) of the mask body (7), and a second hole (14) which is bell-mouth shaped, with an R-shaped inner cross-section, smoothly continuous with the first hole (13), and expanding as it opens in a perfect circle on the back surface (9) of the mask body (7). The cross-sectional shape of the inner surface of the bell-mouth-shaped second hole (14) is configured such that the radius of curvature is small at the upper end portion continuous with the first hole (13), and increases as it goes downwards. A printing metal mask characterized in that, at the upper end of the second hole (14), the tangent to the upper end of the arc formed by the radius of curvature defining the cross-sectional shape of the inner surface of the upper end coincides with the straight line defining the cross-sectional shape of the inner surface of the straight first hole (13).

2. The printing metal mask according to Claim 1, wherein when the thickness (T) of the mask body (7) is 1, the (H1) defined by the hole depth of the first hole portion (13) is set to 0.2 or more and 0.6 or less.

3. The printing metal mask according to Claim 1, wherein when the thickness (T) of the mask body (7) is 1, the (H1) defined by the hole depth of the first hole portion (13) is set to 0.2 or more and less than 0.

5.

4. A printing metal mask according to any one of claims 1 to 3, wherein the hole depth of the second hole (14) is defined as (H2) and half of the enlarged dimension of the second hole (14) is defined as (D3), and the second hole (14) is formed such that the inequality (H2 < D3) is satisfied.

5. A printing metal mask according to any one of Claims 1 to 4, wherein when the opening dimension of the first hole (13) on the surface (8) of the mask body (7) is defined as (D1) and the opening dimension of the second hole (14) on the back surface (9) of the mask body (7) is defined as (D2), the opening dimension (D2) is set to be 1.5 times or more the opening dimension (D1).

6. The printing metal mask according to any one of claims 1 to 5, wherein the thickness (T) of the mask body (7) is set to 25 μm or less.

7. A coating layer (17) is formed on the inner surface of the through-hole (10) and on the back surface (9) of the mask body (7) to suppress the adhesion of the printing paste (4). A printing metal mask according to any one of claims 1 to 6, wherein the coating layer (17) is formed such that the inequality (C1 ≤ C2 ≤ C3) is satisfied when the thickness of the coating layer (17) in the first hole (13) is defined as (C1), the thickness of the coating layer (17) in the second hole (14) is defined as (C2), and the thickness of the coating layer (17) on the back surface (9) of the mask body (7) is defined as (C3).

Images