Metal mask for printing

Abstract

To provide a metal mask for printing capable of forming a high precision and high-quality printed layer by further improving printing precision when forming a printed layer by printing.SOLUTION: A metal mask for printing of the present invention includes a mask body 7 having a back surface 9 facing a print target 2 and a large number of through holes 10 penetrating through the mask body 7 from front to back and filled with printed material 4. The through hole 10 is composed of a first hole portion 13 that opens to a 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. Any one of the first hole portion 13 and the second hole portion 14 is a straight hole, and the other is formed with an inner surface having an R-shaped cross section.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004] , , , , , ,

[0001] The present invention relates to a technique for improving printing defects such as bleeding of a printing layer in a metal mask. Examples of the 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 electroformed master surface side is large. During printing, the electroformed surface side becomes the front surface side, that is, the squeegee surface side, and the electroformed 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 and filled into the through holes. After the filling of the ink paste into the through holes is completed, the metal mask is separated from the printed object, whereby 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] [[ID=​​​​​​​​​​​​​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 consisting of round holes that penetrate the mask body 7 from front to back and are filled with printing paste 4. The through holes 10 are characterized by being composed of a first hole portion 13 consisting of a straight hole that opens onto the surface 8 of the mask body 7, and a second hole portion 14 whose inner cross-sectional shape is formed in an R shape, which is smoothly continuous with the first hole portion 13 and opens onto the back surface 9 of the mask body 7 while expanding.

[0007] The first hole portion 13 can be composed of a straight, round hole, and the second hole portion 14 can be composed of a bell-mouth-shaped hole.

[0008] 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, is set to 0.2 or more and 0.6 or less.

[0009] More preferably, when the thickness T of the mask body 7 is taken as 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 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.

[0015] When the first hole portion 13 is formed of a straight round hole and the second hole portion 14 is formed of a bell mouth-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 printing 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 printing layer being distorted or the printing 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 printing layer being distorted or the printing 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 printing layer having 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 bell mouth-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 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, if the opening dimension D2 is set to 1.5 times or more the opening dimension D1, then, as described above, the curvature of the cross-sectional shape constituting the inner surface of the second hole 14, which consists of a bell-mouth-shaped hole, can be made larger, thereby promoting the peeling of the printing paste 4 in the second hole 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 resolution of printing metal masks increases, the opening dimension D1 of the first hole portion 13 is also reduced. However, if the thickness T of the mask body 7 exceeds 25 μm, the hole depth of the through hole 10 becomes larger than the opening dimension D1, which may result in insufficient filling of the through hole 10 with printing paste 4 by the squeegee.

[0021] If a coating layer 17 that suppresses the adhesion of 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 guidance of the printing paste 4 by the first hole 13 and the peeling of the printing paste 4 at the second hole 14 can be performed smoothly. Furthermore, when the thickness of the coating layer 17 formed in the first hole 13 is defined as C1, the thickness of the coating layer 17 formed in 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 in such a way that the inequality (C1 ≤ C2 ≤ C3) is satisfied. In such a configuration, by setting the thickness C1 of the coating layer 17 to be the smallest possible, 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. In addition, in such a configuration, by forming the thickness C3 of the coating layer 17 to be larger than the thicknesses C1 and C2, the effect of the coating layer 17, which gradually wears down due to contact with the printing target 2, can be maintained for a longer period of time. [Brief explanation of the drawing]

[0022] [Figure 1] This is a longitudinal cross-sectional front view showing the main parts of a printing metal mask according to the first embodiment of the present invention. [Figure 2] It is a plan view showing the whole metal mask for printing. [Figure 3] It is a longitudinal side view showing an example of the usage mode of the metal mask for printing. [Figure 4] It is an explanatory view showing the manufacturing process of the metal mask for printing. [Figure 5] It shows the main part of the metal mask for printing according to the second embodiment of the present invention, where (a) is a longitudinal front view and (b) is a bottom view. [Figure 6] It is a longitudinal side view showing an example of the usage mode of the metal mask for printing according to the third embodiment of the present invention.

Mode for Carrying Out the Invention

[0023] (First Embodiment) FIGS. 1 to 4 show the first embodiment of the 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. The metal mask for printing (hereinafter simply referred to as the mask) 1 is used to print and form a printing layer made of a flux (printing paste) 4 for temporarily adhering solder balls on the electrode 3 formed on the surface of the circuit board (printing target) 2 by the screen printing method as shown in FIG. 3.

[0024] In Figure 2, the mask 1 is based on a mask body 7 made of a thin metal sheet formed by electroforming using an electrodeposited metal such as nickel, copper, or nickel alloys like nickel-cobalt. The mask body 7 has numerous through holes 10, which are circular holes that penetrate its surface from the front 8 to the back 9. The mask 1 is formed in a square shape with sides of 250 mm, and when the mask 1 is divided into four quadrants, a pattern formation region M is demarcated in each quadrant. The through holes 10 are provided within the pattern formation region M, arranged in the electrode patterns corresponding to the electrodes 3 of the circuit board 2. Around the pattern formation region M, a cut mark formation region C is demarcated, enclosing the region M, for printing cut marks used when cutting the circuit board 2 into a specified shape in a process after screen printing. The mask 1 is mounted on the mask fixing part of the screen printing device either on its own or with a frame fixed to its four periphery.

[0025] As shown in Figure 1, the through-hole 10 consists of a first hole 13 that opens onto the surface 8 of the mask body 7 and a second hole 14 that opens onto the back surface 9 of the mask body 7. The first hole 13 is a straight, round hole extending in the thickness direction of the mask body 7, and the second hole 14 is a bell-mouth-shaped hole that smoothly continues from the first hole 13 and expands 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 13 (see Figure 1) is set to be 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 the hole depth H1 when the thickness T of the mask body 7 is 1 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 a 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 set to 1, the hole depth H1 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 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.

[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 diameter D1 and the opening diameter 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 13, the layer thickness C2 of the coating layer 17 in the second hole 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 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, so that its durability can be improved. Therefore, each layer thickness C1, C2, C3 of the coating layer 17 is set so as to satisfy the inequality (C1 ≤ C2 ≤ C3) and further satisfy the formula (C1 ≠ C3).

[0033] 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 13, and is set to 1.0 μm at the adjacent portion to the back surface 9 of the mask body, and the layer thickness C3 is set to 1.0 μm. The layer thickness C2 of the coating layer 17 in the second hole 14 is formed to gradually increase from the side of the first hole 13 toward the side of the back surface 9 of the mask body 7, and is a smooth coating layer 17 without a step portion. The coating layer 17 can be formed by dip formation or 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.

[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 printing and forming a printing 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, both (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 printing 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 printing 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 printing 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 step) 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).

[0038] (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.

[0039] (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.

[0040] 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.

[0041] 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.

[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 shape of the printed layer being distorted or the printed layer being blurred, 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 shape of the printed layer being distorted or the printed layer being blurred, 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. By doing so, the occurrence of the previous printing defects can be suppressed, and a printed 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 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.

[0047] 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.

[0048] 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).

[0049] (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.

[0050] 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.

[0051] 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).

[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, the second hole portion in the first embodiment is on the surface side of the mask body, and the first hole portion is on the back side of the mask body. Note that the coating layer 17 is omitted in Figure 6.

[0053] In this embodiment, the through-hole 10 is composed of a first hole 13 that opens onto the surface (squeegee surface) 8 of the mask body 7 and a second hole 14 that opens onto the back surface (circuit board facing surface) 9 of the mask body 7. The second hole 14 is a straight, round hole extending in the thickness direction of the mask body 7, while the first hole 13 is a bell-mouth shaped hole with an R-shaped inner cross-section that smoothly continues from the second hole 14 and expands upward. In this way, since the first hole 13 that opens onto the surface 8 of the mask body 7 is composed of a bell-mouth shaped hole, the printing paste 4 can be guided by the inner surface of the first hole 13 with its R-shaped cross-section when filling the through-hole 10, thereby guiding the printing paste 4 into the through-hole 10. Furthermore, if the second hole 14 connected to the first hole 13 is formed in a straight shape and opens smoothly and continuously with the first hole 13 to the back surface 9 of the mask body 7, the printing paste 4 is guided along the inner surface of the first hole 13, reaches the vicinity of the boundary between the two holes 13 and 14, and is guided and filled into the second hole 14, allowing the printing paste 4 to reach the back surface 9 side of the mask body 7 of the second hole 14. Thus, according to the printing metal mask of this embodiment, the printing paste 4 guided by the first hole 13 is concentrated near the boundary between the two holes 13 and 14 and guided into the hole of the second hole 14, so that even if the printing paste 4 comes into contact with the inner surface of the through hole 10, it can be guided to the object to be printed 2. As described above, the printing metal mask of this embodiment can suppress the occurrence of printing defects such as distortion of the printed shape of the printed layer on the printing target 2 or 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.

[0054] In the printing metal mask of the present invention, when forming the coating layer 17, it is preferable to form it 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 preferable to form it only on the inner surface of the second hole portion 14. This is because if the coating layer 17 is formed on the surface (squeegee surface) 8 of the mask body 7 or on the inner surface of the first hole portion 13, the printing paste 4 may not roll properly when squeegeeing it with the squeegee S, which could result in poor printing (guiding and filling into the through-holes 10). When forming the coating layer 17 on the back surface 9 of the mask body 7 and on the inner surface of the second hole portion 14, it is preferable to form the thickness of the coating layer 17 on the back surface 9 of the mask body 7 to be greater than or equal to the thickness of the coating layer 17 on the inner surface of the second hole portion 14. Furthermore, in the printing metal mask of the first embodiment, the opening dimension (opening diameter) D1 of the first hole 13 is formed to be smaller than the length dimension (diameter) D4 of the electrode 3, and the opening dimension (opening diameter) D2 of the second hole 14 is formed to be larger than the length dimension (diameter) D4 of the electrode 3. With this configuration, the shape of the printing layer printed on the printing target 2 is formed to be a columnar body with the same dimensions as the opening dimension (opening diameter) D1 of the first hole 13 from the top side to the bottom side, or a mountain-shaped cross-section where the dimensions on the top side are the same as the opening dimension (opening diameter) D1 of the first hole 13 and the dimensions widen towards the bottom side (printing target 2 side). On the other hand, in this embodiment, the printing metal mask has an opening dimension (opening diameter) D1 of the first hole 13 that is larger than the length dimension (diameter) D4 of the electrode 3, and an opening dimension (opening diameter) D2 of the second hole 14 that is smaller than the length dimension (diameter) D4 of the electrode 3. With this configuration, the shape of the printing layer printed on the object to be printed 2 is such that the printing paste 4 is filled into the through-hole 10, and the columnar body is formed from the top side to the bottom side with the same dimensions as the opening dimension (opening diameter) D2 of the second hole 14.Thus, in this embodiment, the printing metal mask has a second hole portion 14 formed in a straight shape that opens on the back surface 9 of the mask. Even when printing paste 4 is filled into the through-hole 10 and the printing paste 4 comes into contact with the entire inner surface of the through-hole 10, when the printing metal mask is separated from the object to be printed 2, the printing paste 4 located on the inner surface of the second hole portion 14 can be printed onto the object to be printed 2. Compared to a metal mask with a rounded cross-sectional shape on the inner surface of the through-hole, the amount of printing paste 4 that adheres to the inner surface of the through-hole 10 and is removed from the object to be printed 2 can be reduced. Therefore, with the printing metal mask of this embodiment, a printing layer with a uniform thickness and high reproducibility can be printed on the object to be printed 2.

[0055] In the above embodiment, the inner surface 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, 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 inner surface cross-sectional shape of the second hole 14 can be any R shape that bulges toward the center of the hole. For example, the inner surface cross-sectional shape 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. Also, in the above embodiment, contact printing is performed by directly placing the printing metal mask 1 on the printing target 2 and printing, but off-contact printing may be performed by providing a gap between the printing target 2 and the printing metal mask 1 and printing. The technology of the present invention can be applied not only to printing metal masks, but also to metal masks such as evaporation masks, solder ball arrangement masks, and solder ball adsorption 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. 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) D4 Electrode Length Dimension (Diameter) D5 Half the enlarged dimension of the opening of the first 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 comprises a metal mask body (7) having a 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 filled with printed material (4), The through-hole (10) is composed of a first hole (13) that opens onto the surface (8) of the mask body (7), and a second hole (14) that is continuous with the first hole (13) and opens onto the back surface (9) of the mask body (7). The first hole (13) is composed of a bell-mouth-shaped hole, and the second hole (14) is composed of a straight-shaped hole. When the thickness (T) of the mask body (7) is 1, the (H2) defined by the hole depth of the second hole (14) is set to 0.2 or more and 0.6 or less. A metal mask for printing, characterized in that, when the radial expansion amount (D5) of the first hole (13) is defined as half of the difference obtained by subtracting the minimum opening diameter (D2) from the maximum opening diameter (D1) of the first hole (13) ((D1 - D2) / 2), and the hole depth of the first hole (13) is defined as (H1), the first hole (13) is formed such that the radial expansion amount (D5) is greater than the hole depth (H1).

2. The printing metal mask according to claim 1, characterized in that (H2), defined by the hole depth of the second hole portion (14), is set to 0.2 or more and less than 0.

5.

3. The printing metal mask according to claim 1 or 2, characterized in that the maximum opening diameter (D1) of the first hole (13) on the surface (8) of the mask body (7) is set to 1.5 times or more the minimum opening diameter (D2) of the first hole (13) on the back surface (9) of the mask body (7).

4. The printing metal mask according to any one of claims 1 to 3, characterized in that the thickness (T) of the mask body (7) is set to 25 μm or less.

5. A printing metal mask according to any one of claims 1 to 4, characterized in that a coating layer (17) is formed on the back surface (9) of the mask body (7) and on the inner surface of the holes of the second hole portion (14) to suppress the adhesion of printed material (4).

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