Mask for screen printing

Abstract

To prevent surface smoothness of a mask main body from becoming impaired caused by generating such a tensile stress that surpasses an elastic limit in a mask body in a mask for screen printing.SOLUTION: A mask for screen printing includes: a mask main body 2 having many independent through holes 8 penetrating in a vertical direction; a holding frame 4 having a mask opening 3 for disposing the mask main body 2; and a connection body 5 for connecting the mask main body 2 with the holding frame 4 by extending to an opening center from an inner peripheral surface of the mask opening 3. The connection body 5 is constituted by an expansion and contraction body having self-reconstruction property.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a screen printing mask used when forming a fine pattern such as an internal electrode of an electronic component by a screen printing method.

Background Art

[0002] This type of screen printing mask is disclosed, for example, in Patent Document 1 by the applicant of the present patent. The printing mask described in Patent Document 1 includes a mask body formed by an electroforming method and a frame body having a mask opening in which the mask body is disposed. A pattern portion is formed in the inner region of the mask body, and a printing pattern composed of a large number of independent through holes for printing is formed in the pattern portion. The frame body is composed of a support fixed to the upper surface of the mask body so as to support the outer peripheral edge of the mask body and a frame main body fixed to the upper surface of the support. The mask body, the support, and the frame main body are each formed of metal as a material, and the mask body and the support, and the support and the frame main body are respectively fixed inseparably and integrally. The screen printing mask is used for printing with the frame main body fixed to a screen printing machine.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the screen printing method, there are contact printing in which a printing material placed on the upper surface of a mask body is squeegeed with the lower surface of a printing mask in contact with the printing surface (the upper surface of the object to be printed), and offset printing (off-contact printing) in which the printing material placed on the upper surface of the mask body is squeegeed with the lower surface of the printing mask separated from the printing surface. In offset printing, by displacing the mask body downward by the pressing force of the squeegee, the lower surface of the mask body on the back side where the squeegee contacts comes into contact with the printing surface, and squeegeeing proceeds while the contact portion moves. Therefore, even for an object to be printed having undulations on the printing surface, the mask body can be brought into close contact with the object to be printed to form a printing pattern of an appropriate shape on the printing surface.

[0005] In order to perform offset printing using the printing mask of Patent Document 1, it is necessary to elastically deform a mask body and a support made of metal and displace them downward. However, when the mask body is elastically deformed, tensile stress is generated inside due to the elongation of the mask body. When this tensile stress exceeds the elastic limit of the metal material forming the mask body, permanent strain occurs in the mask body. Thus, when permanent strain occurs in the mask body, even if the pressing force by the squeegee is released, it remains as elongation or bending of the mask body, so the flatness of the mask body is impaired.

[0006] An object of the present invention is to prevent the flatness of a mask body from being impaired due to the generation of tensile stress exceeding the elastic limit in a screen printing mask.

Means for Solving the Problems

[0007] The screen printing mask according to the present invention includes a mask body 2 having a large number of independent through holes 8 penetrating in the vertical direction, a holding frame 4 having a mask opening 3 in which the mask body 2 is disposed, and a connecting body 5 extending from the inner peripheral surface of the mask opening 3 toward the opening center to connect the mask body 2 and the holding frame 4. And the connecting body 5 is characterized by being composed of an elastic body having self-restoring properties.

[0008] The connecting body 5 is made of a mesh sheet made of resin.

[0009] A reinforcing frame 9 is provided which is fixed to the surface along the outer peripheral edge of the mask body 2 to reinforce the mask body 2.

[0010] The reinforcing frame 9 is fixed to the upper surface of the mask body 2, and the mask body 2 is connected to the connecting body 5 via the reinforcing frame 9.

[0011] The reinforcing frame 9 is fixed to the lower surface of the mask body 2, and the mask body 2 is connected to the connecting body 5.

Effect of the Invention

[0012] When the connecting body 5 that connects the mask body 2 and the holding frame 4 is composed of an elastic body having self - restoring properties like the mask for screen printing of the present invention, even when an external force is applied to push down the mask body 2 during offset printing, the connecting body 5 elongates and deforms to relieve and absorb the external force, preventing the external force from directly acting on the mask body 2. From the above, according to the present invention, it is possible to prevent tensile stress exceeding the elastic limit from occurring in the mask body 2, so that permanent strain does not occur in the mask body 2 and the smoothness of the mask body 2 is not impaired.

Brief Description of the Drawings

[0013]

Figure 1

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Mode for Carrying Out the Invention

[0014] (First Embodiment) FIGS. 1 to 6 show a first embodiment of a mask for screen printing according to the present invention. In the present embodiment, front and rear, left and right, and up and down follow the cross arrows shown in FIGS. 1 and 2 and the front and rear, left and right, and up and down indications written in the vicinity of each arrow. In FIG. 2, a mask for screen printing (hereinafter simply referred to as a mask) 1 is formed by electroforming using a mask body 2 made of a nickel alloy such as copper, nickel, nickel cobalt, or other electrodeposited metal, and has a mask opening 3 in which the mask body 2 is disposed, a holding frame 4 that supports the mask body 2, and a connecting body 5 that extends from the inner peripheral surface of the mask opening 3 toward the opening center and connects the mask body 2 and the holding frame 4. Each figure does not show the actual state of the mask 1 but shows it schematically. Also, the number of through holes 8, the opening dimensions, the thickness dimensions of the mask body 2, etc. in FIG. 1 and the like are shown for the convenience of drawing creation.

[0015] As shown in FIGS. 2 and 3, the mask body 2 is formed of a metal thin plate having a square shape in plan view, and includes a solid portion 6 provided on the outer peripheral side and having a square outer shape and no through holes, and a pattern portion 7 formed inside the solid portion 6 and having a square outer shape. As shown in FIG. 1, a printing pattern composed of a large number of independent through holes 8 for printing penetrating in the vertical direction is formed in the pattern portion 7.

[0016] As shown in FIGS. 1 and 3, a reinforcing frame 9 for reinforcing the mask body 2 is integrally and inseparably fixed to the upper surface of the solid portion 6 of the mask body 2. The reinforcing frame 9 is a rectangular frame made of a metal (low thermal expansion material) having a smaller coefficient of thermal expansion than the electrodeposited metal constituting the mask body 2, such as 42 alloy, invar material, or SUS430. It is desirable that the outer peripheral shape thereof is formed to coincide with the outer peripheral shape of the mask body 2. The width dimensions of the respective side portions of the rectangular frame constituting the reinforcing frame 9 are the same. The thickness dimension of the reinforcing frame 9 is formed larger than the thickness dimension of the mask body 2. The reinforcing frame 9 as described above can be formed by punching a plate material with a press machine, etching with an etching solution, laser processing with a laser beam, or electroforming (plating).

[0017] As shown in FIGS. 1 and 2, the holding frame 4 is a rectangular metal molded product having a mask opening 3 which is a rectangular opening in the central portion. The inner peripheral shape of the holding frame 4, that is, the opening dimension of the mask opening 3, is set larger than the outer shape of the mask body 2. The metal constituting the holding frame 4 has a coefficient of thermal expansion equivalent to that of the metal constituting the reinforcing frame 9 or larger than that of the metal constituting the reinforcing frame 9. The wall thickness dimension of the holding frame 4 is set larger than the wall thickness dimension of the reinforcing frame 9. The holding frame 4 having the above-described configuration can be formed by punching a plate material with a press machine or cutting it out from a plate material by laser processing.

[0018] As shown in FIGS. 1 and 2, the connecting body 5 is composed of a square frame body whose inner peripheral shape is smaller than the outer peripheral shape of the reinforcing frame 9 and whose outer peripheral shape is larger than the inner peripheral shape of the holding frame 4. The reinforcing frame 9 and the connecting body 5 are inseparably joined by adhering the outer peripheral edge portion (outer over half portion) of the upper surface at each side portion of the reinforcing frame 9 and the inner peripheral edge portion of the lower surface at each side portion of the connecting body 5. Further, the connecting body 5 and the holding frame 4 are inseparably joined by adhering the outer peripheral edge portion of the upper surface at each side portion of the connecting body 5 and the inner peripheral edge portion (inner half portion) of the lower surface at each side portion of the holding frame 4. In the present embodiment, the fixed widths at each side portion of the reinforcing frame 9 and the connecting body 5 are formed to be the same, and the fixed widths at each side portion of the connecting body 5 and the holding frame 4 are the same. Further, the fixed widths (adhesion regions in cross-sectional view) of the reinforcing frame 9 and the connecting body 5 and the fixed widths (adhesion regions in cross-sectional view) of the connecting body 5 and the holding frame 4 are the same. From the above, in the mask 1 of the present embodiment, the connecting body 5 is disposed below the holding frame 4, the reinforcing frame 9 is disposed below the connecting body 5, and the mask body 2 is disposed below the reinforcing frame 9.

[0019] The connecting body 5 is composed of an elastic body having self-restoring properties. Specifically, the connecting body 5 is formed by cutting a mesh sheet (woven fabric made of polyester fibers) formed of polyester (resin) into a square frame shape. Such a mesh sheet exhibits self-restoring properties of stretching when a tensile force is applied and contracting back to its original shape when the tensile force is released. Therefore, in the mask 1 of the present embodiment, when a vertical pressing force is applied to the mask body 2, a tensile force is applied to the connecting body 5 and the connecting body 5 stretches, whereby the mask body 2 is displaced in the acting direction (vertical direction) of the pressing force. Further, when the pressing force on the mask body 2 is released from this state, the connecting body 5 returns to its original posture by the restoring force, whereby the mask body 2 can also be returned to its original position. The mesh size of the mesh sheet constituting the connecting body 5 is preferably #100 to #300.

[0020] Next, the offset printing in the screen printing method using mask 1 will be described with reference to FIGS. 1 and 4. First, mask 1 is attached to a screen printing machine (not shown). At this time, mask 1 is attached to the screen printing machine in a state where it can be changed in posture between a printing posture in which mask body 2 faces the upper surface 17 (printing surface) of printing object 16 and a retracted posture in which mask body 2 retracts from the upper surface 17 of printing object 16. Also, printing object 16 is held on the printing table of the screen printing machine. When performing offset printing, first, as shown in FIG. 1, printing object 16 is set on the printing table, and further, mask 1 is switched from the retracted posture to the printing posture so that mask body 2 faces the upper surface 17 of printing object 16. At this time, the upper surface 17 of printing object 16 and the lower surface 18 of mask body 2 are arranged to be separated by a predetermined distance L. This distance L is set to be equal to or greater than the thickness dimension of mask body 2.

[0021] Subsequently, as shown in FIG. 4, printing material 20 is placed on the upper surface of mask body 2, and this printing material 20 is filled into through hole 8 while being extended in one direction with squeegee 19 to form a printing pattern on the upper surface 17 of printing object 16. Specifically, after printing material 20 is placed on the upper surface of mask body 2, the tip of squeegee 19 is brought into contact with the upper surface of mask body 2, and further, squeegee 19 is pressed downward so as to displace mask body 2 downward, and the lower surface 18 of mask body 2 is brought into contact with the upper surface 17 of printing object 16. At this time, although the portion receiving the pressing force from squeegee 19 is partially displaced downward with respect to holding frame 4 as connecting body 5 extends, the entire mask body 2 is slightly displaced upward by the self-restoring force of connecting body 5. As described above, as shown in FIG. 4, mask body 2 is curved and deformed in a downward protruding shape with the pressing position of squeegee 19 as the lowest point.

[0022] Subsequently, while the pressing force of the squeegee 19 is acting on the mask body 2, the squeegee 19 is moved from the upstream side in its moving direction toward the downstream end. At this time, while the portion where the upper surface 17 of the printing target 16 and the lower surface 18 of the mask body 2 are in contact moves in the advancing direction of the squeegee 19, the through hole 8 is filled with the printing material 20. Also, at the portion where the pressing force of the squeegee 19 is acting, the mask body 2 is in close contact with the upper surface 17 of the printing target 16. Finally, the pressing force by the squeegee 19 is released, the mask 1 is switched to the retracted posture, and the mask body 2 is removed from above the printing target 16. From the above, a printing pattern made of the printing material 20 can be formed on the upper surface 17 of the printing target 16. In the mask 1 of the present embodiment, since the mask body 2 is arranged in the lowermost layer of the mask 1, even when the planar size of the upper surface 17 of the printing target 16 exceeds the planar size of the mask body 2, a printing pattern can be formed on the upper surface 17 of the printing target 16 without any problem.

[0023] FIGS. 5 and 6 show an example of a method for manufacturing the mask 1 according to the present embodiment. First, as shown in FIG. 5(a), a photoresist layer 23 is formed on the surface of a master mold 22 made of, for example, stainless steel or brass having conductivity, and a pattern film 24 having the through holes 8 and light-transmitting holes 24a corresponding to the outer peripheral shape of the mask body 2 is adhered onto this photoresist layer 23. The photoresist layer 23 is formed by laminating one or several sheets of negative-type photosensitive dry film resist according to a predetermined height and performing thermocompression bonding. Next, the photoresist layer 23 is exposed by irradiating ultraviolet light with an ultraviolet lamp 25, and after performing each process of development and drying, the unexposed portion is dissolved and removed, thereby forming a pattern resist 26 having a straight resist body 26a corresponding to the through holes 8 and the outer peripheral shape of the mask body 2 on the master mold 22 as shown in FIG. 5(b).

[0024] Subsequently, the master mold 22 was placed in an electroforming bath conditioned under predetermined conditions, and as shown in FIG. 5(c), within the range of the height of the resist body 26a and exceeding the thickness dimension of the mask body 2, electroforming (plating) of an electrodeposited metal such as nickel alloy was performed on the surface of the master mold 22 not covered by the resist body 26a to form an electroformed layer 27. Next, as shown in FIG. 5(d), the surfaces of the pattern resist 26 and the electroformed layer 27 were polished and flattened, and then the pattern resist 26 was dissolved and removed, whereby, as shown in FIG. 5(e), an electroformed layer 27 adjusted to the thickness dimension of the mask body 2 and having a smooth surface was formed on the master mold 22.

[0025] Subsequently, as shown in FIG. 6(a), after fixing the pre-formed reinforcing frame 9 to the upper surface of the electroformed layer 27 with an adhesive or the like, the electroformed layer 27 was peeled off from the master mold 22 to form a mask body 2 with the reinforcing frame 9 integrated on the upper surface side as shown in FIG. 6(b). Finally, using a jig, the pre-formed connecting body 5 was fixed to the upper surface of the reinforcing frame 9 with an adhesive or the like, and then the pre-formed holding frame 4 was fixed to the upper surface of the connecting body 5 with an adhesive or the like. Thus, a mask 1 in which the mask body 2 is supported by the holding frame 4 as shown in FIG. 6(c) can be obtained. When forming the mask body 2 using a master mold 22 whose planar size matches the outer shape of the mask body 2, the pattern film 24 (see FIG. 5(a)) that adheres to the photoresist layer 23 formed on the surface of the master mold 22 should be one having a light-transmitting hole 24a corresponding to the through-hole 8.

[0026] The mask 1 of this embodiment is preferably used for offset printing, but can also be used for contact printing. The mask 1 includes one mask body 2, but may also be in a form including a plurality of mask bodies 2. For example, when the mask 1 includes four mask bodies 2, the holding frame 4 may be formed in a grid shape including four mask openings 3. The connecting body 5 may be a mesh body made of metal or a sheet body made of rubber. The connecting body 5 can also be fixed to the upper surface of the holding frame 4. It is desirable that the fixing width (adhesive area in cross-sectional view) of the reinforcing frame 9 and the connecting body 5 is the same width as or larger than the fixing width (adhesive area in cross-sectional view) of the connecting body 5 and the holding frame 4.

[0027] In the manufacturing process of the mask 1, the reinforcing frame 9 can also be formed integrally with the mask body 2 by forming a resist pattern corresponding to the reinforcing frame 9 after the formation of the mask body 2 and performing electroforming (plating). In the above manufacturing process, the reinforcing frame 9 was fixed to the electroformed layer 27 on the master mold 22 (see Fig. 6(a)). However, it is also possible to first peel the electroformed layer 27 from the master mold 22 and use a jig to fix the reinforcing frame 9, the connecting body 5, and the holding frame 4 to the peeled electroformed layer 27 to obtain the mask 1. Further, following the step of fixing the reinforcing frame 9 to the electroformed layer 27 on the master mold 22 (see Fig. 6(a)), the connecting body 5 is fixed to the reinforcing frame 9, and then the holding frame 4 is fixed to the connecting body 5. After that, the electroformed layer 27, the reinforcing frame 9, the connecting body 5, and the holding frame 4 can be peeled from the master mold 22 to obtain the mask 1. A pre-integrated connecting body 5 and holding frame 4 can be prepared and fixed to the reinforcing frame 9.

[0028] (Second Embodiment) Figures 7 to 9 show the second embodiment of the mask for screen printing according to the present invention. In this embodiment, the difference from the previous first embodiment is that the mask body 2 is joined to the connecting body 5. The mask body 2 and the connecting body 5 are integrally joined inseparably by adhering the outer peripheral edge portion of the upper surface at each side portion of the solid portion 6 of the mask body 2 and the inner peripheral edge portion of the lower surface at each side portion of the connecting body 5. Further, the connecting body 5 and the holding frame 4 are integrally joined inseparably by adhering the outer peripheral edge portion of the upper surface at each side portion of the connecting body 5 and the inner half portion of the lower surface at each side portion of the holding frame 4. In this embodiment, the fixed widths at each side portion of the mask body 2 and the connecting body 5 are formed to be the same, and the fixed widths at each side portion of the connecting body 5 and the holding frame 4 are the same. Also, the fixed width between the mask body 2 and the connecting body 5 and the fixed width between the connecting body 5 and the holding frame 4 are the same. From the above, in the mask of this embodiment, the connecting body 5 is arranged below the holding frame 4, the mask body 2 is arranged below the connecting body 5, and the reinforcing frame 9 is arranged below the mask body 2.

[0029] Figure 9 shows the manufacturing method of the mask 1 according to this embodiment. First, through the same steps as the manufacturing method of the previous first embodiment (refer to FIGS. 5(a) to (e), 6(a)), as shown in FIG. 9(a), the reinforcing frame 9 is fixed to the upper surface of the electroformed layer 27. Next, the electroformed layer 27 is peeled from the master mold 22, and further turned upside down to form a mask body 2 with the reinforcing frame 9 integrated on the lower surface side as shown in FIG. 9(b). Finally, the pre-formed connecting body 5 is fixed to the upper surface of the solid portion 6 of the mask body 2 with an adhesive or the like, and then the pre-formed holding frame 4 is fixed to the upper surface of the connecting body 5 with an adhesive or the like, whereby a mask 1 in which the mask body 2 is supported by the holding frame 4 as shown in FIG. 9(c) can be obtained. Since the rest is the same as the first embodiment, the same members are denoted by the same reference numerals and the description thereof is omitted. The same applies to the following third embodiment.

[0030] (Third Embodiment) Figure 10 shows the third embodiment of the mask for screen printing according to the present invention. The difference from the previous embodiments in this embodiment is that the reinforcing frame 9 for reinforcing the mask body 2 is eliminated.

[0031] In the mask 1 according to each of the above embodiments, since the connecting body 5 that connects the mask body 2 and the holding frame 4 is configured by an elastic body having self - restoring properties, even when an external force that presses down on the mask body 2 is applied during offset printing, the connecting body 5 elongates and deforms to relieve and absorb the external force, preventing the external force from directly acting on the mask body 2. From the above, according to this mask 1, it is possible to prevent tensile stress exceeding the elastic limit from occurring in the mask body 2, so that permanent strain does not occur in the mask body 2 and the smoothness of the mask body 2 is not impaired. Further, according to this mask 1, by preventing tensile stress exceeding the elastic limit from occurring in the mask body 2, it is possible to prevent the through - hole 8 through which the printing material 20 passes from deforming, so that a printing pattern with a more appropriate shape can be formed on the printing surface.

[0032] Since the connecting body 5 is configured by a mesh sheet made of resin, a mask 1 with better durability can be obtained. That is, compared with metal, resin has resistance to fatigue failure caused by elastic deformation accompanying repeated expansion and contraction. Therefore, according to each of the above embodiments, a mask 1 with better durability can be obtained. Also, since the connecting body 5 is configured by a mesh sheet, greater stretchability can be imparted to the connecting body 5 compared to the case where the connecting body 5 is configured by a plate - like sheet. From the above, the mask body 2 can be displaced more greatly in the vertical direction, so that it is possible to more reliably prevent permanent strain from occurring in the mask body 2 and the smoothness of the mask body 2 from being impaired.

[0033] Since a reinforcing frame 9 is provided that is fixed to the surface along the outer peripheral edge of the mask body 2 to reinforce the mask body 2, the elastic deformation of the mask body 2 can be suppressed by the reinforcing frame 9. This also makes it possible to prevent permanent strain from occurring in the mask body 2 and the smoothness of the mask body 2 from being impaired.

[0034] Since the reinforcing frame 9 is fixed to the upper surface of the mask body 2 and the mask body 2 is connected to the connecting body 5 via the reinforcing frame 9, the mask body 2 can be arranged at the lowermost layer of the mask 1. According to this, since the distance L between the lower surface 18 of the mask body 2 and the upper surface 17 of the printing target 16 during offset printing can be made smaller, the downward displacement amount of the mask body 2 can be made smaller. Therefore, it is possible to suppress the generation of tensile stress inside the mask body 2 due to the displacement of the mask body 2.

[0035] Since the reinforcing frame 9 is fixed to the lower surface of the mask body 2 and the mask body 2 is connected to the connecting body 5, compared with the form in which the above-described mask body 2 is supported by the connecting body 5 via the reinforcing frame 9, there is no member intervening between the mask body 2 and the connecting body 5, so the relative positional accuracy between the holding frame 4 and the mask body 2 can be improved. Therefore, the mask body 2 can be arranged at an optimal position with respect to the printing target 16 during offset printing, and a printing pattern can be accurately formed on the upper surface 17 of the printing target 16.

[0036] The screen printing mask according to the present invention can contribute to Goal 9 (Build the infrastructure for industry and technological innovation) and Goal 12 (Responsibility to produce, responsibility to consume) of the Sustainable Development Goals (SDGs) proposed by the United Nations. In addition, the structure of the screen printing mask according to the present invention can also be applied to various metal masks such as for vapor deposition, for solder ball array, or for solder ball adsorption.

Explanation of reference numerals

[0037] 1 Screen printing mask 2 Mask body 3 Mask opening 4 Holding frame 5 Connecting body 8 Through hole 9 Reinforcing frame

Claims

1. A mask body (2) having a number of independent through-holes (8) penetrating in the vertical direction, a holding frame (4) having a mask opening (3) in which the mask body (2) is disposed, a connecting body (5) extending from the inner peripheral surface of the mask opening (3) toward the opening center to connect the mask body (2) and the holding frame (4), comprising: The screen printing mask is characterized in that the connecting body (5) is composed of an elastic body having self-restoring properties.

2. The screen printing mask according to claim 1, wherein the connecting body (5) is made of a mesh sheet made of resin.

3. The screen printing mask according to claim 1, further comprising a reinforcing frame (9) fixed to the surface along the outer peripheral edge of the mask body (2) to reinforce the mask body (2).

4. The reinforcing frame (9) is fixed to the upper surface of the mask body (2), The screen printing mask according to claim 3, wherein the mask body (2) is connected to the connecting body (5) via the reinforcing frame (9).

5. The reinforcing frame (9) is fixed to the lower surface of the mask body (2), The screen printing mask according to claim 3, wherein the mask body (2) is connected to the connecting body (5).

Images