Metal mask for printing

Abstract

To prevent variations in the amount of paste applied caused by differences in plate release speed depending on a position of a squeegee.SOLUTION: A printing metal mask 10 comprises a metal mask 2 provided inside a frame 1, and prints paste 6 onto a printed object 3 disposed below the metal mask 2 by means of a squeegee 5 moving on an upper surface of the metal mask 2, the printing metal mask 10 being provided, on a lower surface of the metal mask 2, with a plurality of belt-like projections 7 made of a non-metallic material and arranged substantially perpendicular to a moving direction of the squeegee 5.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a printing metal mask for printing paste or flux in the manufacturing process of electronic components and the like.

Background Art

[0002] Conventionally, when printing paste (hereinafter including flux) on electronic components such as printed circuit boards, a mesh screen plate is used in which a photosensitive emulsion is applied to a metal or resin woven in a mesh shape, and then the printing pattern is exposed and developed to form openings in the emulsion. In addition, a metal mask having a large number of fine holes corresponding to the printing form of the object to be printed is used for the same purpose as the mesh screen plate, but to achieve a higher-definition printing form. This metal mask forms fine holes by an electroforming method using a plating process and has the characteristic of being able to realize a printing form with high accuracy. Here, without distinguishing between the mesh screen plate and the metal mask, they will be collectively referred to as the screen plate.

[0003] As a method of printing paste on an object to be printed using a screen plate and a squeegee, a gap printing method is known in which a gap is provided between the object to be printed and the screen plate for printing. The gap printing method presses the upper surface of the screen plate with a squeegee to eliminate the gap at that part, and then moves the squeegee horizontally in a tilted state to print the paste on the object to be printed (see FIG. 5). The gap printing method is also called the off-contact method and is a printing method that is still widely used at present.

[0004] However, in the gap printing method, the screen plate is sequentially separated from the object to be printed following the movement of the squeegee. Since the moving speed of the squeegee is constant, as a result, the plate separation speed varies depending on the moving position of the squeegee. For example, when the squeegee is at the position shown in Fig. 5(A), the angle θ1 formed between the object to be printed and the screen plate on the left side of the squeegee is relatively large, so the plate separation speed is relatively high. On the other hand, when the squeegee is at the position shown in Fig. 5(B), the angle θ2 formed between the object to be printed and the screen plate on the left side of the squeegee is relatively small (θ1 > θ2), so the plate separation speed is relatively low. This difference in the plate separation speed affects the coating amount of the paste, resulting in variations in the coating amount depending on the printing site and a problem of deterioration in printing quality. On the other hand, since the gap printing method can be realized with a relatively simple device, it has the advantages of low initial cost, being applicable to small-scale production, and being applicable to various objects to be printed.

[0005] In view of the above circumstances, various proposals have been made to suppress the deterioration of printing quality due to variations in the coating amount of the paste in the gap printing method.

[0006] One of them is a gap printing method in which the frame of the screen plate is inclined so that the end side of printing is lower than the start side in the moving direction of the squeegee, and the inclination of the frame is maintained in conjunction with the movement of the squeegee to separate the screen plate from the object to be printed (see Patent Document 1).

[0007] Also, a printing method using a metal mask in which a step portion (groove) for air venting is provided around the fine opening on the back surface of the screen plate in contact with the object to be printed so as to facilitate plate separation has been proposed (see Patent Document 2).

[0008] Furthermore, a printing method has been proposed in which, instead of the gap printing method, a dedicated printing device is introduced to improve plate separation (see Non-Patent Document 1).

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Non-Patent Document

[0010]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] In the screen printing method described in Patent Document 1, in order to maintain the inclination of the screen plate in conjunction with the movement of the squeegee, a lifting part and a control part are required, and there is a problem that it is not suitable for printing multi-variety and small-scale printed matter.

[0012] In the printing method using a metal mask according to Patent Document 2, although some improvement in peeling of the plate is achieved, the quality of peeling of the plate depends on the air venting structure, and it was difficult to realize a good air venting structure depending on the printing pattern. Further, since this printing method is an on-contact printing in which a metal mask is placed on the upper surface of the object to be printed, after filling the printing paste into the opening of the printing pattern by the movement of the squeegee, it is necessary to separate the metal mask from the object to be printed. And the quality of peeling of the plate depends on the method of separating the metal mask from the object to be printed, and it did not fundamentally solve the problem of peeling of the plate inherent in on-contact printing.

[0013] The screen printing method according to Non-Patent Document 1 is a closed pressurization printing method, and since it is necessary to introduce a dedicated device, the initial cost is high. Therefore, although it is applicable to mass production, there is a problem that it is not suitable for multi-variety and small-quantity production in which it is necessary to print on various objects to be printed.

[0014] In view of the problems of the above-described prior art, the present invention aims to solve the problem of deterioration of printing quality due to variations in coating amount by realizing pseudo-gap printing so as to achieve a uniform plate separation speed regardless of the moving position of the squeegee, while being on-contact printing in which a metal mask is placed on the upper surface of an object to be printed.

Means for Solving the Problems

[0015] The present invention relates to a printing metal mask for printing paste on an object to be printed disposed below the metal mask by a squeegee that moves on the upper surface of the metal mask, the metal mask being provided inside a printing frame, and a plurality of strip-shaped protrusions made of a non-metallic material are provided on the lower surface of the metal mask substantially perpendicular to the moving direction of the squeegee.

[0016] Further, the present invention is a printing metal mask according to claim 1, characterized in that the non-metallic material is a synthetic resin.

[0017] Furthermore, the present invention is a printing metal mask according to claim 1 or 2, characterized in that the height of the strip-shaped protrusions is 25 μm to 150 μm.

Effects of the Invention

[0018] According to the printing metal mask of the present invention, pseudo-gap printing can be performed in the printing range, although it is on-contact printing that does not require a complicated and expensive device. In addition, since a plurality of strip-shaped protrusions are provided substantially perpendicular to the moving direction of the squeegee, the same plate separation speed can be realized in the printing range disposed between the strip-shaped protrusions. Therefore, deterioration of printing quality due to variations in paste coating amount can be suppressed.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a printing metal mask 10 showing a surface (lower surface) provided with a plurality of strip-shaped protrusions 7, and FIG. 2 is a cross-sectional view showing a view taken along the line A-A in FIG. 1. The plate frame 1 is composed of a rectangular frame made of aluminum having a thickness that is easy for an operator to work with. A metal mask 2 as a screen plate is fixed to the lower surface of the plate frame 1. Therefore, the operator can easily handle the printing metal mask 10 by gripping the plate frame 1.

[0021] The metal mask 2 is manufactured by a well-known electroforming method applying plating technology. It is often made of a nickel material, but is not limited to the nickel material. The thickness of the metal mask 2 is appropriately determined according to the specifications of the object to be printed 3. The thickness of the metal mask 2 in the embodiment is formed to be 50 μm. A plurality of printing pattern portions 4 are formed at a plurality of locations on the metal mask 2 corresponding to the printing range of the object to be printed 3. The printing pattern portion 4 is provided with a large number of pores (not shown) filled with paste 6 by the movement of the squeegee 5. The size, thickness, form of the printing pattern, number of pores, size of pores, etc. of the metal mask 2 are appropriately determined according to the specifications of the object to be printed 3.

[0022] On the lower surface of the metal mask 2, that is, the surface opposite to the upper surface on which the squeegee 5 moves, a plurality of strip-shaped protrusions 7 are provided substantially perpendicular to the moving direction of the squeegee 5. The number of the strip-shaped protrusions 7 is appropriately determined according to the printing form of the object to be printed 3, and a printing pattern portion 4 is disposed between the plurality of strip-shaped protrusions 7.

[0023] The actual size of the printing frame 1 is standardly 656 mm × 656 mm in inner dimensions, but in FIG. 1, a range of 250 mm × 250 mm is shown as an example of the moving area of the squeegee 5. On the lower surface of the metal mask 2 fixed to the printing frame 1, strip-shaped protrusions 7 with a width of 11 mm are provided at four locations along the moving direction of the squeegee 5. In other words, between the strip-shaped protrusions 7 provided along the moving direction of the squeegee 5, there is a portion of only the metal mask where the strip-shaped protrusions 7 are not attached. The dimension of this portion in the moving direction of the squeegee 5 is formed to be 54 mm, and a printing pattern portion 4 is provided at this portion. In the embodiment, the printing pattern portion 4 is a 24 mm square rectangle, and a large number of pores are formed in each printing pattern portion 4.

[0024] As the material of the strip-shaped protrusions 7, a synthetic resin material having a smaller longitudinal elastic modulus than a metal material is used. The longitudinal elastic modulus of a preferable synthetic resin material is 1 to 7 GPa, and a more preferable longitudinal elastic modulus is 1 to 2 GPa. When a compressive force is applied to the strip-shaped protrusions 7 formed of such a synthetic resin material having a relatively small longitudinal elastic modulus, a large compressive deformation that cannot be obtained with a metal material can be obtained for the strip-shaped protrusions 7. In the embodiment, as the synthetic resin material, a photosensitive film HM-4000 series for forming a thick film resist of Resonac Co., Ltd. was used.

[0025] The number and width dimension of the strip-shaped protrusions 7 are appropriately determined according to the specifications of the object to be printed 3. The height dimension of the strip-shaped protrusions 7 is also determined according to the specifications of the object to be printed 3, but there are the following restrictions. If the height (thickness) dimension of the strip-shaped protrusions 7 is too low, the amount of compressive deformation of the strip-shaped protrusions 7 is insufficient, and the separation from the printing plate when the squeegee 5 passes becomes poor. On the other hand, if the height dimension of the strip-shaped protrusions 7 is too high, even if a predetermined pressing force is applied to the squeegee 5, the metal mask 2 will not partially contact the upper surface of the object to be printed 3, resulting in insufficient printing.

[0026] The photosensitive film HM-4000 series for thick film resist formation of Resonac Co., Ltd. used in the examples has films with multiple film thicknesses on sale. By stacking multiple of these films to form the strip-shaped protrusions 7, strip-shaped protrusions 7 with various heights can be realized. In the example, two films with a film thickness of 56 μm were stacked and used. The total height of the strip-shaped protrusions 7 formed by stacking two films was approximately 120 μm (see Fig. 4(A)).

[0027] Hereinafter, the printing metal mask 10 of the present invention and the method for forming the strip-shaped protrusions 7 will be specifically described in order. (1) The metal mask 2 is formed to a predetermined thickness using a nickel material by a well-known electroforming method. At that time, a large number of pores are formed in the printing pattern portion 4 according to the specifications of the object to be printed 3. (2) Stack the required number of photosensitive films for thick film resist formation on the entire lower surface of the metal mask 2. The thickness and the required number of the photosensitive films for thick film resist formation are selected and determined so that the height of the strip-shaped protrusions 7 becomes the required height. (3) Expose the portion where the strip-shaped protrusions 7 are to be formed using a laser direct imaging device (LDI). (4) Develop and wash the photosensitive film for thick film resist formation in the unexposed portion. (5) Perform post-exposure (UV cure or heat cure in an oven) on the photosensitive film for thick film resist formation formed as the strip-shaped protrusions 7. These cure conditions can be implemented according to the conditions recommended by the manufacturer of the photosensitive film for thick film resist formation. The longitudinal elastic modulus of the strip-shaped protrusions 7 of the example formed by such a method was about 1.0 GPa.

[0028] Next, the state of peeling of the printing metal mask 10 manufactured by the above-described process will be described. As shown in FIG. 3, the printing metal mask 10 according to the present invention places the strip-shaped protrusion 7 adhered to the lower surface of the metal mask 2 on the upper surface of the object to be printed 3, presses the upper surface of the metal mask 2 with the squeegee 5, and moves it while tilting forward to print the paste 6 on the object to be printed 3. Therefore, the printing using the printing metal mask according to the present invention belongs to on-contact printing. For this reason, a configuration for securing a gap is not required, and printing can be performed with a simple configuration, so the initial cost is low, and it has the characteristic of good peeling.

[0029] In the metal mask 2 of the embodiment, printing pattern portions 4 are provided at three locations on the left side, the center, and the right side along the moving direction of the squeegee 5. The squeegee 5 moves at a constant speed from the left side to the right side while maintaining the tilted state, and the paste 6 is filled into the pores of the pattern portion 4 of the metal mask 2. FIG. 3(A) shows a state of printing at the left printing pattern portion 4, FIG. 3(B) shows a state of printing at the central printing pattern portion 4, and FIG. 3(C) shows a state of printing at the right printing pattern portion 4.

[0030] In the state shown in FIG. 3(A), the metal mask 2 pressed by the squeegee 5 contacts the upper surface of the object to be printed 3 only at the left printing pattern portion 4, and the paste 6 is printed. In the state shown in FIG. 3(B), the metal mask 2 pressed by the squeegee 5 contacts the upper surface of the object to be printed 3 only at the central printing pattern portion 4, and the paste 6 is printed. In the state shown in FIG. 3(C), the metal mask 2 pressed by the squeegee 5 contacts the upper surface of the object to be printed 3 only at the right printing pattern portion 4, and the paste 6 is printed.

[0031] In the printing of these three states, the same plate separation conditions can be achieved. As in the conventional printing method shown in Fig. 5, the angles θ1 and θ2 at which the upper surface of the object to be printed 3 contacts the lower surface of the metal mask 2 do not vary significantly depending on the position of the squeegee 5. Moreover, since the moving distance of the squeegee 5 in the printing pattern portion 4 disposed between adjacent strip-shaped protrusions 7 is short, the change in the angle at which the upper surface of the object to be printed 3 contacts the lower surface of the metal mask 2 is also small. For these reasons, substantially the same plate separation conditions can be achieved in any state. Therefore, it is possible to suppress a decrease in printing quality caused by differences in the plate separation speed depending on the moving position of the squeegee 5.

[0032] Next, the appropriate value of the longitudinal elastic modulus of the synthetic resin material used for the strip-shaped protrusion 7 of the present invention will be described based on examples. In order to achieve the same plate separation speed in the printing pattern portions 4 provided at three locations on the left side, the center, and the right side along the moving direction of the squeegee 5, it is important that each strip-shaped protrusion 7 provided on the lower surface of the metal mask 2 undergoes appropriate compressive deformation by the pressing force F of the squeegee 5.

[0033] When the metal mask 2 is fixed to the plate frame 1, a predetermined tension is applied and fixed in consideration of temperature changes and the like due to the usage environment of the metal mask 2 so that no excessive slack occurs in the metal mask 2. Therefore, even when the upper surface of the metal mask 2 is pressed by the squeegee 5, the metal mask itself, which is a metal material, does not stretch significantly. In the printing metal mask 10 according to the present invention, the amount of change in the gap (clearance) between the upper surface of the object to be printed 3 and the lower surface of the metal mask 2 caused by the pressing force of the squeegee 5 depends greatly on the compressive deformation of the strip-shaped protrusion 7, which is a synthetic resin material having a small longitudinal elastic modulus.

[0034] Figure 4 shows the measurement of the downward displacement of the metal mask 2 when a downward force is applied by the squeegee 5 at the center of the printing metal mask 10 placed on the upper surface of the object to be printed 3. The side length of the movement range of the squeegee 5 is 250 mm, and the unit of the horizontal axis is mm. The scale of the vertical axis is about 200 times that of the horizontal axis for easy understanding. Therefore, the actual downward displacement of the metal mask 2 is about 1 / 200 of the diagram shown in Fig. 4(A).

[0035] As shown in Fig. 4(B), the pressing force F by the squeegee 5 is applied at the center along the moving direction of the squeegee 5, that is, at a position 125 mm from both ends of the moving range of the squeegee 5. The magnitude of the pressing force F by the squeegee 5 is about 160 N / m in terms of the unit width of the blade of the squeegee 5.

[0036] In the state where there is no pressing force F by the squeegee 5, since the strip-shaped protrusions 7 are not compressed and the height does not change, the gap (clearance) between the upper surface of the object to be printed 3 and the lower surface of the metal mask 2 is about 112 μm. On the other hand, in the state where the pressing force F is applied to the center of the metal mask 2, it can be seen that all the strip-shaped protrusions 7 provided at four positions along the moving direction of the squeegee 5 are compressed and displaced. From the diagram shown in Fig. 4(A), it can be seen that the strip-shaped protrusions 7 on the left and right are symmetrically compressed and displaced with the center part where the pressing force F is applied as the boundary. The specific amount of compression displacement is about 60 μm at two positions near the center and about 10 μm at two positions near both ends.

[0037] In the printing metal mask 10 of this embodiment, printing is performed only in the printing pattern portion of the metal mask 2 pressed by the squeegee 5, and it can be seen that a gap with a size of approximately 60 μm or more is ensured between the upper surface of the object to be printed 3 and the lower surface of the metal mask 2 in other printing pattern portions.

[0038] In an actual printing scenario, when the squeegee 5 moves from the left side to the right side, the portion where the metal mask 2 is pressed by the squeegee 5 and the gap disappears, that is, the portion where printing is performed, also moves from the left side to the right side, and a large gap is ensured in other portions. Therefore, in the printing metal mask 10 of the present invention, it is possible to pseudo-realize gap printing while being an on-contact printing.

[0039] In the above-described embodiment, the strip-shaped protrusions 7 with a width of 11 mm are provided at four locations at equal intervals along the moving direction of the squeegee 5, but the strip-shaped protrusions 7 may be provided at unequal intervals. Further, the strip-shaped protrusions 7 do not have to be continuous strips and may be discontinuous. The shape and dimensions of the strip-shaped protrusions 7 can be variously deformed and are not limited to the embodiment.

Industrial Applicability

[0040] The printing metal mask according to the present invention can be used as a printing metal mask for printing paste or flux in a manufacturing process of electronic components and the like.

Explanation of Reference Numerals

[0041] 1 Frame 2 Metal Mask (Screen Plate) 3 Object to be Printed 5 Squeegee 6 Paste 7 Strip-shaped Protrusion 10 Printing Metal Mask

Claims

1. A printing metal mask having a metal mask inside a printing frame, and printing paste on a printed object disposed below the metal mask by a squeegee that moves on the upper surface of the metal mask, wherein a plurality of strip-shaped protrusions made of a non-metallic material are provided on the lower surface of the metal mask substantially perpendicular to the moving direction of the squeegee. The printing metal mask is characterized by this.

2. The printing metal mask according to claim 1, wherein the non-metallic material is a synthetic resin.

3. The printing metal mask according to claim 1 or 2, wherein the height of the strip-shaped protrusion is 25 μm to 150 μm.

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