JP7501951B1 - Metal mask for printing - Google Patents

Abstract

[Problem] To prevent the plate release speed from varying depending on the position of the squeegee, resulting in variation in the amount of paste applied. [Solution] A printing metal mask 10 is provided with a metal mask 2 inside a frame 1, and a squeegee 5 moves over the top surface of the metal mask 2 to print paste 6 on a print substrate 3 disposed below the metal mask 2. The problem is solved by the printing metal mask 10 having a plurality of band-shaped protrusions 7 made of a non-metallic material provided on the bottom surface of the metal mask 2, approximately perpendicular to the direction of movement of the squeegee 5. [Selected Figure] Figure 1

Description

The present invention relates to a printing metal mask for printing paste or flux in the manufacturing process of electronic components, etc.

Traditionally, when printing paste (hereinafter including flux) on electronic components such as printed circuit boards, mesh screen plates have been used in which a photosensitive emulsion is applied to metal or resin woven into a mesh pattern, and then the printing pattern is exposed and developed to form openings in the emulsion. Metal masks, which have the same purpose as mesh screen plates but have many fine holes corresponding to the printing shape of the substrate, are also used to achieve higher resolution printing shapes. These metal masks form fine holes by electroforming using a plating process, and are characterized by their ability to achieve printing shapes with high precision. Here, we will refer to mesh screen plates and metal masks without distinguishing between them as screen plates.

Gap printing is a method of printing paste onto a substrate using a screen and squeegee, in which a gap is created between the substrate and the screen and printing is performed. In gap printing, the squeegee is pressed against the top surface of the screen to eliminate the gap in that area, while the squeegee is moved horizontally in a forward tilted state to print the paste onto the substrate (see Figure 5). Gap printing is also known as the off-contact method, and is a printing method that is still widely used today.

However, in the gap printing method, the screen plate is separated from the printed material in sequence following the movement of the squeegee, and the moving speed of the squeegee is constant, so the plate separation speed varies depending on the moving position of the squeegee. For example, when the squeegee is in the position shown in Figure 5 (A), the angle θ1 formed by the printed material and the screen plate on the left side of the squeegee is relatively large, so the plate separation speed is relatively large. On the other hand, when the squeegee is in the position shown in Figure 5 (B), the angle θ2 formed by the printed material and the screen plate on the left side of the squeegee is relatively small (θ1>θ2), so the plate separation speed is relatively small. This difference in plate separation speed affects the amount of paste applied, so there is a problem that the amount applied varies depending on the printing area, resulting in a decrease in printing quality. On the other hand, the gap printing method has the advantages of being able to be realized with a relatively simple device, having low initial costs, being suitable for small-scale production, and being applicable to a variety of printed materials.

In light of the above-mentioned circumstances, various proposals have been made to prevent deterioration of print quality due to variations in the amount of paste applied in the gap printing method.

One of these is the gap printing method, in which the screen plate frame is tilted so that the end of printing is lower in the direction of the squeegee movement than the start of printing, and the inclination of the plate frame is maintained in conjunction with the movement of the squeegee, separating the screen plate from the material to be printed (see Patent Document 1).

A printing method using a metal mask has also been proposed in which the back surface of the screen plate that comes into contact with the printed material has stepped portions (grooves) around the fine openings for air release to facilitate removal of the plate (see Patent Document 2).

In addition, instead of the gap printing method, a printing method has been proposed that uses a dedicated printing device to improve plate release (see non-patent document 1).

JP 2006-123327 A JP 2000-313179 A

Journal of the Japanese Society of Printing Science, Vol. 47, No. 6 (2010) "Fine Circuit Formation Technology Using Screen Printing Method"

The screen printing method described in Patent Document 1 requires a lifting unit and a control unit to maintain the inclination of the screen in conjunction with the movement of the squeegee, which makes it unsuitable for printing a wide variety of small-scale printed materials.

In the printing method using a metal mask according to Patent Document 2, a certain degree of improvement in plate release was achieved, but the quality of plate release depended on the air vent structure, and depending on the printing pattern, it was difficult to achieve a good air vent structure. In addition, because this printing method is on-contact printing in which a metal mask is placed on the top surface of the substrate, it was necessary to separate the metal mask from the substrate after filling the openings of the printing pattern with printing paste by moving the squeegee. And the quality of plate release depended on the method of separating the metal mask from the substrate, and did not fundamentally solve the plate release problem that exists with on-contact printing.

The screen printing method described in Non-Patent Document 1 is a sealed pressurized printing method, and requires the introduction of dedicated equipment, resulting in high initial costs. Therefore, although it can be applied to mass production, it has the problem that it is not suitable for high-mix, low-volume production, which requires printing on a variety of substrates.

In consideration of the problems with the conventional technology described above, the present invention aims to achieve pseudo-gap printing that achieves a uniform plate release speed regardless of the squeegee movement position, while using on-contact printing in which a metal mask is placed on top of the substrate, thereby solving the problem of reduced print quality due to variations in the amount of coating.

The present invention relates to a printing metal mask which has a metal mask attached inside a frame and which prints paste on a substrate placed below the metal mask using a squeegee that moves over the top surface of the metal mask, and which is characterized in that the bottom surface of the metal mask has a plurality of band-shaped protrusions formed by stacking multiple synthetic resin films having a longitudinal elastic modulus of 1 to 2 GPa on top of each other , approximately perpendicular to the direction of squeegee movement.

Furthermore, the present invention provides a printing metal mask as set forth in claim 1 , characterized in that the height of the band-shaped protrusions is 25 μm to 150 μm.

The printing metal mask of the present invention allows pseudo-gap printing in the printing range, despite being on-contact printing that does not require complex and expensive equipment. In addition, by providing multiple band-shaped protrusions approximately perpendicular to the direction of squeegee movement, the same plate release speed can be achieved in the printing range disposed between the band-shaped protrusions. This makes it possible to suppress deterioration of printing quality due to variations in the amount of paste applied.

FIG. 1 is a plan view of a printing metal mask according to the present invention. FIG. 1 is a cross-sectional view of a printing metal mask of the present invention. FIG. 2 is a cross-sectional view showing a state in which the printing metal mask of the present invention is used. FIG. 4 is a diagram showing the vertical displacement of the printing metal mask of the present invention. 1 is a schematic diagram showing a prior art gap printing method.

The following describes an embodiment of the present invention with reference to the drawings. Fig. 1 is a plan view of a printing metal mask 10 showing the surface (lower surface) on which a plurality of band-shaped protrusions 7 are provided, and Fig. 2 is a cross-sectional view taken along the line A-A in Fig. 1. The frame 1 is made of a rectangular aluminum frame having a thickness that allows an operator to work with it easily. A metal mask 2 is fixed to the lower surface of the frame 1 as a screen plate. Therefore, an operator can easily handle the printing metal mask 10 by gripping the frame 1.

The metal mask 2 is produced by a well-known electroforming method that applies plating technology. It is often produced from nickel material, but is not limited to nickel material. The thickness of the metal mask 2 is appropriately determined according to the specifications of the substrate 3. In the embodiment, the metal mask 2 is formed to a thickness of 50 μm. The metal mask 2 has a printing pattern portion 4 formed in multiple locations corresponding to the printing range of the substrate 3. The printing pattern portion 4 has a large number of pores (not shown) that are filled with paste 6 by the movement of the squeegee 5. The size, thickness, form of the printing pattern, number of pores, size of the pores, etc. of the metal mask 2 are appropriately determined according to the specifications of the substrate 3.

On the underside of the metal mask 2, i.e., the side opposite to the upper surface along which the squeegee 5 moves, a number of belt-shaped protrusions 7 are provided at approximately right angles to the direction of movement of the squeegee 5. The number of belt-shaped protrusions 7 is appropriately determined according to the printing form of the printing substrate 3, and the printing pattern portion 4 is disposed between the multiple belt-shaped protrusions 7.

The actual size of the printing frame 1 is normally 656 mm x 656 mm inside, but in FIG. 1, a range of 250 mm x 250 mm is shown as an example of the movement range of the squeegee 5. On the underside of the metal mask 2 fixed to the printing frame 1, four belt-shaped protrusions 7 with a width of 11 mm are provided along the movement direction of the squeegee 5. In other words, between the belt-shaped protrusions 7 provided along the movement direction of the squeegee 5, there is a portion where only the metal mask has no belt-shaped protrusions 7 attached. The dimension of this portion in the movement direction of the squeegee 5 is 54 mm, and the printing pattern portion 4 is provided in this portion. In this embodiment, the printing pattern portion 4 is a rectangle with a square of 24 mm, and each printing pattern portion 4 has a large number of pores formed therein.

The material used for the strip-shaped protrusions 7 is a synthetic resin material with a smaller modulus of longitudinal elasticity than metal materials. The preferred synthetic resin material has a modulus of longitudinal elasticity of 1 to 7 GPa, and more preferably a modulus of longitudinal elasticity of 1 to 2 GPa. When a compressive force is applied to the strip-shaped protrusions 7 made of a synthetic resin material with a relatively small modulus of longitudinal elasticity, the strip-shaped protrusions 7 undergo a large compressive deformation that cannot be achieved with metal materials. In the embodiment, the synthetic resin material used was Resonac Corporation's HM-4000 series photosensitive film for forming thick-film resists.

The number and width of the band-shaped protrusions 7 are determined appropriately according to the specifications of the substrate 3. The height of the band-shaped protrusions 7 is also determined according to the specifications of the substrate 3, but is subject to the following constraints. If the height (thickness) of the band-shaped protrusions 7 is too low, the amount of compressive deformation of the band-shaped protrusions 7 will be insufficient, and the plate will not separate properly when the squeegee 5 passes by. On the other hand, if the height of the band-shaped protrusions 7 is too high, even if a predetermined pressing force is applied to the squeegee 5, the metal mask 2 will not come into contact with part of the top surface of the substrate 3, resulting in insufficient printing.

The photosensitive film for forming thick-film resist, HM-4000 series, manufactured by Resonac Corporation, used in the examples, is available in a variety of thicknesses, and by stacking multiple sheets of these films to form the belt-like protrusions 7, belt-like protrusions 7 of various heights can be realized. In the examples, two sheets of film with a thickness of 56 μm were used. The total height of the belt-like protrusions 7 formed by stacking two sheets of film was approximately 120 μm (see Figure 4 (A)).

The printing metal mask 10 of the present invention and the method for forming the belt-shaped protrusions 7 thereof will be described in detail below. (1) The metal mask 2 is formed to a predetermined thickness using nickel material by a well-known electroforming method. At that time, a large number of fine holes are formed in the printing pattern portion 4 according to the specifications of the printed material 3. (2) The required number of thick-film resist-forming photosensitive films are laminated on the entire lower surface of the metal mask 2. The thickness and required number of thick-film resist-forming photosensitive films are selected and determined so that the height of the belt-shaped protrusions 7 is the required height. (3) The portion where the belt-shaped protrusions 7 are to be formed is exposed using a laser direct imaging device (LDI). (4) The unexposed portion of the thick-film resist-forming photosensitive film is developed and washed. (5) The thick-film resist-forming photosensitive film formed as the belt-shaped protrusions 7 is exposed to light (UV curing or thermal curing in an oven). The conditions for these cures can be performed according to the conditions recommended by the manufacturer of the thick-film resist-forming photosensitive film. The longitudinal elastic modulus of the band-shaped protrusion 7 in the example formed by this method was approximately 1.0 GPa.

Next, the release of the printing metal mask 10 produced by the above-mentioned process will be described. As shown in FIG. 3, the printing metal mask 10 of the present invention is configured such that the band-shaped protrusions 7 attached to the underside of the metal mask 2 are placed on the upper surface of the substrate 3, the upper surface of the metal mask 2 is pressed with a squeegee 5, and the metal mask 2 is moved while tilting forward to print the paste 6 onto the substrate 3. Therefore, printing using the printing metal mask of the present invention belongs to on-contact printing. As a result, no configuration is required to ensure a gap, and printing can be performed with a simple configuration, resulting in low initial costs and good plate release.

In the metal mask 2 of the embodiment, the printing pattern portion 4 is provided at three locations on the left, center, and right side along the movement direction of the squeegee 5. The squeegee 5 moves from left to right at a constant speed while maintaining a forward tilt, and the paste 6 fills the pores of the pattern portion 4 of the metal mask 2. Figure 3 (A) shows the state of printing with the printing pattern portion 4 on the left side, Figure 3 (B) shows the state of printing with the printing pattern portion 4 in the center, and Figure 3 (C) shows the state of printing with the printing pattern portion 4 on the right side.

In the state shown in FIG. 3(A), the metal mask 2 pressed by the squeegee 5 contacts the top surface of the substrate 3 only at the left-hand print 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 top surface of the substrate 3 only at the central print 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 top surface of the substrate 3 only at the right-hand print pattern portion 4, and the paste 6 is printed.

In printing in these three states, the same plate release conditions can be achieved. Unlike the conventional printing method shown in Figure 5, the angles θ1 and θ2 at which the upper surface of the substrate 3 and the lower surface of the metal mask 2 meet do not vary significantly depending on the position of the squeegee 5. Moreover, since the movement distance of the squeegee 5 in the printing pattern portion 4 arranged between adjacent band-shaped protrusions 7 is short, the change in the angle at which the upper surface of the substrate 3 and the lower surface of the metal mask 2 meet is also small. For these reasons, approximately the same plate release conditions can be achieved in all states. Therefore, it is possible to suppress the deterioration of printing quality caused by differences in plate release speed depending on the movement position of the squeegee 5.

Next, the optimum value of the Young's modulus of the synthetic resin material used for the belt-shaped protrusions 7 of the present invention will be explained based on an example. In order to achieve the same plate release speed in the print pattern sections 4 provided at three locations on the left, center, and right along the movement direction of the squeegee 5, it is important that each belt-shaped protrusion 7 provided on the underside of the metal mask 2 undergoes an appropriate compressive deformation due to the pressing force F of the squeegee 5.

When the metal mask 2 is fixed to the frame 1, a certain tension is applied to prevent excessive slack in the metal mask 2, taking into consideration temperature changes due to the environment in which the metal mask 2 is used. Therefore, even when the top surface of the metal mask 2 is pressed with the squeegee 5, the metal mask itself, which is a metal material, does not stretch significantly, and in the printing metal mask 10 of the present invention, the amount of change in the gap (gap) between the top surface of the print substrate 3 and the bottom surface of the metal mask 2 caused by the pressing force of the squeegee 5 depends largely on the compressive deformation of the band-shaped protrusions 7, which are made of a synthetic resin material with a small modulus of longitudinal elasticity.

Figure 4 shows the measurement of the downward displacement of the metal mask 2 when a downward force is applied by the squeegee 5 to the center of the printing metal mask 10 placed on the top surface of the printing substrate 3. The side length of the movement range of the squeegee 5 is 250 mm, and the horizontal axis is in mm. The scale of the vertical axis is approximately 200 times that of the horizontal axis to make it easier to understand. Therefore, the actual downward displacement of the metal mask 2 is approximately 1/200 of the line shown in Figure 4 (A).

As shown in FIG. 4B, the pressing force F of the squeegee 5 is applied to the center along the direction of movement of the squeegee 5, i.e., at positions 125 mm from both ends of the range of movement of the squeegee 5. The magnitude of the pressing force F of the squeegee 5 is approximately 160 N/m, calculated per unit blade width of the squeegee 5.

When there is no pressing force F from the squeegee 5, the band-shaped protrusions 7 are not compressed and their height does not change, so the gap (gap) between the top surface of the print substrate 3 and the bottom surface of the metal mask 2 is approximately 112 μm. On the other hand, when pressing force F is applied to the center of the metal mask 2, it can be seen that all of the band-shaped protrusions 7 provided at four locations along the movement direction of the squeegee 5 are compressed and displaced. From the diagram shown in Figure 4 (A), it can be seen that the left and right band-shaped protrusions 7 are compressed and displaced symmetrically across the center where pressing force F is applied. The specific amount of compression displacement is approximately 60 μm at the two locations near the center, and approximately 10 μm at the two locations near the left and right ends.

In this embodiment of the printing metal mask 10, 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 in the other printing pattern portions, a gap of approximately 60 μm or more is maintained between the upper surface of the printing substrate 3 and the lower surface of the metal mask 2.

In an actual printing situation, when the squeegee 5 moves from left to right, the area where the metal mask 2 is pressed by the squeegee 5 and the gap is eliminated, i.e., the area where printing is performed, also moves from left to right, while a large gap is maintained in other areas. Therefore, with the printing metal mask 10 of the present invention, it is possible to achieve pseudo-gap printing while using on-contact printing.

In the above-described embodiment, the band-shaped protrusions 7 are provided at four equal intervals along the moving direction of the squeegee 5, each having a width of 11 mm. However, the band-shaped protrusions 7 may be provided at unequal intervals. Furthermore, the band-shaped protrusions 7 do not have to be continuous bands, and may be discontinuous. The shape and dimensions of the band-shaped protrusions 7 may be modified in various ways and are not limited to those in the embodiment.

The printing metal mask of the present invention can be used as a printing metal mask for printing paste or flux in the manufacturing process of electronic components, etc.

1. Screen frame 2. Metal mask (screen plate)
3 Printing object 5 Squeegee 6 Paste 7 Strip-shaped protrusion 10 Metal mask for printing

Claims (2)

A printing metal mask includes a metal mask inside a frame, and a squeegee moves over an upper surface of the metal mask to print a paste on a substrate disposed below the metal mask,
A printing metal mask characterized in that a plurality of band-shaped protrusions are provided on the underside of the metal mask, the band-shaped protrusions being formed by stacking a plurality of synthetic resin films having a modulus of longitudinal elasticity of 1 to 2 GPa, approximately perpendicular to the direction of movement of the squeegee. 2. The metal mask for printing according to claim 1 , wherein the height of the band-shaped protrusions is 25 μm to 150 μm.

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