Screen printing method, screen printing device, and screen mask

Abstract

This screen printing method is a method for applying flux (F) to a solder precoat (3) of a substrate (1) using a screen mask (420). The screen mask (420) is provided with a mask plate (421) that has an opening (421c). The opening (421c) has a shape that fits within a contour line of the corresponding solder precoat (3). This screen printing method is provided with a positioning step and a squeegeeing step. In the squeegeeing step, a peripheral portion of the opening (421c) in a lower surface (421b) of the mask plate (421) is pressed against the solder precoat (3) by a squeegee (413c), thereby functioning as a seal surface to suppress leakage of the flux (F), with which the opening (421c) is filled, between the lower surface (421b) of the mask plate (421) and the solder precoat (3). After the squeegee (413c) passes through the solder precoat (3), said peripheral portion separates from the solder precoat (3).

Description

Screen printing method, screen printing device, and screen mask CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-065397, filed on April 15, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a screen printing method, a screen printing apparatus, and a screen mask.

[0003] Conventionally, a method for applying flux to a solder precoat of a substrate on which the solder precoat is provided has been known (for example, Patent Document 1). Patent Document 1 discloses "a mounting substrate manufacturing method for soldering terminals of electronic components to lands on a substrate, the method comprising: a paste placement step of placing solder paste on the lands; a melting and solidification step of melting and solidifying the solder paste to form a solder precoat on the lands; a destruction step of destroying residue covering the surface of the precoat by pressing a tool against the precoat; a flux placement step of placing flux on the precoat; a component mounting step of mounting the electronic component on the substrate with the terminals of the electronic component aligned with the precoat; and a reflow step of heating the substrate to melt the precoat and solder the terminals to the lands."

[0004] International Publication No. 2022 / 054384

[0005] In recent years, electronic components mounted on solder precoats have become increasingly smaller, and these small electronic components may unintentionally move on the flux applied to the solder precoat. The movement of the electronic components may impair the quality of the soldering. In this situation, one of the objectives of the present disclosure is to prevent the movement of electronic components.

[0006] One aspect of the present disclosure relates to a screen printing method for applying flux to a solder precoat of a substrate having lands on which the solder precoat is formed, using a screen mask, the screen mask including a mask plate having an upper surface and a lower surface and a printing opening penetrating from the upper surface to the lower surface, the opening having a shape that fits within an outline of the corresponding solder precoat when viewed from a normal direction of the upper surface of the mask plate, and a positioning step of positioning the screen mask so that the opening is located above the solder precoat; and a squeegeeing process in which flux supplied to the upper surface of the mask plate is moved with a squeegee to apply the flux to the solder precoat through the opening. In the squeegeeing process, the peripheral portion of the opening on the lower surface of the mask plate is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the opening from leaking between the lower surface of the mask plate and the solder precoat, and the squeegee separates from the solder precoat after passing through the solder precoat.

[0007] Another aspect of the present disclosure relates to a screen printing apparatus that applies flux to a solder precoat on a substrate having lands on which the solder precoat is formed using a screen mask, the screen mask including a mask plate having upper and lower surfaces and printing openings penetrating from the upper surface to the lower surface, the openings having a shape that fits within an outline of the corresponding solder precoat when viewed from a direction normal to the upper surface of the mask plate, and a squeegee that moves the flux supplied to the upper surface of the mask plate to apply the flux to the solder precoat through the openings, and a peripheral portion of the lower surface of the mask plate around the openings is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the openings from leaking between the lower surface of the mask plate and the solder precoat.

[0008] Another aspect of the present disclosure relates to a screen mask used in screen printing to apply flux to a solder precoat of a substrate having lands on which the solder precoat is formed, the screen mask comprising a mask plate having upper and lower surfaces and printing openings penetrating from the upper surface to the lower surface, each opening having a shape that fits within an outline of the corresponding solder precoat when viewed from a direction normal to the upper surface of the mask plate, the screen mask being configured to apply flux to the solder precoat through the openings by moving the flux supplied to the upper surface of the mask plate with a squeegee, and a peripheral portion of the opening on the lower surface of the mask plate being pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface to prevent the flux filled in the openings from leaking between the lower surface of the mask plate and the solder precoat.

[0009] According to the present disclosure, movement of electronic components can be suppressed.

[0010] 1 is a front view schematically illustrating the configuration of an example of a mounting substrate manufacturing apparatus. It is a diagram for explaining the manufacturing process of a mounting substrate, where (a) shows a substrate provided with a solder precoat, (b) shows a substrate coated with flux, (c) shows a substrate with electronic components mounted thereon, (d) shows a substrate immediately before the solder precoat melts, (e) shows a substrate in a state where the solder precoat is melted, and (f) shows a completed mounting substrate. It is a front view schematically illustrating the configuration of an example of a screen printing apparatus according to the present disclosure. It is a side view schematically illustrating the configuration of an example of a screen printing apparatus according to the present disclosure. It is a diagram schematically illustrating an example of a screen mask according to the present disclosure, where (a) is a plan view of the screen mask and (b) is a cross-sectional view taken along line V-V. It is an enlarged view showing a solder precoat and a mask plate positioned so that an opening is located above it. It is a diagram for explaining a squeegeeing process, where (a) shows a state before squeegeeing begins, (b) shows a state during squeegeeing, and (c) shows a state after squeegeeing is completed. 7(a) is an enlarged view of an area G in FIG. 7(b), and FIG. 7(b) is an enlarged view of an area H in FIG. 7(b). It is a diagram showing a main part during squeegeeing in a modified example, in which the solder precoat is covered with an oxidation prevention film.

[0011] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0012] The following describes exemplary embodiments of a screen printing method, a screen printing apparatus, and a screen mask according to the present disclosure. However, the present disclosure is not limited to the exemplary embodiments described below. While the following description may use specific numerical values ​​and materials, other numerical values ​​and materials may be used as long as the effects of the present disclosure are achieved.

[0013] (Screen Printing Method) The screen printing method according to the present disclosure is a method for applying flux to a solder precoat on a substrate having lands on which the solder precoat is formed, using a screen mask. The screen mask includes a mask plate. The mask plate has an upper surface and a lower surface, and a printing opening that penetrates from the upper surface to the lower surface. The opening has a shape that fits within the outline of the corresponding solder precoat when viewed from the normal direction of the upper surface of the mask plate. The mask plate does not have a mesh structure. In other words, the mask plate is solid except for the opening.

[0014] The dimensions of the land may be, for example, 0.08 mm or more and 0.30 mm or less. The dimensions of the opening may be, for example, 0.05 mm or more and 0.12 mm or less. More specifically, for example, when the dimensions of the land are 0.08 mm or more and 0.10 mm or less, the dimensions of the opening may be 0.05 mm or more and 0.07 mm or less. Furthermore, for example, when the dimensions of the land are 0.10 mm or more and 0.20 mm or less, the dimensions of the opening may be 0.07 mm or more and 0.90 mm or less. Furthermore, for example, when the dimensions of the land are 0.15 mm or more and 0.30 mm or less, the dimensions of the opening may be 0.08 mm or more and 0.12 mm or less. When the projected area of ​​the land on the substrate is S, the projected area of ​​the opening on the substrate may be, for example, 0.15S or more and 0.65S or less. More specifically, for example, when the land dimensions are 0.08 mm or more and 0.10 mm or less, the projected area of ​​the opening on the substrate may be 0.30 S or more and 0.60 S or less. Also, for example, when the land dimensions are 0.10 mm or more and 0.20 mm or less, the projected area of ​​the opening on the substrate may be 0.25 S or more and 0.50 S or less. Also, for example, when the land dimensions are 0.15 mm or more and 0.30 mm or less, the projected area of ​​the opening on the substrate may be 0.15 S or more and 0.65 S or less.

[0015] The screen printing method according to the present disclosure includes a positioning step and a squeegeeing step.

[0016] In the positioning step, the screen mask is positioned so that the openings of the mask plate are positioned above the solder precoat. At this time, it is preferable to position each opening so that it is within the outline of the corresponding solder precoat when viewed from above. The distance from the top of the solder precoat to the underside of the mask plate during positioning may be, for example, 1 mm or more and 5 mm or less.

[0017] In the squeegeeing process, flux is applied to the solder precoat by moving the flux supplied to the upper surface of the mask plate with a squeegee through the openings in the mask plate. Here, as described above, each opening has a shape that fits within the outline of the corresponding solder precoat when viewed from the normal direction of the upper surface. In other words, the openings in the mask plate of the screen mask used in this disclosure are smaller than conventional openings (e.g., the mask openings in Patent Document 1). Therefore, the amount of flux applied to the solder precoat can be reduced, thereby suppressing the movement of electronic components that are subsequently mounted.

[0018] The size of the electronic component may be, for example, 0.4 mm length x 0.2 mm width, 0.3 mm length x 0.15 mm width, 0.25 mm length x 0.125 mm width, 0.2 mm length x 0.1 mm width, or 0.1 mm length x 0.5 mm width. For example, the electronic component may include electronic components such as JIS (Japanese Industrial Standards) 0402, 03015, 0201, and 01005. As the size of the electronic component decreases, its weight decreases, and therefore, bonding defects due to unintended movement of the electronic component are typically more likely to occur. This tendency is particularly pronounced in extremely small components such as 03015, 0201, and 01005. On the other hand, the screen printing method according to the present disclosure can suppress unintended movement of electronic components as described above, making it particularly suitable for use with such extremely small components.

[0019] Furthermore, in the squeegeeing process, the peripheral portion of the opening on the underside of the mask plate (hereinafter simply referred to as the peripheral portion) is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the opening from leaking between the underside of the mask plate and the solder precoat, and after the squeegee passes through the solder precoat, it separates from the solder precoat. In other words, in the squeegeeing process of the present disclosure, so-called off-contact printing is performed, and in this process, the peripheral portion functions as a sealing surface that prevents the flux from leaking.

[0020] If the flux leaks between the underside of the mask and the solder precoat, the leaked flux will contaminate the underside of the mask, making it necessary to clean the mask, which can reduce the efficiency of the flux application process.

[0021] In contrast, as described above, the squeegeeing process of the present disclosure is less likely to cause such flux leakage, making it less likely for the underside of the mask plate to become dirty and improving the efficiency of flux application. The peripheral portion may be pressed directly or indirectly against the solder precoat by the squeegee. An example of the latter is a case in which the surface of the solder precoat is covered with a flux residue film, and the peripheral portion is indirectly pressed through this flux residue film.

[0022] Furthermore, extensive research has revealed that applying flux by so-called contact printing results in flux contamination of the underside of the mask plate, particularly the peripheral portion. This is presumably due to the fact that, in contact printing, even after applying flux through the openings in the mask plate, i.e., after the squeegee passes through the solder precoat, the underside of the mask plate remains in close proximity to or in contact with the substrate or solder precoat, allowing the flux to penetrate by capillary action into the minute gaps between the substrate or solder precoat and the mask plate. In contrast, in the squeegeeing process of the present disclosure, as described above, the peripheral portion separates from the solder precoat after the squeegee passes through the solder precoat. Therefore, flux penetration by capillary action is less likely to occur, suppressing flux contamination of the underside of the mask plate and ultimately improving the efficiency of flux application.

[0023] The screen mask may further include a frame surrounding the mask plate and an elastic sheet that secures the mask plate to the frame while applying outward tension to the mask plate. In the squeegeeing process, the peripheral portion may be separated from the solder precoat by the tension applied to the mask plate by the sheet. In this configuration, the peripheral portion of the mask plate is separated from the solder precoat after the squeegee passes through the solder precoat because the entire mask plate is pulled outward. The frame may be made of, for example, metal. The sheet may be made of, for example, resin.

[0024] The thickness of the mask plate may be 15 μm or more and 50 μm or less. When the thickness of the mask plate is within this range, the peripheral portion is easily deformed to conform to the surface of the solder precoat, thereby enabling the mask plate to function more effectively as the sealing surface. The thickness of the mask plate may be 15 μm or more and 30 μm or less.

[0025] The mask plate may be made of a metal, which can increase the durability of the mask plate. Examples of metals that can be used to make the mask plate include stainless steel and nickel.

[0026] The solder precoat may have a flat top. Such a shape of the solder precoat can be formed by forming the solder precoat and then squashing the top. When the solder precoat has a flat top, the peripheral portion of the mask plate can more easily perform its sealing function, and the mask plate can be further prevented from being contaminated with flux.

[0027] (Screen Printing Apparatus) The screen printing apparatus according to the present disclosure is an apparatus that applies flux to a solder precoat on a substrate having lands on which the solder precoat is formed using a screen mask, and is an apparatus for carrying out the screen printing method according to the present disclosure. The screen mask includes a mask plate having the above-described characteristics. That is, the mask plate has an upper surface and a lower surface, and a printing opening that penetrates from the upper surface to the lower surface. The opening has a shape that fits within the outline of the corresponding solder precoat when viewed from the normal direction of the upper surface of the mask plate. The mask plate does not have a mesh structure. In other words, the mask plate is solid except for the opening.

[0028] The screen printing apparatus according to the present disclosure includes a squeegee. The squeegee applies flux to the solder precoat through the openings by moving the flux supplied to the upper surface of the mask plate. As described above, each opening has a shape that fits within the outline of the corresponding solder precoat when viewed from the normal direction of the upper surface. This reduces the amount of flux applied to the solder precoat, thereby suppressing movement of electronic components that are subsequently mounted. The screen printing apparatus may further include a flux supply unit that supplies flux to the upper surface of the mask plate.

[0029] Furthermore, the area around the opening on the underside of the mask plate is pressed against the solder precoat by the squeegee, and functions as a sealing surface that prevents the flux filled in the opening from leaking between the underside of the mask plate and the solder precoat. This sealing function prevents the underside of the mask plate from being contaminated with flux, improving the efficiency of the flux application process.

[0030] The screen mask may further include a frame surrounding the mask plate and an elastic sheet that fixes the mask plate to the frame while applying outward tension to the mask plate. In this configuration, the peripheral portion of the mask plate separates from the solder precoat after the squeegee has passed through the solder precoat because the entire mask plate is pulled outward.

[0031] (Screen Mask) The screen mask according to the present disclosure is used in screen printing to apply flux to a solder precoat of a substrate having lands on which the solder precoat is formed. The screen mask according to the present disclosure includes a mask plate having the above-described characteristics, and the mask plate has an upper surface and a lower surface and a printing opening that penetrates from the upper surface to the lower surface.

[0032] The openings have a shape that fits within the outline of the corresponding solder precoat when viewed from the normal direction of the top surface of the mask plate. In other words, the openings of the screen mask according to the present disclosure are smaller than conventional openings (e.g., the mask openings of Patent Document 1). The screen mask is configured to apply flux to the solder precoat through the openings by moving the flux supplied to the top surface of the mask plate with a squeegee. Applying flux to the solder precoat using a screen mask with small openings reduces the amount of flux applied, thereby suppressing movement of electronic components to be subsequently mounted.

[0033] Furthermore, the area around the opening on the underside of the mask plate is pressed against the solder precoat by the squeegee, and functions as a sealing surface that prevents the flux filled in the opening from leaking between the underside of the mask plate and the solder precoat. This sealing function prevents the underside of the mask plate from being contaminated with flux, improving the efficiency of the flux application process.

[0034] As described above, according to the present disclosure, by using a screen mask having smaller openings than conventional ones, it is possible to suppress movement of electronic components mounted on a solder precoat. Furthermore, according to the present disclosure, when using such a screen mask, it is possible to suppress contamination of the underside of the mask plate with flux, thereby improving the efficiency of flux application.

[0035] Below, examples of a screen printing method, a screen printing apparatus, and a screen mask according to the present disclosure will be described in detail with reference to the drawings. The above-described processes and components can be applied to the processes and components of the example screen printing method, screen printing apparatus, and screen mask described below. The processes and components of the example screen printing method, screen printing apparatus, and screen mask described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above-described embodiment. Among the processes and components of the example screen printing method, screen printing apparatus, and screen mask described below, processes and components that are not essential to the screen printing method, screen printing apparatus, and screen mask according to the present disclosure may be omitted. Note that the diagrams shown below are schematic and do not accurately reflect the shapes and numbers of actual components.

[0036] The screen printing apparatus 400 of this embodiment is provided in a mounting substrate manufacturing apparatus 10 (hereinafter also simply referred to as the manufacturing apparatus 10) for manufacturing a mounting substrate on which a plurality of electronic components are mounted.

[0037] (Mounted Board Manufacturing Apparatus) As shown in FIG. 1 , the manufacturing apparatus 10 includes a substrate conveying line 11, an information processing device 20, a loader 50, a solder precoat forming device 90, a solder precoat inspection device 300, a screen printing device 400, electronic component mounting devices 501 and 502, a mounting state inspection device 600, a reflow device 700, a substrate inspection device 800, and an unloader 900. The components from the loader 50 to the unloader 900 are arranged in this order from upstream to downstream. A known configuration may be applied to configurations other than those specific to the present disclosure. Hereinafter, the electronic component mounting devices 501 and 502 may be collectively referred to as the electronic component mounting device 500.

[0038] (Substrate conveyance line) The information processing device 20 is communicably connected to other devices included in the manufacturing apparatus 10 (solder precoat forming device 90, solder precoat inspection device 300, screen printing device 400, electronic component mounting device 500, reflow device 700, etc.) via a wired or wireless local area network 20N. The information processing device 20 exchanges data with these devices. In this way, the information processing device 20 manages the processes performed in the manufacturing apparatus 10.

[0039] The information processing device 20 has an arithmetic processing unit and a storage device. The arithmetic processing unit is configured with a CPU (Central Processing Unit) and the like. The storage device is configured with one or more RAMs (Random Access Memory) and hard disks and the like. These may be configured as separate circuits or LSIs (Large Scale Integrated Circuits), or may be configured as an integrated unit. The storage device stores programs and data required for each device of the manufacturing apparatus 10.

[0040] (Loader and Unloader) The loader 50 supplies substrates stored in a rack (not shown) to the solder precoat forming device 90. The unloader 900 retrieves completed mounted substrates into the rack. Each device from the solder precoat forming device 90 to the substrate inspection device 800 includes a conveyor (substrate transport line 11) for transporting substrates. Each conveyor is positioned so that it can receive substrates from a device on the upstream side (loader 50 side) and hand them over to a device on the downstream side (unloader 900 side).

[0041] (Solder Precoat Forming Apparatus) The solder precoat forming apparatus 90 is an apparatus that forms a solder precoat 3 (see FIG. 2) on the lands 2 (see FIG. 2) of the substrate 1. The solder precoat forming apparatus 90 has a solder paste supply section 100, a heating section 210, and a cooling section 220. A part of the substrate conveying line 11 is arranged inside these sections.

[0042] The solder paste supply unit 100 supplies solder paste to the lands 2 of the substrate 1 by, for example, screen printing. The heating unit 210 heats the solder paste supplied to the lands 2 to melt the solder particles contained in the solder paste. The cooling unit 220 cools and solidifies the melted solder particles. As a result, a solder precoat 3 is formed on the lands 2 of the substrate 1. The substrate 1 with the solder precoat 3 formed thereon is transported by the substrate transport line 11 to the solder precoat inspection device 300.

[0043] (Solder Precoat Inspection Device) The solder precoat inspection device 300 is a device that inspects whether the solder precoat 3 has been properly formed. The solder precoat inspection device 300 may, for example, detect the thickness of the solder precoat 3 and determine whether the solder precoat 3 has been properly formed based on the detected thickness. The board 1 that has been determined to have the solder precoat 3 properly formed is transported by the board transport line 11 to the screen printing device 400.

[0044] (Screen Printing Apparatus) The screen printing apparatus 400 is an apparatus that applies flux for reflow soldering onto the solder precoat 3 using a screen printing method. The configuration of the screen printing apparatus 400 will be described in detail later. The substrate 1 to which the flux has been applied is transported to the electronic component mounting apparatus 500 by the substrate transport line 11.

[0045] (Electronic Component Mounting Device) The electronic component mounting device 500 is a device that mounts electronic components 7 (see FIG. 2 ) on a solder precoat 3 covered with flux. The electronic component mounting device 500 may mount the electronic components on the solder precoat 3 using, for example, a suction nozzle (not shown) that sucks the electronic components. The board 1 on which the electronic components have been mounted is transported by the board transport line 11 to the mounting state inspection device 600.

[0046] (Mounting State Inspection Device) The mounting state inspection device 600 is a device that inspects the mounting state of electronic components. The mounting state inspection device 600 may use an optical measurement device such as a camera or a three-dimensional measuring machine to recognize the mounting state of electronic components, such as their mounting position, posture, and presence or absence, and determine whether these meet predetermined standards. After inspection, the board 1 is transported to the reflow device 700 by the board transport line 11.

[0047] (Reflow Apparatus) The reflow apparatus 700 heats the board 1 on which electronic components are mounted to melt the solder precoat 3 and solder the electronic components 7 to the lands 2 (see FIG. 2 ). This produces a mounted board on which electronic components are mounted. The board 1 on which the electronic components have been soldered is transported by the board transport line 11 to the board inspection apparatus 800.

[0048] (Board Inspection Device) The board inspection device 800 is a device that inspects the quality of mounted boards. After the board inspection by the board inspection device 800 is completed, the board 1 is transported to the unloader 900 by the board transport line 11. The unloader 900 collects the completed mounted board into a rack.

[0049] (Manufacturing Process of Mounting Board) Here, the manufacturing process of the mounting board will be briefly described with reference to FIG. 2 . First, a substrate 1 having lands 2 on which solder precoats 3 are formed is prepared ( FIG. 2( a)). Next, a screen printing apparatus 400 applies flux to the solder precoats 3 ( FIG. 2( b)). Next, an electronic component mounting apparatus 500 mounts electronic components 7 on the flux-applied solder precoats 3 ( FIG. 2( c)). Next, a reflow apparatus 700 heats the substrate 1 on which the electronic components 7 are mounted, causing the solder precoats 3 to begin to melt ( FIG. 2( d)), and then the solder precoats 3 completely melt ( FIG. 2( e)). Finally, the substrate 1 is cooled, connecting the lands 2 and the electronic components 7 at the connection portions 5 (i.e., the connection portions 5 formed by solidifying the molten solder precoats 3), completing the mounting board ( FIG. 2( f)).

[0050] (Details of Screen Printing Apparatus) Next, the screen printing apparatus 400 will be described in detail with reference to Figures 3 to 6. In the following description, the transport direction of the substrate 1 is referred to as the X direction, the vertical direction as the Z direction, and the direction perpendicular to these as the Y direction. Furthermore, the axes extending along each direction are referred to as the X axis, Y axis, and Z axis, respectively.

[0051] 3 and 4, a support frame 411 is erected on each of both ends in the X direction of the base 401. The components of the screen printing apparatus 400 are arranged between the pair of support frames 411.

[0052] A print stage movement mechanism 403 and a print stage 402 that is moved thereby are provided on the upper surface of the base 401 between the pair of support frames 411. The print stage movement mechanism 403 has a structure in which a print stage lifting mechanism 403z is stacked on top of a print stage table 403xyθ. When the print stage table 403xyθ is driven, the print stage 402 moves horizontally along the X-axis and Y-axis and rotates around the Z-axis. When the print stage lifting mechanism 403z is driven, the print stage 402 moves up and down. The print stage 402 has the function of holding the substrate 1 that is carried in from the upstream side and aligning the substrate 1 with respect to a screen mask 420 that has a mask plate 421 in which printing openings 421c (see FIG. 6) are formed.

[0053] The printing stage 402 includes a lifting table 404 connected to a printing stage lifting mechanism 403z. Support members 404a are erected on both ends of the upper surface of the lifting table 404. As shown in Figure 4, a holding block 404b extending in the X direction is connected to the upper end of the support member 404a. A printing stage conveyor 406b equipped with a drive belt for transporting the substrate 1 is provided on the inner surface of the holding block 404b.

[0054] The printing stage conveyor 406b is connectable to an inlet conveyor 406a and an outlet conveyor 406c which are provided through openings provided in the upstream and downstream support frames 411, respectively. The substrate 1 carried in by the inlet conveyor 406a is transferred to the printing stage conveyor 406b and held by the printing stage 402. After screen printing is completed on the printing stage 402, the substrate 1 is transferred from the printing stage conveyor 406b to the outlet conveyor 406c and carried out. The printing stage conveyor 406b, the inlet conveyor 406a, and the outlet conveyor 406c each constitute part of the substrate transport line 11.

[0055] A backup lifting mechanism 405a and a backup unit 405 that is driven to move up and down by the backup lifting mechanism 405a are provided on the upper surface of the lifting table 404. When the backup lifting mechanism 405a is driven while the substrate 1 is loaded onto the printing stage conveyor 406b, the backup unit 405 rises and supports the underside of the substrate 1 transported by the printing stage conveyor 406b.

[0056] Side clampers 407 that grip the sides of the substrate 1 are provided on the upper surfaces of the pair of holding blocks 404b. These side clampers 407 can be opened and closed relative to one another by a side clamper drive mechanism (not shown). When the side clampers 407 are closed while the backup section 405 supports the underside of the substrate 1, both sides of the substrate 1 are clamped between the side clampers 407 on the printing stage 402. In this way, the substrate 1 is clamped and fixed.

[0057] To align the substrate 1 held on the printing stage 402 with the screen mask 420 in this manner, an alignment operation is performed in which the printing stage 402 holding the substrate 1 is moved relative to the screen mask 420. In other words, the printing stage table 403xyθ, which moves the printing stage 402 horizontally, functions as an alignment mechanism that moves the printing stage 402 and the screen mask 420 relatively to align the substrate 1 and the screen mask 420.

[0058] A print head support beam 412 that supports a print head 413 is mounted on the upper ends of the pair of support frames 411 so as to be movable along the Y axis via a linear guide mechanism 412a. One end of the print head support beam 412 is connected to one of the support frames 411 via a print head movement mechanism 414 configured as shown in FIG. 4. The print head movement mechanism 414 has a nut portion 414c that is threadedly engaged with a feed screw 414b that is driven to rotate by a print head motor 414a, and is connected to the print head support beam 412. By driving the print head motor 414a forward and backward, the print head 413 supported by the print head support beam 412 moves back and forth (squeezing operation) along the Y axis.

[0059] As shown in Figure 4, the print head 413 includes a pair of rear squeegees 413b and front squeegees 413c that extend downward from the print head support beam 412. By driving a squeegee drive unit 413a provided on the upper surface of the print head support beam 412, either the rear squeegee 413b or the front squeegee 413c descends and lands on the screen mask 420 depending on the direction of the squeegeeing operation. Specifically, the rear squeegee 413b lands on the screen mask 420 when the squeegeeing operation is performed to the left in Figure 4. On the other hand, the front squeegee 413c lands on the screen mask 420 when the squeegeeing operation is performed to the right in Figure 4. The front squeegee 413c and rear squeegee 413b are each an example of a squeegee.

[0060] As shown in FIGS. 5 and 6 , the screen mask 420 includes a metal mask plate 421, a frame 422 surrounding the mask plate 421, and an elastic sheet 423. The mask plate 421 has an upper surface 421a and a lower surface 421b, and a printing opening 421c (i.e., the opening 421c corresponds to the printing pattern on the substrate 1) that penetrates from the upper surface 421a to the lower surface 421b. When viewed from the normal direction of the upper surface 421a of the mask plate 421, the opening 421c has a shape that fits within the outline of the corresponding solder precoat 3. That is, when aligned with the corresponding solder precoat 3, the opening 421c of the mask plate 421 has a dimension A that is smaller than a dimension B of the solder precoat 3 in any cross section, an example of which is shown in FIG. 6 . The thickness of the mask plate 421 is preferably 15 μm or more and 50 μm or less, and more preferably 15 μm or more and 30 μm or less. The sheet 423 fixes the mask plate 421 to the frame 422 while applying an outward tension to the mask plate 421. Note that the opening 421c is not shown in FIG.

[0061] A camera movement mechanism 416 is provided between the upper surface of the printing stage 402 and the lower surface 421b of the mask plate 421. The camera movement mechanism 416 moves a camera mounting base 417, to which a first camera 418 and a second camera 419 are attached, along the X and Y axes. The camera movement mechanism 416 is composed of a camera X-axis movement mechanism 416X that moves the camera mounting base 417 in the X direction along the camera X-axis beam 415, and a camera Y-axis movement mechanism 416Y that moves the camera X-axis beam 415 in the Y direction. The movement of the camera X-axis beam 415 is guided by a linear guide mechanism 412a arranged on the inner surface of the support frame 411.

[0062] The camera X-axis moving mechanism 416X is composed of a camera X-axis motor 415a and a feed screw 415b shown in Fig. 3, and a nut portion 415d shown in Fig. 4. By driving the camera X-axis motor 415a, the camera mounting base 417 connected to the nut portion 415d moves along the X-axis. The camera Y-axis moving mechanism 416Y is composed of a camera Y-axis motor 416a, a feed screw 416b, and a nut portion 416c connected to the camera X-axis beam 415, as shown in Fig. 4. By driving the camera Y-axis motor 416a, the camera X-axis beam 415 connected to the nut portion 416c moves along the Y-axis.

[0063] Here, the functions of the first camera 418 and the second camera 419 will be described. The first camera 418 is positioned with its imaging direction facing downward, and captures an image of the substrate 1 held on the printing stage 402. By recognizing and processing the image results, the position of the substrate 1 and the positions of the electrodes to be printed on the substrate 1 are detected. The second camera 419 is positioned with its imaging direction facing upward, and captures an image of a mask recognition mark (not shown) formed on the screen mask 420. By recognizing and processing the image results, the mask center in the screen mask 420 and the positions of the printing openings 421c are recognized.

[0064] Next, the application of flux using the screen printing method performed by the screen printing apparatus 400 will be described with reference to Fig. 7 and Fig. 8. Note that Fig. 7 omits illustrations other than the backup section 405, the substrate 1 supported thereby, the screen mask 420, and the front squeegee 413c.

[0065] First, as shown in FIG. 7A , flux F is supplied to the upper surface 421 a of the mask plate 421 of the screen mask 420, and the mask plate 421 is positioned above the substrate 1 supported by the backup unit 405 at a distance. At this time, the screen mask 420 is positioned so that each opening 421 c of the mask plate 421 is positioned above the solder precoat 3 formed on the substrate 1 (positioning step of the screen printing method). Note that the solder precoat 3 has a flat top, but this is not a limitation. The flat top may be formed by crushing the solder precoat 3 from above. Although not shown, the crushing mechanism for this purpose may be provided within the screen printing apparatus 400 or may be provided separately from the screen printing apparatus 400.

[0066] Next, as shown in Fig. 7(b), the flux F supplied to the upper surface 421a of the mask plate 421 is moved by the front squeegee 413c, so that the flux F is applied to the solder precoat 3 through the openings 421c of the mask plate 421 (squeegeeing step of the screen printing method). Here, Fig. 8(a) is an enlarged view of region G in Fig. 7(b) (i.e., the region where the front squeegee 413c is located), and Fig. 8(b) is an enlarged view of region H in Fig. 7(b) (i.e., the region after the front squeegee 413c has passed).

[0067] 8( a), in the region where the front squeegee 413c performing the squeegeeing operation is located, the peripheral portion of the opening 421c on the lower surface 421b of the mask plate 421 is pressed against the solder precoat 3 by the front squeegee 413c, thereby functioning as a sealing surface that prevents the flux F filled in the opening 421c from leaking between the lower surface 421b of the mask plate 421 and the solder precoat 3. Then, as shown in FIG. 8( b), after the front squeegee 413c has passed the solder precoat 3, the peripheral portion separates from the solder precoat 3 due to the tension applied by the sheet 423 to the mask plate 421.

[0068] 8 shows an embodiment in which flux F is applied to the solder precoat 3 with an exposed surface, but this is not limiting. For example, as shown in FIG. 9, flux F may be applied to the solder precoat 3 whose surface is covered with an anti-oxidation film 4. Such an anti-oxidation film 4 may be, for example, a flux residue film formed when forming the solder precoat 3. In the latter case, the peripheral portion of the opening 421c on the lower surface 421b of the mask plate 421 is indirectly pressed against the solder precoat 3, and such an embodiment is also considered to be within the scope of the present disclosure.

[0069] <<Appendix>> The above description of the embodiments discloses the following techniques: (Technology 1) A screen printing method for applying flux to a solder precoat of a substrate having lands on which the solder precoat is formed, using a screen mask, wherein the screen mask comprises a mask plate having upper and lower surfaces and printing openings penetrating from the upper surface to the lower surface, the openings having a shape that fits within the corresponding outline of the solder precoat when viewed from a direction normal to the upper surface of the mask plate, the method comprising: a positioning step of positioning the screen mask so that the openings are located above the solder precoat, and a squeegeeing step of applying flux to the solder precoat through the openings by moving the flux supplied to the upper surface of the mask plate with a squeegee. The screen printing method, in which, in the squeegeeing step, a peripheral portion of the opening on the underside of the mask plate is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the opening from leaking between the underside of the mask plate and the solder precoat, and is separated from the solder precoat after the squeegee has passed through the solder precoat. (Technology 2) The screen printing method according to Technology 1, in which the screen mask further comprises: a frame that surrounds the mask plate; and an elastic sheet that fixes the mask plate to the frame while applying outward tension to the mask plate, and in which, in the squeegeeing step, the peripheral portion is separated from the solder precoat by the tension applied to the mask plate by the sheet. (Technology 3) The screen printing method according to Technology 1 or 2, in which the thickness of the mask plate is 15 μm or more and 50 μm or less. (Technology 4) The screen printing method according to any one of Technology 1 to 3, in which the mask plate is made of metal. (Technology 5) The screen printing method according to any one of Technologies 1 to 4, wherein the solder precoat has a flat top.(Technology 6) A screen printing apparatus that applies flux to a solder precoat of a substrate having lands on which the solder precoat is formed, using a screen mask, wherein the screen mask comprises a mask plate having an upper surface and a lower surface and a printing opening that penetrates from the upper surface to the lower surface, wherein the opening has a shape that fits inside the outer contour of the corresponding solder precoat when viewed from a direction normal to the upper surface of the mask plate, and the screen printing apparatus comprises a squeegee that moves the flux supplied to the upper surface of the mask plate to apply the flux to the solder precoat through the opening, and wherein a peripheral portion of the opening on the lower surface of the mask plate is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the opening from leaking between the lower surface of the mask plate and the solder precoat. (Technology 7) The screen printing apparatus according to Technology 6, wherein the screen mask further comprises: a frame surrounding the mask plate; and an elastic sheet fixing the mask plate to the frame while applying outward tension to the mask plate. (Technology 8) The screen printing apparatus according to Technology 6 or 7, wherein the mask plate has a thickness of 15 μm or more and 50 μm or less. (Technology 9) The screen printing apparatus according to any one of Technology 6 to 8, wherein the mask plate is made of metal. (Technology 10) The screen printing apparatus according to any one of Technology 6 to 9, wherein the solder precoat has a flat top.(Technology 11) A screen mask used in screen printing to apply flux to a solder precoat of a substrate having lands on which the solder precoat is formed, the screen mask comprising: a mask plate having an upper surface and a lower surface, and a printing opening that penetrates from the upper surface to the lower surface, wherein the opening has a shape that fits inside the outer contour of the corresponding solder precoat when viewed from a direction normal to the upper surface of the mask plate, the screen mask is configured to apply flux to the solder precoat through the opening by moving the flux supplied to the upper surface of the mask plate with a squeegee, and a peripheral portion of the opening on the lower surface of the mask plate is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the opening from leaking between the lower surface of the mask plate and the solder precoat. (Technology 12) The screen mask according to Technology 11, further comprising: a frame surrounding the mask plate; and an elastic sheet fixing the mask plate to the frame while applying outward tension to the mask plate. (Technology 13) The screen mask according to Technology 11 or 12, wherein the mask plate has a thickness of 15 μm or more and 50 μm or less. (Technology 14) The screen mask according to any one of Technologies 11 to 13, wherein the mask plate is made of metal. (Technology 15) The screen mask according to any one of Technologies 11 to 14, wherein the solder precoat has a flat top.

[0070] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0071] The present disclosure can be used for a screen printing method, a screen printing apparatus, and a screen mask.

[0072] 1: Substrate 2: Land 3: Solder precoat 4: Antioxidant film 5: Connection part 7: Electronic component 10: Mounting substrate manufacturing device 11: Substrate conveying line 20: Information processing device 20N: Local area network 50: Loader 90: Solder precoat forming device 100: Solder paste supply unit 210: Heating unit 220: Cooling unit 300: Solder precoat inspection device 400: Screen printing device 401: Base 402: Printing stage 403: Printing stage movement mechanism 403xyθ: Printing stage table 403z: Printing stage lifting mechanism 404: Lifting table 404a: Support member 404b: Holding block 405: Backup part 405a: Backup lifting mechanism 406a: Loading conveyor 406b: Printing stage conveyor 406c: Unloading conveyor 407: Side clamper 411: Support frame 412: Print head support beam 412a: Linear guide mechanism 413: Print head 413a: Squeegee drive unit 413b: Rear squeegee (squeegee) 413c: Front squeegee (squeegee) 414: Print head movement mechanism 414a: Print head motor 414b: Feed screw 414c: Nut unit 415: Camera X-axis beam 415a: Camera X-axis motor 415b: Feed screw 415d: ​​Nut unit 416: Camera movement mechanism 416a: Camera Y-axis motor 416b: Feed screw 416c: Nut unit 416X: Camera X-axis movement mechanism 416Y: Camera Y-axis movement mechanism 417: Camera mounting base 418: First camera 419: Second camera 420: Screen mask 421: Mask plate 421a: Upper surface 421b: Lower surface 421c: Opening 422: Frame 423: Sheet 500: Electronic component mounting device 501: Electronic component mounting device 502: Electronic component mounting device 600: Mounting state inspection device 700: Reflow device 800: Board inspection device 900: Unloader F: Flux

Claims

1. A screen printing method for applying flux to a solder precoat on a substrate having lands on which the solder precoat is formed, using a screen mask, wherein the screen mask comprises a mask plate having upper and lower surfaces and printing openings that penetrate from the upper surface to the lower surface, and the openings have shapes that fit within the outline of the corresponding solder precoat when viewed from the normal direction of the upper surface of the mask plate, the method comprising: a positioning step of positioning the screen mask so that the openings are located above the solder precoat; and a squeegeeing step of applying flux to the solder precoat through the openings by moving the flux supplied to the upper surface of the mask plate with a squeegee. In the squeegeeing process, the peripheral portion of the opening on the underside of the mask plate is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the opening from leaking between the underside of the mask plate and the solder precoat, and the squeegee separates from the solder precoat after passing through the solder precoat.

2. The screen printing method of claim 1, wherein the screen mask further comprises a frame surrounding the mask plate and an elastic sheet fixing the mask plate to the frame while applying outward tension to the mask plate, and wherein in the squeegeeing step, the peripheral portion separates from the solder precoat due to the tension applied to the mask plate by the sheet.

3. A screen printing method according to claim 1 or 2, wherein the thickness of the mask plate is 15 μm or more and 50 μm or less.

4. A screen printing method according to claim 1 or 2, wherein the mask plate is made of metal.

5. The screen printing method according to claim 1 or 2, wherein the solder precoat has a flat top.

6. A screen printing apparatus that applies flux to a solder precoat on a substrate having lands on which the solder precoat is formed using a screen mask, wherein the screen mask comprises a mask plate having an upper surface and a lower surface and a printing opening that penetrates from the upper surface to the lower surface, wherein the opening has a shape that fits inside the outer contour of the corresponding solder precoat when viewed from the normal direction of the upper surface of the mask plate, and the screen printing apparatus comprises a squeegee that moves the flux supplied to the upper surface of the mask plate to apply the flux to the solder precoat through the opening, and the peripheral portion of the opening on the lower surface of the mask plate is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the opening from leaking between the lower surface of the mask plate and the solder precoat.

7. The screen printing apparatus according to claim 6, wherein the screen mask further comprises: a frame that surrounds the mask plate; and an elastic sheet that fixes the mask plate to the frame while applying outward tension to the mask plate.

8. A screen printing apparatus according to claim 6 or 7, wherein the thickness of the mask plate is 15 μm or more and 50 μm or less.

9. The screen printing apparatus according to claim 6 or 7, wherein the mask plate is made of metal.

10. The screen printing apparatus of claim 6 or 7, wherein the solder precoat has a flat top.

11. A screen mask used in screen printing to apply flux to a solder precoat of a substrate having lands on which the solder precoat is formed, the screen mask comprising a mask plate having upper and lower surfaces and printing openings that penetrate from the upper surface to the lower surface, the openings having a shape that fits within the corresponding outline of the solder precoat when viewed from the normal direction of the upper surface of the mask plate, the screen mask being configured to apply flux to the solder precoat through the openings by moving the flux supplied to the upper surface of the mask plate with a squeegee, and the peripheral portion of the opening on the lower surface of the mask plate is pressed against the solder precoat by the squeegee, thereby functioning as a sealing surface that prevents the flux filled in the openings from leaking between the lower surface of the mask plate and the solder precoat.

12. The screen mask according to claim 11, further comprising: a frame that surrounds the mask plate; and an elastic sheet that fixes the mask plate to the frame while applying outward tension to the mask plate.

13. The screen mask according to claim 11 or 12, wherein the thickness of the mask plate is 15 μm or more and 50 μm or less.

14. The screen mask according to claim 11 or 12, wherein the mask plate is made of metal.

15. The screen mask of claim 11 or 12, wherein the solder precoat has a flat top.

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