WO2024157387A1 - Screen-printing method and screen-printing device - Google Patents

Abstract

A screen-printing method according to the present disclosure is for printing cream solder on a substrate using a mask, and comprises: a normal-printing step; and an overlay-printing step in which the normal-printing step is performed a plurality of times on a single substrate. In the normal-printing step, a plate alignment operation of overlaying and aligning the substrate and the mask with each other in a first direction, a printing operation of printing the cream solder on the substrate through openings provided in the mask, and a plate separation operation of separating the substrate and the mask from each other in the first direction are carried out. The overlay-printing step comprises a first normal-printing step and a second normal-printing step. The second normal-printing step is performed, after the first normal-printing step, without moving the substrate from a printing space.

Description

Screen printing method and screen printing apparatus

This disclosure relates to a screen printing method and a screen printing device.

　A conventional screen printing method is described in JP 2005-205826 A (Patent Document 1 below). In this screen printing method, if the screen printing device is stopped during the automatic operation process for a time period that is longer than a preset reference time period for which confirmation of the paste state is required, the automatic operation is stopped and a warning to that effect is issued. The warning prompts the operator to visually check the state of the cream solder. If it is determined that the cream solder is somewhat dry and that normal printing will not ensure good filling of the pattern holes in the mask plate, the operator instructs the screen printing device to perform overprinting. Overprinting here refers to printing multiple consecutive overprints of cream solder on the same board. Overprinting is preferably performed by reciprocating the squeegee.

By overlapping the printing, even if the cream solder is somewhat dry, the reduced filling ability can be compensated for by overlapping the cream solder, and printing defects can be prevented. After the overlapping printing, the machine can then switch to normal automatic operation and resume production.

JP 2005-205826 A

In the above screen printing method, the steps of checking the condition of the cream solder, determining whether overprinting is necessary, and issuing instructions to the screen printing device must be performed by an operator. Also, depending on the screen printing conditions, etc., there may be cases where printing defects cannot be prevented even if the above screen printing method is followed.

The screen printing method disclosed herein is a screen printing method for printing cream solder on a substrate using a mask, and includes a normal printing process and an overprinting process in which the normal printing process is performed multiple times on one substrate. The normal printing process includes a plate alignment operation in which the substrate and the mask are overlaid in a first direction, a printing operation in which the cream solder is printed on the substrate through an opening provided in the mask, and a plate separation operation in which the substrate and the mask are separated in the first direction. The overprinting process includes a first normal printing process and a second normal printing process, and the second normal printing process is performed after the first normal printing process without moving the substrate from the printing space.

The screen printing device of the present disclosure is a screen printing device that prints cream solder on a substrate using a mask, and includes a substrate transport unit that moves the substrate to a printing space, a mask holder that holds the mask, a substrate holding unit that holds the substrate, a positioning mechanism that moves at least one of the mask holder and the substrate holding unit to bring the substrate and the mask into contact with and separate from each other in a first direction, a printing unit that prints cream solder on the substrate through an opening in the mask, and a control unit, and the control unit performs normal printing processing and pre-printing on one of the substrates when it is determined that a predetermined pre-condition is satisfied. and an overprinting process in which the normal printing process is performed multiple times. In the normal printing process, a plate alignment operation is performed in which the positioning mechanism is controlled to overlay the substrate and the mask in the first direction, a printing operation is performed in which the printing unit is controlled to print solder paste on the substrate, and a plate separation operation is performed in which the positioning mechanism is controlled to separate the substrate and the mask in the first direction. In the overprinting process, a first normal printing process and a second normal printing process are performed, and the second normal printing process is performed after the first normal printing process without moving the substrate from the printing space.

This disclosure provides technology that reduces printing defects in screen printing devices.

FIG. 1 is a perspective view showing the appearance of a screen printing apparatus according to a first embodiment. FIG. 2 is a front view of the screen printing apparatus. FIG. 3 is a side view of the screen printing apparatus. FIG. 4 is a perspective view of the mask. FIG. 5 is a diagram showing the electrical configuration of the screen printing apparatus. FIG. 6 is a flow chart showing the process of printing cream solder onto a board. FIG. 7 is a flowchart showing the normal printing process. FIG. 8 is a flowchart showing the overprinting process. FIG. 9A is an explanatory diagram showing the first plate alignment operation. FIG. 9B is an explanatory diagram showing the first printing operation. FIG. 9C is an explanatory diagram showing the first plate separating operation. FIG. 9D is an explanatory diagram showing the second plate alignment operation. FIG. 9E is an explanatory diagram showing the second printing operation. FIG. 9F is an explanatory diagram showing the second plate separating operation. FIG. 10 is a graph showing the average volume ratio of cream solder in Experiment 1. FIG. 11 is a graph showing the average volume ratio of cream solder in Experiment 2. FIG. 12 is a flowchart showing the overprinting process according to the second embodiment.

[Description of the embodiments of the present disclosure]
First, the embodiments of the present disclosure will be listed and described.
(1) The screen printing method disclosed herein is a screen printing method for printing cream solder on a substrate using a mask, the screen printing method comprising: a normal printing process; and an overprinting process in which the normal printing process is performed multiple times on one substrate, the normal printing process comprising a plate alignment operation in which the substrate and the mask are overlaid in a first direction; a printing operation in which the cream solder is printed on the substrate through an opening provided in the mask; and a plate separation operation in which the substrate and the mask are separated in the first direction, the overprinting process comprising a first normal printing process and a second normal printing process, the second normal printing process being performed after the first normal printing process without moving the substrate from the printing space.

With this screen printing method, the overlap printing process includes a first normal printing process and a second normal printing process, so the amount of cream solder printed on the board can be increased by the overlap printing process. This makes it possible to suppress printing defects.

(2) In the screen printing method described in (1), the overprinting process further includes a cleaning process for cleaning the mask, and it is preferable that the cleaning process is performed after the first normal printing process and before the second normal printing process.

With this type of screen printing method, a cleaning process is performed between the first and second normal printing processes, which can prevent the openings in the mask from being filled with excess cream solder.

(3) In the screen printing method described in (1), it is preferable that the second normal printing process is performed immediately and consecutively after the first normal printing process.

This type of screen printing method can prevent the flux of the cream solder from drying on the inner walls of the openings in the mask between the first and second normal printing processes. This makes it easier to increase the amount of cream solder printed on the board in the second normal printing process.

(4) In the screen printing method described in any one of (1) to (3), it is preferable that an inspection of the state of the cream solder printed on the substrate is not performed between the first normal printing process and the second normal printing process.

This type of screen printing method allows the overlapping printing process to be carried out smoothly.

(5) In the screen printing method described in any one of (1) to (4), it is preferable that the conditions for the first normal printing process and the conditions for the second normal printing process are the same.

This type of screen printing method allows for uniform printing quality of the cream solder.

(6) In the screen printing method described in any one of (1) to (5), it is preferable that the overprinting process is carried out when a predetermined precondition is satisfied.

With this type of screen printing method, when certain preconditions that tend to reduce the filling rate of the cream solder are met, an overprinting process can be carried out, making it possible to suppress printing defects.

(7) In the screen printing method described in (6), it is preferable that the overprinting process is performed on a predetermined number of the substrates after the preconditions are satisfied.

This type of screen printing method makes it easier to ensure print quality in the normal printing process when it is carried out after the overprinting process.

(8) In the screen printing method described in (6) or (7), it is preferable that the precondition is replacement of the mask.

After replacing the mask, no flux is supplied to the inner walls of the openings in the new mask, making it difficult for the cream solder to separate from the inner walls of the openings. However, with the above-mentioned screen printing method, the overlapping printing process can be carried out, making it possible to suppress printing defects.

(9) In the screen printing method described in any one of (6) to (8), it is preferable that the precondition is cleaning of the mask.

Since no flux is supplied to the inner walls of the openings in the mask after cleaning, the cream solder is less likely to separate from the inner walls of the openings. However, with the above-mentioned screen printing method, the overlapping printing process is carried out, which makes it possible to suppress printing defects.

(10) In the screen printing method described in any one of (6) to (9), it is preferable that the precondition is a predetermined time that has elapsed after the normal printing process.

Normally, after a certain amount of time has passed since the printing process, the flux in the mask opening dries, making it difficult for the cream solder to separate from the inner walls of the opening. However, with the above-mentioned screen printing method, the overlapping printing process is carried out, making it possible to suppress printing defects.

(11) In the screen printing method described in any one of (6) to (10), it is preferable that the precondition is drying of the cream solder.

When the cream solder dries, it becomes difficult for the cream solder to separate from the inner wall of the mask opening. However, with the above screen printing method, the overlapping printing process can be carried out, which can reduce printing defects.

(12) The screen printing device of the present disclosure is a screen printing device that prints cream solder on a substrate using a mask, and includes a substrate transport unit that moves the substrate to a printing space, a mask holder that holds the mask, a substrate holding unit that holds the substrate, a positioning mechanism that moves at least one of the mask holder and the substrate holding unit to bring the substrate and the mask into contact with and separate from each other in a first direction, a printing unit that prints cream solder on the substrate through an opening provided in the mask, and a control unit, and the control unit performs normal printing processing and pre-printing on one of the substrates when it is determined that predetermined pre-conditions are satisfied. and an overprinting process in which the normal printing process is performed multiple times. In the normal printing process, a plate alignment operation is performed in which the positioning mechanism is controlled to overlay the substrate and the mask in the first direction, a printing operation is performed in which the printing unit is controlled to print solder paste on the substrate, and a plate separation operation is performed in which the positioning mechanism is controlled to separate the substrate and the mask in the first direction. In the overprinting process, a first normal printing process and a second normal printing process are performed, and the second normal printing process is performed after the first normal printing process without moving the substrate from the printing space.

With this configuration, the overprinting process is executed when certain preconditions that tend to reduce the filling rate of the cream solder are met. Because the overprinting process includes a first normal printing process and a second normal printing process, the amount of cream solder printed on the board can be increased. This makes it possible to suppress printing defects.

(13) In the screen printing device described in (12), it is preferable that the control unit further performs a cleaning process to clean the mask during the overprinting process, and that the cleaning process is performed after the first normal printing process and before the second normal printing process.

With this configuration, a cleaning process is performed between the first normal printing process and the second normal printing process, which can prevent the openings in the mask from being filled with excess cream solder.

(14) In the screen printing device described in (12), it is preferable that the control unit immediately and continuously executes the second normal printing process after the first normal printing process.

This configuration makes it possible to prevent the flux of the cream solder from drying on the inner walls of the openings in the mask between the first and second normal printing processes. This makes it easier to increase the amount of cream solder printed on the board in the second normal printing process.

(15) In the screen printing device described in any one of (12) to (14), it is preferable that the control unit does not inspect the condition of the cream solder printed on the substrate between the first normal printing process and the second normal printing process.

This configuration allows the overprinting process to be carried out smoothly.

(16) In the screen printing device described in any one of (12) to (15), it is preferable that the control unit determines that the preconditions are satisfied when the mask is replaced.

After replacing the mask, no flux is supplied to the inner walls of the openings of the new mask, making it difficult for the cream solder to separate from the inner walls of the openings. However, with the above configuration, the overlapping printing process can be performed, making it possible to suppress printing defects.

(17) In the screen printing device described in any one of (12) to (16), it is preferable that the control unit determines that the preconditions are satisfied when the mask is cleaned.

Since no flux is supplied to the inner walls of the openings in the mask after cleaning, the cream solder is less likely to separate from the inner walls of the openings. However, with the above configuration, the overlapping printing process can be performed, which can reduce printing defects.

(18) In the screen printing device described in any one of (12) to (17), it is preferable that the control unit determines that the preconditions are satisfied when a predetermined time has elapsed after the normal printing process.

Normally, after a certain amount of time has passed since the printing process, the flux in the mask opening dries, making it difficult for the cream solder to separate from the inner wall of the opening. However, with the above configuration, the overlapping printing process can be performed, making it possible to suppress printing defects.

(19) In the screen printing device described in any one of (12) to (18), it is preferable that the control unit determines that the preconditions are satisfied when the cream solder is dry.

When the cream solder dries, it becomes difficult for the cream solder to separate from the inner wall of the opening in the mask. However, with the above configuration, the overlapping printing process can be performed, making it possible to suppress printing defects.

[Details of the embodiment of the present disclosure]
Hereinafter, embodiments of the present disclosure will be described. Note that the present disclosure is not limited to these examples, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims.

[Embodiment 1]
A first embodiment of the present disclosure will be described with reference to Fig. 1 to Fig. 11. In the following description, the left-right direction shown in Fig. 1 is defined as the X direction, the front-rear direction as the Y direction, and the up-down direction as the Z direction. Note that, for multiple identical members, only some of the members may be labeled with reference numerals, and the reference numerals of the other members may be omitted.

<Overall Configuration of Screen Printing Apparatus>
The screen printing apparatus 1 according to the first embodiment is an apparatus that prints cream solder on a substrate P using a mask 12. As shown in Fig. 1, the screen printing apparatus 1 includes a box-shaped housing 10. An entrance through which the substrate P is carried in is formed in the right wall of the housing 10. An exit through which the substrate P is carried out is formed in the left wall of the housing 10. The substrate P is carried into the housing 10 from the entrance in the right wall, and after a circuit pattern is printed with cream solder inside the housing 10, it is carried out from the exit in the left wall.

As shown in FIG. 2, the screen printing device 1 includes a metal base 11, a mask 12, a mask holder 13, a substrate transport section 14, a printing table 15 (an example of a positioning mechanism), a printing section 16, an inspection section 17, a mask replacement unit 18 (see FIG. 5), and a cleaning section 19 (see FIG. 5).

As shown in FIG. 4, the mask 12 comprises a frame-shaped mask frame 12A and a plate-shaped mask body 12C that is supported inside the mask frame 12A via an elastic member 12B. The mask body 12C is made of aluminum, iron, or the like. The mask body 12C has an opening 12D formed therein that corresponds to the circuit pattern to be printed. The elastic member 12B is made of a plate-shaped resin, rubber, or the like.

As shown in FIG. 2, the mask holder 13 is provided between the printing unit 16 and the inspection unit 17. The mask holder 13 is composed of two rail portions 13A spaced apart in the X direction and extending in the Y direction (perpendicular to the paper surface). The left rail portion 13A has a bottom wall and a side wall portion that rises upward from the left edge of the bottom wall. The right rail portion 13A has a bottom wall and a side wall portion that rises upward from the right edge of the bottom wall. The two rail portions 13A support both sides of the mask 12 in the X direction.

The board transport section 14 has three conveyors (upstream conveyor 14A, main conveyor 14B, downstream conveyor 14C) lined up in the X direction. The upstream conveyor 14A and downstream conveyor 14C are provided on the base 11, and the main conveyor 14B is provided on the printing table 15. Each conveyor has a pair of conveyor belts (not shown) that are spaced apart in the Y direction and driven to circulate in the X direction, and a motor (not shown) that drives the conveyor belts.

As shown in Figures 2 and 3, the printing table 15 is provided on the upper surface of the base 11. The printing table 15 includes a flat table 20, a ball screw 21 extending vertically, a motor (not shown) for rotating the ball screw 21, a substrate fixing unit 22 (an example of a substrate holder) for fixing the substrate P, and a backup unit 23 for supporting the substrate P fixed to the substrate fixing unit 22 from below. The table 20 rises and falls as the ball screw 21 rotates. In other words, the printing table 15 can raise and lower the substrate P fixed to the substrate fixing unit 22.

As shown in FIG. 3, the substrate fixing unit 22 is composed of a pair of clamps 22A that clamp the substrate P from both sides in the Y direction and fix it, and a motor (not shown) that drives the clamps 22A. The clamps 22A fix the substrate P that has been transported to the printing space above the backup unit 23. A through hole that penetrates in the vertical direction is formed in the clamps 22A. The lower side of the through hole is connected to an air supply device via an air hose. When the table 20 rises with the substrate fixing unit 22 fixing the substrate P, the upper surface of the clamps 22A comes into close contact with the lower surface of the mask body 12C of the mask 12, and in this state, negative pressure is supplied to the through hole, so that the mask body 12C is adsorbed to the clamps 22A.

As shown in Figures 2 and 3, the backup unit 23 includes a plate-shaped lower plate 23A, a plate-shaped upper plate 23B disposed above the lower plate 23A, a number of backup pins 23C that support the substrate P from below, a ball screw 23D that extends vertically, and a motor (not shown) that rotates the ball screw 23D. The backup unit 23 rises and falls as the ball screw 23D rotates.

Although not shown, the upper plate 23B has multiple rows of holes spaced apart in the X direction and aligned in a row in the Y direction. Backup pins 23C are inserted into these holes. The positions of the holes into which the backup pins 23C are inserted vary depending on the type of substrate P. When the type of substrate P being produced is changed, the arrangement of the backup pins 23C is changed according to the type of substrate P after the change.

The printing section 16 includes a squeegee unit 16A shown in FIG. 2, a pair of guide rails 16B that support the squeegee unit 16A so that it can move back and forth in the Y direction, a ball screw (not shown), and a motor (not shown) that rotates the ball screw. The squeegee unit 16A moves in the Y direction as the ball screw rotates.

As shown in Figures 2 and 3, the squeegee unit 16A includes a solder supply section 16C that supplies paste-like cream solder onto the mask 12 (mask body 12C), a squeegee 16E that evens out the supplied cream solder, a motor (not shown) that raises and lowers the squeegee 16E, and a motor (not shown) that rotates the squeegee 16E around a rotation axis that extends in the X direction (perpendicular to the paper surface in Figure 3). The squeegee 16E is elongated in the X direction.

As shown in FIG. 2, the inspection unit 17 is provided between the mask holder 13 and the printing table 15. The inspection unit 17 is for capturing images of the underside of the mask 12 and the upper surface of the substrate P to inspect the condition of the underside of the mask 12 and the circuit pattern of the cream solder printed on the substrate P. The inspection unit 17 includes a camera unit 17A, a beam 17B that supports the camera unit 17A so that it can move back and forth in the X direction, a ball screw 17C fixed to the beam 17B and extending in the X direction, a pair of guide rails 17D arranged on both sides of the beam 17B in the X direction and extending in the Y direction, a ball screw (not shown) that extends in the Y direction, and a motor (not shown) that rotates the ball screw.

A mask imaging camera 17E that images the lower surface of the mask 12, and a substrate imaging camera 17F that images the upper surface of the substrate P are fixed to the camera unit 17A. The camera unit 17A moves in the XY directions within a predetermined movable range as the ball screws rotate. The inspection section 17 may be configured to move the camera unit 17A by a linear motor.
Inspection by inspection unit 17 may be performed for each substrate P, or for multiple substrates P. Alternatively, inspection may be performed at regular time intervals, or when a designated time is reached.

As shown in FIG. 3, the squeegee unit 16A is fitted with a detection sensor 16F for measuring the volume of the cream solder (solder roll R1) on the mask 12. The detection sensor 16F is fitted with its detection surface facing downward. The detection sensor 16F is, for example, a reflective optical sensor, and detects the presence or absence of the solder roll R1 supplied onto the mask 12 based on the level of a light reception signal obtained by receiving light reflected from the surface of the mask 12. In detail, the detection sensor 16F can be used to detect the width (dimension in the Y direction) of the solder roll R1, etc., and measure the volume of the solder roll R1.

Although not shown in Figures 1 to 3, the screen printing apparatus 1 includes a mask replacement unit 18 and a cleaning section 19 (see Figure 5). The mask replacement unit 18 is a mechanism for automatically replacing the mask 12. The mask replacement unit 18 is configured with a plurality of magazines capable of housing the masks 12, a motor for raising and lowering the magazines, and the like. The magazines house replacement masks 12. The mask replacement unit 18, for example, returns the mask 12 held in the mask holder 13 to an empty magazine, and moves another mask 12 housed in the magazine to the mask holder 13.

The cleaning unit 19 includes, for example, a sheet roll on which a cleaning sheet such as paper or cloth is wound, a sheet roll shaft that rotatably holds the sheet roll, a take-up roll that winds up used cleaning sheets, a take-up shaft that rotatably holds the take-up roll, a motor that rotates the take-up shaft, a cleaning head disposed between the sheet roll shaft and the take-up shaft, and a cylinder that raises and lowers the cleaning head.

The cleaning sheet is wound around the sheet roll and the take-up roll. When positive pressure is applied to the cylinder of the cleaning unit 19, the cleaning head rises and the cleaning sheet is pressed against the lower surface of the mask 12. In this state, the take-up roll rotates, thereby cleaning the lower surface of the mask 12.
Cleaning of the mask 12 may be performed after each substrate P, or after every several substrates P. Alternatively, cleaning may be performed at regular time intervals, or when a designated time is reached.

<Electrical Configuration of Screen Printing Apparatus>
5, the electrical configuration of the screen printing apparatus 1 will be described. The screen printing apparatus 1 includes a control unit 30, a display unit 31, and an input unit 32.
The control unit 30 includes a CPU 30A, a RAM 30B, and a storage unit 30C. The storage unit 30C is a storage device having a non-volatile storage medium such as a hard disk. Various programs and data executed by the CPU 30A are stored in the storage unit 30C. The control unit 30 is connected to a display unit 31, an input unit 32, a substrate transport unit 14, a printing table 15, a printing unit 16, an inspection unit 17, a mask exchange unit 18, a cleaning unit 19, and the like.
The display unit 31 is a display device such as a liquid crystal display, etc. The input unit 32 is an input device such as a touch panel, a mouse, a keyboard, etc.

<Printing solder paste onto the circuit board>
The screen printing apparatus 1 prints cream solder on the substrate P in accordance with the flow chart shown in Fig. 6. First, the substrate P is transported to the printing space by the substrate transport section 14 (S10). Here, the printing space is a space disposed above the backup unit 23, and in this printing space, a normal printing process or an overprinting process, which will be described later, is carried out.

In this embodiment, if at least one of the preset preconditions (S20, S30, S40, S50) is satisfied, the overprinting process (S70) is executed. If none of the preconditions is satisfied, the normal printing process (S60) is executed. The overprinting process is a process in which the normal printing process is executed at least twice on the same substrate P (details will be described later). The preconditions are conditions that are empirically known to be likely to result in poor printing of the cream solder on the substrate P. A state in which the cream solder printing state is poor is, for example, a state in which the amount of cream solder printed on the substrate P through the opening 12D of the mask 12 is insufficient. If the preconditions are satisfied, the overprinting process is executed, thereby making it possible to suppress poor printing of the cream solder on the substrate P.

One of the preconditions may be, for example, that the substrate P to be printed is the Nth (≦n) substrate P after the mask 12 has been replaced (S20: Yes). Here, n is a predetermined natural number, and N is any natural number less than or equal to n. n can be set by the operator or the control unit 30 depending on the mask 12, substrate P, type of cream solder, printing conditions, past production results, etc.

One of the preconditions may be, for example, that the substrate P to be printed is the M (≦m)th substrate P after cleaning of the mask 12 (S30: Yes). Here, m is a predetermined natural number, and M is any natural number less than or equal to m. m can be set by the operator or the control unit 30 depending on the mask 12, substrate P, type of cream solder, printing conditions, past production results, etc. m may be the same as n, or may be different.

One of the preconditions may be, for example, that a predetermined time has passed since the most recent printing (S40: Yes). When the predetermined time has passed, it can be determined that the cream solder is dry without actually checking the state of the cream solder. Here, the predetermined time can be set by the operator or the control unit 30 depending on the type of cream solder, printing conditions, past production results, etc.

One of the preconditions may be, for example, that the cream solder is dry (S50: Yes). As described above, it is possible to determine that the cream solder is dry after a predetermined time has passed, but if the temperature or air volume in the production environment changes due to, for example, an air conditioning malfunction, the cream solder may dry before the predetermined time has passed. Whether the cream solder is dry may be determined by the control unit 30 or by the operator. For example, the screen printing device 1 may be equipped with a viscometer capable of measuring the viscosity of the cream solder, and the control unit 30 may determine that the cream solder is dry when the measured value of the viscosity of the cream solder measured by the viscometer exceeds a predetermined threshold value. The operator may also visually check the state of the cream solder and determine whether the cream solder is dry.

The parameters related to the above preconditions (such as n, m, the specified time, and the viscosity threshold value) are stored in the memory unit 30C. The control unit 30 can determine whether the above preconditions are met based on these parameters and various data during production stored in the RAM 30B.

After the normal printing process (S60) or the overprinting process (S70) is performed on the substrate P, the printing state of the substrate P may be inspected by the inspection unit 17 (S80). In inspecting the substrate P, for example, the cream solder pattern printed on the substrate P is captured by the substrate imaging camera 17F of the inspection unit 17, and the captured image is processed by the control unit 30 to determine whether the amount and position of the cream solder printed on the substrate P are appropriate. The inspection of the substrate P may be performed in the printing space, or may be performed in a position other than the printing space within the screen printing apparatus 1.

After the inspection of the substrate P (S80), the substrate P is transported out of the screen printing device 1 by the substrate transport unit 14 (S90). The substrate P that has been transported out is sent to, for example, an inspection device or a component mounting device.

<Normal printing process>
7 is a flow chart showing the normal printing process. In the normal printing process, a plate alignment operation (S61) is performed in which the substrate P and the mask 12 are superimposed in the vertical direction (an example of the first direction) (see FIG. 9A). In this embodiment, the plate alignment operation is performed by moving the substrate P relative to the mask 12 held by the mask holder 13. In detail, the substrate P fixed to the substrate fixing unit 22 is raised by the rotation of the ball screws 21, 23D of the printing table 15 and is pressed against the lower surface of the mask 12.

After the plate alignment operation (S61), a printing operation (S62) is performed to print cream solder on the substrate P through the opening 12D of the mask 12 (see FIG. 9B). A solder roll R1 is formed on the surface of the mask 12 by cream solder supplied from the nozzle 16D of the solder supply unit 16C. The solder roll R1 is rod-shaped and extends in the X direction. The control unit 30 lowers the squeegee 16E onto the mask 12 and moves it from one side to the other in the Y direction (front-back direction). At this time, the squeegee 16E slides over the surface of the mask 12, causing the solder roll R1 to spread over the mask 12, and the opening 12D formed in the mask 12 is filled with cream solder. This allows cream solder to be printed on the substrate P superimposed on the lower surface of the mask 12.

After the printing operation (S62), a plate separation operation (S63) is executed to separate the substrate P and the mask 12 in the vertical direction (see FIG. 9C ). In this embodiment, the plate separation operation is performed by moving the substrate P downward relative to the mask 12 held by the mask holder 13 in the opposite manner to the plate alignment operation.
This completes the normal printing process.

<Overprinting process>
FIG. 8 is a flowchart showing the overprinting process. In the overprinting process of this embodiment, the normal printing process is performed twice. That is, the overprinting process includes a first normal printing process and a second normal printing process. In the first normal printing process, a first plate alignment operation (S71, see FIG. 9A), a first printing operation (S72, see FIG. 9B), and a first plate release operation (S73, see FIG. 9C) are performed. In the second normal printing process, a second plate alignment operation (S74, see FIG. 9D), a second printing operation (S75, see FIG. 9E), and a second plate release operation (S76, see FIG. 9F) are performed on the substrate P after the first normal printing process. The second normal printing process is performed after the first normal printing process without moving the substrate P from the printing space. In detail, between the first normal printing process and the second normal printing process, the substrate transport unit 14 does not move the substrate P in the X direction.

In the first printing operation, the squeegee 16E moves from one side to the other in the Y direction, whereas in the second printing operation, the squeegee 16E moves from the other side to one side in the Y direction. That is, the movement direction of the squeegee 16E is opposite between the first printing operation and the second printing operation. Except for the movement direction of the squeegee 16E in the printing operation, it is preferable that the conditions of the first normal printing process and the second normal printing process are the same. The conditions here include, for example, the speed at which the squeegee 16E moves, the angle between the squeegee 16E and the mask 12 (attack angle), the pressure at which the squeegee 16E is pressed against the mask 12 (printing pressure), and the like. By making these conditions uniform, the printing quality can be made uniform.

In the overlap printing process of this embodiment, no extra processing related to the substrate P, such as inspection of the printing state of the substrate P, is performed between the first normal printing process and the second normal printing process. In addition, the second normal printing process is performed immediately and continuously after the first normal printing process.

<Experiment 1>
Next, Experiments 1 and 2 conducted to verify the effects of the present disclosure will be described. In Experiment 1, a mask that had been left for 20 minutes after cleaning was used to perform an overlapping printing process on five substrates in succession. For comparison, a normal printing process and a reciprocating printing process were performed under the same conditions. Here, the reciprocating printing process is a process in which a plate alignment operation, a first printing operation, a second printing operation, and a plate release operation are performed in sequence. In the reciprocating printing process, a plate release operation is not performed between the first printing operation and the second printing operation.

The average volume ratio of cream solder was calculated for each board obtained by the above process. Here, the volume ratio of cream solder is a value that represents the ratio of the volume of cream solder actually printed on the board through the mask opening to the internal space of the opening. And the average volume ratio of cream solder is a value obtained by averaging over all mask openings.

In experiment 1, the board used was Yamaha Motor's demo board CUK-B1311-000, the mask used was Sun Kohgei's printability evaluation mask CUK-M1311-100, and the cream solder used was Senju Metal Industry's M705-GRN360-K2V (Type 4). The squeegee speed was set to 50 mm/sec, the printing pressure to 60 N, and the attack angle to 55°.

<Results of Experiment 1>
Graphs A, B, and C in Fig. 10 show the results of experiment 1, corresponding to the overlap printing process, normal printing process, and reciprocating printing process, respectively. As shown in graph B, when cream solder was printed using the normal printing process, the average volume ratio of cream solder was low on the first and second boards. On the other hand, for the third board and onwards, the average volume ratio of cream solder was stable at around 100%.

As shown in graph C, when cream solder was printed using a reciprocating printing process, the average volume ratio of cream solder was slightly lower on the first board.

As shown in graph A, when cream solder is printed using the overlap printing process, the average volume ratio of the cream solder is about 100% even on the first and second boards, and the print quality is better than with normal printing or reciprocating printing.

<Considerations on the results of Experiment 1>
The results of Experiment 1 will be considered with reference to Figures 9A to 9F. The cream solder is composed of liquid flux and particulate solder balls. In Figures 9B to 9F, the flux of the cream solder (solder roll R1) is shown by the shaded area, and the solder balls are shown by the white circles within the shaded area.

As shown in FIG. 9A, it is believed that no flux is attached to the inner wall of the opening 12D of the cleaned mask 12. When cream solder is printed (see FIG. 9B) and the plate is removed while there is insufficient flux on the inner wall of the opening 12D, the cream solder is difficult to separate from the inner wall of the opening 12D. For this reason, it is believed that some of the cream solder adheres to the inner wall of the opening 12D (see FIG. 9C). Therefore, as shown in graph B of FIG. 10, in the normal printing process, it is believed that the average volume ratio of cream solder became smaller for the first and second boards after cleaning. For the third and subsequent boards, it is believed that the average volume ratio of cream solder stabilized at about 100% because the inner wall of the opening was sufficiently wetted with flux.

In the overprinting process, a second plate alignment operation (see FIG. 9D), a second printing operation (see FIG. 9E), and a second plate release operation (see FIG. 9F) are further performed on the substrate P in the state of FIG. 9C. This supplies flux to the inner wall of the opening 12D, improving the escape of cream solder from the opening 12D, and is thought to supply the amount of cream solder that was lacking in the first normal printing process to the substrate P. As a result, it is thought that the average volume ratio of cream solder has improved, as shown in graph A of FIG. 10.

The reciprocating printing process is similar to the overlapping printing process in that two printing operations are performed, but differs from the overlapping printing process in that no plate separation operation is performed between the first and second printing operations. Although the detailed mechanism is unknown, it is believed that this difference makes it easier to supply flux to the inner wall of the opening with the overlapping printing process than with the reciprocating printing process.

As described above, it has been shown that printing defects can be suppressed by performing the overprinting process after cleaning the mask. Furthermore, when the mask is replaced with a new one, or when the cream solder is in a dry state, it is believed that there is a lack of flux on the inner walls of the mask openings. Therefore, it is believed that it is preferable to perform the overprinting process even in such cases.

<Experiment 2>
In experiment 2, the mask was left for 10 minutes after cleaning, and the first board was subjected to overprinting, while the second to fifth boards were subjected to normal printing. For comparison, normal printing was also performed on all five boards under the same conditions. The average volume ratio of the cream solder was then calculated for each board.

In experiment 2, the board used was Yamaha Motor's demo board CUK-B1311-000, the mask used was Sun Kohgei's printability evaluation mask CUK-M1311-100, and the cream solder used was Harima Chemical's CLR-B. The squeegee speed was set to 50 mm/sec, the printing pressure to 60 N, and the attack angle to 55°.

<Results of Experiment 2>
Graphs D and E in Fig. 11 show the results of experiment 2. Graph D shows the average volume ratio of cream solder when the overprinting process was performed only on the first board, and the normal printing process was performed on the second to fifth boards. Graph E shows the average volume ratio of cream solder when the normal printing process was performed on all five boards. As shown in graph E, when cream solder was printed by the normal printing process, the average volume ratio of cream solder was low on the first board. On the other hand, the average volume ratio of cream solder on the second and subsequent boards was stable at around 100%.

As shown in graph D, when cream solder is printed using normal printing after the overprinting process, the average volume ratio of cream solder is stable at about 100% for the first to fifth boards.

Under the conditions of experiment 2, it was shown that if the overprinting process was performed only on the first substrate after cleaning the mask, printing defects could be suppressed by normal printing process for the second and subsequent substrates. In this way, by performing the overprinting process under conditions where printing defects are particularly likely to occur (here, the first substrate after cleaning the mask), and performing normal printing process otherwise, it is possible to suppress printing defects while minimizing declines in production efficiency.

[Effects of the First Embodiment]
As described above, the screen printing method of embodiment 1 is a screen printing method for printing cream solder on substrate P using mask 12, and includes a normal printing process and an overprinting process in which the normal printing process is performed multiple times on one substrate P. The normal printing process includes a plate alignment operation in which substrate P and mask 12 are overlaid in a first direction, a printing operation in which cream solder is printed on substrate P through opening 12D provided in mask 12, and a plate separation operation in which substrate P and mask 12 are separated in the first direction. The overprinting process includes a first normal printing process and a second normal printing process, and the second normal printing process is performed after the first normal printing process, without moving substrate P from the printing space.

In this type of screen printing method, the overlap printing process includes a first normal printing process and a second normal printing process, so the amount of cream solder printed on the substrate P can be increased by the overlap printing process. This makes it possible to suppress printing defects.

In the screen printing method of embodiment 1, it is preferable that the second normal printing process is performed immediately and consecutively after the first normal printing process.

This type of screen printing method can prevent the flux of the cream solder from drying on the inner wall of the opening 12D of the mask 12 between the first normal printing process and the second normal printing process. This makes it easier to increase the amount of cream solder printed on the substrate P in the second normal printing process.

In the screen printing method of embodiment 1, it is preferable that the condition of the cream solder printed on the substrate P is not inspected between the first normal printing process and the second normal printing process.

This type of screen printing method allows the overlapping printing process to be carried out smoothly.

In the screen printing method of embodiment 1, it is preferable that the conditions for the first normal printing process are the same as the conditions for the second normal printing process.

This type of screen printing method allows for uniform printing quality of the cream solder.

In the screen printing method of embodiment 1, it is preferable that the overprinting process is carried out when predetermined preconditions are met.

With this type of screen printing method, when certain preconditions that tend to reduce the filling rate of the cream solder are met, an overprinting process can be carried out, making it possible to suppress printing defects.

In the screen printing method of embodiment 1, the overlap printing process is preferably performed on a predetermined number of substrates P after the preconditions are met.

This type of screen printing method makes it easier to ensure print quality in the normal printing process when it is carried out after the overprinting process.

In the screen printing method of embodiment 1, the precondition is preferably replacement of the mask 12.

After replacing the mask 12, no flux is supplied to the inner walls of the openings 12D of the new mask 12, making it difficult for the cream solder to separate from the inner walls of the openings 12D. However, with the above-mentioned screen printing method, the overlapping printing process is performed, making it possible to suppress printing defects.

In the screen printing method of embodiment 1, the precondition is preferably cleaning of the mask 12.

Since no flux is supplied to the inner wall of the opening 12D of the mask 12 after cleaning, the cream solder is less likely to separate from the inner wall of the opening 12D. However, with the above-mentioned screen printing method, the overlapping printing process is performed, which makes it possible to suppress printing defects.

In the screen printing method of embodiment 1, the precondition is preferably a predetermined time that has elapsed after the normal printing process.

Normally, after a certain time has elapsed after the printing process, the flux in the opening 12D of the mask 12 dries, making it difficult for the cream solder to separate from the inner wall of the opening 12D. However, with the above-mentioned screen printing method, the overlapping printing process is performed, making it possible to suppress printing defects.

In the screen printing method of embodiment 1, the precondition is preferably drying of the cream solder.

When the cream solder dries, it becomes difficult for the cream solder to separate from the inner wall of the opening 12D of the mask 12. However, with the above-mentioned screen printing method, the overlapping printing process is performed, which makes it possible to suppress printing defects.

The screen printing apparatus 1 of the first embodiment is a screen printing apparatus 1 that prints cream solder on a substrate P using a mask 12, and includes a substrate transport section 14 that moves the substrate P to a printing space, a mask holder 13 that holds the mask 12, a substrate holding section (substrate fixing unit 22) that holds the substrate P, a positioning mechanism (printing table 15) that moves at least one of the mask holder 13 and the substrate holding section to bring the substrate P and the mask 12 into contact with and separate from each other in a first direction, a printing section 16 that prints cream solder on the substrate P through an opening 12D provided in the mask 12, and a control section 30, and the control section 30 is configured to perform a normal printing process and a predetermined and an overlap printing process in which a normal printing process is performed multiple times on one substrate P if it is determined that the preconditions set forth above are satisfied. In the normal printing process, a plate alignment operation is performed in which the positioning mechanism is controlled to overlap the substrate P and the mask 12 in a first direction, a printing operation is performed in which the printing unit 16 is controlled to print cream solder on the substrate P, and a plate separation operation is performed in which the positioning mechanism is controlled to separate the substrate P and the mask 12 in the first direction. In the overlap printing process, a first normal printing process and a second normal printing process are performed, and the second normal printing process is performed after the first normal printing process without moving the substrate P from the printing space.

With this configuration, the overprinting process is executed when certain preconditions that tend to reduce the filling rate of the cream solder are met. Because the overprinting process includes a first normal printing process and a second normal printing process, the amount of cream solder printed on the substrate P can be increased. This makes it possible to suppress printing defects.

In the screen printing device 1 of embodiment 1, it is preferable that the control unit 30 immediately and continuously executes the second normal printing process after the first normal printing process.

This configuration makes it possible to prevent the cream solder flux from drying on the inner wall of the opening 12D of the mask 12 between the first normal printing process and the second normal printing process. This makes it easier to increase the amount of cream solder printed on the substrate P in the second normal printing process.

In the screen printing device 1 of embodiment 1, it is preferable that the control unit 30 does not inspect the condition of the cream solder printed on the substrate P between the first normal printing process and the second normal printing process.

This configuration allows the overprinting process to be carried out smoothly.

In the screen printing device 1 of embodiment 1, it is preferable that the control unit 30 determines that the preconditions are satisfied when the mask 12 is replaced.

After replacing the mask 12, no flux is supplied to the inner walls of the openings 12D of the new mask 12, making it difficult for the cream solder to separate from the inner walls of the openings 12D. However, with the above configuration, the overlapping printing process can be performed to prevent printing defects.

In the screen printing device 1 of embodiment 1, it is preferable that the control unit 30 determines that the preconditions are met when the mask 12 is cleaned.

Since no flux is supplied to the inner wall of the opening 12D of the mask 12 after cleaning, the cream solder is less likely to separate from the inner wall of the opening 12D. However, with the above configuration, the overlapping printing process is performed, making it possible to suppress printing defects.

In the screen printing device 1 of embodiment 1, it is preferable that the control unit 30 determines that the preconditions are met when a predetermined time has elapsed after the normal printing process.

After a normal printing process, when a certain amount of time has passed, the flux in the opening 12D of the mask 12 dries, making it difficult for the cream solder to separate from the inner wall of the opening 12D. However, with the above configuration, the overlapping printing process is performed, making it possible to suppress printing defects.

In the screen printing device 1 of embodiment 1, it is preferable that the control unit 30 determines that the preconditions are met when the cream solder is dry.

When the cream solder dries, it becomes difficult for the cream solder to separate from the inner wall of the opening 12D of the mask 12. However, with the above configuration, the overlapping printing process can be performed to prevent printing defects.

[Embodiment 2]
A second embodiment of the present disclosure will be described with reference to Fig. 12. Note that the configuration of the second embodiment is the same as that of the first embodiment except for the procedure of the overprinting process, and therefore a duplicated description will be omitted. Hereinafter, the same reference numerals as those in the first embodiment will be used to designate the same configuration as in the first embodiment.

<Cleaning process>
FIG. 12 is a flowchart showing the overprinting process (S100) according to the second embodiment. In the overprinting process (S100), cleaning of the mask is performed between the first normal printing process and the second normal printing process. In the first normal printing process, a first plate alignment operation (S101, see FIG. 9A), a first printing operation (S102, see FIG. 9B), and a first plate release operation (S103, see FIG. 9C) are performed. After the first normal printing process, a cleaning process (S104) of the mask 12 is performed. After the cleaning process, a second normal printing process is performed. In the second normal printing process, a second plate alignment operation (S105), a second printing operation (S106), and a second plate release operation (S107) are performed on the substrate P after the first normal printing process. The second normal printing process is performed without moving the substrate P from the printing space after the first normal printing process.

In the overlap printing process of the present disclosure, the normal printing process is performed two or more times on the same substrate P, but in the overlap printing process of embodiment 1, depending on the type of mask 12 and substrate P, the amount of cream solder filled into the opening 12D of the mask 12 may be excessive. In this embodiment, a cleaning process is performed between the first normal printing process and the second normal printing process of the mask, which is thought to be able to remove the cream solder adhering to the inner wall of the opening 12D of the mask 12 appropriately and wet the inner wall of the opening 12D with flux. Therefore, in the second normal printing process, it is thought that it is possible to prevent the cream solder from being filled excessively into the opening 12D while improving the escape of the cream solder from the opening 12D.

The cleaning process performed in the overprinting process may not be included in the preconditions for the overprinting process.

[Effects of the Second Embodiment]
In the screen printing method of the second embodiment, the overprinting step further includes a cleaning step of cleaning the mask 12, and the cleaning step is preferably performed after the first normal printing step and before the second normal printing step.

With this type of screen printing method, a cleaning process is performed between the first normal printing process and the second normal printing process, which makes it possible to prevent the opening 12D of the mask 12 from being filled with excess cream solder.

In the screen printing device 1 of embodiment 2, the control unit 30 further executes a cleaning process to clean the mask 12 during the overprinting process, and it is preferable that the cleaning process is performed after the first normal printing process and before the second normal printing process.

With this configuration, a cleaning process is performed between the first normal printing process and the second normal printing process, which makes it possible to prevent the opening 12D of the mask 12 from being filled with excess cream solder.

[Other embodiments]
(1) In the above embodiment, the normal printing process is executed two times in the overprinting process. However, the normal printing process may be executed three or more times in the overprinting process.

(2) In the above embodiment, the plate alignment operation and the plate separation operation were performed by raising and lowering the substrate P relative to the fixed mask 12, but the mask may be configured to raise and lower relative to the substrate.

(3) In the above embodiment, the control unit 30 is configured to automatically execute the overprinting process when at least one of the preconditions S20, S30, S40, and S50 is satisfied, but the preconditions may be different from those described above. Also, the preconditions may not be set, and the overprinting process may be executed when necessary by an operator issuing an instruction.

(4) In the above embodiment, the screen printing method of the present disclosure was executed by the control unit 30 of the screen printing device 1. However, for example, the screen printing method of the present disclosure may be executed by an operator or a control unit of a control PC connected to the screen printing device so as to be able to communicate with it.

1: Screen printing apparatus 10: Housing 11: Base 12: Mask 12A: Mask frame 12B: Elastic member 12C: Mask body 12D: Opening 13: Mask holder 13A: Rail section 14: Substrate transport section 14A: Upstream conveyor 14B: Main conveyor 14C: Downstream conveyor 15: Printing table 16: Printing section 16A: Squeegee unit 16B: Guide rail 16C: Solder supply section 16E: Squeegee 16F: Detection sensor 17: Inspection section 17A: Camera unit 17B: Beam 17C: Ball screw 17D: Guide rail 17E: Mask imaging camera 17F: Substrate imaging camera 18: Mask replacement unit 19: Cleaning section 20: Table 21: Ball screw 22: Substrate fixing unit 22A: Clamp section 23: Backup unit 23A: Lower plate 23B: Upper plate 23C: Backup pin 23D: Ball screw 30: Control unit 30A: CPU 30B: RAM 30C: Storage unit 31: Display unit 32: Input unit P: Substrate R1: Solder roll

Claims (19)

A screen printing method for printing cream solder on a substrate using a mask, comprising the steps of:
The normal printing process,
and an overprinting process of performing the normal printing process multiple times on one substrate,
In the normal printing process,
a plate alignment operation of overlapping the substrate and the mask in a first direction;
a printing operation of printing cream solder on the board through an opening provided in the mask;
a plate separation operation for separating the substrate and the mask in the first direction;
The overprinting step includes a first normal printing step and a second normal printing step,
A screen printing method, wherein the second normal printing step is performed after the first normal printing step without moving the substrate from a printing space. The overprinting step further includes a cleaning step of cleaning the mask,
The screen printing method according to claim 1 , wherein the cleaning step is performed after the first normal printing step and before the second normal printing step. The screen printing method according to claim 1, wherein the second normal printing process is performed immediately and consecutively after the first normal printing process. The screen printing method according to any one of claims 1 to 3, wherein an inspection of the state of the cream solder printed on the substrate is not performed between the first normal printing process and the second normal printing process. The screen printing method according to any one of claims 1 to 4, wherein the conditions for the first normal printing process and the conditions for the second normal printing process are the same. The screen printing method according to any one of claims 1 to 5, wherein the overprinting process is carried out when a predetermined precondition is satisfied. The screen printing method according to claim 6, wherein the overprinting process is performed on a predetermined number of the substrates after the preconditions are satisfied. The screen printing method according to claim 6 or 7, wherein the precondition is replacement of the mask. The screen printing method according to any one of claims 6 to 8, wherein the precondition is cleaning of the mask. The screen printing method according to any one of claims 6 to 9, wherein the precondition is the passage of a predetermined time after the normal printing process. The screen printing method according to any one of claims 6 to 10, wherein the precondition is drying of the cream solder. A screen printing apparatus for printing cream solder on a substrate using a mask,
A substrate transport unit that moves the substrate to a printing space;
A mask holder for holding the mask;
A substrate holder for holding the substrate;
a positioning mechanism that moves at least one of the mask holder and the substrate holding part to bring the substrate and the mask into contact with and separate from each other in a first direction;
a printing unit that prints cream solder on the board through an opening provided in the mask;
A control unit,
the control unit executes a normal printing process, and an overprinting process in which the normal printing process is executed multiple times on one of the substrates when it is determined that a predetermined precondition is satisfied;
In the normal printing process,
a plate alignment operation for controlling the positioning mechanism to align the substrate and the mask in the first direction;
a printing operation of controlling the printing unit to print cream solder on the board;
a plate separation operation for separating the substrate and the mask in the first direction by controlling the positioning mechanism;
In the overprinting process,
Executing the first normal printing process and the second normal printing process;
A screen printing apparatus, wherein the second normal printing process is performed after the first normal printing process, without moving the substrate from the printing space. The control unit further performs a cleaning process for cleaning the mask in the overprinting process,
The screen printing apparatus according to claim 12 , wherein the cleaning process is performed after the first normal printing process and before the second normal printing process. The screen printing device according to claim 12, wherein the control unit immediately and continuously executes the second normal printing process after the first normal printing process. The screen printing device according to any one of claims 12 to 14, wherein the control unit does not inspect the state of the cream solder printed on the substrate between the first normal printing process and the second normal printing process. The screen printing device according to any one of claims 12 to 15, wherein the control unit determines that the precondition is satisfied when the mask is replaced. The screen printing device according to any one of claims 12 to 16, wherein the control unit determines that the precondition is satisfied when the mask is cleaned. The screen printing device according to any one of claims 12 to 17, wherein the control unit determines that the preconditions are satisfied when a predetermined time has elapsed after the normal printing process. The screen printing device according to any one of claims 12 to 18, wherein the control unit determines that the precondition is satisfied when the cream solder is dry.

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