JP2002225224A - Method for screen printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for screen printing which can prevent a defective printing caused by curing of a paste. SOLUTION: In the screen-printing method for printing a cream solder 5 on a substrate through pattern holes by sliding a squeegee head 13 on a mask plate 12 by pressuring the cream solder 5 held inside of the squeegee head 13 of a closed type by a pressuring plate 32, the press force to be imposed by press means for pressuring the squeegee head 13 to the mask plate 12 in readiness for printing before print-motion starting is decreased from a press force F2 to F4, then with this condition the press force of the cream solder 5 by a cylinder 16 is increased from a press force F1 to F3. Thereby, the up/ downward motion of the cream solder 5 in the squeegee head 13 is accelerated, and the cream solder 5 is prevented from curing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screen printing method for printing paste such as cream solder or conductive paste on a substrate.

[0002]

2. Description of the Related Art In an electronic component mounting process, screen printing is used as a method for printing paste such as cream solder or conductive paste on a substrate. In this method, a mask plate having pattern holes formed in accordance with a printing target portion is set on a substrate, and the paste is printed on the substrate through the pattern holes of the mask plate by squeezing.

As a squeezing method for screen printing, a method using a closed squeegee head is known. This method differs from ordinary screen printing in that a paste is not directly supplied onto a mask plate, but a squeegee head in which paste is stored inside is used. In this method, the opening in the pattern hole of the mask plate is formed by pressing the paste in the squeegee head while the opening as the paste contact surface provided on the lower surface of the squeegee head is in contact with the mask plate. Paste is pushed through. Then, by sliding the squeegee head on the mask plate, each pattern hole is sequentially filled with the paste.

[0004]

However, screen printing using the above-mentioned conventional closed-type squeegee head involves the following.
There were the following problems. In the closed type squeegee head, the paste is always pressurized in the squeegee head during the printing operation as described above. For this reason,
As the pressing time elapses, the granular components contained in the paste at a high density are pressed against each other, whereby the paste gradually loses fluidity and hardens.

[0005] When the paste in such a cured state is supplied to the upper surface of the mask plate via the lower surface of the squeegee head, improper press-fitting into the pattern holes results in poor printing such as "fading". Occurs. As described above, the conventional screen printing using the closed squeegee head has a problem that a printing failure is likely to occur due to the curing of the paste by pressurization.

Accordingly, an object of the present invention is to provide a screen printing method capable of preventing a printing failure caused by curing of a paste.

[0007]

According to a first aspect of the present invention, there is provided a screen printing method in which a squeegee head storing a paste therein is slid on a mask plate while the paste is pressed by a paste pressing means. A screen printing method for printing a paste on a substrate through a pattern hole of a mask plate, wherein the squeegee head is pressed against the mask plate in a printing standby state before starting a printing operation in which the squeegee head is slid on the mask plate. A pressing force lowering step of lowering the pressing force by the pressing means, and a pressing step of pressing the paste by the paste pressing means in a state where the pressing force is reduced, are performed so as to execute a paste movement promoting operation. did.

According to the present invention, the pressing force reducing step for reducing the pressing force by the pressing means for pressing the squeegee head against the mask plate, and the pressing of the paste by the paste pressing means with the pressing force reduced. By executing the paste movement promoting operation including the pressing step at a predetermined timing, the movement of the paste within the squeegee head can be promoted, and the curing of the paste can be prevented.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a front view of a screen printing apparatus according to one embodiment of the present invention, FIG. 2 is a side view of the screen printing apparatus of one embodiment of the present invention, and FIG. 3 is a screen printing apparatus according to one embodiment of the present invention. FIG. 4 is an explanatory view of the movement promotion operation of the cream solder in the screen printing according to the embodiment of the present invention.

First, the structure of the screen printing apparatus will be described with reference to FIGS. 1 and 2, the substrate positioning unit 1 is configured by disposing a substrate holding unit 2 on a moving table (not shown). The substrate 3 to be screen-printed is held by a clamper 4 of the substrate holding unit 2, and by driving a moving table (not shown), the substrate 3 held by the substrate holding unit 2 is positioned in the horizontal and vertical directions. .

A screen mask 10 is provided above the positioning section 1. The screen mask 10 is configured by mounting a mask plate 12 on a holder 11, and a pattern hole 12 a corresponding to a printing portion of the substrate 3 to be printed is formed in the mask plate 12.

A squeegee head 13 is arranged on the screen mask 10 so as to be able to move up and down by a head elevating unit 20. The head elevating unit 20 includes a cylinder 22 erected on a plate member 21. The cylinder 22 is connected to the air source 18 via a valve V1 and a regulator R1. At the lower end of the rod 22a of the cylinder 22,
The squeegee head 13 is connected via the connecting member 15.

By driving the cylinder 22, the squeegee head 13 moves up and down with respect to the mask plate 12 and presses the squeegee head 13 against the mask plate 12. The head elevating unit 20 is a squeegee head 1
3 is a lifting means for raising and lowering the screen mask 3 with respect to the screen mask 10. Also, the cylinder 22 is a squeegee head 1
3 is a pressing means for pressing the mask plate 3 against the mask plate 12. At this time, the lifting / pressing control is performed by the control unit 19.
By controlling the valve V1 and the regulator R1.

Sliders 23 are fixed at both ends to the lower surface of the plate member 21 of the head elevating unit 20, and the slider 23 is slidably fitted on a guide rail 24 disposed on the upper surface of the frame 25. I have. A nut 26 is connected to the lower surface of the plate member 21, and a feed screw 27 screwed to the nut 26 is driven to rotate by a motor 28.

By driving the motor 28, the plate member 21 moves horizontally, and therefore the head lifting / lowering unit 20 is moved.
Is also moved horizontally. By driving the motor 28 with the squeegee head 13 lowered, the squeegee head 13 moves horizontally on the mask plate 12. That is, the motor 28, the feed screw 27, and the nut 26 are moving means for horizontally moving the squeegee head 13 on the mask plate 12.

At the lower part of the squeegee head 13, there is provided a printing section 14 which abuts on the surface of the mask plate 12 and fills the pattern holes 12a with the cream solder 5 as a paste. The structure of the printing unit 14 will be described with reference to FIG. In FIG. 3, reference numeral 30 denotes a main body, which is a block-shaped member elongated in the width direction of the mask plate 12. The length of the main body 30 is set to cover the width of the substrate 3 to be printed as shown in FIG. Main unit 30
Is formed with a concave portion 30a in which a cartridge 31 storing the cream solder 5 is removably mounted.

The cartridge 31 is a reservoir (paste reservoir) for the cream solder 5 in which a predetermined amount of the cream solder 5 is stored in advance, and is mounted on the main body 30 at the time of printing. A pressure plate 32 for pressing the cream solder 5 inside is fitted into the opening on the upper surface of the cartridge 31. The pressure plate 32 is connected to the rod 16a of the cylinder 16 disposed above, and by driving the cylinder 16,
The pressure plate 32 moves up and down in the cartridge 31.

The cylinder 16 is connected to an air source 18 via a valve V2 and a regulator R2. The regulator R2 can set the pressure of the air supplied to the cylinder 16 according to the pressure setting signal from the control unit 19, and pushes down the cream solder 5 in the cartridge 31 at a predetermined pressure.

The bottom of the cartridge 31 has a cream solder 5
The extruding plate 31a has a large number of openings 31b. When the pressing plate 32 is pressed downward by the cylinder 16, the cream solder 5 in the cartridge 31 is pressed, and the pressing plate 31a is pressed.
Through the opening 31b. Cylinder 1
The pressing plate 6 and the pressing plate 32 serve as a paste pressing means for pressing the cream solder 5 which is a paste. The control of the pressurization at this time is performed by controlling the valve V2 and the regulator R2 by the control unit 19.

At the bottom of the main body 30, a cartridge 31 is provided.
A diaphragm plate 34 provided with a large number of openings 34a is mounted similarly to the extrusion plate 31a. When the cream solder 5 is extruded by the cylinder 16, the extruding plate 3
It passes through the opening 31b of 1a and the opening 34a of the diaphragm plate 34 in two stages and moves downward. The extruded cream solder 5 forms a space formed below the main body 30, that is, two scraping members 36 </ b> A and 36 </ b> B disposed obliquely inward below the main body 30 and the lower surface of the main body 30. And arrives at the printing space 35 surrounded by.

The scraping members 36A and 36B are flexible plate-shaped members which form the front and rear walls of the printing space 35 in the squeezing direction, and the scraping members 36A and 36B when the squeegee head 13 is lowered. Is in contact with the surface of the mask plate 12. During the printing operation, the printing space 35 stores the pressurized cream solder 5 and brings the cream solder 5 into contact with the surface of the mask plate 12 through the opening between the scraping members 36A and 36B.

The pressure plate 32 is depressed so that the cartridge 31
By pressing the cream solder 5 inside, the cream solder 5 passes through the extruding plate 31a and the squeezing plate 34 and moves into the printing space 35. The flow path in the movement path of the cream solder 5 is provided with a narrowed portion whose cross-sectional area is narrowed by a number of small openings 31b and 34a, and the pressurized cream solder 5 passes through the narrowed portion. By doing
The viscosity of the cream solder 5 is reduced, and is modified to a property suitable for screen printing.

In the screen printing, the squeegee head 13 in a state where the cream solder 5 inside which has been modified to have the proper viscosity as described above is filled in the printing space 35 by the pressurizing plate 32 is pressed. Is slid on the mask plate 12. Thus, the paste in the printing space 35 is filled into the pattern holes 12a of the mask plate 12 through the openings between the scraping members 36A and 36B.

Then, by moving the squeegee head 13, the cream solder 5 is sequentially filled in the respective pattern holes 12a. When all the pattern holes 12a are filled with the cream solder, the substrate holding unit 2 is lowered to release the plate. That is, the cream solder 5 in the pattern hole 12a descends together with the substrate 3 and separates from the pattern hole 12a, whereby the screen printing of the cream solder 5 on the substrate 3 is completed.

Next, in the printing process of the cream solder 5, the movement promoting operation of the cream solder 5 is performed to promote the downward movement of the cream solder 5 in the squeegee head 13 to maintain the viscosity at an appropriate value. Will be described with reference to FIG. In screen printing using a closed squeegee head, the cream solder 5 is
Since the pressure is always pressurized from above in 3 within a predetermined pressure, the viscosity tends to increase with time. When the viscosity of the cream solder 5 increases, the fluidity decreases, and poor filling into the pattern holes at the time of screen printing tends to occur, which causes printing failure. Therefore, it is required to maintain the viscosity of the cream solder 5 appropriately. This movement promoting operation is to prevent the cream solder 5 from hardening by promoting the movement of the cream solder 5 in the squeegee head 13.

FIG. 4 shows the substrate 3 by the squeegee head 13.
This shows a print standby state before the start of squeegeeing above, in which the squeegee head 13 is located on the clamper 4 and is received from below. In the printing standby state, first, as shown in FIG.
In this state, the pressing force of the cylinder 22 on the squeegee head 13 is increased to a high pressing force F2. Thus, the scraping portions 36A, 36B of the squeegee head 13
Of the squeegee head 1
3 moves downward by this amount of bending. By this lowering, the cream solder 5 in the squeegee head 13 relatively moves upward in the squeegee head 13.

Next, as shown in FIG. 4B, the pressing force of the squeegee head 13 is reduced to a pressing force F4 smaller than F2. Accordingly, the bending of the scraping portions 36A and 36B is reduced, and the squeegee head 13 is displaced upward by the amount of the reduced bending. Then, in this state, the pressing force of the cylinder 16 is increased to a pressing force F3 larger than F1.
Thereby, the cream solder 5 in the squeegee head 13 is
Moves relatively downward in the squeegee head 13.
By repeating the operations shown in FIGS. 4A and 4B a predetermined number of times, the cream solder 5 in the squeegee head 13 repeats the forcible vertical movement. By repeating such movements, the cream solder 5 gradually increases its fluidity and is prevented from being hardened.

[0028]

According to the present invention, the pressing force reducing step for reducing the pressing force by the pressing means for pressing the squeegee head against the mask plate, and the pressing of the paste by the paste pressing means with the pressing force reduced. Is performed at a predetermined timing, so that the movement of the paste within the squeegee head can be promoted to prevent the paste from hardening.

[Brief description of the drawings]

FIG. 1 is a front view of a screen printing apparatus according to an embodiment of the present invention.

FIG. 2 is a side view of the screen printing apparatus according to the embodiment of the present invention.

FIG. 3 is a partial sectional view of a squeegee head of the screen printing apparatus according to the embodiment of the present invention;

FIG. 4 is an explanatory diagram of a movement promoting operation of cream solder in screen printing according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 3 board 5 cream solder 12 mask plate 12a pattern hole 13 squeegee head 14 printing unit 16 cylinder 19 control unit 22 cylinder 31 cartridge 32 pressure plate 35 printing space

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takahiro Fukagawa 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Terms (reference) 2C035 AA06 FC07 FD05 FD15 FD17 FD27 FD31 FD35 5E319 BB05 CD29 CD38 GG15 5E343 AA02 BB54 BB72 DD04 FF04 GG11

Claims (1)

[Claims] 1. A paste is printed on a substrate through a pattern hole of a mask plate by sliding a squeegee head having a paste stored therein on a mask plate in a state where the paste is pressed by a paste pressing means. A screen printing method, wherein in a printing standby state before the start of a printing operation in which the squeegee head slides on a mask plate, a pressing force reducing step of reducing a pressing force by a pressing unit that presses the squeegee head against the mask plate; A pressurizing step of pressing the paste by the paste pressurizing means in a state where the pressing force is reduced.