JP3513779B2 - Screen printing method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screen device for printing a viscous printing material with a squeegee through a screen having a plurality of apertures having a predetermined print pattern on a plate-shaped printing material.

[0002]

2. Description of the Related Art In a screen printing apparatus, a scan
The liner is slid linearly in contact with the upper surface of the screen, and the sliding causes the viscous printing material to move.
It is indispensable as a mechanical element for forcibly introducing it into a plurality of pattern openings in the hole, but as it is described in, for example, Japanese Patent Publication No. 1-19275, it has a rubbery elasticity. A flexible body formed of a relatively thick plate has been widely and generally used. And
In the screen printing using such a squeegee, as described in the publication, generally, the squeegee is reciprocated once while making contact with the upper surface of the screen, so that each time A method of ending the printing process was adopted.

Conventionally known screen printing apparatuses are of the so-called single squeegee type having a single squeegee, and so-called double squeegee having a pair of squeegees. Is known as a type,
The apparatus disclosed in Japanese Patent Publication No. 19275/1989 is a single squeegee type, and the latter double squeegee type is disclosed in, for example, Japanese Patent Laid-Open No. 61-209158. Mention may be made of the disclosed device. The one disclosed in JP-A-61-209158 has a first squeegee and a second squeegee, both of which have a large wall thickness.
The printing process is completed each time by reciprocating. In this respect, the single scan is performed.
Although the same type as that of the first type, the first squeegee is used on the outward path and the second squeegee is used on the return path, and the same squeegee is reciprocally printed. The printing method is different from the single squeegee type.

[0004]

In the known technique as described above, in which the printing process is completed each time by reciprocating the squeegee once, the time required for the reciprocating movement of the squeegee is the following. -As long as the moving speed of J is constant, it will be at least twice as long as the time required for one-way movement in the forward or return path. Therefore, in order to enable high-speed screen printing, it is necessary to speed up the moving speed of the squeegee, but in order to obtain a good printing effect, it is necessary to speed up the speed. There are limits naturally.

Next, regarding the conventionally known flexible squeegee as described above, it is a printing material having a relatively low viscosity, for example, a viscosity of 0.2 to 2.0 × 10 ⁸ cP ( It is said that there are few points to be particularly problematic in the case of screen printing printing ink, adhesive, etc. of about centipoise) and when high precision or high density printing is not particularly required. You may However, a printing material having a high viscosity, for example, an alloy powder made of lead, tin or the like and a high-viscosity liquid flux are kneaded to form a cream-like solder paste having a viscosity of ≧ 700,000 cP. When screen printing certain printing materials, and when high precision or high density printing is required,
The use of a flexible squeegee such as the previously known squeegee for screen printing causes various inconveniences as described below.

That is, for example, when a chip electronic component is mounted on a printed circuit board, screen printing of a solder paste to the board is performed prior to the mounting work. First, since the solder paste has a very high viscosity and the squeegee is flexible, the degree of flexural deformation of the squeegee during screen printing is inevitably large. As shown in A),
The larger the hole 1A of the screen 1, the larger the degree of deformation and projection of the tip of the squeegee N into the hole 1A, and accordingly, as shown in FIG. 1B, the printed circuit board. The depressions on the upper surface of the printed film S'of the solder paste S printed on P tend to increase, and secondly, the printing pressure of the flexible squeegee N on the screen 1, that is, its Since the sliding contact pressure when the tip portion comes into contact with the surface of the screen 1 and slides is relatively weak, the forced introduction of the solder paste S having high viscosity into the hole 1A of the screen 1 is not allowed. As the hole 1A becomes smaller, it tends to become more difficult, and as the viscosity of the solder paste S becomes higher, a larger bending load acts on the tip of the squeegee N. Since the degree of flexural deformation also becomes larger, the tip of the squeegee N A subscription - a gap between the emissions 1, the solder from the gap Bae - flux separated from the solder particles are stringent S or its composition components Li - and click,
Inconvenient situations such as band-like accumulation on the upper surface of the screen 1 as a residue are likely to occur, and thirdly, since the solder paste has a high viscosity, the squeegee S tip portion or its periphery is likely to occur. The solder paste S sticks to the area (see FIG. 1 (C)), and the contact surface accuracy or adhesion of the squeegee S to the screen 1 becomes poor, which adversely affects the printing effect.

The present invention has been made in view of the above-mentioned problems, and has made screen printing highly efficient, highly accurate, and
It is a main object of the present invention to provide a screen printing apparatus which can achieve high density, and which is particularly suitable for screen printing solder paste for mounting chip-shaped electronic components on a printed circuit board. .

In order to achieve the above object, a screen printing apparatus according to the invention of claim 1 comprises a squeegee device having a housing in which a pair of front and rear squeegees are suspended and projecting, and a screen having a plurality of pattern openings. A screen printing apparatus for printing a viscous printing material on a flat plate-shaped printing object surface by using the squeegee device to repeatedly reciprocate in the front-rear direction along the screen upper surface, and each forward and backward path and While allowing each different printing material to perform printing in the return path, during each printing step, while moving the following squeegee while contacting the upper surface of the screen,
In a screen printing apparatus in which a preceding squeegee is floated from the upper surface of the screen to a predetermined height, the housing is fixed to a rectangular top plate extending in a direction orthogonal to its moving direction and both end portions of the top plate. Rectangular parallelepiped housing composed of opposed side walls and a bottom plate pivotably supported between the opposed side walls around a horizontal axis and provided with an opening for supplying a printing material to the upper surface of the screen. That is, the pair of squeegees are made of thin strip steel plates having high elasticity and rigidity, and the lower end portions thereof are formed into a circular arc shape in cross section, and are expanded outward from each other on the bottom plate. It is provided so as to project in an open manner, so that it can be swung around the horizontal axis integrally with the bottom plate, and the forward movement of the squeegee device. And at each end point of the return path, the squeegee to be followed is pressed against the upper surface of the screen as the direction of movement is changed to the opposite direction, and the squeegee to be preceded is lifted off from the upper surface of the screen. In this case, two pneumatic actuators that operate to swing and displace the bottom plate are vertically attached to each of the front and rear sides of the housing.

The screen printing apparatus according to the present invention is characterized in that, in the first aspect, the strip-shaped steel sheet is produced from an alloy steel strip used as a thin leaf spring material. It is a thing.

For further advantageous embodiments of the device according to the invention, reference is made to the respective claims 3-8.

[0011]

In the screen printing apparatus according to the present invention,
Since the squeegee device has a horizontal reciprocating movement, the preceding squeegee of the pair of squeegees does not come into contact with the screen and floats from the upper surface thereof. Therefore, the squeegee does not act as a squeegee, and only the squeegee following the other one comes into contact with the upper surface of the screen and slides to perform a screen printing action. The details will be described later in the description of the embodiments.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A screen printing method and apparatus according to the present invention will be described in detail below with reference to the accompanying drawings showing an example in which the apparatus is applied to a solder paste screen printing apparatus.

In the drawings, A is a squeegee device, 1 is a metal screen having a plurality of pattern openings 1A, and 2 is a metal screen.
Is a housing of the squeegee device A, 3 is a pair of horizontally extending parallel guide rails, and the squeegee device A follows the guide rails 3 along with a belt drive mechanism (Fig. (Not shown) allows it to reciprocate in the front-back direction.

The housing 2 of the squeegee device A has a rectangular top plate 4 extending at right angles to its moving direction, opposing side walls 5 and 5 fixed to both ends of the top plate 4, and the opposing side walls 5 ,. 5 is composed of a bottom plate 7 pivotably supported around a horizontal axis through a pivot 6 in the center of the lower part of each inner wall surface of 5, and an opening 8 is formed in the center of the bottom plate 7. As a whole, it is formed as a rectangular parallelepiped open type housing in which both front and rear surfaces are entirely opened.

The bottom plate 7 of the housing 2 has front and rear sides thereof.
A squeegee holder with squeegee mounting parts 7A and 7B provided at the ends.
Is configured as loaders, the said squeegee mounting section squeegee 9A having both rigidity and elasticity, 9B are respectively suspended projected. As well understood from FIGS. 2 to 4 to 7 to 8, in the illustrated example, the squeegees 9 </ b> A and 9 </ b> B are projected on both front and rear sides of the squeegee holder 7 in a state of being expanded and inclined outward respectively. Has been done, specifically,
As shown in FIG. 5, the squeegee holder 7 projecting downward.
Upper end formed on the outer lower part of the squeegee mounting parts 7A, 7B
Fitted in fitting recesses 7C each having a locking step portion 7C '
And a first tightening plate 10 that is pressure-welded to the outside thereof
A and 10B and the second fastening plates 11A and 11B, which are superposed on the outer sides of the fastening plates 10A and 10B, are tightly sandwiched by tightening with a plurality of fastening screws 12.

The squeegees 9A and 9B are preferably formed of a thin strip-shaped steel plate made of a steel plate having high elasticity and rigidity such as a carbon steel strip or an alloy steel strip used as a thin leaf spring material. , The bottom edges 9A 'and 9B' that come into contact with the upper surface of the screen 1 are each formed into a circular arc shape in cross section in order to minimize friction when sliding in contact with the upper surface of the screen. . The thickness of the squeegees 9A and 9B is
It is desirable that the thickness is 0.5 mm or less, and when using a steel strip having high elasticity and rigidity as described above, it is possible to reduce the thickness to about 0.1 to 0.05 mm. Even with an extremely thin thickness, it is possible to exhibit excellent practicality as a squeegee during the printing operation. The squeegees 9A and 9B may be formed of a reinforced synthetic resin having excellent mechanical properties and scientific properties or an engineering plastic of nylon type or fluororesin type instead of the thin steel plate as described above. It is desirable that the product has mechanical strength comparable to that of a thin steel plate.

Reference numerals 13A and 13B denote squeegees 9A and 9B.
The elastic plates 13 </ b> A and 13 </ b> B are used to reinforce each B and absorb or reduce the vibration of the squeegee during screen printing. In the illustrated example, these elastic plates 13 </ b> A and 13 </ b> B are as shown in FIGS. The second tightening plate 1
A locking step portion 11 is formed on the upper end formed on the lower inside of 1A, 11B.
Respectively fitted into the fitting recesses 11C with C ', and
With the second tightening plate and the first tightening plates 10A and 10B,
Firmly be clamped respectively Te, the lower end squeegee 9
A and 9B are elastically abutted on the outer side surfaces,
During screen printing, the vibration of the squeegee that adversely affects the printing result can be effectively absorbed or mitigated by so-called plate-to-plate friction. These elastic plates 13A and 13B are squeegees 9A and 9B as described above.
It can be produced with the same material as the above, and multiple sheets can be used if necessary.

Reference numerals 14A, 14A and 15A, 15A
Are pneumatic actuators, which are vertically mounted on both front and rear sides of the housing 2 of the squeegee device A, as a drive mechanism for alternately swinging the bottom plate 7 around the horizontal axis of the pivot shaft 6. . Actuator 14A,
15A piston rods 14A 'and 15A' are provided at their lower ends with pushers 14A "and 15A", respectively, which actuate the actuator 14A or 15A and move the piston rod 14A 'or 15A' downward. Then, the presser 14A ″ or 15A ″ is the second tightening plate 1 described above.
The bottom plate 7 of the housing 2 is pressed against the upper end surface 11A 'or 11B' of 1A or 11B to oscillate in a counterclockwise or clockwise direction over a predetermined angular range with the pivot shaft 6 as a fulcrum in FIG. 4 (FIG. 7). And 8). This alternating swinging motion of the bottom plate 7 is controlled by a sequence control mechanism connected to the circuit of a compressor (not shown) of the actuators 14A and 15A, and the forward and backward paths of the squeegee device A are controlled. It is performed every time the moving direction is changed to the opposite direction at each end point, and the actuators 14A, 15A
Among the pair of squeegees 9A and 9B, a squeegee to be followed along with the direction change is placed on a printed circuit board (hereinafter, simply referred to as a board) P.
While making contact with the upper surface of the screen 1, the squeegee to be preceded is disengaged from the upper surface of the screen and operated so as to be levitated to a predetermined height. Therefore, in the screen printing apparatus according to the present invention, only the squeegee 9A or 9B, which will follow after each direction change, comes into contact with the upper surface of the screen 1 and slides, and the screen Perform printing.

The screen printing apparatus according to the present invention is constructed so that the printing process can be completed once in each of the forward path and the backward path by reciprocating the squeegee apparatus A once. The printed substrate P is transferred at the end of each printing process on the outward and return paths of the device A,
It then comprises a mechanism (not shown) for setting a new substrate to be printed in the printing position.

Next, the operation of the screen printing apparatus according to the present invention constructed as above will be described with reference to FIGS.
This will be described with reference to (D).

As shown in FIG. 9A, the print table 1 is moved up and down by a vertical movement mechanism (not shown).
When the substrate P, which is an object to be printed, is set on 6, the metal screen 1 is placed on the upper surface of the substrate P, and the squeegee device A is horizontally moved in the direction of the arrow X from the position shown in the drawing. The screw 9B slides while being pressed against the upper surface of the screen 1 with a predetermined force by the actuator 15A, and the screen 9B slides.
Screen an appropriate amount of solder paste S supplied on the upper surface of
It is forcibly introduced into the opening 1A of the substrate 1 and the printed film S'is formed at a predetermined portion of the substrate P through the opening. When the squeegee device A reaches the end point of the movement in the X direction indicated by the imaginary line, that is, the end point of the outward path, one printing process is completed. During the forward printing process, the preceding squeegee 9A is levitated from the upper surface of the screen 1 to a predetermined height, so that the solder paste S ahead of the preceding squeegee 9A is squeezed. As the device A moves, the tip and screen of the preceding squeegee 9A move.
Through the gap 17 formed between the upper surface of the
It is introduced between the pages 9A and 9B, and is screen printed by the trailing squeegee 9B.

When the forward printing process is completed as described above, the printing table 16 is lowered as shown in FIG. 9B, and the printed substrate P is transferred to the next mounting process. Instead, a new substrate is supplied and set on the print table 16. By the time the new substrate P is set in this way, the squeegee device A is ready to move in the direction of the arrow Y opposite to the forward path, and this time, as shown in FIG. 9C. , The preceding squeegee 9A is moved downward by the actuator 14A on the outward path to become a backward squeegee, while the backward squeegee 9B.
Becomes the preceding squeegee, and the backward screen printing is performed by the squeegee 9A. FIG. 9D shows a state in which the squeegee device A has completed the printing process on the return path and has begun the process of exchanging the substrate P. After going through this process, the squeegee device A returns to the state shown by the solid line in FIG. 9 (A), and the next printing process is started. In this way, the squeegee device completes the printing process twice for each round trip.

FIGS. 10 (A) and 10 (B) respectively illustrate the contact surface state of the squeegees 9A and 9B with respect to the metal screen 1 and the finished state of printing in the apparatus of the present invention. Since the squeegees 9A and 9B have both elasticity and rigidity and do not cause excessive deformation, the projection of the tip of the screen 1 due to the deformation into the opening 1A does not occur, so that the opening 1A is formed. Regardless of the size, the uniform and good printing can be always realized.

The screen used for screen printing of solder paste is generally made of a stainless steel plate, and the thickness of the screen is made as thin as possible. By making it small and narrowing the space between adjacent holes, it is possible to perform high-precision and high-density screen printing with a minute printing pattern, but if that is truly possible. In addition to these conditions, it is necessary to improve the squeegee itself in order to achieve this. The apparatus of the present invention aims to increase the speed of screen printing, and in consideration of this point, a squeegee having both rigidity and elasticity is adopted, and its thickness is made as thin as possible. It is also intended to enable high-precision and high-density screen printing using an extremely thin metal screen having fine pattern openings.

The opening 8 of the bottom plate 7 described above has a
The viscous printing material can be replenished to the upper surface of the screen 1 through the apparatus A even during the operation of the apparatus A, which is intended to facilitate the replenishment and improve the efficiency of the printing work. It was done.

[0026]

Since the present invention is constructed as described above, it has the following effects.

A screen printing apparatus according to a first aspect of the present invention uses a squeegee device having a housing in which a pair of front and rear squeegees are provided so as to project downward, and a screen having a plurality of pattern openings formed therein, for viscous printing on the surface of a flat substrate. A screen printing device for printing a material, wherein the squeegee device is reciprocally moved back and forth in the front-rear direction along the upper surface of the screen, and printing is performed on each different printed material in each forward and backward path. Let's do it,
During each of the printing steps, the squeegee that follows the one of the pair of squeegees is moved while being in contact with the upper surface of the screen, while the preceding squeegee is floated from the upper surface of the screen to a predetermined height. In the printing apparatus, the housing includes a rectangular top plate extending in a direction orthogonal to a moving direction of the housing, opposite side walls fixed to both end portions of the top plate, and a shaft swingable around a horizontal axis between the opposite side walls. The pair of squeegees are formed as a rectangular parallelepiped housing that is supported and has a bottom plate provided with an opening for supplying the printing material to the upper surface of the screen. It is made of a steel plate, and its lower end is formed into a circular arc shape in cross section, and is protruded from the bottom plate in a manner in which they are expanded outward from each other. The squeegee device is designed so that it can be swung integrally with the bottom plate about a horizontal axis, and at each end point of the forward and return paths of the squeegee device, the movement direction is switched to the opposite direction. In addition, a pneumatic actuator that operates to oscillate and displace the bottom plate in order to press the squeegee to be followed by the direction change and press the squeegee to precede and to float from the screen upper surface. Since it is characterized in that two vertical attachments are provided on each of the front and rear sides of the housing, the speed of screen printing can be increased, the efficiency thereof can be markedly increased, and the accuracy of screen printing can be improved. The density of the squeegee can be increased and the upper surface of the screen and the lower end of each squeegee rounded in an arcuate cross section In addition to touch area becomes very small, the friction when the squeegee slides becomes extremely small, thereby reducing the risk of damage to the squeegee to the screen, it is possible to improve the contact surface accuracy with respect to the screen of the squeegee.

According to the second and third aspects,
The strip-shaped steel sheet forming the squeegee is produced from a steel strip having a large elasticity and rigidity used as a thin leaf spring material, and has an extremely strong physical strength, so that the squeegee can be made extremely thin. Therefore, according to the present invention, it is possible to obtain a suitable screen printing apparatus that is particularly suitable for screen printing of a solder paste for mounting a chip-shaped electronic component on a printed circuit board.

According to the fifth and sixth aspects,
Since the vibration of the squeegee during screen printing is absorbed or mitigated by the elastic plate, even when printing a high-viscosity printing material such as solder paste, the sliding state of the elastic plate is combined with the reinforcing function of the elastic plate. It is stable, and it is possible to effectively prevent the occurrence of print unevenness due to fluctuations in printing pressure due to vibration, and since the bending stress acting on the squeegee can be dispersed by the elastic plate, its service life is increased. It can be extended.

According to the seventh and eighth aspects,
The squeegee is fitted in a fitting recess provided with an engaging step portion on the upper end formed in the squeegee mounting portion of the bottom plate, and is held at a narrow pressure by a tightening plate that is tightened with a tightening screw. It is possible to reliably prevent the dropout.

[Brief description of drawings]

FIG. 1 (A) is a partially longitudinal front view showing a sliding contact state of a known flexible squeegee with a screen.

FIG. 1 (B) is a partially longitudinal front view showing a finished state of printing by the squeegee shown in FIG. 1 (A).

FIG. 1 (C) is a side view showing a state in which a solder paste is attached to a known flexible squeegee.

FIG. 2 is a perspective view of a squeegee device according to an embodiment of the present invention.

FIG. 3 is a perspective view of the squeegee device of FIG. 2 as viewed obliquely from below.

FIG. 4 is a side view of the squeegee device of FIG.

FIG. 5 is an enlarged vertical sectional view of a mounting portion of a squeegee.

FIG. 6 is a partially enlarged vertical sectional view of a squeegee.

FIG. 7 is a side view of the main part showing the printing operation in the outward path of the squeegee device shown in FIG.

FIG. 8 is a side view of the main part showing the printing operation in the returning path of the squeegee device shown in FIG.

FIG. 9 (A) is a schematic side view showing an operating state of the screen printing apparatus according to the embodiment of the present invention.

FIG. 9 (B) is a schematic side view showing a state in which the squeegee device shown in FIG. 9 (A) has completed the printing process on the outward path.

FIG. 9 (C) is a schematic side view showing a state in which the squeegee device starts a printing process in a return path.

FIG. 9 (D) is a schematic side view showing a state in which the squeegee device has completed the printing process on the return path.

FIG. 10 (A) is a partially longitudinal sectional front view showing a contact surface state of a steel plate squeegee with respect to a screen in the device of the present invention.

FIG. 10 (B) is a partially longitudinal front view showing a finished state of printing by the squeegee shown in FIG. 10 (A).

[Explanation of symbols]

1 screen 1A screen opening A squeegee device 2 housing 3 guide rail 4 top plate 5 Opposing side walls 6 Axis 7 Bottom plate 8 openings 9A squeegee 9B squeegee 9A 'Squeegee bottom edge 9B 'Squeegee bottom edge 13A elastic plate 13B elastic plate 14A Actuator 14A 'Piston rod 15A actuator 15A 'piston rod P printed circuit board S solder paste S'printed film

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Claims (8)

(57) [Claims] 1. A screen printing apparatus for printing a viscous printing material on the surface of a flat substrate by using a squeegee device having a housing in which a pair of front and rear squeegees are suspended and protruding and a screen having a plurality of pattern openings formed therein. And
The squeegee device is repeatedly moved back and forth along the upper surface of the screen in the front-rear direction, and printing is performed on each different printed material in each of the forward and backward passes of each reciprocating movement, and each printing step. Among the pair of squeegees, in the screen printing apparatus, the trailing squeegee is moved while contacting the upper surface of the screen, while the preceding squeegee is floated from the upper surface of the screen to a predetermined height. The housing has a rectangular top plate extending in a direction orthogonal to its moving direction, opposed side walls fixed to both ends of the top plate, and pivotally supported between the opposed side walls so as to be swingable about a horizontal axis, and It is formed as a rectangular housing consisting of a bottom plate provided with an opening for supplying printing material to the upper surface of the screen. Together are made of a thin steel strip the pair of squeegee made large elasticity and stiffness, respectively,
The lower end thereof is formed into a circular arc shape in cross section, and is projectingly provided on the bottom plate in such a manner that the bottom plate is expanded outwardly, so that the bottom plate can be swung integrally with the bottom plate around a horizontal axis. And the squeegee to be followed is pressed against the upper surface of the screen each time the moving direction is changed to the opposite direction at each of the forward and backward ends of the squeegee device. , Two pneumatic actuators are vertically installed on each of the front and rear sides of the housing, the pneumatic actuators operating to swing and displace the bottom plate so that a squeegee to be preceded is detached from the upper surface of the screen and floated. Screen printing device. 2. The screen printing apparatus according to claim 1, wherein the strip-shaped steel plate is produced from an alloy steel strip used as a thin leaf spring material. 3. The screen printing apparatus according to claim 1, wherein the strip-shaped steel plate is produced from a carbon steel strip used as a thin leaf spring material. 4. The thickness of each squeegee is 0.1 to 0.05 m.
The screen printing apparatus according to claim 1, 2 or 3, wherein m is m. 5. The screen printing apparatus according to claim 1, wherein at least one outer plate of each squeegee is in pressure contact with each elastic plate. 6. The screen printing device according to claim 5, wherein the elastic plate is made of a thin steel plate. 7. Each squeegee is fitted in a fitting recess having a locking step at the upper end formed in the squeegee mounting portion of the bottom plate, and is held at a narrow pressure by a tightening plate tightened with a screw from the outside. The screen printing device according to claim 1, wherein the screen printing device is a screen printing device. 8. The screen printing device according to claim 5, wherein the elastic plate is made of a material similar to that of the squeegee.