JP3989065B2 - Screen printing method and screen printing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fully automatic screen printing apparatus that prints a printing paste such as a conductor paste or cream solder on a printed material such as a printed circuit board with high accuracy in an electronic circuit board mounting process.
[0002]
[Prior art]
In recent years, screen printing apparatuses have been used in cream solder printing processes in electronic circuit board mounting processes. As electronic components have become smaller, electronic circuit mounting boards have become increasingly finer, and correspondingly, solder cream High-precision printing is also required.
[0003]
An example of a conventional screen printing method and screen printing apparatus will be described with reference to FIGS. FIG. 3 is a schematic view showing a conventional screen printing apparatus. In the figure, reference numeral 1 denotes a printed circuit board, which is positioned and fixed by a stage unit 3. A screen plate 4 fixed by a screen frame 5 is disposed above the stage unit 3. 6 is a printing paste placed on the screen plate 4, and the left squeegee 7 and the right squeegee 8 are horizontally moved while contacting the screen plate 4, whereby the printing paste 6 is printed on the printed circuit board 1. Further, the left squeegee 7 and the right squeegee 8 are supported by squeegee holders 9c and 9d that are movable up and down by the print head 9 via elevating members 9a and 9b, and are configured to be movable in the vertical and horizontal directions.
[0004]
A screen printing method for printing on the printed circuit board 1 using the screen printing apparatus having the above configuration will be described with reference to FIG.
After the printed circuit board 1 is positioned and fixed by the stage unit 3, the printed circuit board 1 is raised to a position just below the screen plate 4 fixed to the screen frame 5 by lifting means (not shown). At the time of alignment, positioning is performed so that the opening pattern of the screen plate 4 matches the land pattern of the printed circuit board 1. Thereafter, the left squeegee 7 (see FIG. 4A) in the standby position is lowered vertically (see FIG. 4B) until it abuts on the screen plate 4 as the printing start position (see FIG. 4B). The left squeegee 7 is moved horizontally and the printing paste 6 is printed on the printed board 1 (see FIG. 4C). Thereafter, the printed circuit board 1 is released from the stage unit 3, and the printed circuit board 1 is unloaded. Thereafter, the left squeegee 7 is raised from above the screen plate 4 and moved to a standby position for the next printing (see FIG. 4D).
[0005]
The above operation is repeated, and printing is performed on the printed circuit board 1 alternately by the left and right squeegees 7 and 8.
[0006]
[Problems to be solved by the invention]
However, in the conventional screen printing method as shown in FIGS. 3 and 4, printing is performed while rolling the printing paste 6 on the screen plate 4 using the squeegees 7 and 8, and after printing, the squeegees 7 and 8 are vertically aligned. In order to raise in the direction, the printing paste 6 adheres as if it hangs down from the squeegees 7 and 8 (see FIG. 4D).
[0007]
Thereafter, when the next printing is started, the squeegees 7 and 8 are lowered in the vertical direction and come into contact with the screen plate 4, so that the printing paste 6 that is attached to the tip of the squeegees 7 and 8 and hangs down is removed. Each time the number of printing is repeated at the upper printing start position, the accumulated printing paste 6 wraps around the back of the squeegees 7 and 8 and is dragged on the screen plate 4 together with the squeegees 7 and 8 during printing. In some cases, the tear was caused on the opening of the screen plate 4 (see FIG. 4C). Then, the torn print paste 6 supplies more than necessary print paste 6 onto the printed circuit board 1, which is one of the factors that cause bridges and solder balls on the printed circuit board 1 after reflow.
[0008]
Further, when the back surface of the screen plate 4 is cleaned, the printing paste 6 left after the opening portion of the screen plate 4 wraps around from the top of the screen plate 4 to the back surface of the screen plate 4 by the vacuum force. As a result, defects such as bleeding and solder balls may occur when the next printed board 1 is printed.
[0009]
Since the printed circuit board 1 for supporting high-density mounting in recent years contains many fine patterns and narrow pitch patterns, the printing paste 6 has also been improved, but there are various types such as low viscosity and high viscosity. And the conventional screen printing method as described above cannot cope with the printed circuit board 1 having a fine pattern or a narrow pitch pattern.
[0010]
SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a screen printing method and a screen printing apparatus that can reduce the occurrence of defects in a printed circuit board due to a printing paste that wraps around the squeegee during printing.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a screen printing method in which a printing paste is screen-printed on a printed board from above a screen plate, and a squeegee is brought into contact with the screen plate from a predetermined standby position above the screen plate. After starting the printing operation, the squeegee is attached to the tip of the squeegee so that the printing paste hanging from the squeegee wraps around the squeegee in the printing direction. When moving down in the direction opposite to the printing direction of the squeegee and making it come into contact with the screen plate, and moving down in the direction opposite to the printing direction after this screen plate contact, stick to the tip of the squeegee Depending on the amount of the printing paste that hangs down, the distance moved in the opposite direction, the squeegee moving speed at that time, and the Set the Chigi lowering speed, and moves diagonally downward squeegee at a predetermined set angle.
[0012]
By this screen printing method, it is possible to reduce the occurrence of defects on the printed circuit board due to the printing paste that has sneak outside the squeegee during printing.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The invention according to claim 1 is a screen printing method in which a printing paste is screen-printed on a printed board from above the screen plate, and printing is performed by bringing the squeegee into contact with the screen plate from a predetermined standby position above the screen plate. The printing direction after contacting the screen plate so that the printing paste hanging from the squeegee at the tip of the squeegee wraps around the squeegee's printing direction at the start of printing. When moving down in the opposite direction to the screen plate and moving it in the direction opposite to the printing direction after this screen plate contact, it drops and adheres to the tip of the squeegee. Depending on the amount of printing paste being used, the distance traveled in the opposite direction, the squeegee moving speed at that time, and the squeegee descending at that time Set the degrees, and moves diagonally downward squeegee at a predetermined set angle.
[0014]
According to the above method, when the squeegee comes into contact with the printing start position on the screen plate, the printing paste that has adhered to the tip of the squeegee and hangs around to the printing direction side inside the squeegee. Accumulation of printing paste can be reduced, and it is no longer the case that printing paste wraps around the outside of the squeegee and is dragged at the time of printing and torn off during printing. Ball generation can be prevented. Further, according to the above method, the squeegee descending angle when the squeegee comes into contact with the printing start position on the screen plate is adjusted, and the printing paste adhered to the tip of the squeegee and hangs down regardless of the amount. Since it is possible to wrap around the inside well, it is possible to reliably reduce the accumulation of printing paste at the start position of the squeegee, and the printing paste wraps around the outside of the squeegee and is dragged during printing as in the conventional case. This prevents the occurrence of bridges, blurring, and solder balls, which are defects during printed circuit board printing.
[0019]
According to a second aspect of the present invention, there is provided a stage portion for positioning and fixing a printed circuit board, a screen plate disposed above the stage portion, and a squeegee that is movably disposed on the screen plate and prints a printing paste. a lifting means for raising and lowering the squeegee against the screen plate, is moved in a direction opposite to a moving means for moving in the opposite direction, and orientation of the squeegee and print direction and print direction a squeegee against the screen plate Setting means for setting the distance to be moved, the squeegee moving speed at that time, and the squeegee descending speed at that time, and from the predetermined standby position above the screen plate to the position where printing starts by contacting the screen plate A printing paste that hangs down with the squeegee attached to the tip of the squeegee at the start of printing. In such a way as to wrap around the printing direction side of the squeegee, a screen printing apparatus and a control means for causing the operation of lowering while moving in a direction opposite to the printing direction after the screen plate abutting, wherein the control means The squeegee is set in a predetermined manner by setting the distance to move in the opposite direction, the squeegee moving speed and the squeegee lowering speed at that time, according to the amount of the printing paste hanging on the tip of the squeegee. It is controlled to move diagonally downward at an angle .
[0020]
According to the above configuration, the squeegee is placed at the tip of the squeegee at the start of printing for performing the operation of lowering the squeegee from the predetermined standby position above the screen plate to the position at which printing starts by contacting the screen plate. At the tip of the squeegee, it is moved downward while moving in the direction opposite to the printing direction after the screen plate contact, so that the attached printing paste hangs around to the printing direction side of the squeegee. The printing paste that is attached and hangs down can be brought into contact with the screen plate while wrapping around in the printing direction side of the squeegee, which can reliably reduce the accumulation of the printing paste at the start position of the squeegee. In other words, the printing paste does not wrap around the outside of the squeegee and is dragged during printing and torn off in the middle. Bridge and bleeding is bad at the time of door board printing, it is possible to prevent the occurrence of solder balls. Further, according to the above configuration, the squeegee descending angle when the squeegee comes into contact with the printing start position on the screen plate is adjusted, and the printing paste adhered to the tip of the squeegee and hangs down regardless of the amount. Since it is possible to wrap around the inside well, it is possible to reliably reduce the accumulation of printing paste at the start position of the squeegee, and the printing paste wraps around the outside of the squeegee and is dragged during printing as in the conventional case. This prevents the occurrence of bridges, blurring, and solder balls, which are defects during printed circuit board printing.
[0025]
Hereinafter, an embodiment of a screen printing method and a screen printing apparatus according to the present invention will be described with reference to FIGS.
First, a screen printing apparatus used in the screen printing method of the present embodiment will be described with reference to FIG.
[0026]
The apparatus of this embodiment is shown in FIG. Note that components having the same functions as those of the conventional screen printing apparatus are denoted by the same reference numerals, description thereof is omitted, and operation description is also simplified.
[0027]
The left squeegee 7 and the right squeegee 8 are attached to squeegee holders 9c and 9d, respectively, and these squeegee holders 9c and 9d are supported by the print head 9 through the elevating members 9a and 9b so as to be movable up and down. The left squeegee 7 and the right squeegee 8 are moved up and down by a lifting motor 10 as lifting means via lifting members 9 a and 9 b and as moving means via a screw shaft 15 screwed into the print head 9. It is moved in the horizontal direction by the horizontal drive motor 11. The operations of the lift motor 10 and the horizontal drive motor 11 are controlled by a controller 12 as a control means, and the controller 12 has an arithmetic function and a storage function in addition to a control function. The controller 12 is also connected to a data input device 13 and a sensor 14 as a measuring means used for measuring the distance from the tip of the squeegees 7 and 8 to the upper surface of the screen plate 4.
[0028]
Prior to the actual printing operation, the tips of the squeegees 7 and 8 are brought into contact with the screen plate 4, and the distance L 2 from the standby position of the squeegees 7 and 8 at that time is detected by the sensor 14. The information is stored in a storage unit (not shown). In addition, printing is performed in advance under the same conditions as the actual printing operation on a test basis, and the amount of the printing paste 6 (see FIG. 1) that hangs down by adhering to the tip of the squeegees 7 and 8 is observed. Depending on the amount, the distance L1 that moves in the direction opposite to the printing direction, the squeegee moving speed V1 at that time, and the squeegee lowering speed V2 at that time are input from the data input device 13 and set. . The distance L1, the squeegee moving speed V1, and the squeegee descending speed V2 may be calculated by the controller 12 according to the amount of the printing paste 6 and automatically set.
[0029]
The squeegees 7 and 8 are controlled so as to be moved in the direction opposite to the printing direction until immediately before the tips of the squeegees abut against the screen plate 4, while the opposite is the moment when the squeegee 7 abuts against the screen plate 4. It is set by the controller 12 so as to complete the moving operation in the direction.
[0030]
An operation of printing on the printed circuit board 1 using the screen printing apparatus having the above configuration will be described with reference to FIG.
The printed circuit board 1 is positioned and fixed by the stage unit 3 and then lifted up to a position just below the screen plate 4 fixed to the screen frame 5 by a lifting means (not shown). Thereafter, as shown in FIG. 1 (a), the direction opposite to the printing direction (FIGS. 1 (a) and (b)) until the left squeegee 7 at the standby position abuts on the screen plate 4 as the printing start position. In the left direction).
[0031]
That is, at the start of printing, the left squeegee 7 is moved down from a predetermined standby position above the screen plate 4 to a position where printing starts by contacting the screen plate 4 as shown in FIG. The left squeegee 7 is set at a predetermined angle according to the squeegee moving speed V1 and the squeegee lowering speed V2 set based on the horizontal distance L1 and the vertical distance L2 opposite to the printing direction. Moved to the lower left.
[0032]
Thereby, when the left squeegee 7 approaches and comes into contact with the printing start position on the screen plate 4, the printing paste 6 that is attached to the tip of the left squeegee 7 and hangs down is shown in FIG. As shown in the figure, it can be reduced that the printing paste 6 wraps around the inner side (right side) of the left squeegee 7 and is deposited at the printing start position by the left squeegee 7. In addition, since the operation of moving obliquely downward of the left squeegee 7 is set according to the amount of the printing paste 6 hanging from the tip of the left squeegee 7, the printing paste 6 is placed inside the left squeegee 7. It is possible to more reliably perform wrapping around. As a result, the print paste does not wrap around the outside of the squeegee as in the past, and it is not dragged during printing and tearing in the middle, preventing the occurrence of bridges, bleeding, and solder balls that are defective during printed circuit board printing. it can.
[0033]
Further, at this time, until the front end of the left squeegee 7 is brought into contact with the screen plate 4, it is moved in the direction opposite to the printing direction. Control is performed by the controller 12 to complete the operation. As described above, since the squeegee movement in the direction opposite to the printing direction is completed by the time the left squeegee 7 comes into contact with the screen plate 4, the printing direction is changed with the left squeegee 7 in contact with the screen plate 4. The movement in the opposite direction is prevented so that the edge of the tip of the left squeegee 7 is not dragged on the screen plate 4 and the wear life of the left squeegee 7 is not shortened.
[0034]
Thereafter, the left squeegee 7 is moved horizontally in the right direction by the print head 9, and the printing paste 6 is printed on the printed circuit board 1 (see FIG. 1C). Thereafter, the printed circuit board 1 is released from the stage unit 3, and the printed circuit board 1 is carried out. Thereafter, the left squeegee 7 is raised from above the screen plate 4 and moved to the standby position for the next printing (see FIG. 1D).
[0035]
Thereafter, the same movement operation is performed so that the right squeegee 8 is opposite to the left squeegee 7 in the left-right direction, and such operations are repeated to alternately print the left and right squeegees 7, 8. Printing is performed on the substrate 1.
[0036]
Printing evaluation was actually performed by this screen printing apparatus and screen printing method, and compared with the conventional screen printing apparatus and screen printing method.
Specifically, the viscosity of the printing paste 6 used for the evaluation is about 200 Pa · s, the flat squeegees 7 and 8 are set at an attachment angle of 60 degrees, and the distance from the tip of the squeegees 7 and 8 to the screen plate 4 L2 is 10 mm, squeegee movement distance L1 is 30 mm, squeegee movement speed V1 is 45 mm / sec, squeegee lowering speed V2 is 10 mm / sec, and printing is performed by lowering squeegees 7 and 8 vertically as usual ( L1 = 0 mm, L2 = 10 mm, V1 = 0 mm / sec, V2 = 10 mm / sec).
[0037]
The printing paste 6 is attached to the tip of either squeegee 7, 8 and the amount of attachment is about 8-9mm below the tip of the squeegee. Numbers were compared. Of the 50 printed circuit boards printed by the respective methods, those printed by the screen printing apparatus and method of the present invention have no defects, whereas those printed by the conventional screen printing method. Five defects occurred.
[0038]
Thus, it has been confirmed that the screen printing apparatus and method of the present invention can prevent the occurrence of bridges, blurring, and solder balls, which are defects during printed circuit board printing.
[0039]
【The invention's effect】
As described above, according to the screen printing method of the present invention, at the start of printing, the squeegee is moved from a predetermined standby position above the screen plate to a position where the squeegee comes into contact with the screen plate and starts printing. Move the squeegee down to the screen plate while moving it in the direction opposite to the printing direction after contacting the screen plate so that the printing paste hanging from the tip of the squeegee wraps around the printing direction of the squeegee. By making contact, it is possible to reduce the accumulation of printing paste at the start position of the squeegee, and it is no longer the case that the printing paste wraps around the outside of the squeegee and is dragged at the time of printing and torn in the middle. It is possible to prevent the occurrence of bridging, bleeding, and solder balls that are defective at times. Further, in the above screen printing method, depending on the amount of the printing paste hanging on the tip of the squeegee, the distance moved in the direction opposite to the printing direction, the squeegee moving speed at that time, and the squeegee descending speed at that time And by moving the squeegee diagonally downward at a predetermined setting angle, various types of printing pastes such as those with low viscosity and high ones, as well as printed boards with fine patterns and narrow pitch patterns, Regardless of the amount of the printing paste that has adhered to the tip of the squeegee and hung down, the printing paste can be satisfactorily wrapped inside the squeegee.
[0042]
Further, in the screen printing apparatus, lifting means for moving the squeegee up and down with respect to the screen plate, moving means for moving the squeegee with respect to the screen plate in the printing direction and the direction opposite to the printing direction, and the squeegee above the screen plate. At the start of printing, the squeegee is attached to the tip of the squeegee and the printing paste that hangs down is printed on the squeegee. By providing a control means for performing an operation of moving down in the direction opposite to the printing direction after the screen plate contact so as to wrap around in the direction side, bridges and blurring that are defective at the time of printed circuit board printing, Generation of solder balls can be prevented. The screen printing apparatus further includes setting means for setting a moving distance when moving the squeegee in a direction opposite to the printing direction, a squeegee moving speed at that time, and a squeegee lowering speed at that time, and the control means includes The squeegee is set in a predetermined manner by setting the distance to move in the opposite direction, the squeegee moving speed and the squeegee lowering speed at that time, according to the amount of the printing paste hanging on the tip of the squeegee. By controlling it to move diagonally downward at an angle, various types of printing pastes, such as those with low or high viscosity, and printed boards with fine patterns or narrow pitch patterns, adhere to the tip of the squeegee and hang down. Regardless of the amount of the printing paste that has been used, it is possible to wrap around the inside of the squeegee.
[Brief description of the drawings]
FIGS. 1A to 1D are diagrams showing respective steps of a screen printing method according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a main part of the configuration of the screen printing apparatus according to the embodiment of the present invention.
FIG. 3 is a schematic view showing a main part of the configuration of a conventional screen printing apparatus.
FIGS. 4A to 4D are diagrams showing respective steps of a conventional screen printing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Printed circuit board 3 Stage part 4 Screen plate 6 Printing paste 7 Left squeegee 8 Right squeegee 9 Print head 9a, 9b Squeegee part raising / lowering member 9c, 9d Squeegee holder 10 Lifting motor (lifting means)
11 Motor for horizontal movement (moving means)
12 Control unit (control means)
13 Data Input Device 14 Sensor (Measuring Means)

Claims (2)

A screen printing method in which a printing paste is screen-printed on a printed circuit board from above a screen plate, and an operation of lowering a squeegee from a predetermined standby position above the screen plate to a position to start printing by contacting the screen plate When starting printing, move the squeegee in the direction opposite to the printing direction after the screen plate contact, so that the printing paste hanging from the tip of the squeegee wraps around the printing direction of the squeegee. Depending on the amount of printing paste that adheres to the tip of the squeegee and hangs down when it is lowered while being brought into contact with the screen plate and moved down in the direction opposite to the printing direction after the screen plate is brought into contact Then, set the distance to move in the opposite direction, the squeegee moving speed at that time, and the squeegee lowering speed at that time. Screen printing method characterized by moving diagonally downward di at a predetermined set angle. A stage portion for positioning and fixing the printed circuit board, a screen plate disposed above the stage portion, a squeegee that is movably disposed on the screen plate and prints printing paste, and the squeegee is raised and lowered with respect to the screen plate. Elevating means for moving, moving means for moving the squeegee with respect to the screen plate in the printing direction and the direction opposite to the printing direction, moving distance when moving the squeegee in the direction opposite to the printing direction, and the squeegee at that time Setting means for setting the moving speed and the squeegee lowering speed at that time, and at the time of starting printing, the squeegee is lowered from a predetermined standby position above the screen plate to a position where printing starts by contacting the screen plate In addition, the squeegee sticks to the tip of the squeegee and the printing paste that hangs down is on the squeegee's print direction side. So as to go Ri, a screen printing apparatus and a control means for causing the operation of lowering while moving in a direction opposite to the printing direction after the screen plate abutting, the control means, the squeegee tip portion In accordance with the amount of printing paste that is attached to and drooping, the distance moved in the opposite direction, the squeegee moving speed at that time, and the squeegee descending speed at that time are set, and the squeegee is tilted downward at a predetermined setting angle. A screen printing apparatus that is controlled to move.

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