JP2006088709A - The screen printing method and screen printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To offer the method of screen printing and the screen printing apparatus which prevent printing paste stuck on the squeegee nozzle tips from creeping around to the back-side of the nozzle and from the poor printing performance by which the printing screen being dragged and torn at the opening of the screen thus causing poor printing on the printing base plate. <P>SOLUTION: When the printing process begins where the apparatus drops the squeegee 7 and the squeegee 8 from the predetermined stand-by position above the screen plate 4 down to the position to contact the screen plate 4, the squeegee 7 and the squeegee 8 are to move diagonally downward and contact the screen plate 4 in the direction opposite to the printing direction after the squeegees contact the screen plate 4. By this printing method, the apparatus diminishes the poor printing performances on the printing base plate 1 caused by the excessive printing paste 6 which creeps around to the backside of the squeegee 7 and squeegee 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  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.

  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.

  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 can be moved up and down by the print head 9 via lifting members 9a and 9b, and are configured to be movable in the vertical and horizontal directions. Note that this type of screen printing apparatus is disclosed in, for example, Patent Document 1.

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) at the standby position is lowered vertically (see FIG. 4B) until it abuts on the screen plate 4 at 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 carried out. Thereafter, the left squeegee 7 is raised from above the screen plate 4 and moves to a standby position for the next printing (see FIG. 4D).

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.
JP-A-4-14288

  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).

  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 applied to the screen plate 4. 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.

  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.

  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.

  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.

  In order to solve the above problems, the present invention is a screen printing method in which a printing paste is screen-printed on a printed board from above a screen plate, and the squeegee is applied to the screen plate from a predetermined standby position above the screen plate. At the start of printing in which the operation of lowering to the position where printing starts is brought into contact, the squeegee is moved obliquely downward in the direction opposite to the printing direction after the screen plate is brought into contact with the screen plate. .

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.
The present invention also provides a screen having 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. In the 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 a printing direction and a direction opposite to the printing direction, and a predetermined standby above the screen plate Control means for moving the squeegee at a position obliquely downward in a direction opposite to the printing direction after the screen plate contact by the squeegee to contact the screen plate is performed.

  According to the screen printing method of the present invention, the squeegee is removed from the predetermined standby position above the screen plate to the position where the squeegee comes into contact with the screen plate and starts to be printed. It is possible to reduce the accumulation of printing paste at the squeegee start position by moving it diagonally downward in the direction opposite to the printing direction after contact, and making it contact the screen plate. The paste wraps around and is not dragged at the time of printing and tearing off in the middle, preventing the occurrence of bridging, bleeding, and solder balls, which are defective during printed circuit board printing.

  Further, in the screen printing apparatus, there are 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 above the screen plate. Control means for performing an operation of moving the squeegee at a predetermined standby position obliquely downward in a direction opposite to the printing direction after the screen plate contact by the squeegee to contact the screen plate. Even for various types of printing pastes, such as those with low or high viscosity, and printed boards with fine patterns or narrow pitch patterns, the printing paste that hangs down and adheres to the tip of the squeegee regardless of the amount of squeegee. It can wrap around inside well.

  The present 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 the squeegee is printed by contacting the screen plate from a predetermined standby position above the screen plate. When starting printing to perform the operation of lowering to the position where the printing is started, the squeegee is moved obliquely downward in the direction opposite to the printing direction after the screen plate contact to contact the screen plate.

  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 the inside of the squeegee, so that the printing paste accumulates at the squeegee start position. This eliminates the possibility of printing paste wrapping around the outside of the squeegee and being dragged during printing and tearing along the way, preventing the occurrence of bridging, bleeding and solder balls that are defective during printed circuit board printing. be able to.

  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. The screen printing apparatus has a lifting and lowering means for moving the squeegee up and down with respect to the screen plate, a 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 above the screen plate. Control means for performing an operation of moving the squeegee in a predetermined standby position obliquely downward in a direction opposite to the printing direction after the screen plate contact by the squeegee to contact the screen plate It is.

  According to the above configuration, the squeegee at the predetermined standby position above the screen plate is moved obliquely downward in the direction opposite to the printing direction after the screen plate is in contact with the squeegee to contact the screen plate. By performing the operation, the squeegee can be brought into contact with the screen plate while the printing paste hanging from the tip of the squeegee wraps around the inside of the squeegee. Accumulation can be reliably reduced, and the print paste does not wrap around the outside of the squeegee and is dragged during printing and tearing in the middle as in the past. Bridges, smudges, and solder balls that are defective during printed circuit board printing Can be prevented.

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.

  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.

  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.

  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.

  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.

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.
After the printed circuit board 1 is positioned and fixed by the stage portion 3, it is raised 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).

  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.

  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.

  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.

  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).

  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.

  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).

  Printing paste 6 is attached to the tip of both squeegees 7 and 8, and the amount of attachment is about 8 to 9 mm 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.

  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.

(A)-(d) is a figure which shows each process of the screen printing method in one embodiment of this invention, respectively. It is the schematic which shows the principal part of the structure of the screen printing apparatus in one embodiment of this invention. It is the schematic which shows the principal part of the structure of the conventional screen printing apparatus. (A)-(d) is a figure which shows each process of the conventional screen printing method, respectively.

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 Elevating motor (elevating 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,
At the start of printing, the operation of lowering the squeegee from a predetermined standby position above the screen plate to a position to start printing by contacting the screen plate,
A screen printing method in which a squeegee is moved obliquely downward in a direction opposite to the printing direction after contact with the screen plate to contact the screen plate. In a screen printing apparatus having 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.
Elevating means for elevating and lowering the squeegee relative to the screen plate;
Moving means for moving the squeegee with respect to the screen plate in the direction opposite to the printing direction and the printing direction;
Control for moving the squeegee at a predetermined standby position above the screen plate obliquely downward in a direction opposite to the printing direction after the screen plate contact by the squeegee to contact the screen plate. And a screen printing apparatus.

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