JP2005225235A - Screen printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screen printing method capable of preventing inferiority in printing caused by hardening of a paste. <P>SOLUTION: In a print preparing process for pressurizing a cream solder 5 by pushing down a pressure plate 32 with a cylinder 16 in a state wherein a squeegee head 13 is positioned outside a range of a substrate 3 on the master plate 12 in the screen printing method for printing cream solder on a substrate via a pattern hole by sliding a squeegee head 13 on a mask plate 12 while the cream solder 5 stored inside the hermetically closed type squeegee head 13 is pressurized by a pressure plate 32 on a mask plate 12, a pressurizing force with the cylinder 16 is stepwise increased to a set value F0 with the cylinder 16. Thereby, an impact to the cream solder 5 in pressurizing is prevented and hardening of the cream solder 5 is suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a screen printing method for printing paste such as cream solder or conductive paste on a substrate.

  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 in which pattern holes are formed according to a printing target portion is set on a substrate, and paste is printed on the substrate through the pattern holes of the mask plate by squeezing.

  As a screen printing squeezing method, a method using a sealed squeegee head is known. Unlike normal screen printing, this method uses a squeegee head in which the paste is stored, instead of supplying the paste directly onto the mask plate. In this method, the paste in the squeegee head is pressed through the paste contact surface by pressing the paste in the squeegee head with the paste contact surface provided on the lower surface of the squeegee head in contact with the mask plate. Is pushed in. Then, by sliding the squeegee head on the mask plate, each pattern hole is sequentially filled with paste. The present invention relates to.

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

  When such a hardened paste is supplied to the upper surface of the mask plate via the lower surface of the squeegee head, the press into the pattern holes is not performed normally, resulting in printing defects such as “fading”. As described above, the screen printing using the conventional sealed squeegee head has a problem that printing failure is likely to occur due to the curing of the paste by pressurization.

  Then, an object of this invention is to provide the screen printing method which can prevent the printing defect resulting from hardening of a paste.

  In the screen printing method of the present invention, the squeegee head storing the paste therein is slid on the mask plate in a state where the paste is pressurized by the paste pressurizing means, and is applied to the substrate through the pattern hole of the mask plate. A screen printing method for printing a paste, wherein a pressure applied by the paste pressurizing unit in a printing preparation step in which the paste is pressed by the paste pressurizing unit in a state where the squeegee head is positioned outside the substrate range on the mask plate Was gradually increased to the set value.

According to the present invention, in the printing preparation process in which the paste is pressed by the paste pressing unit in a state where the squeegee head is positioned outside the range of the substrate on the mask plate, the pressure applied by the paste pressing unit is stepped up to a set value. By increasing the thickness of the paste, it is possible to prevent the paste from being impacted during pressurization and suppress the hardening of the paste.

  Next, embodiments of the present invention will be described with reference to the drawings. 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 an embodiment of the present invention, and FIG. 3 is a screen printing apparatus according to an embodiment of the present invention. FIG. 4 and FIG. 5 are diagrams for explaining the operation of the screen printing method 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 the substrate 3 held by the substrate holding unit 2 is positioned in the horizontal direction and the vertical direction by driving a moving table (not shown). .

  A screen mask 10 is disposed above the positioning unit 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 a substrate 3 to be printed is opened in the mask plate 12.

  A squeegee head 13 is disposed on the screen mask 10 so as to be movable up and down by a head lifting unit 20. The head lifting / lowering 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. The squeegee head 13 is coupled to the lower end portion of the rod 22 a of the cylinder 22 via the coupling member 15.

  By driving the cylinder 22, the squeegee head 13 moves up and down relative to the mask plate 12 and presses the squeegee head 13 against the mask plate 12. The head elevating unit 20 is an elevating unit that elevates and lowers the squeegee head 13 with respect to the screen mask 10. The cylinder 22 is a pressing unit that presses the squeegee head 13 against the mask plate 12. The up / down / press control at this time is performed by controlling the valve V <b> 1 and the regulator R <b> 1 by the control unit 19.

  Sliders 23 are fixed to both ends of the lower surface of the plate member 21 of the head elevating unit 20, and the sliders 23 are slidably fitted to guide rails 24 disposed on the upper surface of the frame 25. A nut 26 is coupled to the lower surface of the plate member 21, and a feed screw 27 screwed into 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 squeegee head 13 coupled to the head elevating unit 20 also moves 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 moving the squeegee head 13 horizontally on the mask plate 12.

  Below the squeegee head 13, there is provided a printing unit 14 that contacts the surface of the mask plate 12 and fills the pattern holes 12 a with cream solder 5 that is 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-like member that is elongated in the width direction of the mask plate 12. The length of the main body 30 is set so as to cover the width of the substrate 3 to be printed as shown in FIG. The main body 30 is formed with a recess 30a in which the cartridge 31 storing the cream solder 5 is detachably mounted.

  The cartridge 31 is a cream solder storage part (paste storage part) in which a predetermined amount of cream solder is stored in advance, and is attached to the main body 30 during printing. A pressure plate 32 that pressurizes the internal cream solder 5 is fitted into the opening on the upper surface of the cartridge 31. The pressure plate 32 is coupled to the rod 16 a of the cylinder 16 disposed above, and the pressure plate 32 moves up and down within the cartridge 31 by driving the cylinder 16.

  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 with a predetermined pressure.

  The bottom surface of the cartridge 31 is a cream solder extrusion plate 31a, and the extrusion plate 31a has a large number of openings 31b. By pressing the pressure plate 32 downward with the cylinder 16, the lower surface of the pressure plate 32 comes into contact with the cream solder 5 in the cartridge 31 and pressurizes it, and is pushed downward through the opening 31b of the extrusion plate 31a. The cylinder 16 and the pressure plate 32 serve as paste pressurizing means for pressurizing the cream solder 5 that is a paste. The pressurization control at this time is performed by controlling the valve V2 and the regulator R2 by the control unit 19.

  A diaphragm plate 34 provided with a large number of openings 34 a is mounted on the bottom of the main body 30 in the same manner as the extrusion plate 31 a of the cartridge 31. When the cream solder 5 is pushed out by the cylinder 16, it passes through the opening 31b of the extrusion plate 31a and the opening 34a of the diaphragm plate 34 in two stages and moves downward. The extruded cream solder is formed in a space formed below the main body portion 30, that is, two scraping members 36 </ b> A and 36 </ b> B disposed obliquely inward at the lower portion of the main body portion 30 and the lower surface of the main body portion 30. The print space 35 surrounded by is reached.

  The scraping members 36 </ b> A and 36 </ b> B form front and rear walls in the squeezing direction of the printing space 35, and the lower ends of the scraping members 36 </ b> A and 36 </ b> B abut on the surface of the mask plate 12 when the squeegee head 13 is lowered. During the printing operation, the printing space 35 accommodates the pressurized cream solder 5, and the cream solder 5 is brought into contact with the surface of the mask plate 12 through the opening between the scraping members 36A and 36B.

  By pressing down the pressure plate 32 to pressurize the cream solder 5 in the cartridge 31, the cream solder 5 moves through the extrusion plate 31 a and the diaphragm plate 34 into the printing space 35. The flow path in the movement path of the cream solder 5 is provided with a throttle portion whose cross-sectional area is reduced by a large number of small openings 31b and 34a, and the pressed cream solder 5 passes through this throttle portion. As a result, the viscosity of the cream solder 5 is lowered and modified to a property suitable for screen printing.

  This screen printing apparatus is configured as described above, and the screen printing method will be described below with reference to FIGS. FIG. 4 shows the pressing process of cream solder in the printing preparation process before the start of the printing operation on the substrate. This pressurization is performed in order to sufficiently push the cream solder 5 into the print space 35 at the start of printing, and is performed by pressing down the pressurization plate 32 with the set pressure by the cylinder 16.

At this time, as shown in FIG. 4A, the cylinder 16 is actuated stepwise with the squeegee head 13 positioned outside the range of the substrate 3, and the pressurizing force F is printed as shown in FIG. 4C. It is raised stepwise to the set value F0 in the operation. This pressure control is performed by adjusting the air pressure supplied to the cylinder 16 stepwise by the regulator R2. By controlling the applied pressure, a large impact due to the pressing plate 32 being abruptly pressed against the cream solder 5 in the squeegee head 13 does not act, and the curing of the cream solder 5 due to the impact can be prevented.

  That is, in general, when a shocking pressure is applied to the cream solder, the solder particles are pressed against each other in the cream solder in the vicinity where the impact is applied. Decreases locally. For this reason, a hardened region in which the viscosity of the cream solder is increased and hardened is likely to occur in a portion where the impact is applied. Once the cured region is generated, the cured region prevents the entire flow of the cream solder. As a result, the state in which the cream solder is retained in the printing space is promoted, and the curing becomes easier to proceed.

  On the other hand, in the present embodiment, the pressurizing force is increased stepwise so that no shocking pressurizing force acts on the cream solder 5 in the pressurizing process of the cream solder 5. Therefore, in the printing preparation process shown in FIG. 4A, a hardened area due to impact does not occur in the cream solder 5 in the squeegee head 13.

  Thereafter, as shown in FIG. 4B, the squeegee head 13 moves on the mask plate 12 into the range of the substrate 3, and the cream solder is printed on the substrate 3. At this time, since the cured area of the cream solder 5 does not exist in the squeegee head 13, the flow of the cream solder 5 in the printing space 35 is not hindered in the squeezing operation after the start of printing. 5 rolls well. Thereby, hardening of the cream solder 5 in a printing process can be suppressed, and the printing defect resulting from hardening can be prevented.

  Next, with reference to FIG. 5, the pressurization to the cream solder 5 in the process of repeating the printing operation will be described. FIG. 5A shows a state where the pressurization during the printing preparation process shown in FIG. Thereafter, the squeegee head 13 moves into the range of the substrate 3 as shown in FIG. 5B, and the cream solder 5 is printed on the substrate 3 by performing a squeezing operation. At this time, the cylinder 16 pressurizes the cream solder 5 in the squeegee head 13 via the pressure plate 32.

  When the printing operation on the substrate 3 is finished and the squeegee head 13 reaches the clamper 4 outside the substrate range as shown in FIG. 5C, the supply of air pressure to the cylinder 16 is stopped and the cream solder Stop pressurizing to 5. At this time, the cylinder 16 does not move up, and the lower surface of the pressure plate 32, which is a contact portion with the cream solder 5, keeps the state in contact with the cream solder 5 in the squeegee head 13. This state continues in the same way in the plate separation step shown in FIG. 5D and the substrate unloading step performed thereafter.

  Then, as shown in FIG. 5E, pressurization by the cylinder 16 is started before the clamper 4 that clamps the newly supplied substrate 3 is raised and the printing operation is started again. Thereafter, as shown in FIG. 5 (f), the squeegee head 13 moves into the range of the substrate 3, and the cream solder 5 is printed again. In pressurization of the cream solder 5 before the start of the printing operation, pressurization is started from a state where the lower surface of the pressurization plate 32 is already in contact with the cream solder 5 in the squeegee head 13. The pressing force is transmitted to the cream solder 5 without performing the descending operation by the rod. Therefore, no impact is applied to the cream solder 5 at the start of pressurization, and the progress of curing of the cream solder 5 due to repeated impact can be prevented.

As described above, in the screen printing method shown in the present embodiment, when the cream solder 5 in the squeegee head 13 is pressed by the pressure plate 32, the impact on the cream solder 5 is alleviated as much as possible. By reducing the number of occurrences of impact, curing of the cream solder 5 caused by impact is suppressed. Thereby, generation | occurrence | production of the printing defect resulting from hardening of the cream solder 5 can be reduced.

  According to the present invention, in the printing preparation process in which the paste is pressed by the paste pressing unit while the squeegee head is located outside the substrate range on the mask plate, the pressure applied by the paste pressing unit is increased step by step to the set value. Because it can prevent the impact on the paste during pressurization and suppress the curing of the paste, it is useful in the field of screen printing technology for printing paste such as cream solder or conductive paste on the substrate. is there.

1 is a front view of a screen printing apparatus according to an embodiment of the present invention. The side view of the screen printing apparatus of one embodiment of this invention The fragmentary sectional view of the squeegee head of the screen printing apparatus of one embodiment of this invention Operation explanatory diagram of the screen printing method of one embodiment of the present invention Operation explanatory diagram of the screen printing method of one embodiment of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Board | substrate 5 Cream solder 12 Mask plate 12a Pattern hole 13 Squeegee head 14 Printing part 16 Cylinder 19 Control part 22 Cylinder 31 Cartridge 32 Pressure plate 35 Printing space

Claims (1)

A screen printing method in which paste is printed on a substrate through a pattern hole of a mask plate by sliding a squeegee head storing paste inside the mask plate in a state where the paste is pressurized by a paste pressing means. In the printing preparation process in which the paste is pressed by the paste pressing unit in a state where the squeegee head is positioned outside the substrate range on the mask plate, the pressure applied by the paste pressing unit is gradually increased to a set value. A screen printing method, characterized by:

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