Patent Grant
9352409
1. Technical Field
An aspect of the present invention relates to a screen printing machine for forming a print of paste such as cream solder on a board. Another aspect of the present invention relates to an electronic component mounting system including the screen printing machine.
2. Description of Related Art
Screen printing is known as a method for forming a print of paste such as cream solder or conductive paste on a board in an electronic component mounting process. In this method, a paste print is formed on a board through pattern holes that are formed so as to conform to print subject portions. A paste print is formed on a board that is set on the bottom surface of a mask plate by filling the pattern holes with paste by a squeegeeing operation of moving a spatula-shaped squeegee member in a horizontal direction with its bottom end pressed against the mask plate.
In recent years, with the demand of productivity increase and increased difficulty of printing due to reduction of the pitches of printing portions on boards, it has become an important issue to supply sufficient amounts of paste to printing portions even in the case of a high-speed squeegeeing operation. One means for satisfying this requirement is a method that uses two kinds of squeegee members, that is, a filling squeegee and a scraping squeegee (refer to JP-A-H11-042763, for example). In the method disclosed in JP-A-H11-042763, two scraping squeegees are provided, which are elevated or lowered being driven via drive shafts of a vertical driving device. Further, a filling squeegee which is also elevated or lowered being driven via a drive shaft of the vertical driving device is provided between the two scraping squeegees.
In a squeegeeing operation, the filling squeegee is moved over the mask plate in a state that a prescribed clearance is set between the bottom end of the filling squeegee and the mask plate. This makes it possible to supply sufficient amounts of paste to printing portions on a board by increasing the filling pressure at the time of filling the pattern holes with paste by means of the filling squeegee. Paste remaining on the mask plate after passage of the filling squeegee is scraped off by the scraping squeegees.
In screen printing using the above filling squeegee, to keep the print quality constant, it is important to set the clearance between the bottom end of the filling squeegee and the mask plate. However, in the above related art technique, the height of the filling squeegee is adjusted such that a control device causes the drive shaft of the vertical driving device to go up or down on the basis of output information of a reaction detector attached to the drive shaft. This results in problems that the machine becomes complex in configuration and is increased in cost.
In view of the above, an object of aspects of the present invention is to provide a screen printing machine which is simplified in configuration and reduced in cost while the quality of a paste print formed on a board is kept high, as well as an electronic component mounting system including the screen printing machine.
According to an aspect of the present invention, there is provided a screen printing machine for forming, on a board, a print of paste supplied to a mask plate having pattern holes in a state where the board contacts the mask plate, the screen printing machine including: a filling squeegee which is held to have a given clearance with respect to the mask plate, and which fills the pattern holes with the paste by moving the filling squeegee relative to the mask plate in a printing direction; an urging member which urges the filling squeegee toward the mask plate such that at least the given clearance is maintained; and a scraping squeegee which is held to maintain a given interval from the filling squeegee in the printing direction, and which scraps off paste remaining on the mask plate after passage of the filling squeegee by moving the scraping squeegee together with the filling squeegee in the printing direction.
According to aspects of the present invention, it is simplify the configuration of machine and reduce the cost thereof while the quality of a paste print formed on a board is kept high.
First, the overall configuration of an electronic component mounting system will be described with reference to
The screen printing machine M1 screen-prints paste layers on electronic component joining electrodes formed on a board. The print inspection machine M2 performs print inspection including judgment as to whether or not the paste layers formed on the board are in good print states and detection of deviations of printed paste layers from electrodes. The electronic component mounting machines M3 and M4 mount electronic components on the board on which the paste layers have been formed by the screen printing machine M1. The reflow machine M5 joins the electronic components to the board by melting the solder by heating the electronic-components-mounted board according to a prescribed temperature profile.
Next, the overall configuration of the screen printing machine M1 will be described with reference to
The structure of the first Z-axis table 9 will be described below. A horizontal base plate 9a is held by an elevation guide mechanism (not shown) in an elevatable manner on the side of the top surface of a horizontal base plate 8a which is disposed on the top surface of the θ-axis table 8. The base plate 9a is elevated and lowered by a Z-axis elevation mechanism which rotationally drives plural feed screws 9c with a motor 9b via a belt 9d.
Vertical frames 9e are erected from the base plate 9a and a board conveying mechanism 11 is held by top end portions of the vertical frames 9e. The board conveying mechanism 11 is equipped with two conveyance rails which are disposed parallel with a board conveying direction (in the X direction which is perpendicular to the paper surface of
Next, the structure of the second Z-axis table 10 will be described. A horizontal base plate 10a is disposed between the board conveying mechanism 11 and the base plate 9a so as to be elevatable along an elevation guide mechanism (not shown). The base plate 10a is elevated and lowered by a Z-axis elevation mechanism which rotationally drives plural feed screws 10c with a motor 10b via a belt 10d. A board receiving member 13 whose top surface is a receiving surface for holding the substrate 12 is disposed on the top surface of the base plate 10a.
By driving the second Z-axis table 10, the board receiving member 13 can be elevated or lowered with respect to the board 12 being held by the board conveying mechanism 11. The receiving surface of the board receiving member 13 comes into contact with the bottom surface of the board 12 and thereby supports the board 12 from below. A clamp mechanism 14 is disposed on the top surfaces of the board conveying mechanism 11. The clamp mechanism 14 is equipped with two clamp members 14a which are opposed to each other in the left-right direction. The board 12 is fixed being pressed from both sides by advancing one clamp member 14a by means of the drive mechanism 14a.
Next, a description will be made of the screen printing mechanism 5 which is disposed over the board positioning unit 4. As shown in
As shown in
As shown in
As shown in
Next, the structures of the squeegee units 18 of the squeegee head 17 will be described with reference to
The first squeegee unit 32 has a first member 34 and a second member 35 which are inclined (overhang) in an advancement direction (printing direction; indicated by arrow “a” in
As shown in
As shown in
As shown in
One side surface of each attachment member 43 is formed with a recess 43b (see
Next, filling squeegee holders 47 which are attached to the respective attachment members 43 will be described in detail. As shown in
A flat-plate-shaped projection 48 is formed in such a manner as to adjoin the recess 43b of the associated attachment member 43 and project from a bottom end portion of the attachment connection portion 47a of each filling squeegee holder 47 toward the attachment member 43 in a state that the filling squeegee holder 47 is attached to the attachment member 43. The spring 45 is located over the projection 48 and pushes down the projection 48 to urge the filling squeegee holder 47 downward.
An opening 49 which extends approximately vertically is formed through the attachment connection portion 47a at such a position as to correspond to the projection 46 of the associated attachment member 43. The width of the opening 49 is approximately equal to the diameter of the projection 46. The filling squeegee holder 47 is connected to the attachment member 43 so as to be slidable approximately in the vertical direction relative to the attachment member 43 by fitting the projections 46 and 48 into the opening 49 and the recess 43b, respectively.
To attach the filling squeegee holder 47 to the attachment member 43, a plate-like member 50 for covering part of the side surface of the attachment member 43 is prepared (see
As shown in
As shown in
As seen from the above description, the projection 46 and the opening 49 serve as a filling squeegee guiding means for guiding the filling squeegee 41 approximately vertically over a prescribed stroke. While the filling squeegee 41 assumes an ordinary posture without being pushed up externally, the filling squeegee holder 47 takes such a posture that the projection 46 is in contact with the top end of its opening 49 (see
The squeegee holding portion 47b has an extension 53 which projects in the squeegeeing direction at the bottom. Setting is made so that the bottom end of the squeegee holding portion 47b including the bottom end of the extension 53 is located at the same height as the bottom end 33c of the scraping squeegee 33 in a state that the filling squeegee 41 assumes the ordinary posture. The extension 53 functions as a damming means for preventing a phenomenon that paste flows out of the mask plate 15 going around the side edge of the filling squeegee 43 during a squeegeeing operation.
Next, a sectional shape of the filling squeegee 41 will be described with reference to
When the filling squeegee 41 is slid over the mask plate 15, the pattern holes 15a are filled with paste while its flow passage is narrowed gradually as the position goes along the non-corner-cut surface 60B and the corner-cut surface 60A in the direction opposite to the squeegeeing direction. The corner-cut surface 60A and the non-corner-cut surface 60B are a first filling surface and a second filling surface, respectively, for filling the pattern holes 15a of the mask plate 15 with paste. The filling squeegee 41 is formed with the plural (two) filling surfaces which form different angles with the top surface of the mask plate 15.
In a squeegeeing operation, the filling time of filling the pattern holes 15a with paste P can be made longer by increasing the length L1, in the squeegeeing direction, of the corner-cut surface 60A which is a closest surface to the mask plate 15. In the following description, the angle α1 which is formed by the corner-cut surface 60A and the top surface of the mask plate 15 will be referred to as a “filling angle” and the angle α2 which is formed by the non-corner-cut surface 60B and the top surface of the mask plate 15 will be referred to as an “attack angle.”
The holding position of the filling squeegee 41 with respect to the filling squeegee holder 47 is set so that in a state that the filling squeegee 41 assumes the ordinary posture its corner C3 which is the lowest point of the filling squeegee 41 is higher than the bottom end 33c of the scraping squeegee 33 by Δh1. More specifically, the screws 57 are screwed into the screw holes 41a and 41b through the attachment holes 52a and 52b, respectively, in a state that the filling squeegee 41 is located at such a position that the corner C3 of the filling squeegee 41 is higher than the bottom end 33c of the scraping squeegee 33 by Δh1. Therefore, when the bottom end 33c of the scraping squeegee 33 is brought into contact with the mask plate 15 by lowering one squeegee unit 18 by the corresponding squeegee elevation mechanism 19, a clearance of Δh1 is obtained between the filling squeegee 41 and the mask plate 15. The spring 45 urges the filling squeegee 41 toward the mask plate 15 in such a manner that at least the prescribed clearance of Δh1 is maintained. A paste printing operation is performed in this state using the filling squeegee 41 and the scraping squeegee 33. How a printing operation is performed will be described later.
Next, a height adjustment mechanism for adjusting the upper limit height of the filling squeegee 41 when the filling squeegee 41 is pushed up will be described with reference to
In a state that the first squeegee unit 32 and the second squeegee unit 40 are fastened to each other, a bottom surface 54b, having the bottom opening of the screw hole 54a, of each screw holder 54 is located over a top surface 41c of the filling squeegee 41. Therefore, when the filling squeegee 41 is pushed up, the bottom surface 54b of the screw holder 54 or the bottom end of the threaded shank 55a of the screw 55 comes into contact with a top surface 41c of the filling squeegee 41 and thereby restricts upward movement of the filling squeegee 41.
As shown in
As seen from the above description, the screws 55 serve as stoppers for restricting displacement of the filling squeegee 41 in such a direction that it goes away from the mask plate 15. The screw holders 54 serve as fixing members for fixing the stoppers over the filling squeegee 41. The fixing position of each stopper above the filling squeegee 41 can be adjusted by the corresponding fixing member.
The attachment member 43 is formed with a pin-shaped contact portion 56 at such a position as to be opposed to the screw holder 54 (also see
The configuration of the screen printing machine M1 according to the embodiment has been described above. Next, a printing operation will be described with reference to
First, as soon as a board 12 is carried in to a prescribed printing position by the board conveying mechanism 11, as shown in
Subsequently, as shown in
In a printing operation, as shown in
As described above, since the flow passage area of paste P is decreased gradually, the filling pressure that occurs in filling paste P into the pattern holes 15a is increased, whereby a sufficient amount of paste P can be supplied to the electrodes 12a (print targets) of the board 12. Since the filling squeegee 41 has the corner-cut surface 60A, the filling time of filling the pattern holes 15a with (by pushing) paste P can be increased, a sufficient amount of paste P can be supplied to the electrodes 12a of the board 12 even in the case of high-speed printing.
During a printing operation, a part (denoted by symbol Pa), not having been pushed into the pattern holes 15a by the filling squeegee 41, of the paste P flows out through the clearance Δh1. Since the printing operation is performed in the state that the clearance Δh1 is formed, the ability to filling the pattern holes 15a with paste P can be increased further. The paste Pa that has flown out through the clearance Δh1 is scraped off by the scraping squeegee 33. That is, the scraping squeegee 33 scrapes off the paste Pa remaining on the mask plate 15 after passage of the filling squeegee 41.
During a printing operation, the filling squeegee 41 receives, via the paste P, force (reaction force) F that serves to push it up. Since the filling squeegee 41 is urged downward by the springs 45, the filling squeegee 41 moves in the printing direction while its position relative to the mask plate 15 varies according to the amount of paste P captured by itself (i.e., the magnitude of the reaction force received by it) and the states (e.g., warp and inclination) of the top surface of the mask plate 15.
As described above, since a printing operation is performed with the filling squeegee 41 urged downward, reduction of the paste filling pressure is prevented and hence good print quality can be secured. Furthermore, since it is not necessary to employ an inspection device for electrically detecting reaction force that acts on the filling squeegee 41 using a central processing unit (control unit) unlike in the conventional case, the configuration of the screen printing machine M1 can be simplified and the machine cost can thereby be lowered while the quality of a paste print formed on a board 12 is kept high.
Still further, the clearance Δh1 in the initial state can be changed by adjusting the screwing positional relationship between the attachment holes 52a and 52b formed in the squeegee holding unit 47b of each filling squeegee holder 47 and the screwing holes 41a and 41b formed in the filling squeegee 41.
Next, modifications that relate to the sectional shape of the filling squeegee will be described with reference to
The filling squeegee 41A shown in
The filling squeegee 41B shown in
The filling squeegee 41C shown in
In the above-described manners, filling surfaces having various sizes and various filling angles and attack angles can be obtained by cutting away desired corner portions of the rectangular basic shape (vertical sectional shape) and further cutting away a portion including a resulting apex. It is noted that a sufficient amount of paste P can be supplied to the electrodes 12a of a board 12 by increasing the filling time of filling the pattern holes 15a with paste P by increasing the lengths L1, L2, L3, and L4 in the squeegeeing direction of the filling surfaces (corner-cut surfaces 60A, third filling surface 41Aa, fifth filling surface 41Ba, and seventh filling surface 41Ca) each of which forms the filling angle with the top surface of the mask plate 15.
Capable of simplifying the machine configuration and lowering the machine cost while keeping the quality of a paste print formed on a board high, aspects of the invention is particularly useful when applied to the field of electronic component mounting.
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