JP3198699B2 - Screen printing method of cream solder - 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 printing method of cream solder for applying cream solder for soldering electronic components to a printed circuit board.

[0002]

2. Description of the Related Art Prior to surface mounting electronic components such as ICs, LSIs, capacitor chips, and resistor chips on a printed circuit board, the electronic components are soldered to electrodes of a circuit pattern on the printed circuit board by a cream solder screen printing apparatus. Cream solder is applied.

[0003] A screen printing apparatus of this kind of cream solder generally has a printed circuit board brought close to the lower surface of a screen mask and a squeegee is slid over the screen mask as shown in, for example, JP-A-4-65243. Then, cream solder is applied to a predetermined portion of the printed circuit board through a pattern hole opened in the screen mask.

FIG. 6 shows a state where cream solder is applied to a printed circuit board by a conventional screen printing apparatus. The screen mask 1 is configured by mounting a mask plate 2 on the lower surface of a frame-shaped holder 3. The printed circuit board 4 is held on a table 5. Nuts 6a and 6b are mounted on both sides of the table 5, and vertical ball screws 7a and 7b are screwed into the nuts 6a and 6b. One ball screw 7a is driven by a motor 8 to rotate. Timing pulleys 9a, 9b are mounted on the ball screws 7a, 7b.
The timing belt 10 is tuned to a and 9b.
Reference numeral 11 denotes a bearing for the ball screw 7b.

When the motor 8 is driven, one ball screw 7
a rotates, and this rotation is performed via the timing pulleys 9a and 9b and the timing belt 10 to the other ball screw 7b.
The table 5 and the printed board 4 are moved up and down with respect to the mask plate 2 by the simultaneous rotation of the ball screws 7a and 7b. Reference numeral 12 denotes a squeegee that slides on the mask plate 2, and reference numeral 13 denotes cream solder applied to the printed circuit board 4.

Next, the operation will be described. The motor 8 is rotated forward to raise the printed circuit board 4, and the upper surface of the printed circuit board 4 is brought into contact with the lower surface of the mask plate 2. Next, when the squeegee 12 is slid to the left on the mask plate 2 by a driving means (not shown), the cream solder 13 is applied to the upper surface of the printed circuit board 4 through a pattern hole (not shown) formed in the mask plate 2. Is done. Next, by reversely rotating the motor 8, the printed circuit board 4 is lowered and separated from the mask plate 2, and the application process of the cream solder 13 is completed.

[0007]

Conventionally, when the cream solder 13 is applied as described above, a slight gap (generally called "snap-off") is secured between the mask plate 2 and the upper surface of the printed circuit board 4. It had been. However,
As the pitch of electronic component leads becomes increasingly narrower,
The snap-off has been gradually reduced, and in recent years, the snap-off has become zero as shown in FIG. 6 and the upper surface of the printed circuit board 4 is brought into contact with the lower surface of the mask plate 2 to apply the cream solder 13. ing.

However, the upper surface of the printed circuit board 4 is brought into contact with the lower surface of the mask plate 2 so that the
When the coating 3 is applied, there is a problem that the cream solder 13 applied to the printed board 4 is easily deformed when the printed board 4 is lowered and separated from the mask plate 2. Next, the reason why the shape collapse occurs will be described with reference to FIG.

FIG. 7A shows a state immediately after the application of the cream solder after the sliding of the squeegee 12 is completed. The cream holes 13 are filled in the pattern holes of the mask plate 2 by sliding the squeegee 12, and the lower surface of the mask plate 2 is adhered to the upper surface of the printed circuit board 4 due to the adhesive force. Next, when the printed board 4 is lowered by rotating the motor 8 in the reverse direction, the mask plate 2 is gradually bent downward due to its own elasticity because it is stuck to the printed board 4 (see FIG. 7B). When the printed board 4 is further lowered, the mask plate 2 is peeled off from the printed board 4 at a stretch as shown in FIG. 7C, and returns to a horizontal state shown by the solid line in FIG.
Incidentally, the mask plate 2 is formed of a flexible thin metal plate having a spring property such as a stainless steel plate.

As described above, when the printed board 4 is lowered to separate the printed board 4 from the mask plate 2, the mask plate 2 is immediately removed from the printed board 4 by its own elasticity when the printed board 4 is lowered to some extent. As a result, the cream solder 13 in the pattern hole is disturbed by the impact at that time, and the plate removability is deteriorated and the shape of the cream solder 13 on the printed circuit board 4 is lost.

FIG. 8 shows a typical shape of the cream solder transferred to the printed circuit board 4. The cream solder 13a on the left is a non-defective product, and the cream solder 13b on the right is a defective product that has been deformed for the above-described reason. In this example, the edge portion thereof unnecessarily protrudes upward. Depending on the cream solder 13b that has been deformed as described above, it is difficult to correctly solder the leads of the electronic component. Such deterioration of the print-out property is remarkable when applying the cream solder at a fine pitch by the fine-pitch pattern holes, and is particularly problematic when electronic components having narrow pitch leads are surface-mounted on a printed circuit board. Become.

In the above-mentioned conventional example, the screen printing apparatus of cream solder for raising and lowering the printed circuit board 4 with respect to the screen mask 1 has been described as an example. The same problem as in the case described above occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cream solder screen printing method capable of preventing the shape of the cream solder from being lost when the printed board and the mask plate are separated.

[0014]

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for screen printing cream solder, comprising: a table disposed below a screen mask for mounting a printed circuit board; Elevating means for moving, a squeegee that slides on the upper surface of the mask plate in which the pattern holes of the screen mask are opened, and a mask plate support member that abuts on the lower surface of the mask plate to prevent downward bending of the mask plate. Prepared , this
The support member of the squeegee is separate from the mask plate.
After applying cream solder to the printed circuit board,
Lower the printed circuit board relative to the mask plate.
When separating the mask plate and printed circuit board,
The mask plate is supported from below by
The rate is prevented from sagging downward . Preferably, the support member is made of a hard plate and has a frame-shaped planar shape surrounding the pattern hole.

[0015]

In the above arrangement, the upper surface of the printed circuit board is brought into contact with the lower surface of the mask plate, and a squeegee is slid in this state to apply cream solder to the upper surface of the printed circuit board.

Next, the printed circuit board is lowered from the mask plate to separate the printed circuit board from the mask plate. In this case, the mask plate is supported by a support member, and more preferably surrounds the pattern hole.
Since the printed circuit board and the mask plate are supported by the frame-shaped support member, the portion of the mask plate where the pattern holes are formed does not bend when the printed circuit board and the mask plate are separated, and cream solder transferred from the pattern holes to the printed circuit board is not bent. The shape can be eliminated.

[0017]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a screen mask of a cream solder screen printing apparatus according to an embodiment of the present invention. The screen mask 1 is formed by mounting a mask plate 2 on a lower surface of a frame-shaped holder 3. A pattern hole 20 is formed in the center of the mask plate 2. A support member 14 is mounted on the lower surface of the mask plate 2 such that the support member 14 abuts integrally. The planar shape of the support member 14 is a frame shape, is made of a hard plate having high rigidity such as a metal plate, and is arranged so as to surround the pattern hole 20.

FIG. 2 is a perspective view of a screen printing apparatus for cream solder in one embodiment of the present invention using the screen mask 1, and FIG. 3 is a side view. Both sides of the screen mask 1 are held by a mask holder 21. The mask holder 21 is supported via brackets 24 on columns 23 erected at four corners of a base 22. The table 5 holding the printed circuit board 4 is set on the upper plate 25. The upper plate 25 is installed on a support leg 27 having a U-shaped cross section disposed on the lower plate 26.

Reference numeral 28 denotes a support table, and rods 29 are provided upright at four corners on the upper surface. Also, as shown in FIG.
A motor 31 is provided inside the support base 28. The vertical rotating shaft 32 of the motor 31 is a ball screw,
The lower plate 26 is screwed to a nut 33 mounted at the center. At the four corners of the lower plate 26, ring-shaped sliders 34 into which the rods 29 are inserted are mounted. Therefore, when the motor 31 is driven to rotate the rotating shaft 32, the lower plate 26
The printed circuit board 4 held above the lower plate 26 is guided by the rod 29 and moves up and down in the vertical direction. In this embodiment, the printed board 4 on the table 5 is moved up and down with respect to the screen mask 1. However, a screen printing apparatus that moves the screen mask 1 up and down with respect to the printed board 4 may be used.

The support 28 is placed on a Y table 35 via a plate 30. Y table 35 is X
It is installed on a table 36. Therefore, when the motor 37 of the Y table 35 is driven, the printed circuit board 4
When the motor 38 of the X table 36 is driven in the horizontal direction, the printed circuit board 4 is horizontally moved in the X direction.
By moving the printed circuit board 4 horizontally in the X direction or the Y direction in this manner, alignment with the screen mask 1 is performed.

This screen printing apparatus is configured as described above. Next, the operation will be described with reference to FIG. FIG. 4A shows that the printed circuit board 4 is moved through the pattern holes 20 by sliding the squeegee 12 to the left.
Immediately after the cream solder 13 is applied. Next, as shown in FIG. 4B, the printed board 4 is lowered and separated from the mask plate 2 by rotating the motor 8 in the reverse direction. In this case, the support member 14 is attached to the lower surface of the mask plate 2. As a result, the mask plate 2 attached to the upper surface of the printed circuit board 4 does not bend downward due to the adhesive force of the cream solder 13, and the portion of the mask plate 2 where the pattern holes 20 are formed maintains a horizontal posture. Because it is peeled off from the printed circuit board 4
The cream solder 13 in the pattern hole 20 is transferred to the printed circuit board 4 with good plate removal, and does not lose its shape.

FIG. 5 shows another embodiment of the present invention.
An arm 41 extends inward from the mask holder 21, and the support member 14 is attached to a tip portion of the arm 41. Reference numeral 42 denotes a stop screw of the arm 41, and reference numeral 43 denotes a support rib of the support member 14. That is, in this embodiment, the support member 14 and the mask plate 2 are separate bodies, and the mask plate 2 is supported by the upper surface of the support member 14 being in contact with the lower surface of the mask plate 2.

Also, when cream solder 13 is applied to printed circuit board 4 by squeegee 12, motor 8
Is driven to lower the printed circuit board 4, thereby separating the mask plate 2 and the printed circuit board 4. At this time, the bending of the mask plate 2 below the support member 14
Therefore, the same operation and effect as those of the first embodiment can be obtained.

[0025]

As described above, according to the present invention, when the application of the cream solder is completed and the mask plate of the screen mask is separated from the printed circuit board, the portion of the mask plate where the pattern holes are formed has the cream. The support member prevents the solder from bending downward due to the sticking force of the solder, making it extremely easy to remove the solder from the pattern holes of the cream solder. it can.

[Brief description of the drawings]

FIG. 1 is a perspective view of a screen mask of a cream solder screen printing apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of a cream solder screen printing apparatus according to an embodiment of the present invention.

FIG. 3 is a side view of a cream solder screen printing apparatus according to an embodiment of the present invention.

FIG. 4A is a partial side view of a cream solder screen printing apparatus according to an embodiment of the present invention during operation. FIG. 4B is a partial side view of the cream solder screen printing apparatus according to an embodiment of the present invention during operation.

FIG. 5 is a partial side view of a screen printing apparatus for cream solder according to another embodiment of the present invention.

FIG. 6 is a side view of a conventional cream solder screen printing apparatus.

FIG. 7A is a partial side view of a conventional cream solder screen printing apparatus during operation. FIG. 7B is a partial side view of a conventional cream solder screen printing apparatus during operation. Partial side view of the device during work

FIG. 8 is a cross-sectional view of a cream solder applied by a conventional cream solder screen printing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Screen mask 2 Mask plate 3 Holder 4 Printed circuit board 5 Table 12 Squeegee 13 Cream solder 14 Support member 20 Pattern hole 31 Motor 32 Rotating shaft 33 Nut

Claims (2)

(57) [Claims] 1. A table arranged below a screen mask for mounting a printed circuit board, elevating means for elevating the printed circuit board relative to the screen mask, and pattern holes of the screen mask are formed. It includes a squeegee sliding the upper surface of the mask plate, and a support member of the mask plate to prevent deflection downward of the mask plate in contact with the lower surface of the mask plate, the support member
Is separate from the mask plate, and the squeegee
After applying cream solder to the printed circuit board,
Lower the substrate relative to the mask plate.
When separating the mask plate and the printed circuit board,
The mask plate is supported by the support member from below.
To prevent the mask plate from bending downward
Cream solder screen printing method characterized in that as. 2. The cream solder screen printing method according to claim 1, wherein said support member is made of a hard plate and has a frame-shaped planar shape surrounding said pattern hole.