JP3275445B2 - 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 substrate, cream solder for soldering the electronic components to electrodes of a circuit pattern on a printed circuit board by a screen printing apparatus. Is applied.

[0003] Generally, this type of screen printing apparatus opens a hole in a mask by bringing a substrate close to the lower surface of the mask and sliding a squeegee on the mask as shown in, for example, JP-A-4-65243. The cream solder is applied to a predetermined portion of the substrate through the patterned hole.

FIG. 6 shows a state in which cream solder is applied to a substrate by a conventional screen printing apparatus. The screen mask 31 is configured by mounting a mask 32 on a lower surface of a mask frame 33. The substrate 34 is held on a table 35. Nuts 36a and 36b are mounted on both sides of the table 35,
Vertical ball screws 37a and 37b are screwed into a and 36b. One ball screw 37a is driven by a motor 38 to rotate. Timing pulleys 39a and 39b are mounted on the ball screws 37a and 37b, and a timing belt 40 is tuned to the timing pulleys 39a and 39b. 41 is a bearing of the ball screw 37b.

When the motor 38 is driven, one ball screw 37a rotates, and this rotation is performed by the timing pulley 39a,
The data is transmitted to the other ball screw 37b via the timing belt 39b and the timing belt 40, and both the ball screws 37a and 37b rotate simultaneously, whereby the table 35 and the substrate 34 move up and down with respect to the mask 32. Reference numeral 42 denotes a squeegee that slides on the mask 32, and reference numeral 43 denotes cream solder applied to the substrate 34.

Next, the operation will be described. The motor 34 is rotated forward to raise the substrate 34, and the upper surface of the substrate 34 is
2 is brought into contact with the lower surface. Next, when the squeegee 42 is slid leftward on the mask 32 by a driving means (not shown), the cream solder 43 is applied to the upper surface of the substrate 34 through a pattern hole (not shown) opened in the mask 32. Next, by reversely rotating the motor 38, the substrate 34 is lowered and separated from the mask 32, and the step of applying the cream solder 43 is completed.

Conventionally, when the cream solder 43 is applied as described above, a slight gap (generally called "snap-off") is secured between the mask 32 and the upper surface of the substrate 34. However, as the pitch of the leads of the electronic parts has become increasingly narrower, the snap-off has been gradually reduced. 43 are applied.

[0008]

However, if the cream solder 43 is applied by bringing the upper surface of the substrate 34 into contact with the lower surface of the mask 32 as described above, when the substrate 34 is lowered and separated from the mask 32, There is a problem that the cream solder 43 applied to the substrate 34 is easily deformed. 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 42 is completed. The pattern holes of the mask 32 are filled with cream solder 43 by sliding the squeegee 42, and the lower surface of the mask 32 is adhered to the upper surface of the substrate 34 because of the adhesive force. Next, the motor 38 is rotated in the reverse direction to
Is lowered, the mask 32 is gradually bent downward due to its own elasticity because the mask 32 is adhered to the substrate 34 (FIG. 7B).
reference). When the substrate 34 is further lowered, the mask 32 is peeled off from the substrate 34 at a stretch as shown in FIG. 7C, and returns to the horizontal state shown by the solid line in FIG. Incidentally, the mask 32 is formed of a flexible metal thin plate such as a stainless steel plate, and the periphery thereof is stretched around the mask frame 33 by a resin film having tension.

As described above, the substrate 34 is lowered and the substrate 3
When separating the mask 32 from the mask 4, the mask 32 is separated from the substrate 34 at a stretch by its own elasticity when the substrate 34 is lowered to some extent. Here, the descending speed of the substrate 34 is set so that the solder of the cream solder 43 does not occur and the tact time does not become long. However, when the mask 32 is separated from the substrate 34 at a stretch as described above, the relative speed of the cream solder 43 is obtained by adding the speed at which the mask 32 rises to the set down speed, and the plate removal speed is reduced. It will be excessive. As a result, the cream solder 43 in the pattern hole is disturbed, and the plate removability deteriorates, and the cream solder 4 on the substrate 34 is disturbed.
This causes inconveniences such as shape collapse and chipping of No. 3.

FIG. 8 shows a typical shape of the cream solder transferred to the substrate 34. Cream solder 43 on the left
a is a non-defective product, and the cream solder 43b on the right side 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 43b 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 conventional example, a screen printing apparatus for raising and lowering the substrate 34 with respect to the mask 32 has been described as an example. However, the same problem as described above also occurs in a screen printing apparatus for raising and lowering the mask with respect to the substrate. A point occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cream solder screen printing method that can prevent the shape and breakage of the cream solder when separating the substrate and the mask.

[0014]

According to the present invention, there is provided a screen printing method for cream solder, comprising: a step of superposing a substrate supported by a support table and a mask having pattern holes at a plurality of positions; and sliding a squeegee on the mask. Moving and applying cream solder to the substrate through the pattern holes,
The lower end of the pressing member that presses the mask against the substrate is positioned below the upper surface of the substrate and presses the mask against the substrate, and while continuing the pressing, the substrate is moved relative to the mask. look including a step of Hanareban the mask from the substrate by lowering the squeegee
It also serves as the pressing member.

[0015]

According to the above arrangement, the mask is released while being pressed against the substrate. Therefore, the mask is separated from the substrate at a stretch when the plate is released, and does not rise vigorously. In other words, it is possible to obtain a good releasability without the abnormal removal of the solder paste from the plate by the restoration of the mask.

[0016]

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

FIG. 1 is a perspective view of a cream solder screen printing apparatus according to an embodiment of the present invention. Reference numeral 1 denotes a mask holder. A feed screw 2 is rotatably mounted on the back side of the mask holder 1 in FIG. 3 is this feed screw 2
, A feed nut screwed into the feed screw 2, a moving plate 5 connected to an upper portion of the feed nut 4, a squeegee 6 suspended vertically on the moving plate 5, and a squeegee 6 Is a cylinder provided with a rod 7a (FIG. 3) for raising and lowering the shaft. The mask holder 1 holds a mask frame 8. As shown in FIG. 2, the mask frame 8 supports a mask 9 having a plurality of pattern holes 9 a at a plurality of positions.
By 0, it is held in the mask frame 8 with tension.

Reference numeral 11 denotes a base, and 12 denotes a support table which moves up and down with respect to the base 11, and positions and supports the substrate 13 with a pair of clampers 14. A piezoelectric element 15 as a vibration means is provided integrally with the clamper 14. As this vibration means, an ultrasonic vibrator may be used. As shown in FIG. 4, the upper end of the piezoelectric element 15 slightly protrudes from the upper surface of the clamper 14, and the piezoelectric element 15
Is in direct contact with the mask 9, and the minute vibration by the piezoelectric element 15 is directly transmitted to the mask 9.

As shown in FIG. 3, a rod 16 extends downward from a lower portion of the support table 12, and the rod 16 is slidably inserted into a linear guide 17 provided on an upper portion of the base 11. The support table 12 becomes the base 11
Are supported so as to be able to move up and down. 18 is the base 11
The output of the servomotor is transmitted to the screw shaft 19. The screw shaft 19 is provided on the support table 1.
2 is screwed to a feed nut (not shown) provided in the inside.
Reference numeral 20 denotes a control unit for the servo motor 18, which can drive the servo motor 18 to move the support table 12 (that is, the substrate 13) relatively up and down with respect to the mask 9.

The screen printing apparatus for cream solder according to the present embodiment has the above-described configuration. Next, a printing process using this apparatus will be described. First, as shown in FIG. 5A, the cylinder 7 is driven to drive the rod 7a and the squeegee 6
Is lowered in the direction of arrow N1. On the other hand, the servo motor 18
Is driven to move the support table 12 and the substrate 13 to the arrow N2.
It is raised in the direction Ru to polymerize the mask 9 on the substrate 13. Next, as shown in FIG. 3B, the motor 3 is driven to move the squeegee 6 in the direction of the arrow N3, so that the cream solder 21 supplied on the mask 9 is
a to the substrate 13. Then, when the application of the cream solder 21 is completed (FIG. 3C), the squeegee 6
Will be away from the substrate 13 or the clamper 14,
At this time, the cylinder 7 is pressed so that the lower end of the squeegee 6 is located further below the upper surface of the substrate 13.
In this state, the micro-vibration is transmitted to the mask 9 by driving the piezoelectric element 15. In addition, at this time, the squeegee 6 presses the mask 9 against the substrate 13. As a result, the mask 9 surely causes micro-vibration, the structural viscosity in the portion of the cream solder 21 near the pattern hole 9a decreases, and the cream solder 21 is easily separated from the pattern hole 9a, in other words, adheres to the substrate 13 side. Easier,
It becomes extremely easy to release a plate.

Next, as shown in FIG. 2D, while the pressing by the squeegee 6 as the pressing member is continued, the servo motor 18 is driven to drive the support table 12 and the substrate 1.
3 is slowly lowered in the direction of arrow N4. Here, since the support table 12 is lowered while the pressing is continued to release the printing plate, the speed component of the mask 9 or the like which is to be restored at the time of releasing the printing plate can be suppressed to almost zero. The solder paste 21 can be prevented from being chipped or removed. Thereby, the releasability can be made extremely good (FIG. 3E). In the present embodiment, the squeegee 6 also serves as a pressing member, but it goes without saying that another member dedicated to the pressing member may be provided.

[0022]

According to the method for screen printing of cream solder of the present invention, the lower end of the pressing member for pressing the mask against the substrate is provided.
Position the mask below the top surface of the substrate and push the mask
The substrate against the mask while maintaining this pressing.
The mask from the substrate by lowering
Since the plate is printed, the restoration of the mask when separating the mask from the board is suppressed , and the shape of the cream solder
Prevents chipping and removes solder paste with good board removal
Can be transferred to

[Brief description of the drawings]

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

FIG. 2 is a partially enlarged cross-sectional view of a screen mask according to one embodiment of the present invention.

FIG. 3 is a cross-sectional view of a main part of a screen printing apparatus using a cream solder screen printing method according to an embodiment of the present invention.

FIG. 4 is a partially enlarged view of a screen printing apparatus using a cream solder screen printing method according to an embodiment of the present invention.

FIG. 5 (a) Process explanatory drawing showing another screen printing method of the present invention (b) Process explanatory drawing showing another screen printing method of the present invention (c) Process showing another screen printing method of the present invention (D) Process explanatory diagram showing another screen printing method of the present invention (e) Process explanatory diagram showing another screen printing method of the present invention

FIG. 6 is a front view of a conventional screen printing apparatus.

FIG. 7A is a diagram illustrating a process of a conventional screen printing device. FIG. 7B is a diagram illustrating a process of a conventional screen printing device.

FIG. 8 is a side view of cream solder by a conventional screen printing apparatus.

[Explanation of symbols]

 Reference Signs List 6 squeegee 9 mask 9a pattern hole 12 support table 13 substrate 21 cream solder

Claims (1)

(57) [Claims] 1. A step of superposing a substrate supported by a support table and a mask having pattern holes at a plurality of positions, sliding a squeegee on the mask, and applying cream solder to the substrate through the pattern holes. And pressing the mask against the substrate by positioning the lower end of a pressing member for pressing the mask against the substrate below the upper surface of the substrate, and pressing the mask against the substrate while continuing the pressing. wherein the step of Hanareban from the substrate to mask <br/> viewed free solder paste screen printing method characterized by the squeegee also serve as the pressing member by lowered relative.