JPH07285263A - Screen printing method and screen printing machine - Google Patents

Abstract

(57) [Summary] [Purpose] To print thick solder paste without causing print defects such as blurring and bleeding. [Structure] A spacer 8 is disposed between the printed wiring board 1 and a metal mask 3b for the next step, avoiding the solder paste 5a printed in the previous step, and printed. As a result, since the solder paste 5b can be printed in the next step on the solder paste 5a printed by the pre-fixing,
The solder pastes 5a and 5b having a large film thickness can be printed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention arranges a printed wiring board on one surface (lower surface) side of a screen mask, and
By moving the squeegee on the other surface (upper surface) side of the screen mask, the paste is pressed against the upper surface of the screen mask, and the opening is formed on the printed wiring board through the opening provided in the screen mask. The present invention relates to a screen printing method and a screen printing machine for printing in the shape of a part,
The present invention relates to a screen printing method and a screen printing machine that can perform printing with high accuracy without causing blurring or bleeding in printing a solder paste having a thick solder paste film thickness.

[0002]

2. Description of the Related Art A solder paste is printed on a printed wiring board by using a screen printer in order to fix electronic components such as semiconductor devices, resistors and capacitors to the printed wiring board and realize a required electronic circuit. The way to do is done. Hereinafter, a conventional screen printing method will be described with reference to FIGS. 4 to 6, reference numeral 1 denotes a printed wiring board (printed wiring board). The printed wiring board 1 is provided with a plurality of wiring pads 2 on the upper surface of which a solder paste 5 to be described later is printed. This wiring pad 2
Are connected to terminals of an electronic component (not shown) or the like via a solder paste 5 described later, and are arranged following the terminals of the electronic component to be mounted. In FIGS. 4 to 6, reference numeral 3 denotes a metal screen mask (hereinafter referred to as a metal mask) arranged so that one surface (lower surface) thereof faces the upper surface of the printed wiring board 1. The metal mask 3 is provided with a plurality of openings 4 corresponding to the positions and shapes of the wiring pads 2. 4 to 6, reference numeral 6 is a squeegee for press-fitting the solder paste 7 placed on the upper surface of the metal mask 3 into the opening 4. The squeegee 6 is provided so as to be movable from the right side of FIGS. 4 to 6 to the left side (direction of arrow a). 4 to 6, reference numeral 5 is a solder paste printed on the wiring pad 2 through the opening 4.

Next, a method of manufacturing the printed wiring board 1 by using the screen printing machine having the above-mentioned structure will be described. First, by moving the squeegee 6 in the direction indicated by the arrow a, the squeegee 6 is on the upper surface of the metal mask 3 in the moving direction of the squeegee 6 (when the moving direction of the squeegee 6 is the forward direction). The solder paste 7 placed on the surface on the moving direction side of the
By receiving the acting force in the direction toward the printed wiring board 1 and the rotating force on the surface of the solder paste 5 in the opening 4,
Is filled as. Next, the metal mask 3 is separated from the printed wiring board 1, so that the solder paste 5 remains on the wiring pad 2 for printing. The solder is melted by mounting a terminal such as a semiconductor device on the solder paste 5 of the printed wiring board 1 and then passing the terminal through a reflow furnace. Then, the printed circuit board is completed by being cooled and electronic components such as a semiconductor device being fixedly mounted on the printed wiring board 1.

In order to obtain the required amount of the solder paste 5, the area of the opening 4 of the metal mask 3 and the metal mask 3
However, if the area of the opening 4 is increased, the distance between the adjacent solder pastes 5 becomes narrower to form a bridge when the solder pastes 5 are melted. The distance between them is limited. Therefore, in printing a fine pattern, the amount of the solder paste 5 is adjusted by changing the thickness of the metal mask 3. A screen printing method for changing the thickness of the solder paste 5 to be printed is shown in JP-A-63-144596 and JP-A-2.
-59397 publication.

[0005]

However, when solder printing is performed by the above-mentioned conventional screen printing method, the following problems occur. 1. The thickness of the metal mask 3 is adjusted in order to secure the required amount of the solder paste 5. However, when the thickness of the metal mask 3 is 200 to 300 μm or more, the area of the opening 4 is fine if the area of the fine opening 4 is fine. The area of the inner wall surface of the opening 4 is increased as compared to For this reason, when the metal mask 3 and the printed wiring board 1 are separated from each other, the solder paste 5 filled in the opening 4 has the metal mask 3 as shown in FIG. 6B.
It is carried away while a part of it is attached to the (inner wall of the opening 4) side. Since the solder paste 5 attached to the inner wall of the opening 4 of the metal mask 3 is fixed in time, the required amount of the solder paste 5 to be printed on the printed wiring board 1 cannot be secured gradually, and the solder paste 5 may be blurred. In order to eliminate the above-mentioned defects, the number of times of cleaning the inner wall of the opening 4 of the metal mask 3 has to be increased, which lowers the productivity.

2. In order to solve the above problem, the wall surface of the inner periphery of the opening 4 of the metal mask 3 may be smoothed to reduce the resistance and enhance the peelability between the inner wall of the opening 4 and the solder paste 5. As the above method, there is a so-called additive method of shaping the metal mask 3 by metal plating,
Since the plating thickness is limited to around 300 μm, it is not suitable for manufacturing a thick metal mask 3.

3. The opening 4 of the thick metal mask 3
In order to fill the inside with the solder paste 5, it is necessary to increase the pressure of the squeegee 6 or decrease the moving speed.
In this way, the internal pressure when the solder paste 5 is filled in the opening 4 of the metal mask 3 increases, so that the solder paste 5 is applied from between the metal mask 3 and the printed wiring board 1.
A so-called bleeding defect that bulges out occurs.

An object of the present invention is to provide a screen printing method and a screen printing machine capable of printing a solder paste having a large film thickness without causing printing defects such as blurring and bleeding.

[0009]

According to the present invention, which achieves the above object, a printed wiring board is arranged on the lower surface (one surface) side of a metal mask, and the upper surface (other surface) side of the metal mask is scanned.
Screen for printing the paste in the shape of the opening on the printed wiring board through the opening provided in the metal mask by pressing the solder paste against the upper surface of the metal mask by moving the solder paste. In a screen printing method and a screen printing machine, a spacer having substantially the same thickness as the solder paste printed on the printed wiring board in the previous step is arranged above the printed wiring board while avoiding the solder paste printed in the previous step. Then, the spacer is interposed between the printed wiring board and the metal mask, and the solder paste is further stacked and printed on the solder paste printed in the previous step.

[0010]

According to the present invention, when the solder paste having the desired thickness is printed by the above-described structure, the solder paste is first printed on the printed wiring board. Next, a spacer having substantially the same thickness as the solder paste printed in the previous step is placed on the printed wiring board while avoiding the solder paste printed in the previous step, and the spacer is solder paste in the previous step. The solder paste is printed by interposing it between the printed printed wiring board and the metal mask for the next step. Then, since the solder paste printed through the opening of the metal mask for the next process is printed on the solder paste printed in the previous process, a thick solder paste can be printed on the printed wiring board. At this time, since the spacers are arranged so as to avoid the portions of the solder paste printed in the next step, they can be removed from the printed wiring board and the solder paste without touching the solder paste printed in the next step. As a result, like the thin metal mask, the metal mask for the next step can be easily separated from the printed wiring board and the solder paste without attaching the solder paste to the inner wall of the opening, and the required amount of solder paste can be secured. . Therefore, it is possible to print a solder paste having a small area and a high thickness with high accuracy without causing printing defects such as blurring and bleeding.

[0011]

Embodiments of the screen printing method and screen printing machine according to the present invention will be described below in detail with reference to FIGS. FIG. 1 is an explanatory diagram of a printing process showing a first embodiment of a screen printing method and a screen printing machine of the present invention. In FIG. 1, the same or corresponding parts as those shown in FIGS. 4 to 6 are designated by the same reference numerals to avoid repeating the description. In FIG. 1, 3a is a metal mask for the previous process. In the metal mask 3a for this pre-process, a plurality of openings 4a are provided corresponding to the positions and shapes of the wiring pads 2 of the printed wiring board 1. In FIG. 1, 3b is a metal mask for the next step. The metal mask 3b for the next step is provided with a plurality of openings 4b corresponding to the positions and shapes of the wiring pads 2 of the printed wiring board 1. In FIG. 1, reference numeral 8 is a spacer interposed between the printed wiring board 1 on which the solder paste 5a is printed in the previous step and the metal mask 3b for the next step. The spacer 8 has a plurality of openings 9
Are provided corresponding to the position and shape of the wiring pad 2 of the printed wiring board 1. Metal mask 3 for the previous step
The plate thicknesses of a, the metal mask 3b for the next process and the spacer 8 are the same. In addition, the metal mask 3 for the previous step
The opening 4a of a, the opening 4b of the metal mask 3b for the next step, and the opening 9 of the spacer 8 have a substantially similar shape, and the size thereof is the opening 9 of the spacer 8> the metal mask 3a for the previous step. 4a> metal mask 3 for the next step
There is a relationship of the opening 4b of b.

The spacer 8 is integrated with the metal mask 3b for the next step to form a metal mask 3A. That is, in the metal mask 3A, the spacer 8 is provided on the surface (lower surface) of the metal mask 3b for the next step facing the printed wiring board 1, and the spacer 8 is provided in the opening 4b of the metal mask 3b for the next step. And the opening 9 of the spacer 8 are made to coincide with each other in the center and are bonded together.

In FIG. 1, 5a and 5b are the metal mask 3a for the previous process and the metal mask 3b for the next process.
Is a solder paste printed by. The volume of the solder pastes 5a and 5b is the same as the opening 4a of the metal mask 3a for the previous process and the metal mask 3b for the next process.
The opening 4b of the metal mask 3a for the previous step is used.
Solder paste 5a printed by <> Solder paste 5 printed by the metal mask 3b for the next step
There is a relationship of b.

Specific values such as the thicknesses of the metal masks 3a and 3b and the spacer 8 and the dimensions of the openings 4a and 4b and the opening 9 are determined by the adhesiveness of the solder paste, the dimension of the printing pad 2, the metal mask. It is determined by the alignment accuracy of 3a and 3b. For example, the opening dimensions and the thickness dimensions of the openings 4a and 4b of the metal masks 3a and 3b are set to values such that the solder pastes 5a and 5b are easily separated from the respective metal masks 3a and 3b when printing is performed. It is restricted.

Next, using the metal masks 3a and 3b of the screen printing machine of the present invention having the above-described structure, the solder paste 5a is applied to the wiring pads 2 on the printed wiring board 1.
The screen printing method of the present invention for printing 5b will be described with reference to the explanatory drawing of the printing process in FIG. First, Figure 1
As shown in (a), the metal mask 3a for the pre-process is arranged on the printed wiring board 1 by aligning the opening 4a with the wiring pad 2. By moving the squeegee 6 on the upper surface of the metal mask 3a for the previous step in the direction of arrow A, the solder paste 7 on the upper surface of the metal mask 3a for the previous step is filled into the opening 4a. By separating the metal mask 3a for this pre-process from the printed wiring board 1, the solder paste 5 is formed on the wiring pad 2.
a is printed.

Next, as shown in FIG. 1B, the metal mask 3A is placed above the printed wiring board 1 and
So that the spacer 8 of A faces the printed wiring board 1,
The openings 4b and 9 of the metal mask 3A (the metal mask 3b and the spacer 8 for the next process) are arranged and the solder paste 5 printed on the wiring pad 2 in the previous process.
Align with a. At this time, since the opening 9 of the spacer 8 of the metal mask 3A is made larger than the opening 4a of the metal mask 3a for the previous process, when the metal mask 3A is arranged on the printed wiring board 1, the opening of the spacer 8 is formed. The paste 5a printed in the previous step does not touch the inner wall of the portion 9.

Then, as shown in FIG. 1 (c), the squeegee 6 is moved in the direction of arrow a on the upper surface of the metal mask 3b for the next step, whereby the solder paste 7 on the upper surface of the metal mask 3b for the next step. Are filled in the opening 4b. Then, the metal mask 3A is separated from the printed wiring board 1. At this time, the metal mask 3 for the next process
The solder paste 5b filled in the opening 4b of b does not contact the portion of the spacer 8 but only the portion of the metal mask 3b for the next process. Therefore, the contact area between the solder paste 5b and the metal mask 3A is equal to the contact area between the solder paste 5b and the metal mask 3b. As a result, the metal mask 3A in which the metal mask 3b for the next process and the spacer 8 are integrated is used as the opening 4 for the metal mask 3A as in the case of the metal mask 3b for the next process alone.
It can be easily peeled off from the printed wiring board 1 and the solder paste 5b without the solder paste 5b adhering to the inner wall of b.

Then, as shown in FIG. 1D, since the solder paste 5b is printed in the next step on the solder paste 5a printed in the previous step, the thick solder paste is printed with bleeding or fading. Printing can be performed without causing defects.

Using the above method, for example, a thickness of 400 μm
In the case of printing the solder pastes 5a and 5b, the metal mask 3a for the pre-process and the metal mask 3 for the next process having the thickness of 200 μm having the openings 4a and 4b, respectively.
b and a spacer 8 made of the same material as the metal masks 3a and 3b and having the same thickness and an opening 9 are used.
First, the metal mask 3a for the pre-process having the opening 4a
Is used to print the lower solder paste 5a having a thickness of 200 μm. Next, the spacer 8 having the opening 9 larger than the solder paste 5a printed in the previous step is placed on the printed wiring board 1 side, and the metal for the next step having the opening 4b smaller than the solder paste 5a printed in the previous step. The mask 3b is arranged above the spacer 8 and the metal mask 3b
If the solder paste 5b having a thickness of 200 μm is printed on the solder paste 5a printed in the previous step by overlapping the spacers 8 in the next step, the solder paste 5a and 5b having a desired thickness of 400 μm can be printed. You can

In the above embodiment, the metal mask 3A in which the spacer 8 and the metal mask 3b are integrated with each other.
Since the work of aligning and removing can be done at once, the printing time can be shortened. Further, since the error due to the alignment between the spacer 8 and the metal mask 3b does not occur, the accuracy is improved. The spacer 8 and the metal mask 3b may be separated. If the metal mask 3a for the previous process and the metal mask 3b for the next process and the spacer 8 have the same thickness, the spacer 8 can be manufactured using the same material as the metal masks 3a, 3b.

In the above embodiment, the opening 4a of the metal mask 3a for the previous process and the metal mask 3 for the next process are used.
The shape of the opening 4b is substantially similar to that of the opening 4b, and the size of the opening 4b of the metal mask 3a for the previous step is larger than the opening 4b of the metal mask 3b for the next step. Depending on the accuracy, the viscosity of the solder pastes 5a and 5b, the printing conditions such as the speed and pressing of the squeegee 6, the size of the opening 4a of the metal mask 3a for the previous process and the opening 4b of the metal mask 3b for the next process can be determined. It may be about the same.
If the opening 4a of the metal mask 3a for the previous process and the opening 4b of the metal mask 3b for the next process have the same size, the metal mask 3a for the previous process and the metal mask 3b for the next process are formed. Since they can be used in common, the number of metal masks to be manufactured can be reduced, and the mounting time to the printing apparatus can be reduced, thus improving productivity. Moreover, the spacer 8
The size of the opening 9 is set to the opening 4a of the metal mask 3a for the previous process and the opening 4b of the metal mask 3b for the next process.
If the size is the same, the spacer 8 can be used as both the metal masks 3a and 3b, and the productivity can be improved.

Further, in the above-mentioned embodiment, the thickness of the metal mask 3a for the previous step and the thickness of the spacer 8 are the same, but the thickness of the metal mask 3a for the previous step and the thickness of the spacer 8 are different. Is also good. For example, as shown in FIG.
If the spacer 8 side is made thick, the metal mask 3b for the next process and the solder paste 5a printed in the previous process can be separated, so that when performing the alignment work of the metal mask 3b for the next process, etc. There is no risk of destroying the solder paste 5a printed in the process, and the solder paste 5a printed in the previous process adheres to the lower surface (the surface facing the printed wiring board 1) side of the metal mask 3b for the next process to be contaminated. Can be prevented. The thickness of the spacer 8 is such that when the metal mask 3b for the next process is pressed by the squeegee 6 during printing, the solder paste 5a printed in the previous process on the lower part can be adhered to the solder paste 5b printed in the next process on the upper part. It should be within the range. Further, the thickness of the spacer 8 may be smaller than the thickness of the metal mask 3a for the previous process. In the above-described first embodiment of FIG. 1, the solder pastes 5a and 5b having the same thickness are printed by using the metal mask 3a for the previous process and the metal mask 3b for the next process having the same thickness. The thickness of the solder pastes 5a and 5b printed by using the metal mask 3a for the previous process and the metal mask 3b for the next process having different thicknesses may be changed in each stage. For example,
As shown in FIG. 2, the thickness of the solder paste 5a printed in the previous step is made thicker than the thickness of the solder paste 5b printed in the next step, or vice versa. The thickness may be thinner than the thickness of the solder paste 5b printed in the next step.

Further, in the above-described embodiment, the solder paste 5a printed in the previous step (the opening 4a of the metal mask 3a for the previous step) and the opening 9 of the spacer 8 are made substantially similar to each other, and the opening of the spacer 8 is formed. The portion 9 and the solder paste 5a printed in the previous step (opening 4a of the metal mask 3a for the previous step) are arranged so as to avoid one-to-one correspondence, but as shown in FIG. It is also possible to avoid the solder pastes 5a printed in the plurality of previous steps so as to be contained in the solder paste 9a. By doing so, the structure of the spacer 8 can be simplified. Moreover, the opening 4a of the metal mask 3a for the previous process for printing and the metal mask 3 for the next process
The openings 4b of b are made to correspond one-to-one. However, as shown in FIG. 2, as for a portion having a wide print pattern that can secure the amount of the solder paste 5a only by the metal mask 3a for the previous step, as shown in FIG. The opening 4b on the side of the metal mask 3b for the process (the opening 4b of the metal mask 3b for the next process corresponding to the solder paste 5a printed in the second previous process from the right side in FIG. 2) is not provided. Is also good. With this configuration, the metal mask 3 for the next process
The structure of b can be simplified.

Further, as shown in FIG. 3, the spacer 8a does not have to be a single piece. For example, the spacer 8a may be divided for each component according to the pattern of the IC or the like printed on the printed wiring board 1. The spacer 8a divided as described above is attached to the printed wiring board 1 side of the metal mask 3b for the next step to be integrated, and printing in the next step is performed. In this way, the spacer 8a can be standardized, and the cost of the metal mask 3A for the next process can be reduced.

The components of the solder pastes 5a and 5b to be printed may be changed in each stage. For example, the solder paste 5a printed on the printed wiring board 1 and filled in the large opening 4a (of the metal mask 3a for the previous process) which is easily peeled off is made of a highly adhesive material and is used as the wiring pad 2 The solder paste 5b which is surely adhered and which is filled in the small opening portion 4b (of the metal mask 3b for the next step) which is hard to be peeled off has low adhesiveness and is printed in the next step. The peelability of may be improved. Further, since the upper and lower solder pastes 5a and 5b are mixed with each other when the solder is melted, it may be selected so as to have a desired component at this time.

In the above description, the solder pastes 5a and 5b having a desired thickness are printed by printing in two layers. However, the thickness of the solder paste to be printed and the characteristics such as the adhesiveness of the solder paste are 3 Printing may be performed by stacking more than one layer. That is, a spacer having a thickness suitable for the solder paste printed up to the previous step is interposed between the metal mask and the printed wiring board, and the solder paste printed up to the previous step is overlaid and printed. If it is good.

[0027]

As described above, according to the screen printing method and the screen printing machine of the present invention, the solder paste having a large film thickness can be printed without causing printing defects such as blurring and bleeding.

[Brief description of drawings]

1A, 1B, 1C and 1D are longitudinal cross-sectional explanatory views showing a printing process of an embodiment for printing a solder paste according to the present invention.

FIG. 2 is an explanatory view of a vertical cross section showing a part of a printing process for printing the solder paste of the present invention which is different from the embodiment of FIG.

FIG. 3 is an explanatory view of a vertical cross section showing a part of a printing process for printing the solder paste of the present invention, which is different from the above embodiment.

FIG. 4 is a partial plan view showing a conventional screen printing method.

5 is a cross-sectional view taken along the line AA in FIG.

6 (a) and 6 (b) are longitudinal cross-sectional explanatory views showing a printing step of printing a solder paste by the conventional screen printing method shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Printed wiring board, 2 ... Wiring pad, 3a ... Metal mask for previous process (screen mask), 3b ... Metal mask for next process (screen mask), 4a ... Opening of metal mask for previous process 4b ... Opening of metal mask for the next step, 5a ... Solder paste printed in the previous step, 5b ... Solder paste printed in the next step, 6 ... Squeegee, 7 ... Solder paste, 8, 8a ... Spacers (metal masks), 9 ... Openings.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H05K 3/34 505 B 8718-4E

Claims (6)

[Claims] 1. A printed wiring board is arranged on one surface side of the screen mask, and a mask is formed on the other surface side of the screen mask.
The solder paste is pressed against the other surface of the screen mask by moving the solder paste, and the solder paste is passed through the opening provided in the screen mask to form the opening on the printed wiring board. In the screen printing method of printing in a shape, a spacer having substantially the same thickness as the solder paste printed on the printed wiring board in the previous step is printed above the printed wiring board to avoid the solder paste printed in the previous step. A screen printing method, which comprises arranging the spacers and interposing the spacers between the printed wiring board and the screen mask and further printing the solder pastes on the solder pastes printed in the previous step. 2. A printed wiring board is arranged on one surface side of the screen mask, and a mask is formed on the other surface side of the screen mask.
The paste is pressed against the other surface of the screen mask by moving the screen, and the paste is printed on the printed wiring board in the shape of the opening through the opening provided in the screen mask. In the screen printing method described above, a spacer having a substantially similar thickness opening larger than the solder paste printed on the printed wiring board in the previous step and having substantially the same thickness as the solder paste printed on the printed wiring board is provided. The solder paste printed in the previous step is placed in the opening so that the spacer is interposed between the printed wiring board and the screen mask, and the solder paste is further stacked on the solder paste printed in the previous step. A screen printing method characterized by printing by printing. 3. The spacer is integrally provided on the surface of the screen mask for the next step facing the printed wiring board on which the solder paste is printed in the previous step. Or the screen printing method described in 2. 4. A screen mask, one surface of which is disposed so as to face a printed wiring board, the screen mask having an opening for printing solder paste on the printed wiring board, and the screen mask other than the screen mask. A squeegee movably disposed on the other side of the screen mask, the solder paste is pressed on the other side of the screen mask by moving the squeegee on the other side of the screen mask, and the solder paste is moved to the screen side. In a screen printing machine equipped with a squeegee that prints in the shape of the opening on the printed wiring board through the opening of the screen mask, the thickness is almost the same as the thickness of the solder paste printed in the previous step. A printed wiring board that has a certain spacer and is printed with the solder paste in the previous step so as to avoid the solder paste printed in the previous step. A screen comprising a spacer for interposing a screen mask for the next process and printing the solder paste further printed on the solder paste printed in the previous process.
Printing machine. 5. The spacer has a substantially similar opening whose size is substantially the same as or slightly larger than the size of the solder paste printed in the previous step so that the solder paste printed in the previous step can be accommodated. The screen printing machine according to claim 4, wherein the screen printing machine is provided. 6. The spacer is integrally provided on the surface of the screen mask for the next step facing the printed wiring board on which the solder paste is printed in the previous step. The screen printing machine according to item 5.