JP2001077521A - Method and device forsolder paste printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To coat solder paste with no air bubble on all the soldering part of a printed board by filling a supply vessel with the solder paste, removing the air bubble in the solder paste under a negative pressure within the vessel, and supplying the paste on a mask for printing a printed board. SOLUTION: A refill vessel 13 filled with a solder paste 14 is airtightly inserted in a hole 12 of a supply vessel 1. With a compressed air, a plunger 15 is moved downward so that the paste 14 flows into the vessel 1 from the bottom of the refill vessel 13. A valve 16 is closed, and a flow-rate adjuster 9 is moved to stop between two blades 8 and 10.Then the inside of the vessel 1 is made negative in pressure by a vacuum device 4 so that the air bubble contained in the solder paste is removed. The degassed paste flows downward by rotation of the two rolls 5 and 6 in the same direction, so that the blade contacts a mask M, moving the supply vessel 1 leftward. Then the paste is printed and painted on the soldering part of a printed board P.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for printing solder paste on a printed circuit board and a printing apparatus for printing solder paste on a printed circuit board.

[0002]

2. Description of the Related Art Recently, electronic components used in electronic devices have become so-called "fine pitch" in which leads have been reduced in size and the distance between leads has become narrower. In order to solder this fine-pitch electronic component to a printed circuit board, a soldering method using a soldering iron and a greased wire solder, or an immersion method in which the printed circuit board is brought into contact with molten solder is not suitable. This is because when these methods are used to solder a fine-pitch electronic component and a printed circuit board, a bridge is formed between the narrow leads, where the solder straddles and adheres. When a printed circuit board with a bridge is incorporated in an electronic device, the function of the electronic device cannot be fulfilled at all because the leads are short-circuited.

The reflow method is suitable for fine pitch soldering. With the reflow method, powder solder and high-viscosity liquid flux are kneaded into a viscous solder paste, applied to the soldering part of the printed circuit board, and the electronic parts are mounted on the applied part In addition, the printed board is heated by a heating device such as a reflow furnace to melt the solder paste, thereby soldering the printed board and the electronic component. In the reflow method, since a small amount of solder paste can be applied to each fine pitch soldering portion, when the solder paste is heated and melted in a reflow furnace, the molten solder does not flow to the adjacent soldering portion. Therefore, no bridge occurs.

In general, a printing apparatus for printing and applying a solder paste on a printed circuit board includes a supply container, a squeegee, and a mask. In order to print the solder paste on the printed circuit board with a printing device using this squeegee, first, the solder paste in the replenishing container supplied by the solder paste manufacturer is stirred with a stirrer such as a spatula or a spoon to obtain a uniform viscosity. Make a solder paste that has good properties. Next, the supply container is filled with the solder paste having a uniform viscosity due to stirring, and an appropriate amount is supplied from the supply container onto the mask. Then, the solder paste supplied on the mask is scraped with a squeegee to print and apply the solder paste to the printed circuit board from the holes of the mask.

[0005]

When the solder paste supplied on the mask is printed on a printed circuit board by scraping with a squeegee, the solder paste may not be applied to the soldered portion of the printed circuit board. In particular, fine-pitch printed boards have more uncoated portions than printed boards having a large pitch interval.

The inventor of the present invention has conducted intensive studies on the cause of non-application of the solder paste when the solder paste is printed by a printing apparatus. As a result, air is bubbled in the solder paste supplied on the mask. It was found that this was due to the contamination of In other words, if bubbles are mixed in the solder paste supplied on the mask, the bubbles in the solder paste will be filled when the solder paste on the mask is scratched with a squeegee and the holes in the mask are filled with solder paste. become. The state in which the mask holes are filled with air bubbles is that the mask holes are not filled with solder paste, and the solder paste is applied to the printed circuit board where the holes are not filled with solder paste. It is gone.

Further, a conventional printing apparatus, that is, a printing apparatus which supplies a solder paste onto a mask from a supply apparatus, and scrapes the solder paste with a squeegee to fill the holes of the mask with the solder paste, is a soldering apparatus mounted on a mask. The paste is scraped with a squeegee to fill the holes of the mask with solder paste. The solder paste is applied to the printed circuit board and supplied by a solder paste supply device in an amount reduced. Therefore, the solder paste on the mask is in a state where the old solder paste and the new solder paste supplied by the supply device are mixed. The old state of the solder paste means that the solder paste has been in contact with air for a long time.In such a case, the solder paste is oxidized by oxygen in the air or the solvent in the solder paste volatilizes. Not only does the viscosity change, but the metallic properties of the powdered solder are lost. If the viscosity of the solder paste changes, the printability deteriorates and uncoating is possible, and if the metallic properties of the powder solder are lost, the solderability deteriorates and causes unsoldering.

[0008]

The inventor of the present invention has made it possible to eliminate the non-application of the solder paste by preventing bubbles from being mixed in the solder paste, and to always use a new solder paste containing no bubbles on the mask. The present invention has been completed by paying attention to the fact that non-coating and soldering defects are eliminated if supplied in a state.

According to the first aspect of the present invention, before the solder paste is printed on a printed circuit board by a printing apparatus, the solder paste is filled into a supply container from a replenishing container, and the pressure in the supply container is reduced to a negative pressure. This is a solder paste printing method characterized by supplying solder paste onto a mask after removing air bubbles therein and printing on a printed circuit board.

A second aspect of the present invention is a solder paste printing apparatus, characterized in that a vacuum device is connected to a supply container for supplying the solder paste on the mask. In a third aspect of the present invention, a vacuum device is connected to a supply container for supplying the solder paste on the mask, and a replenishing container is provided in the supply container and the solder paste flows out to the supply container. A spill device is installed,
Moreover, the solder paste printing apparatus is characterized in that two blades are provided at a lower part of the supply container.

By the way, air enters the solder paste at the time of manufacturing the solder paste and at the time of printing.
In the production of solder paste, a powder solder and a high-viscosity liquid flux are stirred by a stirrer to form a viscous solder paste, but air is entrained during stirring by the stirrer. Also, air is mixed in when the refill container is filled with the solder paste produced by the stirrer. When printing with a printing device, the solder paste in the replenishing container is agitated with a stirrer to obtain a uniform viscous property. Also, when air is transferred from the replenishing container to the supply container, air is mixed. That is, it is inevitable that air is mixed in the solder paste during production and use. Therefore, the present inventor tried to extract air at the final stage of using the solder paste, so that the mask can be used with a solder paste free of air bubbles.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, any structure can be used as long as the apparatus is configured to temporarily fill a supply container with a solder paste from a solder paste replenishing container, and then supply the solder paste from the supply container onto a mask for printing. Applicable to devices. The vacuum device used in the present invention has a suction force enough to remove bubbles mixed in the solder paste from the solder paste filled in the supply container. If the suction force of the vacuum device is too strong, external air may be sucked from the outlet of the supply container.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A printing apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a front sectional view of a printing apparatus according to the present invention.

The supply device 1 has a closed box shape, and a pipe 3 having a valve 2 is connected to a side wall, and a vacuum device 4 is connected to the pipe. In the supply device 1, two rolls 5 and 6, which are flow devices for flowing the solder paste from below, are installed at upper and lower positions. A guide plate 7 is installed between the rolls 5 and 6 in contact with the rolls, and a blade 8 is installed on the lower roll 6 in a state of being in contact therewith.

At a position facing the two rolls 5 and 6, a flow rate adjusting member 9 is installed. The flow control body is rotatably supported at an upper part and a blade 10 is provided at a lower part. The gap between the two blades 8 and 10 can be adjusted by pressing one side of the flow rate adjusting body 9 with the adjusting rod 11.

A hole 12 is formed in the upper part of the supply container 1,
The lower part of the replenishing container 13 is inserted from the hole. The refill container 13 is filled with a solder paste 14, and a plunger 15 is placed on the solder paste. A valve 16 is provided below the replenishing container 13, and a lid 7 connected to a compressor (not shown) is fitted over the supply container.

Next, a method of printing a solder paste using the above printing apparatus will be described.

First, the refill container 13 filled with the solder paste 14 is inserted into the hole 12 of the supply container 1 in an airtight state. Then, after opening the valve 16 of the replenishing container 13, the compressor (not shown) connected to the lid 17 is operated. Then, the compressed air flows in from the lid 17 to move the plunger 15 downward, so that the solder paste flows into the container 1 from the lower part of the replenishing container 13.

When the solder paste 13 has flowed to a position slightly above the center of the upper roll 5 in the supply container 1, the valve 16 is closed, and the flow rate adjusting member 9 is moved to the left in the figure to remove the solder paste. The space between the blades 8 and 10 is closed. Thereafter, the vacuum device 4 is operated to make the inside of the supply container 1 a negative pressure. Then solder paste 1 in supply container 1
In No. 3, air bubbles mixed in are lifted upward and defoamed.

When the solder paste 13 in the supply container 1 is defoamed in this manner, the mask M is placed on the printed circuit board P.
Is placed on the lower part of the container 1. And adjustment rod 1
After moving 1 to the right in the figure, the two rolls 5 and 6 are rotated in the same direction as the clock as shown by arrows A and A. Then, with the rotation of the roll, the solder paste flows downward, and the flow rate adjusting member 9 moves rightward, so that the two blades 8, 10 open at a predetermined interval. In this state, when the two blades are brought into contact with the mask M and the supply container 1 is moved from right to left, the solder paste is filled in the holes of the mask M with the blades, and is printed and applied to the soldered portions of the printed circuit board. Will be.

[0021]

As described above, according to the solder paste printing method of the present invention, the air bubbles mixed in the solder paste immediately before supplying the solder paste onto the mask, which is the final stage of the solder paste printing process, are removed. Since bubbles are removed, no air bubbles exist in the solder paste supplied on the mask, and only holes of the mask are filled with the solder paste. Therefore, when the solder paste supplied on the mask is printed on the printed circuit board, soldering with excellent reliability that the solder paste is applied to all the soldered portions of the printed circuit board can be performed.
Further, in the solder paste printing apparatus of the present invention, a vacuum device is connected to a supply container for supplying the solder paste on the mask, and a negative pressure is applied to the inside of the supply container by the vacuum device before the solder paste is supplied on the mask. Thus, air bubbles can be removed from the solder paste in the supply container. Further, since the printing apparatus of the present invention scrapes the solder paste supplied from the supply container onto the mask with two blades, it is possible to always print and apply a new and bubble-free solder paste on the mask. Not only does not occur, but also has an unprecedented excellent effect that soldering excellent in solderability can be performed.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a printing apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Supply container 4 Vacuum device Flow device 8, 10 Blade 13 Refill container 14 Solder paste M Mask P Printed circuit board

Claims (3)

[Claims] Before a solder paste is printed on a printed circuit board by a printing apparatus, the solder paste is filled from a replenishing container into a supply container, and the pressure in the supply container is reduced to remove air bubbles in the solder paste. And then printing the solder paste on a printed circuit board by supplying the solder paste onto a mask. 2. A solder paste printing apparatus, wherein a vacuum device is connected to a supply container for supplying the solder paste on the mask. 3. A supply device for supplying the solder paste on the mask is connected to a vacuum device, and a replenishing container is installed in the supply container and an outflow device for flowing the solder paste into the supply container. , And two blades are provided at a lower portion of the supply container.