JP2000062137A - Method for printing solder paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of properly printing a solder paste on a printed substrate in a more minute pattern compared to a conventional printing method, under a simple hardware constitution. SOLUTION: A substrate 1 is placed at a specified position on a metal base 5 with an imbedded electric heater 6 which is freely temperature-controllable and a mask 2 having plural through holes 2a formed in a specific minute pattern is positioned on the substrate 1. In addition, the through holes 2a are filled with a solder paste 4 on the mask 2 by moving a squeegee 3. Next the solder paste 4 is heated by the electric heater 6 through the substrate 1 and the substrate 1 is separated from the mask 2. Through this heating operation, the volatile component of the paste 4 in the through holes 2a is dissipated by the heating operation resulting in the diminution of the volume of the paste 4. At the same time, the fluidity of the paste 4 and the viscosity of the paste 4 to the internal peripheral face of the through holes 2a are deteriorated. Fort this reason, the external peripheral face of the paste 4 is separated from the internal peripheral face of the through holes 2a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder paste printing method, and more particularly to a method of printing a solder paste in a fine pattern on a printed circuit board through a mask.

[0002]

2. Description of the Related Art As consumer appliances are becoming smaller and more sophisticated, there is a demand for higher density and lower cost packaging. For example, in the manufacture of electronic circuit boards, when soldering electronic circuit parts such as chip parts onto a printed circuit board (hereinafter referred to as the board), a metal formed by solder paste (sometimes called cream solder or solder paste) is used. Screen printing is used. In such solder paste printing, it is required to print with a finer pattern.

By the way, in the conventional printing of the solder paste, the method shown in FIG. 3 has been adopted. In this figure, 1 is a substrate and 2 is a through hole (pattern hole) with a predetermined pattern.
A plurality of masks 2a formed at appropriate intervals from each other,
Reference numeral 3 is a squeegee that moves linearly on the mask, and 4 is a solder paste (hereinafter sometimes referred to as paste).

In printing the paste, the squeegee 3 is moved linearly on the mask 2 with the squeegee 3 being in contact with the mask 2 with an appropriate pressure, so that the paste 4 on the mask 2 is passed through the through holes 2a.
And the paste is applied onto the substrate 1 and then the substrate 1 is separated from the mask 2 to remove the paste 4 from the mask 2.
Is transferred onto the substrate 1 in a predetermined pattern via.

[0005]

However, in the paste printing method of FIG. 3, the pitch between the through holes 2a, 2a is about 200 μm as a limit (minimum value), and printing is performed with a finer pattern than this. Was technically difficult.
Hereinafter, this will be described with reference to the drawings.

That is, when the paste 4 is filled in the through holes 2a of the mask 2 as shown in FIG. 4A, and when the substrate 1 is separated from the mask 2, as shown in FIG. However, it was difficult to perform proper paste transfer because some or all of them remained in the through holes 2a.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a method capable of printing a solder paste in a fine pattern with a simple structure.

[0008]

To achieve the above object, the solder paste printing method according to the present invention places a mask having a large number of through holes formed in a predetermined pattern on a substrate, and moves the squeegee on the mask. After filling the through-hole with the solder paste, the solder paste in the through-hole is transferred onto the substrate by separating the substrate and the mask, in the solder paste printing method, the substrate is placed on a pedestal that can be heated, The solder paste filled in the above through holes is heated by heating the pedestal to raise the volatile components in the paste (such as a solvent that is a component of the flux), and then the substrate and the mask are separated. It is what

In the present invention, the solder paste filling operation can be performed while heating the substrate to an appropriate temperature by heating the pedestal. Further, as the pedestal, it is desirable to use a metal pedestal provided with a heating means capable of controlling the heating temperature of the pedestal.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing a solder paste printing method. 2A and 2B are sectional views for explaining the operation of the printing method of FIG. 1, in which FIG. 2A shows the form of the solder paste after heating the substrate, and FIG. 2B shows the state of the solder paste after separating the substrate from the mask. It is a thing.

As shown in FIG. 1, a metal pedestal 5 (for example, a thick aluminum plate) in which an electric heater 6 is embedded is provided as a heating means, and the electric heater 6 is connected to a temperature control mechanism (not shown). The pedestal 5 can be moved up and down by an elevator mechanism (not shown). Further, for example, the mask 2 made of thin stainless steel is held in a tension state by a support mechanism (not shown).

When printing the solder paste, the substrate 1
Is placed at a predetermined position on the pedestal 5, the pedestal 5 is raised by the elevating mechanism to position the substrate 1 with respect to the mask 2, and the upper surface of the substrate is brought into contact with the lower surface of the mask with a predetermined pressure.
The solder paste 4 heated to a predetermined temperature is supplied onto the mask 2 from a tank (not shown). Then, the squeegee 3 is moved in a state of being in contact with the upper surface of the mask 2 to fill the through holes 2a of the mask 2 with the paste 4 and press the lower surface of the paste 4 onto the substrate 1.

Then, the pedestal 5 is heated to a predetermined temperature by the electric heater 6 and maintained at this temperature for an appropriate time. As a result, as shown in FIG. 2A, since the volatile components such as the solvent in the paste 4 in the through holes 2a are evaporated or volatilized, the volume of the paste 4 is reduced and the paste 4 The fluidity is reduced, and the paste state changes from the original paste state to a semi-solid state (this reduces the adhesiveness of the paste to the inner peripheral surface of the through hole 2a), and the outer peripheral surface of the paste 4 is the inner peripheral surface of the through hole 2a. Leave the plane. Therefore, when the pedestal 5 is lowered by the elevating mechanism in this state, the paste 4 is properly transferred onto the substrate 1 as shown in FIG. 2B.

According to a study by the present inventor, it is determined whether the entire paste in the through hole 2a is transferred onto the substrate 1 by the opening area Sh of the through hole 2a (the area of the through hole in the plan view of the mask). It has been confirmed that the ratio: Sh / Sw of the through hole 2a to the inner peripheral surface area Sw has a great influence. That is, in the conventional method of FIG. 3 in which the substrate is separated from the mask as it is after the pace is filled in the through hole, Sh /
The minimum value of Sw is about 1/2, and the larger the value, the transferability (printability) of the paste to the substrate.
Is reduced. Therefore, the smaller the diameter of the through hole,
It was difficult to perform proper transfer. In other words, as the thickness of the mask is larger and the size of the through hole is smaller, the transferability is lower.

On the other hand, according to the method of the present invention shown in FIG. 1, even if the value of Sh / Sw is smaller than 1/2, proper paste printing can be easily performed. This is
This means that solder printing with a finer pattern than before is possible.

[0016]

As is apparent from the above description, according to the solder paste printing method of the present invention, the substrate is placed on the pedestal that can be heated and the squeegee is used to heat the solder paste filled in the through holes of the mask. The temperature is indirectly heated via the substrate to dissipate the volatile components in the paste, and then the substrate and the mask are separated, so the solder paste can be separated from the mask with a simple configuration. improves.
Therefore, it is possible to reliably transfer the entire paste in the mask through hole to the substrate side, compared to the conventional printing method,
It is possible to easily perform solder printing of a finer pattern.

Specifically, the opening area Sh of the mask through hole is
And the inner surface area Sw of the mask through-holes: Sh / Sw is smaller than 1/2, proper paste printing is possible, and solder printing of patterns finer than 200 μm pitch is easily realized. There is an effect that can be.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a solder paste printing method according to the present invention.

FIG. 2 is a sectional view for explaining the operation of the printing method of FIG.
(A) shows the form of the solder paste after heating the substrate,
(B) shows the state of the solder paste after the substrate is separated from the mask.

FIG. 3 is a schematic cross-sectional view showing a conventional solder paste printing method.

4A and 4B are schematic cross-sectional views for explaining the problems of the printing method of FIG. 3, in which FIG. 4A shows a state after the solder paste is filled in the through holes of the mask, and FIG. 2 shows the state of the solder paste after being separated from.

[Explanation of symbols]

1 ... Substrate, 2 ... Mask, 2a ... Through hole, 3 ... Squeegee,
4 ... Solder paste, 5 ... Pedestal, 6 ... Electrothermal heater.

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[Procedure amendment]

[Submission date] April 22, 1999 (1999.4.2)
2)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

Generally, whether the entire paste in the through hole 2a is transferred onto the substrate 1 depends on the aspect ratio of the opening.
That is, the opening diameter D of the through hole 2a (in the plan view of the mask)
Through hole diameter) and height of through hole 2a (mask plate thickness)
It has been confirmed that the ratio T / D of T has a great influence.
That is, in the conventional method of FIG. 3 in which the paste is filled in the through holes and then the substrate is separated from the mask as it is, the value of T / D is about 1/2 at the minimum value, and if it is larger than this, it is large. As a result, the transferability (printability) of the paste onto the substrate decreases. Therefore, the smaller the diameter of the through hole, the more difficult it is to perform proper transfer. In other words, as the thickness of the mask is larger and the size of the through hole is smaller, the transferability is lower.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

On the other hand, according to the method of the present invention shown in FIG. 1 , proper paste printing can be easily performed even if the value of T / D is larger than 1/2 . This means that solder printing with a finer pattern than before is possible.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

Specifically, the opening diameter D of the mask through hole and the mask diameter
Ratio of height of through-hole (mask thickness) T: T / D is 1
Even if it is larger than / 2 , there is an effect that proper paste printing is possible and solder printing of a pattern finer than 200 μm pitch can be easily realized.

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Claims (3)

[Claims] 1. A mask having a large number of through holes formed in a predetermined pattern is placed on a substrate, the solder paste on the mask is filled in the through holes by moving a squeegee, and then the substrate and the mask are separated to separate the through holes. In the solder paste printing method of transferring the solder paste in the holes onto the substrate, the substrate is placed on a pedestal that can be freely heated, and the solder paste filled in the through holes is heated by heating the pedestal to heat the inside of the paste. A method for printing a solder paste, characterized in that the substrate and the mask are separated after the volatile components of (1) are diffused. 2. The solder paste printing method according to claim 1, wherein the solder paste filling operation is performed while heating the substrate to a predetermined temperature by heating the pedestal. 3. The pedestal according to claim 1 or 2,
A method for printing a solder paste, characterized by using a metal pedestal provided with a heating means capable of controlling a heating temperature.