JPH08250847A - Soldering method for electronic component - Google Patents

Abstract

PURPOSE: To suppress the adherence of flux on a printed board. CONSTITUTION: After an electrode 3 on a printed board 1 is coated with solder cream 2 by a screen method, a paper mask 4 for absorbing the flux is adhered on the upper surface of the board 1. An electronic component 5 is mounted. The component 5 is mounted with the mounting height (stand-off) corresponding to the thickness of the mask 4. The cream 2 is heated and soldered. In such a case, since the flux is absorbed to the mask 4, it is not adhered to the board 1. Then, the mask 4 is removed from the board 1. At this time, the cutout 7 of the mask 4 is formed with one opening together with the extending opening 6, and the component 5 passes through the opening. Accordingly, the mask 4 is not broken, but peeled from the board 1. Thereafter, the board 1 is cleaned by pure water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering method for soldering electronic parts to a printed circuit board.

[0002]

2. Description of the Related Art Generally, in a soldering method for electronic parts of this kind, a flux is used to keep a metal surface to be soldered clean and to suppress its oxidation. During the soldering process, the flux melts together with metal oxides or foreign substances to form a flux residue, or solidifies and adheres to the printed circuit board. Therefore, it is necessary to clean the printed circuit board after the soldering work to remove the flux residue or the solidified flux.

As a cleaning medium for cleaning a printed circuit board,
Conventionally, many organic solvents such as CFCs have been used,
In recent years, for the purpose of protecting the environment, the flux has been changed to a water-soluble flux and cleaning has been performed with pure water.

[0004]

However, when the flux is water-soluble and pure water is used as the cleaning medium, the following problems occur.

Pure water has poor permeability and cannot effectively clean the flux remaining in the corners of the soldered parts or under the parts. Further, since the water-soluble flux has a hygroscopic property, if the flux that cannot be cleaned remains in the vicinity of the electrodes, the insulation degree of the electric circuit will be reduced. Further, since the water-soluble flux is generally highly active and may corrode the electrodes, it is necessary to make cleaning time of the printed circuit board very long to completely remove the flux.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electronic component which can suppress the adhesion of flux onto a printed circuit board and shorten the cleaning time. It is to provide a soldering method.

[0007]

In order to achieve the above object, the invention according to claim 1 is a method of soldering an electronic component, wherein a flux absorbing sheet having an opening is attached onto a printed board. And a step of arranging electronic components on the printed circuit board to which the flux absorbing sheet is attached and soldering in the opening of the flux absorbing sheet, and after the soldering is finished, the flux absorbing sheet is removed from the printed circuit board. It is the gist of having the process.

According to a second aspect of the present invention, in the method of soldering an electronic component according to the first aspect, a plurality of the openings are formed in the flux absorbing sheet, and a cut connecting the openings is formed. What is done is the summary.

[0009]

According to the first aspect of the invention, the flux absorbing sheet is attached to the printed circuit board. At this time, the electrode portion of the printed circuit board to be soldered is exposed from the opening of the flux absorbing sheet. Then, electronic components are arranged on the printed circuit board. Since the flux absorbing sheet is interposed between the electronic component and the printed board, the flux does not enter the lower side of the electronic component, and the electronic component has a predetermined size determined by the thickness of the flux absorbing sheet. It is arranged so as to be separated from the printed circuit board by a distance. Then, the electronic component is soldered to the printed board at the opening of the flux absorbing sheet. Flux scattered from the soldered portion hardly adheres to the printed circuit board and is absorbed by the flux absorbing sheet on the upper surface thereof. When the soldering work is completed, the flux absorbing sheet that has absorbed the flux is removed from the printed board.

According to the second aspect of the present invention, in addition to the above-mentioned function, when the flux absorbing sheet is removed from the printed circuit board, the notch of the sheet is widened and the opening is provided.
Two openings are formed, and electronic parts are passed through the openings.
Therefore, the flux absorbing sheet is removed from the printed circuit board without breaking.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment embodying the present invention will be described below with reference to FIGS.

FIGS. 1A to 1F are views showing the steps of the soldering method in the first embodiment. The soldering method in this embodiment includes a step A of applying the solder cream 2 on the printed circuit board 1, a step B of attaching the paper mask 4 to the printed circuit board 1, a step C of mounting the electronic component 5 on the printed circuit board 1. Step D of heating solder cream 2, paper mask 4
Is removed from the printed circuit board 1, and a cleaning process F is performed. The electronic components 5 are soldered onto the printed circuit board 1 by sequentially performing the processes A to F. Hereinafter, each step will be described in order.

FIG. 1A shows a step A of applying the solder cream 2 on the printed board 1. In process A,
The solder cream 2 is applied to the plurality of electrodes 3 arranged on the printed board 1 by a screen printing method. The solder cream 2 is a mixture of water-soluble flux and powdered solder, and has a cream shape. Also,
The water-soluble flux contained in the solder cream 2 keeps the metal surface to be soldered clean and prevents oxidation of the same surface.

FIG. 1 (b) shows a step B in which a paper mask 4 as a flux absorbing sheet is attached onto the printed board 1. In step B, the paper mask 4 is placed so as to cover the printed circuit board 1 to which the solder cream 2 has been applied in step A. Then, the paper mask 4 is attached to the upper surface of the printed circuit board 1 by a water-soluble adhesive having a very weak adhesive force applied to the back surface thereof. Therefore, until the paper mask 4 is removed from the printed board 1, the paper mask 4 covers the same surface as the upper surface of the printed board 1 while being positioned.

The paper mask 4 is made of bast fibers, such as Sanpei, Japanese pepper, and Manila hemp, which are highly absorbent of flux and have a thickness of about 80 μm. FIG. 4 is an enlarged view of an essential part showing a state where the paper mask 4 is attached to the upper surface of the printed board 1. As shown in the figure, two openings 6 are formed in the paper mask 4, and the electrodes 3 (where the solder cream 2 is applied) on the printed circuit board 1 are exposed through the openings 6. Further, the paper mask 4 is formed with a notch 7 extending from the lower right corner of one opening 6 to the upper left corner of the other opening 6. The notch 7 has a substantially S shape without sharp corners.
It is shaped like a letter. This is to prevent the paper mask 4 from being broken by the cut 7 in the step E of removing the paper mask 4 from the printed board 1.

In this embodiment, after the step A is performed,
Although the process B is performed, the order of the process A and the process B can be changed. That is, the printed circuit board 1
A paper mask 4 as a flux-absorbing sheet is attached on top, and then the solder cream 2 is placed on the printed circuit board 1.
May be applied.

FIG. 1C shows a step C of mounting the electronic component 5 on the printed board 1. In step C, a terminal (not shown) of the electronic component 5 is inserted into a hole (not shown) provided in the electrode 3, and the electronic component 5 is placed on the printed board 1.
Will be implemented. 2 and 3 show a state in which the electronic component 5 is mounted on the printed board 1. When the electronic component 5 is mounted on the printed circuit board 1, the lower surface of the electronic component 5 is placed on the paper mask 4 as shown in FIG.
Therefore, the electronic component 5 is mounted in a state of being separated from the printed board 1 by a predetermined distance determined by the thickness of the paper mask 4. Further, since the paper mask 4 is interposed between the electronic component 5 and the printed board 1, the solder cream 2 does not adhere to the printed board below the electronic component 5.

FIG. 1D shows a process D for heating the solder cream 2. In step D, the solder cream 2 applied on the electrodes 3 of the printed circuit board 1 is heated,
The terminals (not shown) of the electronic component 5 and the electrodes 3 of the printed board 1 are soldered. In step D, the powdery solder contained in the solder cream 2 melts when heated and contracts on the electrode 3. However, a part of the solder becomes a solder ball due to bumping of the flux contained in the solder cream 2 and scatters around the soldered part. In this embodiment, since the scattered solder balls adhere to the paper mask 4, they hardly adhere to the printed circuit board 1 below the paper mask 4. In addition, the electronic component 5
Since the paper mask 4 is interposed between the printed circuit board 1 and the printed circuit board 1, the solder cream 2 does not get under the electronic component 5. Therefore, solder balls are not formed on the lower side of the electronic component 5.

Furthermore, when heating the solder cream 2,
Flux or flux residue scatters around the electrode 3, but since these are absorbed by the paper mask 4, they do not adhere to the printed circuit board 1, or even if they adhere, the amount is extremely small.

FIG. 1E shows a step E for removing the paper mask 4 attached to the printed board 1. In step E, the paper mask 4 that has absorbed flux, flux residue, or has solder balls attached thereto is peeled from the printed board 1 in step E. At this time, the notch 7 provided in the paper mask 4 is expanded in the direction shown by the arrow in FIG. 4, and the tongue 8 of the paper mask 4 below the electronic component 5 is pulled out. Then, one opening is formed by both the opening portions 6 and the notches 7, and the paper mask 4 is peeled off from the printed board 1 while the electronic component 5 is passed through the opening. As a result, the paper mask 4 is removed from the printed board 1 without breaking. Therefore, a part of the paper mask 4 does not remain below the electronic component 5.

Through the above steps A to E, the electronic component 5 is soldered to the printed board 1. Then, the printed board 1 is washed with pure water as shown in FIG. 1 (f) (step F). Since the printed board 1 was covered with the paper mask 4 before the cleaning step F, almost no flux, flux residue, or solder balls were attached. Therefore, the cleaning process F is completed in a short time.

As described above, the process A is performed in this embodiment.
The electronic components 5 are soldered to the printed circuit board 1 by sequentially performing steps from to F. Next, the operation and effect of this embodiment will be described. In the soldering method of this embodiment, the electronic component 5 is placed and mounted on the paper mask 4. Therefore, the electronic component 5 is separated from the printed circuit board 1 by a distance substantially equal to the thickness of the paper mask 4. That is, the so-called standoff is ensured in the electronic component 5. The standoff is necessary to improve the cleanability of the lower side of the electronic component 5 or to enhance the heat radiation effect of the electronic component 5, but it has been difficult to provide a certain standoff by the conventional soldering. . However, in the soldering method of this embodiment, a standoff approximately equal to the thickness of the paper mask 4 is secured, and the standoff can be easily adjusted by changing the thickness of the paper mask 4.

Further, in this embodiment, since the upper surface of the printed board 1 is covered with the paper mask 4, the amount of flux, flux residue or solder balls attached to the printed board 1 is very small. Therefore, the cleaning time of the printed circuit board 1 can be significantly shortened. This effect is obtained by comparing the conventional soldering method with the paper mask 4 on the printed circuit board 1.
It can be obtained by adding a very simple process of attaching, soldering, and then removing this.
Therefore, this embodiment can shorten the time required for the entire soldering work and reduce the cost required for the work.

Next, second to fourth embodiments embodying the present invention will be described. The printed circuit board 1 is used in the second to fourth embodiments.
This is an example in which the shape of the electronic component 5 mounted on the top is different, and the opening 6 and the notch 7 provided in the paper mask 4 are shown.
Is different from the first embodiment described above. Therefore, the difference will be described and the description of the soldering process will be omitted because it is similar to that of the first embodiment.

The second embodiment is an embodiment in which the electronic component 5 mounted on the printed board 1 is small. The paper mask 4 used in this embodiment has the shape shown in FIG.
That is, the openings 6 for exposing the electrodes 3 of the printed circuit board 1 are provided on the paper mask 4, and arcuate cuts 7 are formed between the openings 6. The paper mask 4 is used when the distance between the electrodes 3 arranged on the printed board 1 is small.

The third embodiment is an embodiment in which an electronic component 5 having three terminals such as a transistor is mounted on the printed board 1. As shown in FIG. 6, one opening 6 is formed in the paper mask 4 of this embodiment. Same opening 6
Has a shape surrounding the three electrodes 3 arranged on the printed circuit board 1. In addition, in this embodiment, the cut 7 formed in the first or second embodiment is not provided.

The fourth embodiment is an embodiment in which an electronic component 5 having a plurality of terminals such as an IC is mounted on the printed board 1. As shown in FIG. 7, the paper mask 4 of this embodiment has a plurality of openings 6 at positions corresponding to the electrodes 3 of the printed circuit board 1.
Is provided. A notch 7a is formed between the adjacent openings 6, and an arcuate notch 7b is formed between the pair of opposing openings 6.

The method of removing the paper mask 4 from the printed circuit board 1 in the second to fourth embodiments is the same as in the first embodiment. That is, the tongue piece 8 on the lower side of the electronic component 5 is pulled out in the directions shown by the arrows in FIGS. Then, the opening 6 or the opening 6 and the notches 7, 7a, 7b
By passing the electronic component 5 through the opening formed by, the paper mask 4 can be removed from the printed board 1 without breaking it.

The present invention is not limited to the embodiment described above, but can be carried out as follows. (1) In the above embodiment, the water-soluble flux was used and the printed circuit board 1 was washed with pure water. However, this may be changed to a rosin flux and the printed circuit board 1 may be washed with an organic solvent. . Even in such a case, the same effect as that of the above embodiment can be obtained.

(2) In the above-mentioned embodiment, the paper made from bast fiber was used as the flux absorbing sheet, but it may be made from softwood forest pulp or hardwood forest pulp, for example. Further, the flux absorbing sheet is not limited to paper and may be made of, for example, a thin cloth.

(3) Although the printed circuit board 1 is cleaned in the cleaning step F in the above embodiment, the cleaning step F may be omitted and no cleaning may be performed. Even if the cleaning is not performed, since the excess flux on the printed board 1 is absorbed by the paper mask 4, the amount of the flux remaining on the printed board 1 is very small and there is no practical problem.

While the embodiments embodying the present invention have been described above, the technical ideas that can be understood from the above embodiments will be described below together with their effects. (A) The method of soldering an electronic component according to claim 1 or 2, wherein the flux absorbing sheet is made of paper.

According to the above construction, in addition to the effect of the electronic component soldering method according to the first or second aspect, it becomes easy to form the opening or notch of the flux absorbing sheet into a desired shape, and The manufacturing cost of the sheet can be reduced.

(B) In the invention according to claim 1 or 2, the solder cream is screen-printed on the printed board either before or after the step of adhering the flux absorbing sheet having the openings on the printed board. A method for soldering an electronic component, which comprises a step of applying by a method.

According to the above construction, in addition to the effects of the electronic component soldering method according to the first or second aspect, the time for the entire soldering process can be shortened and the soldering can be automated easily.

[0036]

According to the first aspect of the present invention, it is possible to suppress the adhesion of flux, flux residue or solder balls to the printed circuit board. Therefore, the cleaning time of the printed circuit board can be shortened.
Further, according to the present invention, the electronic component can be mounted in a state of being separated from the printed board by a predetermined distance determined by the thickness of the flux absorbing sheet. In addition, by changing the thickness of the flux absorbent sheet,
The mounting height of the component can be adjusted.

According to the invention described in claim 2, in addition to the above effects, in the step of removing the flux absorbing sheet from the printed circuit board, it is possible to remove the flux absorbing sheet from the printed circuit board without breaking it. ,
The same process can be shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing a soldering process in a first embodiment.

FIG. 2 is a perspective view showing a state in which a paper mask is attached on a printed circuit board and electronic components are mounted.

FIG. 3 is a sectional view showing a state where electronic components are mounted in the same manner.

FIG. 4 is an enlarged view of an essential part showing an opening and a cut of a paper mask.

FIG. 5 is an enlarged view of an essential part showing an opening and a notch of a paper mask in the second embodiment.

FIG. 6 is an enlarged view of a main part showing an opening and a cut of a paper mask in a third embodiment.

FIG. 7 is an enlarged view of a main part showing an opening and a notch of a paper mask in a fourth embodiment.

[Explanation of symbols]

1 ... Printed circuit board, 2 ... Solder cream (including solder and flux), 4 ... Paper mask (flux absorbing sheet), 5 ... Electronic component, 6 ... Opening, 7 ... Notch, 7a ...
Notch, 7b ... Notch.

Claims (2)

[Claims] 1. A step of adhering a flux absorbing sheet having an opening onto a printed circuit board, and disposing electronic components on the printed circuit board to which the flux absorbing sheet is adhered,
A soldering method for an electronic component, comprising: a step of soldering in an opening of a flux absorbing sheet; and a step of removing the flux absorbing sheet from a printed board after the soldering is completed. 2. The soldering method for an electronic component according to claim 1, wherein the flux absorbing sheet is formed with a plurality of the openings and a notch that connects the openings. .