JPS6081894A - Method of mounting electric circuit component on printed board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a method for attaching electrical circuit components to a printed circuit board, and relates to a method for mounting electrical circuit components onto a printed circuit board, in which soldering is performed reliably without being hindered by air or gas. This provides a method for soldering.

[Background technology]

In recent years, as electrical products have become smaller and thinner, there has been an increasing demand for the mounting thickness of printed circuit boards to be as thin as possible.
Circuit components such as coils are miniaturized as chip components and are mounted and soldered on one side of a printed circuit board without having to drill through holes in the printed circuit board.

However, circuit components such as electrolytic capacitors are difficult or expensive to make into chips, so it is necessary to pass the lead legs from the front surface of the printed circuit board through holes to the back surface of the printed circuit board as discrete components, and to solder the lead legs on the back surface.

At this time, in order to reduce the thickness when mounted on a printed circuit board, it is necessary to bring the bottom surface of the discrete component into close contact with the surface of the printed circuit board as much as possible.

The conventional method of mounting discrete components such as electrolytic capacitors on a printed circuit board will be described with reference to FIGS. 1 and 2.

In FIG. 1, a discrete component 2 is placed on the surface of a printed circuit board 1, and its lead leg 3 is inserted into a through hole 4 from the surface side.

At this time, the bottom surface of the discrete component is kept in close contact with the surface of the print 1 to the board.

Thereafter, the copper foil (printed foil) 6 attached to the back surface of the printed circuit board 1 and the lead legs 3 are immersed in a jet solder tank (dipped) to perform soldering 7.

Then, during soldering, the air in the through hole 4 expands due to heat, and the flux gas generated during soldering also expands due to the heat of the jet soldering bath.

By the way, the bottom of the component is in close contact with the surface of the board, so the air or gas trapped in the through hole 4 will blow out from the bottom end of the through hole 4, and the solder in a molten state will leak into the part 7. The soldering causes a blowhole 8 in the part 7, as shown in FIG.

Further, due to the expansion of the gas in the through hole 4, the thickness of the soldered portion 7 becomes thinner, which tends to cause a poor connection state such as a so-called tunnel solder state.

In such an incomplete soldered state, even the slightest impact or temperature change thereafter can cause the connection portion of the lead leg to come off, resulting in poor contact.

As a means to eliminate such drawbacks, conventionally, as shown in FIG. 3, an elongated recess 9 is formed on the surface of the printed circuit board 1, which is connected to the through hole 4 and extends outward from the contact area. ,
A method has been proposed in which gas, etc. in the through hole 4 is released to the outside via the recess 9. However, this method requires a step to provide vents such as recesses 9 in the printed circuit board 1 and the printed circuit board 1. Providing these may weaken the strength of the board, and the discrete components may have small diameters. In this case, it becomes difficult to provide the fourth part 9 adjacent to the through hole 4 for the lead leg 3.

In addition, as shown in Figure 1, the inventor discovered that even though the bottom surface of the discrete component is mounted tightly on the board, the solder often spreads near the through hole on the mounting surface side. Confirmed.

This is seen in products with a rubber sealant as the bottom surface, and is caused by the thermal behavior of the rubber during soldering, or in other words, the thermal deformation behavior such as partial warping of the sealant material itself. It is speculated that this is because the upper end of the through hole 4 located approximately in the center of the 1-point is not completely blocked by the bottom surface of the capacitor, and the solder that is still in a molten state is sucked up to the mount surface side. The solder sucked up in this way causes a problem of bridging between the through holes and shorting the lead legs.

[Summary of the invention]

An object of the present invention is to provide a novel method for mounting electrical components on a printed circuit board, which eliminates intermittent defects in addition to conventional methods.

In order to achieve these objectives, the present invention focuses on foamable paint that expands when heated, and applies the foamable paint to the surface of the printed circuit board that contacts the bottom of the discrete component, and then expands the paint to form the component. A space is formed between the bottom and the surface of the substrate, and flux gas, etc. in the five-holes of the lead legs are allowed to escape to the outside through this space. Additionally, the foamable paint acts as a barrier between adjacent lead legs, preventing the formation of bridges.

[Embodiments of the invention]

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 4 shows a basic embodiment of the method for mounting electrical components on a printed circuit board according to the present invention. In this embodiment, discrete components are mounted on a printed circuit board.

First, in step (a) of FIG. 4, at the discrete component mounting location on the surface of the printed circuit board 11, an unexpanded foaming paint 15 is applied to the area between the two through holes 13 for inserting the lead legs. is applied by screen printing.

This foamable paint has insulating properties, expands and solidifies three-dimensionally when heated, and substantially increases the coating thickness. EXPANCEL made by Nippon Philite ■
(trade name) mixed with acrylic 6-based resin, silicone-based resin, or ultraviolet curing resin may be used. In that case, the thickness of the paint, which is about 20 μm, increases to about 3 Q I1 m after expansion.

Next, in step (b), the lead leg 17 is inserted into the through hole 13 of the printed circuit board until the bottom surface of the discrete component 16 comes into contact with the surface of the printed circuit board, and the mount 1
-Attach to the location.

At this time, the bottom surface of the discrete component and the foamable paint 15 are almost in contact with each other.

Next, in step (c), the back side of the printed circuit board is
It is dipped into a jet soldering bath 18 whose bath temperature is controlled at a temperature of .degree. C. to 260.degree.

At this time, the surface temperature of the printed circuit board also rises, so even if it is not as strong as the stomach thirst T that causes the foaming paint 15 to expand, it expands and pushes up the component 16, causing the bottom of the component and the pudding 1 to rise.
A space 20 is formed between the surfaces of one substrate as shown in (d), and the flux gas is led out to the outside through the space 20 without being confined in the through hole 13. In this way, soldering is performed in a state where the occurrence of blow balls is prevented.

Furthermore, as shown in FIG. 4(E), even if the gas escapes and the solder is sucked into the space 20 through the through hole 13, the foamable paint 15 acts as a barrier, preventing the formation of bridges. This prevents short circuits in the lead legs.

In addition, in order to guide the gas etc. to the outside of the part along the application shape of the foamable paint, the foamable paint crosses between the through holes 13 as shown in the plan view of FIG. It is preferable to apply it in such a way that it protrudes.

As described above, in the above embodiment, blowholes and bridges can be prevented by simply applying foaming paint once using inexpensive equipment such as screen printing. There is no need for processing, and workability is good.

Next, a fifth example will be described in which the present invention is applied to a printed circuit board device in which chip components and discrete components are mixedly mounted.
This will be explained using figures.

In this embodiment, chip components are mounted on one side of a printed circuit board, and chip components and discrete components are mounted on the other side.

As an example of Discre-1~ parts, 40v++φ~6
Assume that an electrolytic capacitor with a diameter of 0 mm is used. The capacitor is formed by winding an electrode foil and impregnating it with a driving electrolyte.] A capacitor element is housed in a metal case, and the opening at the bottom of the metal case is sealed with a sealant such as rubber. The metal case has a general shape in which the outer periphery of the metal case is covered with an insulating tube.

First, in step (a), the surface of the printed circuit board 21 (surface A in the figure) with printed layers formed on both sides is discretized.
1. Apply foaming paint 22 to the parts where the parts are to be mounted by screen printing.

The thickness of the foamable coating 22 is approximately 20 μm.

Next, in step (b), solder paste 23 is applied by screen printing to the location on side A where the chip components are to be mounted. However, if the foaming paint applied in step (b) is too thick, the electrodes of the chip components may However, 9- A process difference is formed on the board where the screen plate cannot adhere to the copper foil land on the board to be soldered, and the solder paste is not sufficiently supplied, resulting in blurring of the solder paste printing. , good printing is inhibited. Therefore, it is conceivable to first print the solder paste and then print the foam coating 1, but since the solder paste is in a sticky state, it is a rotation to perform screen printing twice.

In this example, since the thickness of the foaming paint that is first screen printed is as thin as about 20 μm, the same substrate surface (
Even if similar printing is repeated on side A), the screen plate can adhere to the copper foil land, so there will be no fading and a sufficient amount of solder paste will be supplied.

Next, in a step (c), the chip component 24 is mounted on the A side, and in a step (d), a gluing flow on the A side is performed to solder the chip component 24.

In addition, when the board 21 is passed through a temperature rising furnace, soldering by this reflow soldering method (1 o'clock temperature rise (2
00°C to 250°C), the foamable paint expands.

Next, in step (E), apply adhesive 25 to the place on the back side (B side) of the printed circuit board where the chip components are to be mounted, and in step (F), adhere the chip component 26 to the B side with adhesive 25. Temporarily fix.

In step (f), if the main composition of the adhesive 25 is a thermosetting resin such as an epoxy resin, the temperature is 100°C to 150°C.
A predetermined curing treatment is carried out by holding the resin in the temperature range for about 0.5 to 1 hour, or in the case of an ultraviolet curable resin, by irradiating it with ultraviolet rays for several seconds.

Next, proceed to step (1), and mount the discrete component 27 on the foamable paint 22 from side A, and in step (d),
The chip components 26 and discrete components 27 on the 8th surface are soldered by dipping the surface into a half tank with the surface as the dipping surface.

At this time, as in the embodiment shown in FIG. 4, flux gas and the like escape outward due to the expansion of the foamable paint, thereby preventing the formation of blowholes and further preventing the formation of bridges.

Although the step of applying the adhesive to the foamable paint and solder paste 1 described above was performed by screen printing, the same effect can be obtained even if the adhesive is applied by other methods.

The timing of expansion of foaming paint is not limited to solder dip, but also during flow soldering of chip parts,
Alternatively, depending on the mounting process, it can be carried out incidentally during a temperature raising process such as a curing process when temporarily fixing chip components, and the above effect can be obtained even if the expansion is performed in advance before mounting the discrete components. In terms of the mounting process, the coating process represented by the screen printing method has the advantage of being easier to implement and cheaper in terms of equipment investment compared to the mounting process where parts are attached using an automatic machine such as an insert machine. .

When the coated material is used as a kind of spacer, the thicker the coated material, the more reliable the blowhole prevention effect becomes. , Service Map Ink and other conventionally used paints are insufficient, and we have developed a new paint with an appropriate viscosity.
Also, paints with appropriate thixotropy must be selected.

However, in general, when applying a thick coating, in other words, applying a large amount within a limited area, it is difficult to control the thixotropic properties of the paint, which tends to deteriorate printing accuracy, and screen printing Also, slumbing, mF31 bleeding, etc. are likely to occur. On the other hand, a method of repeating printing until a predetermined thickness is achieved is also considered, but this increases the thickness by as much as 2, which is not practical.

However, according to the present invention, it is possible to reduce the coating thickness, and because the method uses the expansion of the paint after coating to ensure a predetermined thickness, it is possible to make parts with high quality without deteriorating printing accuracy. This is particularly suitable for dense packaging.

Further, as described in the embodiments, if the substrate is a mixed substrate, screen printing after application of the foaming paint is possible, and workability is good.

As described above, the mounting method of the present invention involves applying an insulating foaming paint in an unexpanded state to the mounting location of an electrical circuit component whose bottom surface is in close contact with the surface of a printed circuit board. a step of inserting the lead leg of the electric circuit component into the through hole provided in the print 1 to the board and mounting the electric circuit component at the mounting location; and expanding the foamable paint to increase the coating thickness. At least a step of soldering the lead legs and the copper foil on the back side of the printed circuit board in a substantially increased state by a solder dip method, and the soldering prevents defects and improves productivity. etc., its practical effects are great.

[Brief explanation of the drawing]

1 and 2 are sectional views of main parts of a conventional printed circuit board device, FIG. 3 is a sectional view of main parts of another conventional printed circuit board device, and FIG. 4 is a printed circuit board of an electric circuit component according to the present invention. FIG. 5 is a cross-sectional view of a main part showing a basic embodiment of the mounting method of the present invention, and FIG. 5 is a process diagram showing another embodiment of the method of mounting an electric circuit component on a printed circuit board according to the present invention. Explanation of symbols 1.11.21...Print 1-board 2.16.27...Discrete parts 3.17...
・Lead leg 4.13...Through hole 6.12...Copper foil 23...Solder paste 15.22...Foaming paint 24.26...Chip parts 25...Adhesive agent Akira Asamura 15 - Procedural amendment export) 20 Name of the invention Method for mounting electric circuit components on a printed circuit board 3 Relationship with the case of the person making the amendment Patent applicant address Name Name Aiwa Co., Ltd. 4, Agent 6, Number of inventions increased by amendment 1, “■ Culm difference” in the second line of page 10 of the specification was changed to “height difference”
Correct. 1-

Claims (1)

[Claims] A step of applying an unexpanded foaming paint with good insulating properties to a mounting portion of an electric circuit component having a bottom surface that is brought into close contact with the surface of a printed circuit board; A step of installing the electric circuit component on the substrate before or after the expansion of the foamable paint by inserting the legs into the holes formed in the mounting I of the printed circuit board; The present invention is characterized by comprising at least the step of soldering the lead legs and the copper foil on the back surface of the printed circuit board by a solder dip method in a state where the coating thickness is substantially increased by expanding the paint. A method of mounting electrical circuit components on a printed circuit board.