JPH10313168A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent solder form bridging between lands by forming the lands for connecting flat mount type components on a reflowed soldered surface, and providing holes between the lands. SOLUTION: If the flowing direction of a circuit board 1 is set for soldering it, many solder bridges are apt to occur at both sides of the rear parts of component lands in the flowing direction. When recessed holes 3 are, e.g. formed, air stays in the recesses 3 at soldering and pushes up the solder deposited between the lands sufficient to well cut off the solder end, thereby preventing the solder bridge. The hole 3 may be an elongated circular hole having a major axis corresponding to the length of the land. In this case, it prevents a solder bridge from being formed though the hole. A through-hole formed at the same position as the hole 3 provides the same effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board on which electronic components are mounted, for example, and more particularly to a circuit board suitable for soldering electronic components having a narrow lead pitch.

[0002]

2. Description of the Related Art Conventionally, double-sided mounting substrates include a mounting type in which both surfaces are formed by surface mounting electronic components, and a mounting type in which both surfaces are formed by using an insertion type electronic component and a surface mounting type electronic component.
Particularly, in the latter, the soldering of the surface-mounted electronic components is performed by a reflow method using cream solder, and the insertion-type electronic components are performed by a flow method of dipping in a molten solder bath.

[0003] In a circuit board in which the insert type electronic component and the surface mount type electronic component coexist, the side composed of the surface mount type electronic component and the insert type electronic component is referred to as a component surface (hereinafter referred to by this name). The surface on the opposite side is referred to as a solder surface (hereinafter, referred to by this name).

[0004] In such soldering of a circuit board, in many cases, a lead of an insertion type electronic component and a part of a surface mount type electronic component are soldered on a solder surface side. Due to this configuration, many solder bridges are generated at the soldered portion (called a land) of the lead portion of the surface mount type electronic component during the flow soldering.
In particular, when the lands are arranged along the flowing direction of the substrate, a solder bridge as shown in FIG. 4 is formed between the lands on the rear end side (hereinafter, simply referred to as the rear end side) in the flowing direction of the substrate. Often occurs.

As a countermeasure, various ideas have been devised such as providing unused lands as component lands on the rear end side where solder bridges tend to occur, or providing a resist between component lands.

[0006]

However, when there are leads of an insertion type electronic component on the solder side, and some of them require a large amount of solder, the conditions for flow soldering must be adjusted. Because of the setting of excess solder, solder bridges generated between lands for surface mount components have not been solved yet.

This is because electronic components formed on the solder surface side have a narrow lead pitch, and the conventional method of forming unused lands and forming a resist between lands makes it difficult to form a bridge. It cannot be eliminated.

[0008] The solder bridge causes a decrease in the yield of electrical inspection and an increase in man-hours for rework.

The present invention has been made in view of the above conventional example, and provides a circuit board capable of preventing formation of a solder bridge between lands even when flow soldering is performed on a surface on which lands are formed at a narrow pitch. The purpose is to do.

[0010]

In order to achieve the above object, the present invention has the following arrangement. That is, a circuit board to which one surface is subjected to flow soldering, wherein the surface to which flow soldering is applied is provided with lands for connecting surface mount components and holes between the lands.

[0011] Alternatively, a circuit board having an insertion mounting type component mounted on a first surface and a surface mounting type component mounted on a second surface, wherein the surface mounting type component is connected to the second surface. Lands and holes between the lands are provided.

[0012]

Embodiments of the present invention will be described with reference to the drawings. (First Embodiment) FIGS. 1A and 1B show a solder surface of a circuit board for component mounting according to a first embodiment, wherein FIG. 1A is a top view and FIG. 1B is a cross-sectional view. In FIG. 1, 1 is a circuit board, 2 is a component land, and 3 is a plan view of a recessed hole of the present invention. The flow direction of the substrate is indicated by an arrow.

As shown in FIG. 1, the circuit board 1 at the time of soldering
When the flow direction is set as shown by the arrow, many solder bridges are likely to be generated on both sides of the rear part of the component land 2 in the flow direction.
Air is accumulated in the recess 3 during soldering. This air pushed up the solder adhering between the component lands, thereby improving the solder breakage and preventing the formation of a solder bridge.

FIG. 3 shows a circuit board for component mounting according to the first embodiment in which an insert type component having leads is soldered to a component surface by a flow soldering device, and a surface mount type component is soldered to a solder surface. It is a figure showing the situation seen from the side. The state without a solder bridge can be seen from the recessed hole 3. (Second Embodiment) FIG. 2 shows a circuit board for component mounting according to a second embodiment, wherein 1 is a circuit board, 2 is a component land, and 3 is a recessed elongated hole of the present invention. It is.
The cross-sectional shape is the same as in FIG. With the recessed holes formed in this way, solder bridges can be prevented as in the first embodiment. Further, since the shape of the hole 3 is an elliptical shape whose major axis is equivalent to the length of the land, it is possible to prevent solder bridges formed around the hole. The ellipse is used to provide a recess between the lands, and may be rectangular or elliptical. The same effect can be obtained by arranging a plurality of circular holes.

In addition to the first and second embodiments, the third embodiment
In the embodiment of the present invention, a similar effect could be exerted by providing the through-hole at the same place as the recessed hole 3.

The following table shows a comparison between the number of occurrences of solder bridges according to each embodiment and the number of occurrences according to the conventional method. The total number of parts lands is 24,000.

[0017] Thus, by forming the hole between the lands, the shape of the first embodiment is reduced to approximately 1/25 as compared with the conventional example,
In the shape of the second embodiment, the number of bridges is reduced to approximately 1/60, and in the third embodiment, to approximately 1/14.

As described above, in the single-sided board and the double-sided board of the component mounting circuit board, a recessed hole or a through hole is formed between the solder bonding component lands of the leaded package formed on the solder side. As a result, the breakage of the solder between the component leads is improved, and the solder bridge is eliminated despite the increase in the amount of solder.

In this configuration, it is necessary to set a place for forming a concave hole or a through hole between lands depending on a flowing direction of a circuit board at the time of soldering.

This is because, in the flow soldering, which is a soldering method, a lot of solder bridges are generated in the lands on the rear side of the component lands formed so that the lands are arranged along the flowing direction of the circuit board. is there.

In consideration of the above, the component lands are arranged in a direction perpendicular to the flowing direction of the circuit board, and a concave land is provided between the last land on the rear side with respect to the flowing direction and the land in front thereof. By forming holes and through holes, solder pools during flow soldering can be eliminated, and solder bridges during flow soldering can be eliminated.

[0022]

As described above, according to the present invention,
Even when flow soldering is performed on a surface where soldered parts are formed at a narrow pitch, solder bridges between soldered parts are less likely to occur, and soldering with extremely high reliability of electrical connection can be performed .

[0023]

[Brief description of the drawings]

FIG. 1 is a plan view of a local display of a circuit board for component mounting according to a first embodiment of the present invention.

FIG. 2 is a plan view of a local display of a circuit board for component mounting according to a second embodiment of the present invention.

FIG. 3 is a plan view of a local display when the package is soldered to the circuit board for component mounting according to the first embodiment of the present invention.

FIG. 4 is a plan view of a local display when soldering to a circuit board for component mounting according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Circuit board 2 Component land 3 Concave hole 4 Concave long hole 5 Package 6 Component lead 7 Solder bridge

Claims (6)

[Claims] 1. A circuit board having one surface subjected to flow soldering, wherein the surface to which flow soldering is applied is:
A circuit board comprising lands for connecting surface mount components and holes between the lands. 2. The land is arranged side by side in a transport direction of a circuit board during flow soldering, and the hole is provided between a land at a rear end in the transport direction and a land immediately before the land. The circuit board according to claim 1, wherein: 3. The method of claim 1, wherein the holes are drilled over a length substantially equal to the length of the lands.
Or the circuit board according to 2. 4. The hole according to claim 1, wherein the hole is a non-through hole formed from a surface on which the land is provided.
4. The circuit board according to any one of claims 1 to 3, 5. The circuit board according to claim 1, wherein said hole is a through hole. 6. An insertion mounting type component is mounted on the first surface,
A circuit board on which a surface mount component is mounted on a second surface, wherein a land for connecting the surface mount component and a hole between the lands are provided on the second surface. Circuit board.