JP2002261415A - Connecting structure of circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a connecting section, especially width of it, between circuit boards. SOLUTION: A first circuit board 11 and a second circuit board 12 are connected by a first connecting section C1, the first circuit board 11 and a third circuit board 13 are connected by a second connecting section C2, and these first connecting section C1 and the second connecting section C2 are respectively arranged on the two sides near to one end of the first rectangular circuit board 11. Dividing the connection of the first circuit board 11 and the second circuit board 12 into two opposite faces allow the width of the connecting section C1 and C2 to be miniaturized. A third connecting section C3 for connecting the second circuit board 12 and the thirds circuit board 13 is arranged in the vicinity of proximal section of the first connecting section C1 and the second connecting section C2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board connection structure for electrically connecting circuit boards such as a printed wiring board.

[0002]

2. Description of the Related Art Circuit boards such as printed wiring boards are electrically connected to each other by soldering, by thermocompression bonding via solder, by pressure contact between exposed conductors,
There are various connection means such as those connected by a mounted connector.

[0005] For example, FIG. 5 shows a first conventional example, and is a diagram showing a connection structure between circuit boards by soldering. The first circuit board 51 is flexible. The conductor exposed portions 51a and 52a are formed at respective outer ends of the second circuit board 52, and these conductor exposed portions 51a and 52a are connected by soldering. Therefore, all of the number of wirings from the flexible first circuit board 51 to the flexible second circuit board 52 are equal to the connection portions C.
Are connected at the exposed conductor portions 51a and 52a.

FIG. 6 is a diagram showing a connection structure between circuit boards proposed in, for example, Japanese Utility Model Publication No. 2-199090 as a second conventional example.
The circuit board 61 has a conductor exposed portion 61a forming the first connection portion C1, and a conductor exposed portion provided at the outer end of the rigid first circuit board 61 forming the second connection portion C2. Portion 61b, and these conductor exposed portions 61a, 61b
Are provided on the same surface. The hard second circuit board 62 includes a conductor exposed portion 62a that forms the first connection portion C1, and a second connection portion C2 that is formed on the end of the hard second circuit board 62. Conductor exposed portion 62b provided
And the conductor exposed portions 62a and 62b are provided on the same surface.

The metal rod 64 forming the first connection portion C 1 is previously connected to the conductor exposed portion 6 of the hard first circuit board 61.
The metal bar 64 is inserted into the hole of the first circuit board 1a and soldered to the conductor exposed portion 6 of the hard second circuit board 62.
2a is soldered in a state of penetrating the hole,
Circuit board 61 and a hard second circuit board 62 are connected.

Further, both ends of the metal wire 65 constituting the second connection portion C2 are respectively connected to the conductor exposed portion 61b of the hard first circuit board 61 and the hard second circuit board 62
The first hard circuit board 61 and the second hard circuit board 62 are connected to each other by soldering to the exposed conductor 62b. Therefore, the wiring from the hard first circuit board 61 to the hard second circuit board 62 is connected between the first connection portion C1 via the metal bar 64 and the second connection portion C2. There are two types, one connected via a metal wire 65.

FIG. 7 is a perspective view of a connection structure between circuit boards as a third conventional example. A rigid circuit board 71 has a flexible structure at a first connection portion C1 at the outer end. The first circuit board 72 is connected to the first
A flexible second circuit board 73 is connected to a second connection portion C2 on the same surface as the connection portion C1 and at an external end at a location apart from the connection portion C1. Further, the flexible second circuit board 73 is connected to the flexible first circuit board 72 at the third connection portion C3.

Therefore, the wiring from the hard circuit board 71 to the flexible first circuit board 72 is connected at the first connection portion C1 and connected at the second connection portion C2. There are two types.

[0009]

However, according to the first conventional example, all of the number of wirings from the first flexible circuit board 51 to the second flexible circuit board 52 are connected. Since the connection is made at the portion C, the width L1 of the connection portion C increases as the number of wirings increases. At this time, since the interval between the exposed conductors 51a and 52a cannot be narrowed unnecessarily from the viewpoint of substrate accuracy, workability, and the like.
The connection portion C becomes particularly large in the width direction of the conductor exposed portions 51a and 52a. As a result, the mounting area of the electrical component on the flexible first circuit board 51 is reduced by the increase in the area of the connection portion C. If the reduced area is to be compensated for, the flexibility of There is a possibility that the circuit board becomes large and the manufacturing cost increases.

In the first conventional example, the case where the flexible first and second circuit boards 51 and 52 are connected by soldering has been described. However, for example, thermocompression bonding is performed via solder. In the case or when the exposed conductors are pressed against each other so as to face each other, the same adverse effect occurs because the interval between the exposed portions of the conductor cannot be narrowed from the viewpoint of connection reliability.

According to the second conventional example, the hard first
The wiring from the circuit board 61 to the hard second circuit board 62 is connected to the first connection part C1 via the metal bar 64 and to the metal wire 65 at the second connection part C2.
Metal rod 6
The presence of the conductor exposed portions 61a and 62a to which the solder 4 is soldered imposes a great restriction on the mounting of electric components on the hard first circuit board 61 and the hard second circuit board 62. Further, the conductor exposed portion 61 is connected to the metal wire 65 one by one.
Since it is necessary to solder to the b and 62b, the workability is poor, and further, the installation interval L1 of the conductor exposed portions 61b and 62b needs to be wider than the first conventional example due to the workability. .

Therefore, also in the case of this conventional example, especially the connection portion becomes large in the width direction. As a result, the mounting of the electric components on the rigid first circuit board 61 and the rigid second circuit board 62 is performed. If the area is reduced and the reduced area is to be compensated for, the rigid circuit boards 61 and 62 may become large in size, increasing the manufacturing cost.

Further, according to the third conventional example, the wiring from the hard circuit board 71 to the flexible first circuit board 72 is connected to the first connection portion C1 and the second connection portion C1.
Are connected to each other at the connection portion C2, but since they are present on the same surface, the total area required for connection is substantially equal to that of the first conventional example. The same problem as in the conventional example 1 remains.

Further, if the second connecting portion C2 is arranged on the surface opposite to the first connecting portion C1, the area required for connection can be reduced by half. 2
Circuit board 73 has a second connection portion C2 and a third connection portion C3.
Therefore, the size is increased to increase the production cost. Further, the first flexible circuit board 72 and the second flexible circuit board
Even if a single flexible circuit board is used to cover the circuit board 73, the size of the circuit board is increased, and the manufacturing cost is similarly increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to reduce the width of a connection portion between circuit boards in the width direction to secure a mounting area for components. Another object of the present invention is to provide a connection structure for a circuit board that can connect many signal lines while improving workability and electrical contact reliability and reducing manufacturing cost.

[0016]

According to a first aspect of the present invention, a first circuit board is connected to a second circuit board, and the first circuit board is connected to the second circuit board. A circuit board connection structure for connecting the first circuit board and the second circuit board via a third circuit board; and a first connection portion connecting the first circuit board and the second circuit board. The second connection part for connecting the circuit board and the third circuit board is disposed on each of the front and back surfaces close to one end of the first circuit board, and the second circuit board and the second circuit board are connected to each other. A third connecting portion for connecting the third connecting portion to the circuit board is arranged at a position close to the first connecting portion and the second connecting portion.

According to the present invention, the connection between the first circuit board and the second circuit board is divided into two on the front and back sides, whereby the size in the width direction can be reduced. Since the third circuit board is provided near the first and second connection parts, a small and inexpensive third circuit board is sufficient. Further, the electrical contact reliability at the connection portion is not different from the conventional one.

According to a second aspect of the present invention, the first circuit board is connected to the second circuit board, and the first circuit board and the second circuit board are connected via the third circuit board. In the connection structure of the circuit board for connecting the first circuit board, the first connection portion for connecting the first circuit board and the second circuit board is arranged at a position including one edge of the first circuit board. A second connecting portion connecting the first circuit board and the third circuit board is disposed at a position close to the first connecting portion and not including the one side edge; A third connection portion for connecting the second circuit board and the third circuit board is arranged at a position close to the first connection portion.

According to the present invention, by dividing the connection between the first circuit board and the second circuit board into two parts, it is possible to reduce the size of the connection part in the width direction, and to make the third connection part smaller. , First
Since the third circuit board is provided in the vicinity of the connecting portion, a small and inexpensive circuit board is sufficient.

According to a third aspect of the present invention, the second circuit board is a double-sided circuit board having conductive circuits formed on both front and back sides, and the second circuit board extends from the first connection portion to the second circuit board side. The conductor circuit to be drawn out is formed at least in the vicinity of the third connection portion on the side opposite to the third connection portion.

According to the present invention, it is possible to arrange the wiring from the first connection portion on the side opposite to the third connection portion, thereby reducing the size of the second circuit board in the width direction. Is achieved.

According to a fourth aspect of the present invention, the first circuit board is connected to the second circuit board, and the second circuit board is a flexible circuit board having a main portion and a branch portion. ,
A circuit board connection structure capable of connecting the first circuit board to the first circuit board by folding back the branch section; a first connection section connecting the first circuit board to a main part of the second circuit board;
A second connecting portion that connects the first circuit board and the branch portion of the second circuit board is disposed on both front and back sides close to one end of the first circuit board. It is characterized by the following.

According to the present invention, the connection of the main part as the first connection part and the connection of the branch part as the second connection part
Since the first circuit board is provided so as to be on both front and back sides at one end, the connection between the first circuit board and the second circuit board is bisected on both front and back sides, and the width can be reduced. Can be

According to a fifth aspect of the present invention, the first circuit board is connected to the second circuit board, and the second circuit board is a flexible circuit board having a main portion and a branch portion. ,
In the connection structure of a circuit board that can be connected to the first circuit board by folding back the branch portion, a first connection portion that connects the first circuit board and a main portion of the second circuit board includes the first connection portion, A second connection portion, which is arranged at a position including one side edge of the first circuit board and connects the first circuit board and a branch portion of the second circuit board, is connected to the first connection portion. It is arranged at a position adjacent to and not including the one side edge.

According to the present invention, the connection of the main portion as the first connection portion is arranged at a location including one side edge of the first circuit board, and the branch portion as the second connection portion. Is disposed at a position adjacent to the first connection portion and not including the one side edge of the first circuit board, so that the connection between the first circuit board and the second circuit board is divided into two. The size of the width can be reduced.

The invention according to claim 6 is characterized in that the second circuit board is a flexible single-sided circuit board having a conductor circuit formed only on one side.

According to the present invention, since the second circuit board is a flexible single-sided circuit board having a conductor only on one side, the manufacturing cost is reduced.

[0028]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIGS. 1 (A) to 1 (C)
FIG. 1 is a view showing a first embodiment of the present invention, in which a flexible (flexible) first circuit board 11 is shown.
Has a conductor-exposed portion 11a constituting a first connection portion C1 on the back surface and a second exposed portion on the front surface.
Has the conductor exposed portion 11b constituting the connection portion C2. Further, the flexible second circuit board 12 has a rectangular shape smaller than the first circuit board 11, and is connected to the conductor exposed portion 12a forming the first connection portion C1 and the third connection portion. Part C
3 and a conductor-exposed portion 12b. Furthermore,
The flexible third circuit board 13 has a conductor exposed portion 13a forming the second connection portion C2 and a conductor exposed portion 13b forming the third connection portion C3.

In the above, the first circuit board 11 and the second
In the first connection portion C1, the conductor exposed portion 11a and the conductor exposed portion 12a are connected to the circuit board 12 by thermocompression bonding via solder. Further, the second circuit board 12 and the third circuit board 13 are connected to each other at the third connection portion C3.
The exposed conductor portion 12b and the exposed conductor portion 13b are connected by thermocompression bonding via solder. Further, the first circuit board 1
The first and third circuit boards 13 are connected to each other at the second connection portion C2 by thermocompression bonding between the conductor exposed portion 11b and the conductor exposed portion 13a via solder.

For this reason, the wiring from the first circuit board 11 to the second circuit board 12 is directly connected to the first connection portion C1 via the conductor exposed portions 11a and 12a, and to the second connection portion C1. In the connection portion C2 and the third connection portion C3, the third
And indirectly connected via the circuit board 13 of
The first circuit board 11 is bisected on both front and back sides. Thereby, for example, as shown in FIG. 1B, the required dimension L1 in the width direction of the second connection portion C2 can be reduced.

The second circuit board 12 is a so-called double-sided circuit board in which conductor circuits 120a and 120b are formed on the front and back sides, and the wiring from the first connection portion C1 is a conductor circuit 120a indicated by a broken line. As shown by the third connection portion C3
Is arranged on the surface opposite to the surface on which the third connection portion C3 is arranged. Therefore, in the second circuit board 12, the dimension L2 in the width direction near the third connection portion C3 is set.
It is only necessary to ensure a width in which the conductor exposed portion 12b can be installed, and the third connecting portion C3 is disposed near the first connecting portion C1 and the second connecting portion C2. 2
The circuit board 12 can be made as small as possible.

[Second Embodiment] FIG. 2 is a view showing a second embodiment of the present invention. In FIG. 2, a rigid (rigid) first circuit board 21 has A conductor exposed portion 21a constituting the first connection portion C1 is provided at an end of the substrate including one side edge thereof, and a second connection portion C2 which is close to the first connection portion C1 and is provided on the back surface. The conductor exposed part 21b to be constituted is provided. Further, the hard second circuit board 22 is provided with a conductor exposed portion 22 forming the first connection portion C1.
a and a third conductor exposed portion 22b provided near the first connection portion C1. Further, the flexible third circuit board 23 is provided with a conductor exposed portion 23a constituting the second connection portion C2 and a conductor exposed portion 23b constituting the third connection portion C3.

In the above, the first circuit board 21 and the second
Is connected to the circuit board 22 by soldering the conductor exposed portion 21a and the conductor exposed portion 22a at the first connection portion C1. Further, the second circuit board 22 and the third circuit board 23 are connected at the third connection portion C3 by thermocompression bonding of the conductor exposed portion 22b and the conductor exposed portion 23b in advance via solder. Further, the first circuit board 21 and the third circuit board 23 are connected by soldering the conductor exposed part 21b and the conductor exposed part 23a at the second connection part C2.

Therefore, the wiring from the first circuit board 21 to the second circuit board 22 is directly connected to the first connection portion C1 via the conductor exposed portions 21a and 22a, and to the second connection portion. The part C2 and the third connection part C3 are divided into two parts: one connected indirectly via the third circuit board 23. Thereby, for example, as shown in FIG. 2C, the required dimension L1 in the width direction of the first connection portion C1 can be reduced.

The second circuit board 22 has conductor exposed portions 22a and 22b and conductor circuits 220a and 220b on both front and back sides.
0b is formed, the wiring from the first connection portion C1 is a conductor exposed portion 22a indicated by a broken line.
And a solid line conductor circuit 220a. The conductor circuit 220a is connected to the third connection portion C3 in the vicinity of the third connection portion C3.
Are arranged on the surface opposite to the surface on which the connecting portion C3 is arranged. For this reason, in the second circuit board 22,
The dimension L2 in the width direction in the vicinity of the third connection portion C3 only needs to ensure a width in which the conductor exposed portion 22b can be installed. Furthermore, since the third connection portion C3 is provided at a position close to the first connection portion C1, the second circuit board 22 can be reduced in size.

[Third Embodiment] FIG. 3 is a view showing a third embodiment of the present invention. In FIG. 3, a flexible first circuit board 31 has a first circuit board on its back surface. Is provided with a conductor exposed portion 31a constituting the second connection portion C2, and a conductor exposed portion 31b constituting the second connection portion C2 is provided on the surface. The second circuit board 32 is a flexible circuit board having a main part 32-1 and a branch part 32-2. The main part 32-1 has a first connection part C1. The conductor exposed portion 32a is provided, and the branch portion 32-2 is provided with the conductor exposed portion 32b constituting the second connection portion C2.

In the above, the first circuit board 31 and the second
Is connected to the circuit board 32 by thermocompression bonding of the conductor exposed portions 31a and 32a via solder at the first connection portion C1. Further, the second circuit board 32 is a so-called single-sided circuit board having a conductor circuit only on one side, and the first circuit board 31 and the second circuit board 32 include a branch portion 32-2. The conductor exposed portion 32b is the main portion 32-1.
Is folded back so as to face the conductor exposed portion 32a of the second conductor connecting portion C2.
2b are connected by thermocompression bonding via solder.

Accordingly, the wiring from the first circuit board 31 to the second circuit board 32 is directly connected to the first connection portion C1 via the conductor exposed portions 31a and 32a,
The second connection portion C2 is connected via the conductor exposed portions 31b and 32b, and is divided into two sides on the front and back surfaces. Therefore, for example, as shown in FIG. 3B, the required dimension L1 in the width direction of the second connection portion C2 can be reduced. Further, since the second circuit board 32 is a flexible single-sided circuit board, the manufacturing cost can be reduced.

[Fourth Embodiment] FIG. 4 is a view showing a fourth embodiment of the present invention. In FIG. 4, a rigid (rigid) first circuit board 41 has one side thereof. Conductor exposed portion 41 constituting first connection portion C1 provided at the edge
a and a second connecting portion C2 that is close to the first connecting portion C1 and
And a conductor exposed portion 41b. The second circuit board 42 is a flexible circuit board having a main part 42-1 and a branch part 42-2, and the main part 42-1 has a first connection part C1. The conductor exposed part 42a which comprises is provided, The conductor exposed part 42b which comprises the 2nd connection part C2 is provided in the branch part 42-2.

As described above, the first circuit board 41 and the second circuit board 42 are connected by soldering the conductor exposed portions 41a and 42a at the first connection portion C1. The second circuit board 42 is a so-called flexible single-sided circuit board having a conductor circuit formed only on one side,
The first circuit board 41 and the second circuit board 42 are folded back so that the branch portion 42-2 is disposed so that the conductor exposed portion 42b faces the conductor exposed portion 42a of the main portion 42-1. In the second connection portion C2, the conductor exposed portions 41b, 42
b are connected by thermocompression bonding via solder.

Therefore, the wiring from the first circuit board 41 to the second circuit board 42 is directly connected to the first connection portion C1 via the conductor exposed portions 41a and 42a,
The second connection part C2 is divided into two parts that are connected via the conductor exposed parts 41b and 42b. Therefore, for example, as shown in FIG.
Required dimension L1 in the width direction can be reduced. Further, since the second circuit board 42 is a flexible single-sided circuit board, the manufacturing cost can be reduced.

In the above description, connection between circuit boards by soldering or thermocompression bonding via solder has been described as an example. However, the connection means is not limited to this. It is also possible to apply a means in which the conductor exposed portions are brought into contact with each other and pressed against each other. Further, the combination of the connection between the hard circuit board and the flexible circuit board is not limited to the above embodiment.

That is, according to the above-described embodiment, by dividing the connection between the first circuit board and the second circuit board into the front and back surfaces, the width of the connection portion in the width direction can be reduced. Becomes For this reason, when connecting the circuit boards, it is possible to reduce the size of the connection portion between the circuit boards, particularly in the width direction, without affecting workability and electrical contact reliability at all. It does not affect the component mounting area. Further, according to the present embodiment, since the connection between the circuit boards is divided into two on the front and back surfaces, more signal lines can be connected. Therefore, it is not necessary to increase the size of the circuit board, and the manufacturing cost can be reduced while maintaining workability and contact reliability.

Further, according to the present embodiment, the connection between the second circuit board and the third circuit board is provided near the connection between the first and second circuit boards. The circuit board need only be small, and the manufacturing cost of the third circuit board can be reduced.

[0046]

As described above, according to the first aspect of the present invention, the first connection portion for connecting the first circuit board and the second circuit board, the first connection portion for connecting the first circuit board and the second connection portion are provided. And the second connection part for connecting the circuit board of No. 3 to the front and back sides of the first circuit board close to one end of the first circuit board. Thus, the dimension of the connecting portion in the width direction can be reduced. For this reason, it is possible to secure a mounting area of the circuit board and to connect many signal lines while maintaining electrical contact reliability. In addition, since the third connection portion that connects the second circuit board and the third circuit board is provided near the first and second connection portions, the size of the third circuit board can be reduced. The manufacturing cost of the third circuit board can be reduced.

According to the second aspect of the present invention, the first connecting portion for connecting the first circuit board and the second circuit board is formed by:
The second connection portion, which is arranged at a position including one side edge of the first circuit board and connects the first circuit board and the third circuit board, is close to the first connection portion and the first connection portion is connected to the first connection portion. Since it is located at a position that does not include the side edge, the connection part between the circuit boards is divided into two parts on both front and back sides, reducing the width dimension of the connection part and connecting many signal lines while securing the mounting area can do. In addition, since the third connection portion that connects the second circuit board and the third circuit board is provided near the first connection portion,
The size of the third circuit board can be reduced, and the manufacturing cost can be reduced.

According to the third aspect of the present invention, the second
Is a double-sided circuit board having a conductor circuit formed on both front and back sides, and a conductor circuit drawn from the first connection portion to the second circuit board side is provided at least in the vicinity of the third connection portion. Since the wiring is formed on the surface opposite to the third connection, the wiring from the first connection can be arranged on the surface opposite to the third connection, and the width of the connection in the second circuit board can be reduced. The dimension in the direction can be reduced.

According to the fourth aspect of the present invention, the first connecting portion for connecting the first circuit board to the main portion of the second circuit board, and the first connecting portion for connecting the first circuit board and the second circuit board. Since the second connection part for connecting to the branch part is disposed on both the front and back sides near one end of the first circuit board, the connection between the first and second circuit boards is divided into two parts. As a result, it is possible to connect many signal lines while reducing the width of the connecting portion in the width direction and securing the mounting area.

According to the fifth aspect of the present invention, the first connecting portion for connecting the first circuit board and the main part of the second circuit board is arranged at one side edge of the first circuit board. Since the second connecting portion for connecting the first circuit board and the branch portion of the second circuit board is arranged at a position adjacent to the first connecting portion and not including one side edge, By dividing the connection between the first circuit board and the second circuit board into two, the width in the width direction of the connection portion can be reduced, and many signal lines can be connected while securing a mounting area.

According to the present invention, since the second circuit board is a flexible single-sided circuit board having a conductor circuit formed only on one side, the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1A is a side view after connecting substrates in the first embodiment, FIG. 1B is a perspective view thereof, and FIG. 1C is an exploded perspective view thereof.

FIG. 2A is a side view after connecting substrates in a second embodiment, FIG. 2B is a perspective view thereof, and FIG. 2C is an exploded perspective view thereof.

FIG. 3A is a side view after connection of substrates according to the third embodiment, FIG. 3B is a perspective view thereof, and FIG. 3C is an exploded perspective view thereof.

FIG. 4A is a side view after connection of substrates in a fourth embodiment, FIG. 4B is a perspective view thereof, and FIG. 4C is an exploded perspective view thereof.

FIG. 5A is a side view of a first conventional example after connecting substrates, FIG. 5B is a perspective view thereof, and FIG. 5C is an exploded perspective view thereof.

FIG. 6A is a side view of a second conventional example after connecting substrates, FIG. 6B is a perspective view thereof, and FIG. 6C is an exploded perspective view thereof.

FIG. 7 is a perspective view after connection of substrates in a third conventional example.

[Explanation of symbols]

 11, 21, 31, 41 First circuit board 11a, 11b Conductor exposed part 12, 22, 32, 42 Second circuit board 12a, 12b Conductor exposed part 13, 23 Third circuit board 13a, 13b Conductor exposed part 64 Metal rod 65 Metal wire C1 First connection part C2 Second connection part C3 Third connection part

Claims (6)

[Claims] 1. A circuit board for connecting a first circuit board and a second circuit board and connecting the first circuit board and the second circuit board via a third circuit board. In the connection structure, a first connecting the first circuit board and the second circuit board.
And a second connecting portion for connecting the first circuit board and the third circuit board are respectively disposed on both front and back sides close to one end of the first circuit board. A third connecting the second circuit board and the third circuit board;
Wherein the connecting portion is disposed at a position close to the first connecting portion and the second connecting portion. 2. A circuit board for connecting a first circuit board and a second circuit board and connecting the first circuit board and the second circuit board via a third circuit board. In the connection structure, a first connecting the first circuit board and the second circuit board.
Is disposed at a position including one edge of the first circuit board, and a second connecting section connects the first circuit board and the third circuit board.
Is disposed at a position close to the first connection part and not including the one side edge, and further includes a third connection connecting the second circuit board and the third circuit board. The connection structure of a circuit board, wherein the unit is disposed at a position close to the first connection unit. 3. The second circuit board is a double-sided circuit board having conductor circuits formed on both front and back sides, and the conductor circuit drawn out from the first connection portion to the second circuit board side is The circuit board connection structure according to claim 1, wherein at least a portion near the third connection portion is formed on a surface opposite to the third connection portion. 4. A circuit for connecting a first circuit board and a second circuit board, wherein the second circuit board is a flexible circuit board having a main part and a branch part, and the branch part is folded back. A circuit board connection structure connectable to the first circuit board, wherein: a first connection section connecting the first circuit board to a main part of the second circuit board; and the first circuit The second connection portion that connects the substrate and the branch portion of the second circuit board is disposed on both front and rear sides close to one end of the first circuit board. Circuit board connection structure. 5. A circuit board for connecting a first circuit board and a second circuit board, wherein the second circuit board is a flexible circuit board having a main part and a branch part, and the branch part is folded back. In the connection structure of a circuit board connectable to the first circuit board, a first connection part connecting the first circuit board and a main part of a second circuit board is provided by the first circuit board A second connecting portion, which is disposed at one side edge of the first connecting portion and connects the first circuit board and the branch portion of the second circuit board, is adjacent to the first connecting portion and the one side edge A connection structure for a circuit board, wherein the connection structure is arranged at a position not including 6. The circuit board connection structure according to claim 4, wherein the second circuit board is a flexible single-sided circuit board having a conductor circuit formed only on one side.