JPH10335866A - Heat radiation structure for circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the heat discharge structure of a circuit board by which the electronic circuit of a control system constituted on the same flexible board is not affected by the thermal effects from the electronic circuit of a heat generation system. SOLUTION: In the heat radiation structure of the circuit board, an electronic circuit part 4a of the heat generation system and an electronic circuit part 4b of the control system are provided for the surface of the flexible board 1 having flexibility and heat generated in the electronic circuit part 4a of the heat generation system is radiated to the heat sink 22 which is provided at the back of the flexible board 1. A groove 22c, which reduces the cross section area of the position of the heat sink 22 corresponding to the boundary of the electronic circuit part of the heat radiation system and the electronic circuit part 4b of the control system, and inhibits heat conduction in a lateral direction in the heat sink 22, is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat radiating structure for a flexible substrate, and more particularly to a control system electronic circuit mounted on the same flexible substrate so as not to be thermally affected by a heat generating electronic circuit. The present invention relates to a heat dissipation structure for a simple circuit board.

[0002]

2. Description of the Related Art In order to reduce the size and ease of mounting of electronic devices and to reduce costs, a control system electronic circuit and a heating system (hereinafter referred to as a power system) are mounted on a single flexible substrate. Some electronic circuits are configured. 7A and 7B are views for explaining a conventional heat dissipation structure of a circuit board, wherein FIG. 7A is a top view, and FIG. 7B is a cross-sectional view along AA. Hereinafter, description will be made with reference to the drawings.

[0003] Reference numeral 1 denotes a flexible substrate in which a wiring pattern is formed on a flexible film.
Power transistor 4 which generates a large amount of heat but withstands high temperatures
The power electronic circuit 4a composed of a power electronic circuit 1 and the like is formed on the control board unit 1b. The control electronic circuit 4b composed of an integrated circuit 42 and the like that generates a small amount of heat but is weak to high temperatures. Reference numeral 29 denotes a radiator plate made of a metal having good heat conductivity such as aluminum which radiates heat generated in the power board portion 1a to the outside. The flexible board 1 is fixed to the four corners of the radiator plate 29 to a casing or the like. Mounting hole 29d is provided. Reference numeral 3 denotes an adhesive for bonding the flexible substrate 1 and the heat sink 29. The adhesive 3 is used for the flexible substrate 1
Of the flexible substrate 1 and the heat sink 29
Is in close contact.

First, a method of manufacturing a circuit board will be described. The adhesive 3 is applied on the heat radiating plate 29, and the flexible substrate 1 is placed on the adhesive 3 and bonded by heating. In addition, adhesive 3
Alternatively, a method in which a film-shaped adhesive sheet having a predetermined shape is sandwiched between the flexible substrate 1 and the heat radiating plate 29 may be used. The paste solder 5 is printed on the electrode 1c of the flexible substrate 1 to which the heat sink 29 is attached, and then the corresponding electronic components such as the power transistor 41 and the integrated circuit 42 are mounted. Thereafter, the circuit board is completed by heating in a furnace to melt the solder 5 and soldering the electrode 1c of the flexible board 1 to the power transistor 41 and the terminals 41a and 42a of the integrated circuit 42.

Next, the heat radiation effect of the circuit board will be described. The heat generated in the power board section 1a is effectively radiated to the power radiating portion 29a of the power system of the radiating plate 29 which is in close contact. In addition, the control substrate 1b generates less heat and does not raise the temperature of the integrated circuit 42 or the like. Further, since the flexible substrate 1 is bonded to the heat sink 29, the flexible substrate 1 can be securely fixed to the housing or the like via the mounting hole 29d.

[0006]

In the conventional heat radiating structure for a circuit board, the heat radiating plate 29 is composed of a single plate. Therefore, the power radiating portion 29a of the power system radiates the power radiating portion 29a. The generated heat is radiated to the radiator 29b of the control system in the horizontal direction.
And is transmitted to the control board unit 1b in close contact.
Then, there arises a problem that the heat-sensitive integrated circuit 42 is destroyed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat radiating structure for a circuit board in which a control electronic circuit formed on the same flexible substrate is not thermally affected by a power electronic circuit.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a flexible printed circuit board having both a heating system electronic circuit section and a control system electronic circuit section on the surface of a flexible board. In the heat dissipation structure of the circuit board for releasing the heat generated in the electronic circuit portion of the heat generation system to the heat dissipation plate provided on the back surface of the electronic device, only the rear surface of the flexible substrate corresponding to the electronic circuit portion of the heat generation system has the heat dissipation plate. It is characterized by being adhered to.

Further, an electronic circuit section of a heating system and an electronic circuit section of a control system are both provided on the surface of a flexible substrate having flexibility, and the heat-generating electronic circuit section is provided on a heat sink provided on the back surface of the flexible substrate. In the heat dissipation structure of the circuit board for releasing the heat generated in the portion, the heat dissipation plate corresponding to the boundary between the region in which the electronic circuit portion of the heating system is provided and the region in which the electronic circuit portion of the control system is provided. A heat conduction preventing means for reducing a cross-sectional area of the position and preventing heat conduction in the heat radiating plate in a lateral direction is provided.

The heat conduction preventing means is a groove provided along the boundary line. Further, the heat conduction preventing means is a plurality of through holes provided along the boundary line. In addition, an electronic circuit unit of a heating system and an electronic circuit unit of a control system are both provided on the surface of a flexible substrate having flexibility, and the heat generation electronic circuit unit is provided on a heat sink provided on the back surface of the flexible substrate. In the heat dissipation structure of a circuit board for releasing heat, a metal having poor heat conductivity is laminated on a surface of the heat dissipation plate corresponding to an electronic circuit portion of the control system adhered to the flexible substrate. It is assumed that.

An electronic circuit portion for a heat generating system and an electronic circuit portion for a control system are both provided on a surface of a flexible substrate having flexibility, and a heat radiating plate provided on a back surface of the flexible substrate is provided on a heat radiating plate. In the heat dissipation structure of the circuit board for releasing heat generated in the section, the flexible board corresponding to the electronic circuit section of the heating system is bonded to the heat dissipation plate with an adhesive having good heat conductivity, and the electronic circuit of the control system is provided. The flexible substrate corresponding to the circuit portion is bonded to the heat radiating plate with an adhesive having poor heat conductivity.

An electronic circuit unit for a heat generating system and an electronic circuit unit for a control system are both provided on the surface of a flexible substrate having flexibility, and the heat generating electronic circuit unit is provided on a heat sink provided on the back surface of the flexible substrate. In a heat dissipation structure of a circuit board for releasing heat generated in a portion, an electronic circuit portion of the heating system on the flexible substrate is covered with a resin having good heat conductivity, and an electronic circuit of the control system on the flexible substrate. The portion is covered with a resin having poor heat conductivity.

[0013]

1A and 1B are views for explaining a heat dissipation structure of a circuit board according to a first embodiment of the present invention. FIG. 1A is a top view, and FIG.
FIG. 2 is a sectional view taken along line A-A. Hereinafter, description will be made with reference to the drawings. 1
Is a flexible board in which a wiring pattern is formed on a flexible film, and a power board 1a is provided with a power electronic circuit 4a composed of a power transistor 41 and the like that generates a large amount of heat but withstands high temperatures. An electronic circuit 4b of a control system composed of an integrated circuit 42 or the like that generates a small amount of heat but is weak to high temperatures is formed in the unit 1b. Reference numeral 21 denotes a heat radiating plate made of a metal having good heat conductivity such as aluminum for radiating heat generated in the power substrate portion 1a to the outside. Mounting hole 21d is provided. Reference numeral 3 denotes an adhesive for bonding the flexible substrate 1 and the heat sink 21. The adhesive 3 is applied only to the entire back surface of the power board portion 1a and the back surface of the peripheral portion 1bb of the control board portion 1b, and the flexible board 1 and the radiator plate 21 are adhered to each other at the portion where the adhesive 3 is applied. I have.

First, a method of manufacturing a circuit board will be described. The adhesive 3 is applied to a predetermined position of the heat radiating plate 21, and the flexible substrate 1 is placed on the adhesive 3 and bonded by heating.
Instead of applying the adhesive 3, there is also a method of sandwiching a film-shaped adhesive sheet of a predetermined shape between the flexible substrate 1 and the heat sink 21. The paste solder 5 is printed on the electrode 1c of the flexible board 1 to which the heat sink 21 is attached, and then the corresponding electronic components such as the power transistor 41 and the integrated circuit 42 are mounted. Then, the solder 5 is melted by heating in a furnace, and the electrode 1c of the flexible substrate 1, the power transistor 41, the terminal 41a of the integrated circuit 42,
The circuit board is completed by soldering 42a.

Next, the heat radiation effect of the circuit board will be described. The heat generated in the power board 1a is effectively dissipated to the power-dissipating portion 21a of the power system that is in close contact. But,
Even if the heat generated in the power board 1a is transmitted in the lateral direction from the integrated heat radiating section 21a of the power system to the heat radiating section 21b of the control system, the control board 1b remains in the heat radiating section 21b of the control system.
Air layer that is not adhered to
1 does not flow into the electronic circuit 4b of the control system. Further, the control substrate section 1b generates a small amount of heat by itself. As a result, even when the power electronic circuit 4a and the control electronic circuit 4b are formed on the same flexible substrate 1, the temperature of the integrated circuit 42 and the like is low. There is no fear of rising. Further, the peripheral portion 1b of the control board portion 1b of the flexible board 1
Since b is bonded to the heat radiating plate 21, the flexible substrate 1 can be securely fixed to the housing or the like via the mounting hole 21d of the heat radiating plate 21.

As described above, in the present embodiment, the power system and the control system electronic circuit are formed on the same flexible substrate, and even if the temperature of the radiator plate corresponding to the power system electronic circuit rises, the control system is controlled. Since the electronic circuit is thermally cut off by the air layer, it is possible to prevent the temperature of the integrated circuit and the like constituting the electronic circuit of the control system from rising. FIG. 2 is a view for explaining a heat dissipation structure of a circuit board according to a second embodiment of the present invention.
Is a top view, and (b) is an AA sectional view. Hereinafter, description will be made with reference to the drawings.

Reference numeral 22 denotes a radiator plate mainly made of a metal having good thermal conductivity such as aluminum for radiating heat generated in the power board portion 1a to the outside. The groove 22c is provided at the boundary of the area where the heat radiating portion 22b is provided.
At the corner, a mounting hole 22d for fixing the flexible substrate 1 to a housing or the like is provided. 3 is a flexible board 1
The flexible substrate 1 is an adhesive for bonding the heat sink 22 to the
The heat sink 22 is in close contact with the entire surface. The flexible substrate 1, the power transistor 41, and the integrated circuit 42 are the first
Since the names, functions, and operations are the same as those of the embodiment, the same reference numerals are given and the description is omitted.

First, a method for manufacturing a circuit board will be described. The adhesive 3 is applied to the radiator plate 22, the flexible board 1 is placed on the adhesive, and the radiator plate 22 is bonded by heating. Incidentally, instead of applying the adhesive 3, there is also a method of sandwiching a film-like adhesive sheet between the flexible substrate 1 and the heat sink 22. Electrode 1 of flexible substrate 1 to which heat sink 22 is attached
The paste-like solder 5 is printed on c, and then the corresponding electronic components such as the power transistor 41 and the integrated circuit 42 are mounted. After that, the solder 5 is melted by heating in a furnace, and the electrode 1c of the flexible substrate 1 and the power transistor 41,
The circuit board is completed by soldering the terminals 41a and 42a of the integrated circuit 42.

Next, the heat radiation effect of the circuit board will be described. The heat generated in the power board section 1a is effectively radiated to the heat radiating section 22a of the power system in close contact. But,
Since the amount of heat transmitted in the heat radiating plate 22 in the horizontal direction is substantially proportional to the cross-sectional area, the heat radiating portion 22a of the power system and the heat radiating portion 2 of the control system
The movement of heat is greatly reduced by the groove 22c provided at the boundary of 2b, and the temperature of the heat radiating portion 22b of the control system hardly rises. Therefore, the temperature of the control board section 1b which is in close contact with the heat radiating section 22b of the control system does not rise. In addition, the control substrate 1b generates a small amount of heat by itself. As a result, even when the power electronic circuit 4a and the control electronic circuit 4b are formed on the same flexible substrate 1, the temperature of the integrated circuit 42 and the like is low. There is no fear of rising.

As described above, in this embodiment, the power system and the control system electronic circuits are formed on the same flexible substrate, and even if the temperature of the heat radiator corresponding to the power electronic circuit rises, , The temperature of the integrated circuit and the like constituting the electronic circuit of the control system can be prevented from rising. 3A and 3B are views for explaining a heat dissipation structure of a circuit board according to a third embodiment of the present invention, wherein FIG. 3A is a top view, and FIG. 3B is a cross-sectional view along AA. Hereinafter, description will be made with reference to the drawings.

Reference numeral 23 denotes a radiator plate made of a metal having good thermal conductivity, such as aluminum, for radiating heat generated in the power board portion 1a to the outside. The radiator plate 23 includes a power radiator 23a and a control radiator 23b. A plurality of through holes 23c are provided at the boundary, and the flexible substrate 1
A mounting hole 23d is provided for fixing the device to a housing or the like. Reference numeral 3 denotes an adhesive for bonding the flexible substrate 1 and the heat sink 23, and the flexible substrate 1 and the heat sink 23 are in close contact with each other over the entire surface. Since the flexible substrate 1, the power transistor 41, and the integrated circuit 42 have the same names, functions, and functions as those of the first embodiment, they are assigned the same numbers, and descriptions thereof are omitted.
The method of manufacturing the circuit board is the same as that of the second embodiment and the heat sink 23.
However, the other steps are the same except for the shape, and the description is omitted.

The heat radiating function of this circuit board is the same as that of the second embodiment.
The cross-sectional area is reduced by the plurality of through-holes 23c provided at the boundary portion of, and heat transfer is greatly reduced. As a result, even if the power electronic circuit 4a and the control electronic circuit 4b are formed on the same flexible substrate 1, the temperature of the integrated circuit 42 and the like does not increase.

As described above, in this embodiment, the power system and the control system electronic circuits are formed on the same flexible board, and even if the temperature of the heat radiator corresponding to the power electronic circuit rises, the heat radiator Since the plurality of through-holes provided in the control circuit are thermally shielded, it is possible to prevent an increase in temperature of an integrated circuit or the like constituting an electronic circuit of the control system. FIG. 4 shows a fourth embodiment of the present invention.
FIG. 7 is a diagram for explaining a heat dissipation structure of a circuit board according to the embodiment.
(A) is a top view, (b) is an AA sectional view. Less than,
Description will be made with reference to the drawings.

Reference numeral 24 denotes a heat radiating plate made of a metal having good heat conductivity such as aluminum for radiating heat generated in the power board portion 1a to the outside. The heat radiating portion 24b of the control system has a metal layer having poor heat conductivity. (Clad material) 24c is laminated, and mounting holes 24d for fixing the flexible substrate 1 to a housing or the like are provided at four corners of the heat sink 24. Reference numeral 3 denotes an adhesive for bonding the flexible substrate 1 and the heat sink 24.
The flexible substrate 1 and the heat sink 24 are in close contact with each other over the entire surface. In addition, the flexible substrate 1 and the power transistor 4
1. Since the integrated circuit 42 has the same name, function, and operation as those of the first embodiment, the same numbers are assigned and the description is omitted. The method of manufacturing the circuit board is the same as that of the second embodiment except for the configuration of the heat radiating plate 24, and the other steps are the same.

Next, the heat radiation effect of the circuit board will be described. The heat generated in the power board part 1a is effectively radiated to the heat radiating part 24a of the power system which is in close contact. And
The heat is transmitted laterally from the integrally formed power radiator 24a to the heat radiator 24b of the control system. However, since the metal layer 24c having poor heat conduction is interposed in the control board 1b,
It does not flow into the electronic circuit 4b of the control system. As a result, even if the power electronic circuit 4a and the control electronic circuit 4b are formed on the same flexible substrate 1, the integrated circuit 4
There is no danger that the temperature of 2 etc. will rise.

As described above, in the present embodiment, the power system and the control system electronic circuit are formed on the same flexible substrate, and even if the temperature of the radiator plate corresponding to the power system electronic circuit rises, the control system is controlled. Since the electronic circuit of (1) is thermally blocked by the metal layer having poor heat conduction, it is possible to prevent an increase in temperature of an integrated circuit or the like constituting the electronic circuit of the control system. 5A and 5B are views for explaining a heat dissipation structure of a circuit board according to a fifth embodiment of the present invention. FIG. 5A is a top view, and FIG.
Hereinafter, description will be made with reference to the drawings.

Reference numeral 25 denotes a radiator plate made of a metal having good thermal conductivity, such as aluminum, which mainly radiates heat generated in the power board portion 1a to the outside. An attachment hole 25d is provided for fixing to the like. Reference numeral 31 denotes an adhesive having good heat conductivity for bonding the flexible board 1 of the power board section 1a and the heat sink 25. Reference numeral 32 denotes an adhesive having poor heat conduction for bonding the flexible board 1 of the power board section 1b and the heat sink 25. still,
Since the flexible substrate 1, the power transistor 41, and the integrated circuit 42 have the same names, functions, and functions as those of the first embodiment, they are assigned the same numbers, and descriptions thereof are omitted.

The method of manufacturing the circuit board is the same as that of the second embodiment except that the adhesive is different, and the other steps are the same. The adhesive 31 having good heat conductivity is an epoxy resin containing a filler (metal powder) and the adhesive 3 having poor heat conductivity.
As 2, epoxy resin or the like is used. Next, the heat radiation effect of this circuit board will be described. The heat generated in the power board section 1a is effectively radiated to the power radiating section 25a, which is in close contact with the power system, through the adhesive 31 having good heat conductivity. Then, the heat is transmitted laterally from the integrally formed power radiator 25a to the control system radiator 25b. However, since the control board section 1b is bonded to the heat radiating section 25b of the control system via the adhesive 32 having poor heat conductivity, the control board section 1b does not flow into the electronic circuit 4b of the control system. As a result, even if the power electronic circuit 4a and the control electronic circuit 4b are formed on the same flexible substrate 1, the temperature of the integrated circuit 42 and the like does not increase.

As described above, in the present embodiment, the power system and the control system electronic circuit are formed on the same flexible substrate, and even if the temperature of the radiator plate corresponding to the power system electronic circuit rises, the control system is controlled. Since the electronic circuit is thermally interrupted by the adhesive having poor heat conductivity, the temperature rise of the integrated circuit and the like constituting the electronic circuit of the control system can be prevented. 6A and 6B are views for explaining a heat dissipation structure of a circuit board according to a sixth embodiment of the present invention. FIG. 6A is a top view, and FIG.
Hereinafter, description will be made with reference to the drawings. This example is a heat dissipation structure when a resin coating is applied to improve the moisture resistance of the electronic circuit section.

Reference numeral 7a denotes a resin layer having good heat conductivity which covers the power electronic circuit portion 4a on the flexible substrate 1.
7b is an electronic circuit part 4b of a control system on the flexible substrate 1.
Is a resin layer having poor heat conductivity. Note that the flexible substrate 1, the radiator plate 25, the adhesives 31, 32, the power transistor 41, and the integrated circuit 42 have the same names, functions, and functions as those of the fifth embodiment, and thus are assigned the same numbers, and description thereof is omitted.

The method of manufacturing the circuit board is the same as that of the fifth embodiment except that a resin layer is provided, and the other steps are the same, so that the description is omitted. Incidentally, an epoxy resin is used as the resin layer 7a having good heat conductivity for coating, and a urethane resin is used as the resin layer 7b having poor heat conductivity. Next, the heat radiation effect of this circuit board will be described. The heat generated in the power board portion 1a is effectively radiated to the space from the resin layer 7a having good heat conductivity. On the other hand, the control board portion 1b hardly generates heat. In addition, the resin layer 7b having poor heat conductivity can prevent heat conduction from the electronic circuit portion 4a of the power system to the electrode circuit portion 4b of the control system via a space. In addition, the heat radiation effect of the heat radiating plate 25 is the same as that of the fifth embodiment, and a description thereof will be omitted. As a result, even if the power electronic circuit 4a and the control electronic circuit 4b are formed on the same flexible substrate 1, the temperature of the integrated circuit 42 and the like does not increase.

As described above, in the present embodiment, the power system and the control system electronic circuits are formed on the same flexible substrate, and even if the temperature of the radiator plate corresponding to the power system electronic circuit rises, the space is reduced. Since the electronic circuit of the control system is thermally insulated by the resin layer having poor heat conduction through the intermediary, it is possible to prevent the temperature of the integrated circuit and the like constituting the electronic circuit of the control system from rising.
In this embodiment, the fifth embodiment is adopted as the heat radiation structure under the substrate. However, the present invention is not limited to this, and any one of the first to fourth embodiments may be adopted.

[0033]

As described above, according to the present invention, the electronic circuit of the control system and the electronic circuit of the heat generating system are thermally cut off to thereby control the temperature of the electronic circuit of the control system constituted by an integrated circuit or the like. It is possible to provide a highly reliable heat dissipation structure for a circuit board that does not rise.

[Brief description of the drawings]

FIG. 1 is a diagram showing a heat dissipation structure of a circuit board according to a first embodiment of the present invention.

FIG. 2 is a view showing a heat dissipation structure of a circuit board according to a second embodiment of the present invention.

FIG. 3 is a view showing a heat dissipation structure of a circuit board according to a third embodiment of the present invention.

FIG. 4 is a view showing a heat dissipation structure of a circuit board according to a fourth embodiment of the present invention.

FIG. 5 is a view showing a heat dissipation structure of a circuit board according to a fifth embodiment of the present invention.

FIG. 6 is a view showing a heat dissipation structure of a circuit board according to a sixth embodiment of the present invention.

FIG. 7 is a view showing a conventional heat dissipation structure of a circuit board.

[Explanation of symbols]

1 ··················································································
42 integrated circuit, 1b control board part
5 ... solder, 21 ... heat sink,
22c: groove, 3 ... adhesive, 23c: through hole.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shinichi Sugiura 1-2-28 Goshodori, Hyogo-ku, Kobe City, Hyogo Prefecture Inside Fujitsu Ten Limited

Claims (7)

[Claims] An electronic circuit unit for a heating system and an electronic circuit unit for a control system are both provided on a surface of a flexible substrate having flexibility, and a heat radiation plate provided on a back surface of the flexible substrate is provided on an electronic circuit of the heating system. In the heat dissipation structure of a circuit board for releasing heat generated in a portion, only the back surface of the flexible board corresponding to the electronic circuit portion of the heating system is bonded to the heat dissipation plate. . 2. A heat-generating electronic circuit part is provided on a surface of a flexible substrate having flexibility, and an electronic circuit part of a control system is provided on a front surface of the flexible substrate. In the heat dissipation structure of the circuit board for releasing heat generated in the portion, the heat dissipation plate corresponding to a boundary between a region where the electronic circuit portion of the heating system is provided and a region where the electronic circuit portion of the control system is provided. A heat-dissipating structure for a circuit board, comprising: a heat-conduction preventing means for reducing a cross-sectional area of a position and preventing heat conduction in the heat-dissipating plate in a lateral direction. 3. The heat conduction preventing means is a groove provided along the boundary line.
The heat dissipation structure of the described circuit board. 4. The heat dissipation structure for a circuit board according to claim 2, wherein said heat conduction preventing means is a plurality of through holes provided along said boundary line. 5. An electronic circuit unit for a heating system and an electronic circuit unit for a control system are both provided on a surface of a flexible substrate having flexibility, and a heat radiation plate provided on a back surface of the flexible substrate is provided on an electronic circuit of the heating system. In a heat dissipation structure of a circuit board for releasing heat generated in a portion, a metal having poor heat conductivity is laminated on a surface of the heat dissipation plate corresponding to an electronic circuit portion of the control system adhered to the flexible substrate. A heat dissipation structure for a circuit board, characterized in that: 6. An electronic circuit unit for a heating system and an electronic circuit unit for a control system are both provided on a surface of a flexible substrate having flexibility, and a heat radiation plate provided on a back surface of the flexible substrate is provided on an electronic circuit of the heating system. In the heat dissipation structure of the circuit board for releasing heat generated in the section, the flexible board corresponding to the electronic circuit section of the heating system is bonded to the heat dissipation plate with an adhesive having good heat conductivity, A heat radiating structure for a circuit board, wherein the flexible substrate corresponding to the circuit portion is bonded to the heat radiating plate with an adhesive having poor heat conductivity. 7. An electronic circuit unit for a heating system and an electronic circuit unit for a control system are both provided on a surface of a flexible substrate having flexibility, and a heat radiation plate provided on a back surface of the flexible substrate is provided on an electronic circuit of the heating system. In a heat dissipation structure of a circuit board for releasing heat generated in a portion, an electronic circuit portion of the heating system on the flexible substrate is covered with a resin having good heat conductivity, and an electronic circuit of the control system on the flexible substrate. The heat dissipation structure of a circuit board, wherein the portion is covered with a resin having poor heat conductivity.