JP7656174B2 - Electronics - Google Patents

Description

The present invention relates to an electronic device having a circuit board on which a heat generating element is mounted.

Conventionally, in electronic devices equipped with a circuit board on which a heat generating element such as an LED is mounted, heat generated by the heat generating element is dissipated through a housing or the like on which the circuit board is supported. In order to improve this heat dissipation, a structure can be adopted in which a heat dissipation sheet with high thermal conductivity is interposed between the circuit board and the housing or the like. As an example of a heat dissipation structure using a heat dissipation sheet in this way, the electronic device disclosed in the following Patent Document 1 is known. The heat dissipation sheet used in this electronic device is produced by incorporating inorganic filler made of a material with good thermal conductivity and excellent heat dissipation properties, such as alumina, silicon oxide, titanium oxide, and carbon, into a polymer gel sheet made of silicone or acrylic. By adopting a heat dissipation sheet produced in this way, the ability to follow the unevenness present on the surface of the heat dissipation member is improved, and the contact area effective for heat dissipation is increased, resulting in good heat dissipation.

JP 2011-199055 A

In a heat dissipation structure in which a heat dissipation sheet is brought into contact with a housing to which a circuit board is fastened to dissipate heat, the heat dissipation sheet needs to be in contact with the circuit board and the housing without any gaps in order to ensure stable heat dissipation. For this reason, the gap between the circuit board and the housing is adjusted so that the heat dissipation sheet is crushed by the circuit board and the housing when fastened.

However, in the configuration in which the heat dissipation sheet is crushed when fastened as described above, the reaction force from the heat dissipation sheet acts on the circuit board, which can cause the above-mentioned stress to act on the terminal parts of the electronic components mounted on the circuit board, potentially resulting in poor connections. Even if poor connections caused by the above-mentioned stress can be suppressed by mounting electronic components with metal terminals (e.g., capacitors with metal terminals) on the circuit board as a method for preventing poor connections or by using a heat dissipation sheet with low hardness to reduce the reaction force, there is a problem that the unit price of each electronic component increases or the productivity decreases due to the deterioration of the attachment property of the heat dissipation sheet, resulting in an increase in the manufacturing cost of the electronic device.

The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a configuration that can improve the heat dissipation of a circuit board without applying stress to the circuit board.

In order to achieve the above object, the invention of claim 1 described in the claims is as follows:
A circuit board (20) on one side (21) of which various electronic components including a heating element (23) are mounted;
a housing (30) on which two fastening seats (32) are formed for supporting the circuit board from a surface (22) different from the one surface;
An electronic device (10) comprising:
A heat dissipation sheet (60) is attached to the other surface of the circuit board,
The housing faces, at an opposing surface (31a), the heat dissipation sheet attached to the other surface of the circuit board fastened using the base, with a predetermined gap (G) therebetween;
A liquid heat dissipation material (70) is interposed between the opposing surface and the heat dissipation sheet ,
The other surface of the circuit board is supported by the two pedestals through one opening in the center of the heat dissipation sheet .
The symbols in parentheses above indicate the corresponding relationship with the specific means described in the embodiments described later.

In the invention of claim 1, a heat dissipation sheet is attached to a surface of a circuit board on which various electronic components including heat generating elements are mounted, the surface being different from the one surface. The housing faces the heat dissipation sheet attached to the other surface of the circuit board fastened using a base with a predetermined gap therebetween, and a liquid heat dissipation material is interposed between the facing surface and the heat dissipation sheet.

As a result, heat generated by the heat generating element is dissipated by being transferred to the housing via the heat dissipation sheet and liquid heat dissipation material attached to the other side of the circuit board. In particular, the above-mentioned specified gap is interposed between the heat dissipation sheet attached to the circuit board fastened using the base and the opposing side of the housing, and the liquid heat dissipation material spreads to fill this specified gap, so no stress is generated that acts on the circuit board via the heat dissipation sheet. Therefore, the heat dissipation performance of the circuit board can be improved without applying stress to the circuit board.

In the invention of claim 2, the liquid heat dissipation material is interposed between the opposing surface and the heat dissipation sheet and directly below the heat generating element, so that the heat generated by the heat generating element can be efficiently dissipated through the liquid heat dissipation material.

1 is a plan view showing a vehicle lamp according to a first embodiment. FIG. 2 is a cross-sectional view taken along a line X1-X1 shown in FIG. 1. 2 is a cross-sectional view taken along line X2-X2 of FIG. 1. FIG. 2 is a plan view showing a state in which an outer cover is removed from FIG. 1 . FIG. 4 is an explanatory diagram illustrating the positional relationship between a circuit board and a heat dissipation sheet. FIG. 3 is an enlarged cross-sectional view of a region X3 in FIG. 2 . FIG. 4 is an enlarged cross-sectional view of a region X4 in FIG. 3 . Figure 8(A) is an explanatory diagram showing the state before fastening in which liquid heat dissipation material has been applied to the opposing surfaces of the housing, with respect to a cross-sectional view taken along line X5-X5 in Figure 4, and Figure 8(B) is an explanatory diagram showing the state in which the liquid heat dissipation material has spread by fastening from the state shown in Figure 8(A).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a vehicle lamp to which an electronic device according to the present invention is applied will now be described with reference to the drawings.
The vehicle lamp 10 according to this embodiment is mounted, for example, on the front of a forklift and functions as a work light for illuminating a work area. As shown in Figures 1 to 3, the vehicle lamp 10 mainly includes a circuit board 20 on which various electronic components functioning as a light source are mounted, a housing 30 in which the circuit board 20 is supported, an outer lens 40, and a frame 50.

As shown in FIG. 4 and other figures, one side 21 of the circuit board 20 is equipped with a number of LEDs 23 that function as work lamps, a number of LEDs 24 that function as position lamps, and a number of LEDs 25 that function as front turn signal lamps. Each LED 23 is an example of a "heat generating element", and because of this function, the current value for each LED 24 and each LED 25 becomes high in order to increase the luminosity, and the heat generation temperature becomes high. In addition, other electronic components such as a capacitor are mounted on the one side 21 of the circuit board 20, and through holes 26 for cooling are formed at predetermined positions such as near the LEDs 23 from the one side 21 to the other side 22 (see FIG. 7 and other figures). The one side 21 can be an example of a "one side", and the other side 22 can be an example of a "other side" different from the "one side".

The housing 30 is made of die-cast aluminum and is configured to house the circuit board 20 together with the outer lens 40. A fastening seat 32 for supporting the circuit board 20 from the other side 22 is formed on the bottom surface 31 of the inner surface of the housing 30, which faces the other side 22 of the circuit board 20 (see FIG. 2). A plurality of cooling fins 33 for dissipating heat transmitted via the bottom surface 31 are formed on the outer surface of the housing 30.

The outer lens 40 is made of a highly transparent resin, such as PMMA (polymethyl methacrylate), and is attached to the housing 30 that supports the circuit board 20 so as to cover each of the LEDs 23-25. Therefore, each of the LEDs 23-25 exerts the various functions described above by irradiating light to the outside through the outer lens 40. A reflector 41 that diffuses the light from each of the LEDs 25 is disposed between each of the LEDs 25 and the outer lens 40.

Next, the heat dissipation structure, which is a characteristic feature of this embodiment, will be described with reference to the drawings.
As shown in Figs. 5 to 7, a heat dissipation sheet 60 of a predetermined thickness (for example, 1 mm) is attached to the circuit board 20 in a predetermined range of the other side 22 including directly below each LED 23. This heat dissipation sheet 60 is a sheet for transmitting heat generated by each LED 23 of the circuit board 20 to the housing 30. The through holes 26 near the LEDs 23 are also blocked on the other side 22 side by the heat dissipation sheet 60. The other side 22 of the circuit board 20 is supported by the base 32 via an opening in the center of the heat dissipation sheet 60. In this embodiment, a highly thermally conductive sheet such as TC-CAS-10 manufactured by Shin-Etsu Silicone Co., Ltd. is used as the heat dissipation sheet 60.

The housing 30 is formed such that a part of the bottom surface 31 (hereinafter also referred to as the opposing surface 31a) faces the heat dissipation sheet 60 attached to the other side 22 of the circuit board 20 fastened by the screws 27 using the base 32, with a predetermined gap G between them. By having the predetermined gap G in this way, the heat dissipation sheet 60 is not crushed by the opposing surface 31a even when the circuit board 20 is fastened using the base 32.

A liquid heat dissipation material 70 is disposed between the opposing surface 31a of the housing 30 and the heat dissipation sheet 60. This liquid heat dissipation material 70 is a liquid heat dissipation agent for transferring heat transferred from the heat dissipation sheet 60 to the housing 30. In this embodiment, the liquid heat dissipation material 70 is a heat dissipation agent that has good adhesion before curing because it is liquid, and hardens due to moisture in the air after application, such as ThreeBond's 1225C (a one-part moisture-curing heat dissipation agent made of a silicone polymer base with a thermally conductive filler).

In particular, as can be seen from FIG. 5, in this embodiment, liquid heat dissipation material 70 is applied to 10 locations on the opposing surface 31a that are directly below each LED 23, and the circuit board 20 to which the heat dissipation sheet 60 is attached is fastened to the housing 30 by screws 27 using the base 32, so that the heat dissipation sheet 60 and the opposing surface 31a are thermally connected by the liquid heat dissipation material 70 directly below each LED 23.

When fastening, as shown in Figures 8(A) and (B), the liquid heat dissipation material 70 is crushed by the heat dissipation sheet 60 and spreads around, so no stress acts on the heat dissipation sheet 60 through the liquid heat dissipation material 70. And, because the other side 22 side of the through-hole 26 near the LED 23 is blocked by the heat dissipation sheet 60, the crushed liquid heat dissipation material 70 does not get into the through-hole 26.

As described above, in the vehicle lamp 10 according to this embodiment, the circuit board 20 has one side 21 on which various electronic components including the LEDs 23 are mounted, and the heat dissipation sheet 60 is attached to the other side 22. The housing 30 faces the heat dissipation sheet 60 attached to the other side 22 of the circuit board 20, which is fastened using the base 32, at the opposing side 31a via a predetermined gap G, and a liquid heat dissipation material 70 is interposed between the opposing side 31a and the heat dissipation sheet 60.

As a result, heat generated by each LED 23 is dissipated by being transferred to the housing 30 via the heat dissipation sheet 60 and the liquid heat dissipation material 70 attached to the other side 22 of the circuit board 20. In particular, the above-mentioned predetermined gap G is interposed between the heat dissipation sheet 60 attached to the circuit board 20 fastened using the base 32 and the opposing surface 31a of the housing 30, and the liquid heat dissipation material 70 spreads to fill this predetermined gap G, so that no stress is generated on the circuit board 20 through the heat dissipation sheet 60. Therefore, the heat dissipation property of the circuit board 20 can be improved without applying stress to the circuit board 20. This also eliminates the need to use expensive capacitors with metal terminals as electronic components to be mounted on the circuit board 20.

In particular, the liquid heat dissipation material 70 is disposed between the opposing surface 31a and the heat dissipation sheet 60 and directly below each LED 23, so that the heat generated by each LED 23 can be efficiently dissipated via the liquid heat dissipation material 70.

[Other embodiments]
The present invention is not limited to the above-described embodiment, and may be embodied as follows, for example.
(1) The present invention is not limited to being used in a vehicle lamp 10 having LEDs 23 that function as work lights, and may be used in an electronic device that has a circuit board on which a heat generating element is mounted to realize other functions.

(2) The heat dissipation sheet 60 is not limited to being attached to a specified area of the other side surface 22 that includes directly below each LED 23, but may also be attached to an area that includes directly below other heat generating elements. In addition, the liquid heat dissipation material 70 is not limited to being applied to 10 locations directly below each LED 23 on the opposing surface 31a that faces the heat dissipation sheet 60 via a specified gap G, but may also be applied to at least some of the other heat generating elements described above.

10... Vehicle lighting device (electronic device)
20... Circuit board 21... One side surface (one surface)
22...Other side (other side)
23...LED (heat generating element)
26: through hole 30: housing 31: bottom surface 31a: opposing surface 32: base 60: heat dissipation sheet 70: liquid heat dissipation material G: gap

Claims (2)

A circuit board having various electronic components including a heat generating element mounted on one side thereof;
a housing having two fastening bases for supporting the circuit board from a second surface different from the first surface;
An electronic device comprising:
a heat dissipation sheet is attached to the other surface of the circuit board;
the housing faces, at an opposing surface thereof, the heat dissipation sheet attached to the other surface of the circuit board fastened by the base, with a predetermined gap therebetween;
A liquid heat dissipation material is interposed between the facing surface and the heat dissipation sheet,
an electronic device, characterized in that the other surface of the circuit board is supported by the two pedestals through a single opening in the center of the heat dissipation sheet . The electronic device according to claim 1, characterized in that the liquid heat dissipation material is interposed between the opposing surface and the heat dissipation sheet at a position directly below the heat generating element.

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