JP2024075186A - Heat dissipation structure and electronic device using heat dissipation sheet - Google Patents

Abstract

[Problem] To provide a heat dissipation structure using a heat dissipation sheet that suppresses an increase in cost and allows the installation work of the heat dissipation sheet to be performed in a short time. [Solution] A heat dissipation structure HK includes a substrate 2, a first heating element 21 at a first height H21 on the substrate, a second heating element 22 at a second height H22 equal to or less than the first height H21, a heat sink 3 arranged with an opposing surface 3a that faces the substrate and the first and second heating elements at a distance, and a heat dissipation sheet 5 interposed between the substrate, the first and second heating elements, and the opposing surface and having elasticity in the thickness direction. The opposing surface has a first heating element opposing portion 35 facing the first heating element and a second heating element opposing portion 36 facing the second heating element, and the distance between the substrate opposing portion 31G that directly faces the substrate and the substrate is greater than the substrate opposing portion, and the heat dissipation sheet is in contact with the substrate opposing portion and the first and second heating element opposing portions. [Selected Figure] Figure 1A

Description

The present invention relates to a heat dissipation structure and electronic device using a heat dissipation sheet.

Patent document 1 describes a heat dissipation structure in which a heat dissipation sheet is interposed between an IC, which is a heat generating element mounted on a substrate, and a heat dissipation metal plate, which is a heat sink, and the heat generated by the IC is transferred to the heat dissipation metal plate via the heat dissipation sheet and dissipated.

JP 2010-129954 A

In the heat dissipation structure described in Patent Document 1, the distance between the board and the heat dissipation metal plate is constant, so if there are ICs of different heights, it is necessary to use a heat dissipation sheet of a thickness suitable for filling the gap between the heat dissipation metal plate and each IC. This means that there is room for improvement in that the number of heat dissipation sheet components increases, leading to higher costs, and the installation work of the heat dissipation sheet takes a lot of time because the heat dissipation sheet must be placed independently for each IC of different thickness.

The problem that the present invention aims to solve is to provide a heat dissipation structure and electronic device that uses a heat dissipation sheet, which can suppress increases in costs and enable the installation work of the heat dissipation sheet to be completed in a short time.

In order to solve the above problems, the present invention has the following configurations 1) and 2).
1) a substrate;
a first heating element having a first height and a second heating element having a second height equal to or less than the first height, the first heating element being attached to the substrate;
a heat sink disposed with a surface facing the substrate, the first heating element, and the second heating element at a distance from each other;
a heat dissipation sheet interposed between the substrate, the first heating element, the second heating element, and the opposing surface, the heat dissipation sheet having elasticity in a thickness direction;
Equipped with
The opposing surface is
a substrate facing portion directly facing the substrate;
a first heating element facing portion facing the first heating element and a second heating element facing portion facing the second heating element, the first heating element facing portion being spaced from the substrate by a distance greater than that of the substrate facing portion;
having
The heat dissipation sheet is a heat dissipation structure in contact with the substrate facing portion, the first heating element facing portion, and the second heating element facing portion.
2) An electronic device equipped with the heat dissipation structure described in 1).

According to one aspect of the present invention, it is possible to suppress an increase in costs and to perform the installation work of the heat dissipation sheet in a short time.

FIG. 1A is a cross-sectional view showing a heat dissipation structure HK and an electronic device 91 according to one aspect of the present invention. FIG. 1B is a bottom view of the heat sink 3 included in the heat dissipation structure HK. FIG. 1C is a side view of the heat dissipation sheet 5 included in the heat dissipation structure HK. FIG. 2 is a partial cross-sectional view showing a heat dissipation structure HKA which is a first modified example of the heat dissipation structure HK. FIG. 3 is a partial cross-sectional view showing a heat dissipation structure HKB which is a second modified example of the heat dissipation structure HK. FIG. 4 is a partial cross-sectional view showing a heat dissipation structure HKC which is a third modified example of the heat dissipation structure HK. FIG. 5A is a partial cross-sectional view showing a heat dissipation structure HKD which is a fourth modified example of the heat dissipation structure HK. FIG. 5B is a bottom view of the heat sink 3D included in the heat dissipation structure HKD.

The heat dissipation structure HK according to one aspect of the present invention will be described. The heat dissipation structure HK includes a substrate, a heat generating element such as an IC mounted on the substrate, a heat dissipation sheet, and a heat sink.
The heat dissipation sheet is disposed between the heat generating element and the heat sink so as to be in contact with both, and transfers heat generated by the heat generating element to the heat sink.
The heat dissipation structure HK is used in an electronic device 91. The electronic device 91 is, for example, an in-vehicle device, a communication device, an imaging device, or the like.

The heat dissipation structure HK will be described with reference to Figures 1A and 1B. In this description, the up, down, left, right, front, and rear directions are defined by the directions of the arrows shown in each figure. These directions are defined for the convenience of description and do not limit the mounting posture or usage mode of the heat dissipation structure HK in the electronic device 91.

1A, the heat dissipation structure HK includes a substrate 2, a plurality of heat generating elements 21 to 23 attached to the substrate 2, a heat dissipation sheet 5, and a heat sink 3. The heat generating elements 21 to 23 are, for example, ICs mounted on the substrate 2, but are not limited to ICs.
The substrate 2 is fastened to bosses 1a and 1b provided on a chassis base 1 of the electronic device 91 by fasteners N1 such as screws.
Bosses 1c and 1d are also provided on the chassis base 1, and a heat sink 3 is fastened and fixed by fasteners N2 such as screws at a position on the opposite side of the substrate 2 from the chassis base 1. The heat sink 3 is attached such that an opposing surface 3a thereof, which faces the substrate 2 at its lower surface, is spaced above the upper surface 2a of the substrate 2 by a distance H3a.

Three heating elements 21 to 23 are mounted on the upper surface 2a of the substrate 2. In this example, the heating elements 21 to 23 are ICs.
The heating elements 21, 22, and 23 have different thicknesses. That is, the heating elements 21, 22, and 23 have different heights H21, H22, and H23 from the upper surface 2a of the substrate 2, which correspond to the thicknesses.
In this example, height H22<height H23<height H21. Also, height H21<distance H3a.
Hereinafter, the heating element 21 will also be referred to as the first heating element 21, the heating element 22 as the second heating element 22, and the heating element 23 as the third heating element 23. In addition, the height H21 will also be referred to as the first height H21, the height H22 as the second height H22, and the height H23 as the third height H23.

The heat sink 3 has a plurality of fins 3f on the upper surface 3b, which protrude upward like ribs.
The opposing surface 3a of the heat sink 3 has a concave-convex shape 3M having portions (convex portions) protruding downward and portions (concave portions) recessed upward.
Specifically, in FIG. 1A , the heat sink 3 has an opposing surface 3a, a first convex portion 31, a first heating element opposing portion 35, a second convex portion 32, a second heating element opposing portion 36, a third convex portion 33, a third heating element opposing portion 37, and a fourth convex portion 34.
Hereinafter, the first convex portion 31, the second convex portion 32, the third convex portion 33, and the fourth convex portion 34 will also be collectively referred to as a substrate facing portion 31G. In addition, the first heating element facing portion 35, the second heating element facing portion 36, and the third heating element facing portion 37 will also be collectively referred to as a heating element facing portion 35G.

The substrate facing portion 31G and the heating element facing portion 35G will be described in detail with reference to FIG. 1B. FIG. 1B is a bottom view of the heat sink 3, and in order to facilitate understanding of the relationship between the shapes of the substrate facing portion 31G and the heating element facing portion 35G in plan view and the positions of the heating elements 21-23, the shapes of the heating elements 21-23 are shown by dashed lines at the positions where they are located.

On the opposing surface 3a, the area opposing at least the heating elements 21 to 23 in a planar view is defined as a recessed heating element opposing portion 35G, and a portion of the portion directly opposing the substrate 2 between adjacent heating elements is defined as a protruding substrate opposing portion 31G.
More specifically, of the heating element facing portion 35G, the portion facing the heating element 21 from above is designated as the first heating element facing portion 35, the portion facing the heating element 22 from above is designated as the second heating element facing portion 36, and the portion facing the heating element 23 from above is designated as the third heating element facing portion 37.

The first heating element facing portion 35 to the third heating element facing portion 37 are each formed to have a range that includes the regions corresponding to the heating elements 21 to 23, respectively, in a plan view.
The facing surface 3a of the heat sink 3 is provided with substrate facing portions 31G that protrude relatively downward so as to surround each of the first heat generating element facing portion 35 to the third heat generating element facing portion 37.
1A, the substrate facing portion 31G is shown as a first convex portion 31, a second convex portion 32, a third convex portion 33, and a fourth convex portion 34, which in this example are connected as convex portions of the same height and are formed to surround the heating element facing portion 35G. As shown in FIG. 1A, the vertical distance of the gap between the substrate facing portion 31G and the upper surface 2a of the substrate 2 is a distance H31.

The surfaces connecting the substrate facing portion 31G to the first heating element facing portion 35, the second heating element facing portion 36, and the third heating element facing portion 37 are inclined surfaces that are inclined in a direction that becomes gentler in the vertical direction. In FIG. 1A, these inclined surfaces are shown as inclined surfaces 3s1 and 3s2 for the first heating element facing portion 35, as inclined surfaces 3s3 and 3s4 for the second heating element facing portion 36, and as inclined surfaces 3s5 and 3s6 for the third heating element facing portion 37. The inclined surfaces do not have to be applied to all surfaces connecting the substrate facing portion 31G to the first heating element facing portion 35 and the second heating element facing portion 36. At least one of the substrate facing portion 31G and the first heating element facing portion 35 and the second heating element facing portion 36 may be connected by an inclined surface.

On the other hand, the vertical distances H35, H36, and H37 of the gaps between the first heating element facing portion 35, the second heating element facing portion 36, and the third heating element facing portion 37 and the upper surface 2a of the substrate 2 correspond in order to the heights H21, H22, and H23 of the heating elements 21, 22, and 23 that they respectively oppose.
Specifically, in this example, height H22<height H23<height H21, and corresponding to this order, distance H36<distance H37<distance H35.

The vertical distance Δ1 of the gap between the first heating element facing portion 35 and the heating element 21 is (distance H35 - height H21), the vertical distance Δ2 of the gap between the second heating element facing portion 36 and the heating element 22 is (distance H36 - height H22), and the vertical distance Δ3 of the gap between the third heating element facing portion 37 and the heating element 23 is (distance H37 - height H23).

As shown in FIG. 1C, the heat dissipation sheet 5 is rectangular in plan view and formed as a flat plate with a thickness of T5. The heat dissipation sheet 5 is flexible and elastically compressible in the thickness direction. It is made of, for example, silicone and has a durometer type OO (ASTM D 2240) hardness of "40." Specifically, it is "Silicone Heat Dissipation Sheet FEATHER-S3S" manufactured by Sekisui Polymatech Co., Ltd.

The thickness T5 is larger than the gap distance H31 between the substrate facing portion 31G and the upper surface 2a of the substrate 2 in FIG. 1A. In addition, the thickness T5 is larger than the gap distance Δ1 between the first heating element facing portion 35 and the heating element 21, the gap distance Δ2 between the second heating element facing portion 36 and the heating element 22, and the gap distance Δ3 between the third heating element facing portion 37 and the heating element 23.

Therefore, in the heat dissipation structure HK, the heat dissipation sheet 5 is always elastically compressed in the vertical direction at the board facing portion 31G and the heating element facing portion 35G. Therefore, the heat dissipation sheet 5 adheres well to both the upper surface 2a of the board 2 and the heating elements 21 to 23, and to the board facing portion 31G and the heating element facing portion 35G on the facing surface 3a of the heat sink 3, due to the repulsive force of the compression.
As a result, even if the heights of the heat generating elements 21 to 23 differ, the heat dissipation structure HK can dissipate heat generated in the heat generating elements 21 to 23 by disposing one heat dissipation sheet 5 between the heat generating elements 21 to 23 and the heat sink 3, and can effectively transfer the heat generated in the heat generating elements 21 to 23 to the heat sink 3. Therefore, the heat dissipation structure HK prevents an increase in cost, and the installation work of the heat dissipation sheet 5 can be completed in a short time.

The gap distance H31 between the upper surface 2a of the substrate 2 and the substrate facing portion 31G and the distances Δ1 to Δ3 are preferably equal or close to each other. In this case, the variation in the amount of compression of the heat dissipation sheet 5 is reduced. In other words, the variation in the load applied to the heat dissipation sheet 5 is reduced, making it less likely that problems such as breakage of the heat dissipation sheet 5 will occur, and the heat dissipation structure HK will maintain its long-term reliability.

As shown in FIG. 1A, the heat sink 3 has inclined surfaces 3s1 to 3s6 that are inclined so as to gently connect the heat generating element facing portion 35G and the board facing portion 31G.
Since the heat sink 3 has the inclined surfaces 3s1 to 3s6, the heat dissipation sheet 5 can conform well to the uneven shape 3M of the heat sink 3 and has high adhesion, improving the heat dissipation effect. In addition, the zigzag deformation of the heat dissipation sheet 5 shown in Fig. 1B becomes gentler, which increases the options for the material of the heat dissipation sheet 5 to be used and improves the durability of the heat dissipation sheet 5 used.

The embodiment described above is not limited to the configuration, and may be modified without departing from the spirit of the present invention.

Although an example has been described in which the substrate facing portion 31G is formed continuously at the same height, the height need not be uniform and may have portions of different heights. Furthermore, the substrate facing portion 31G is not limited to being formed so as to completely surround each of the heating elements 21-23, and may be partially missing. Furthermore, the missing portions may become part of the heating element facing portion 35G or the facing surface 3a.

As a first modification, the heat dissipation structure HK may be a heat dissipation structure HKA including a heat sink 3A that does not have the inclined surfaces 3s1 to 3s6 as shown in FIG.
That is, the heat sink 3A has a first heating element facing portion 35A and a second heating element facing portion 36A that face above the heating elements 24, 25 mounted on the substrate 2, respectively, and a substrate facing portion 31GA that faces the upper surface 2a of the substrate 2 between the heating elements 24, 25.
The first heating element facing portion 35A, the second heating element facing portion 36A and the substrate facing portion 31GA are connected by a wall portion 3h extending in the vertical direction, rather than by an inclined surface.
When this modified example 1 is used in a case where the heating elements are arranged close to each other and the width of the substrate facing portion 31GA becomes narrow, the width of the substrate facing portion 31GA can be maintained without being reduced.

In addition, if there is a difference in height between the heating elements 24, 25 but the difference is small, the distances H35A, H36A for the first heating element facing portion 35A and the second heating element facing portion 36A corresponding to the heating elements 24, 25, respectively, may be slightly different in accordance with the heights of the heating elements 24, 25 as shown in FIG. 2, or may be the same.

When adjacent heat generating elements are closely arranged with a distance equal to or less than a predetermined value, which is the first distance, the heat dissipation structure HK may be a heat dissipation structure HKB having a heat sink 3B of modified example 2. As shown in Fig. 3, the heat dissipation structure HKB is configured so that one heat generating element facing portion 35B of the heat sink 3B corresponds to the closely arranged heat generating elements 24, 25. In other words, a plurality of closely arranged heat generating elements are regarded as one heat generating element group, and the heat sink is provided with a heat generating element facing portion that is a recess corresponding to the heat generating element group.
This is because when two heat generating elements are arranged close to each other, the substrate area between the two heat generating elements is narrow, making it difficult to form opposing protrusions in the narrow substrate area.
The predetermined value may be set to an optimum value as appropriate depending on the distance between the substrate 2 and the heat sink 3B, the height H24 of the heating element 24, and the like.

As a result, when the substrate 2 includes a first heating element group K1 (see FIG. 3) in which the first heating element 24 and the second heating element 25 are attached adjacent to each other with a first interval that is equal to or less than a predetermined value, and a second heating element group K2 (see FIG. 2) in which the first heating element 24 and the second heating element 25 are attached adjacent to each other with a second interval that is greater than a predetermined value and is greater than the first interval, the following may be done. That is, on the opposing surface 3a of the heat sink 3, the first heating element facing portion and the second heating element facing portion that face the first heating element group K1 shown in FIG. 3 are connected to each other and formed as one heating element facing portion 35B. Also, the first heating element facing portion 35A and the second heating element facing portion 36A that face the second heating element group K2 shown in FIG. 2 are formed apart from each other.

The heat dissipation structure HKB may be a heat dissipation structure HKC of variant 3 in which two regions with different hollowing amounts are formed in one recess corresponding to two closely arranged heat generating elements according to the heights of the opposing heat generating elements.
4, in the heat dissipation structure HKC, the closely arranged heat generating elements 26 and 27 are regarded as one heat generating element, and the heat sink 3C has one recessed portion 35C facing the heat generating elements. The height H26 of the heat generating element 26 is greater than the height H27 of the heat generating element 27.
In this case, in the heater facing portion 35C, a region 35Ca corresponding to the heater 26 is formed, and the vertical distance of the gap with the substrate 2 is a distance H35Ca, and a region 35Cb corresponding to the heater 27 is formed, and the vertical distance of the gap with the substrate 2 is a distance H35Cb.
The magnitude relationship between the distance H35Ca and the distance H35Cb corresponds to the magnitude relationship between the height H26 and the height H27, and is set to distance H35Ca>distance H35Cb.

When two heat generating elements of significantly different heights are placed close to each other, the heat dissipation structure HKC can make the amount of compression of the heat dissipation sheet 5 more uniform, improving the durability of the heat dissipation sheet 5. In addition, the amount of compression of the portion sandwiched between the heat generating element 27, which is shorter, and the heat sink 3C increases, which improves the adhesion of the heat dissipation sheet 5 and improves the heat dissipation effect.

As shown in Figures 5A and 5B, the heat dissipation structure HK may be a heat dissipation structure HKD that includes a heat sink 3D having a plurality of ribs 3R protruding downward on its bottom surface above a first heating element facing portion 35D, a second heating element facing portion 36D, and a third heating element facing portion 37D that are formed to face the heating elements 51 to 53, respectively.
In this example, the rib 3R has a semicircular cross-sectional shape and extends linearly in the front-rear direction, but the cross-sectional shape is not limited to a semicircular shape and may be a triangular or rectangular shape. Also, the cross-sectional shape is not limited to a linear shape and may be a curved shape, and the number of ribs formed is not limited.
By providing the ribs 3R, the contact area between the heat sink 3D and the heat dissipation sheet 5 is increased, thereby improving the heat dissipation effect.

The cross-sectional shape of the relatively protruding board facing portion 31G is not limited to a rectangle or a trapezoid. The cross-sectional shape may be stepped or may include a curve.

The heat dissipation structure HK and its variations include a heat sink with a recess facing the heat generating element, but the recess may be formed facing a non-heat generating mounted component.

1 Chassis base 1a, 1b, 1c, 1d Boss 2 Substrate 2a Top surface 21-27 Heat generating element 3, 3A, 3B, 3C, 3D Heat sink 3a Opposing surface 3b Top surface 3f Fin 3h Wall portion 3R Rib 31 First convex portion 32 Second convex portion 33 Third convex portion 34 Fourth convex portion 31G, 31GA Substrate opposing portion 35, 35A, 35D First heating element opposing portion 36, 36A, 36D Second heating element opposing portion 37, 37D Third heating element opposing portion 35G, 35B, 35C Heat generating element opposing portion 35Ca, 35Cb Regions 3s1-3s6 Inclined surface 3M Concave-convex shape 5 Heat dissipation sheet 91 Electronic device HK, HKA-HKD Heat dissipation structure H21 to H23, H26, H27 Height H3a, H31, H35 to H37, H35A, H36A, H35Ca, H35Cb Distance K1 First heating element group K2 Second heating element group N1, N2 Fixture T5 Thickness Δ1 to Δ3 Distance

Claims (5)

A substrate;
a first heating element having a first height and a second heating element having a second height equal to or less than the first height, the first heating element being attached to the substrate;
a heat sink disposed with a surface facing the substrate, the first heating element, and the second heating element at a distance from each other;
a heat dissipation sheet interposed between the substrate, the first heating element, the second heating element, and the opposing surface, the heat dissipation sheet having elasticity in a thickness direction;
Equipped with
The opposing surface is
a substrate facing portion directly facing the substrate;
a first heating element facing portion facing the first heating element and a second heating element facing portion facing the second heating element, the first heating element facing portion being spaced from the substrate by a distance greater than that of the substrate facing portion;
having
The heat dissipation sheet is in contact with the substrate facing portion, the first heating element facing portion, and the second heating element facing portion. The heat dissipation structure according to claim 1, in which the substrate facing portion is connected to at least one of the first heating element facing portion and the second heating element facing portion by an inclined surface. The heat dissipation structure according to claim 1 or 2, wherein the distance between the first heating element facing portion and the substrate is equal to or greater than the distance between the second heating element facing portion and the substrate. a first heating element set in which the first heating element and the second heating element are attached adjacent to each other at a first interval on the substrate;
2. The heat dissipation structure according to claim 1, wherein the first heating element facing portion and the second heating element facing portion facing the first heating element set are formed so as to be connected to each other on the facing surface. An electronic device equipped with the heat dissipation structure according to claim 1.

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