WO2023286577A1

WO2023286577A1 - Thermal diffusion device and electronic apparatus

Info

Publication number: WO2023286577A1
Application number: PCT/JP2022/025486
Authority: WO
Inventors: 竜宏沼本; 浩士福田
Original assignee: 株式会社村田製作所
Priority date: 2021-07-15
Filing date: 2022-06-27
Publication date: 2023-01-19

Abstract

A vapor chamber (thermal diffusion device) (1a) comprises: a liquid transport part (LP); an evaporation part (EP) which, in a planar view from the thickness direction (T), is connected to one end of the liquid transport part (LP); a housing (10) which has an internal space; a working medium (20) which is sealed in the internal space of the housing (10); a first capillary structure (30) which is provided in the internal space of the housing (10) and which overlaps with the liquid transport part (LP) in a planar view from the thickness direction (T); and a second capillary structure (40) which is provided in the internal space of the housing (10) and the which overlaps with the evaporation part (EP) in a planar view from the thickness direction (T). In a planar view from the thickness direction (T), the ratio of the area of the placement region (CR1) of the first capillary structure (30) to the area of the internal space of the housing (10) is not more than 50%. In a planar view from the thickness direction (T), the ratio of the area of the placement region (CR2) of the second capillary structure (40) overlapping the evaporation part (EP) to the area of the evaporation part (EP) is not less than 50%.

Description

Heat spreading device and electronic equipment

The present invention relates to heat diffusion devices and electronic equipment.

In recent years, the amount of heat generated has increased due to the high integration and high performance of devices. In addition, due to the miniaturization of products, heat generation density is increasing. Such a situation is particularly conspicuous in the field of mobile terminals such as smartphones and tablets. Under these circumstances, it is important to take heat dissipation measures.

　Graphite sheets and the like are often used as materials for heat dissipation, but their heat transfer capacity is not sufficient, so the use of various materials for heat dissipation is being considered. Among them, the use of a vapor chamber, which is a planar heat pipe, is being studied because it can diffuse heat very effectively.

In Patent Document 1, a heating part to which heat is transferred from the outside is provided in a part of a thin plate-shaped main body, and the heat transferred to the heating part is diffused from the heating part to other parts of the main body. In the diffuser plate, a plurality of hollow passages are formed inside the main body portion so as to pass through the heating portion, and the hollow passages communicate with each other through the heating portion. In addition, a working fluid that radiates heat and condenses is enclosed, and a wick that generates a capillary force when the liquid-phase working fluid permeates inside each hollow passage, and vapor of the working fluid flows inside each hollow passage. A part of each wick is positioned in the heating part, and each steam channel formed inside each hollow channel is in communication with each other in the heating part. A heat spreader plate characterized is disclosed.

JP 2016-223673 A

In the heat diffusion plate described in Patent Document 1, as shown in FIG. 1 and the like of Patent Document 1, wicks functioning as liquid flow paths are arranged linearly, and the ends of the wicks serve as heating portions. are placed in However, in the heat diffusion plate described in Patent Document 1, the wick located in the heating portion is arranged locally with respect to the size of the heating portion, so the efficiency of heat transfer between the wick and the heating portion is low. As a result, there arises a problem that the maximum amount of heat transport is small.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a heat diffusion device capable of improving the maximum amount of heat transport. Another object of the present invention is to provide an electronic device having the above heat diffusion device.

The heat diffusion device of the present invention comprises a housing having, in an internal space, a liquid transporting section and an evaporating section connected to one end of the liquid transporting section in plan view from the thickness direction; an enclosed working medium; a first capillary structure provided in the internal space of the housing and overlapping the liquid transporting portion in plan view from the thickness direction; and provided in the internal space of the housing, and a second capillary structure that overlaps the evaporating portion when viewed in plan from the thickness direction, wherein the ratio of the first capillary structure to the area of the internal space of the housing when viewed in plan from the thickness direction. The ratio of the area of the arrangement region is 50% or less, and the ratio of the area of the arrangement region of the second capillary structure overlapping the evaporator with respect to the area of the evaporator in plan view from the thickness direction is It is characterized by being 50% or more.

An electronic device of the present invention includes the heat diffusion device of the present invention and an electronic component attached to an outer wall surface of the housing of the heat diffusion device, and when viewed in plan from the thickness direction, the electronic component is , overlapping the evaporator of the housing.

According to the present invention, it is possible to provide a heat diffusion device capable of improving the maximum amount of heat transport. Further, according to the present invention, it is possible to provide electronic equipment having the above heat diffusion device.

FIG. 1 is a schematic perspective view showing an example of a heat diffusion device according to Embodiment 1 of the present invention. FIG. 2 is a schematic plan view showing the internal structure of an example of the heat diffusion device of Embodiment 1 of the present invention. FIG. 3 is a schematic cross-sectional view showing a cross section along line segment A1-A2 of the heat diffusion device shown in FIG. FIG. 4 is a schematic cross-sectional view showing a cross section along line segment B1-B2 of the heat diffusion device shown in FIG. FIG. 5 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 2 of the present invention. FIG. 6 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 3 of the present invention. FIG. 7 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 4 of the present invention. FIG. 8 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 5 of the present invention. 9 is a schematic cross-sectional view showing a cross section along line A3-A4 of the heat diffusion device shown in FIG. 8. FIG. FIG. 10 is a schematic cross-sectional view showing a cross section along line segment B3-B4 of the heat diffusion device shown in FIG. FIG. 11 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 6 of the present invention. 12 is a schematic cross-sectional view showing a cross section along line A5-A6 of the heat diffusion device shown in FIG. 11. FIG. 13 is a schematic cross-sectional view showing a cross section along line B5-B6 of the heat diffusion device shown in FIG. 11. FIG. FIG. 14 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 7 of the present invention. 15 is a schematic cross-sectional view showing a cross section along line A7-A8 of the heat diffusion device shown in FIG. 14. FIG. 16 is a schematic cross-sectional view showing a cross section along line B7-B8 of the heat diffusion device shown in FIG. 14. FIG. FIG. 17 is a schematic perspective view showing an example of the electronic device of the present invention.

The heat diffusion device of the present invention and the electronic device of the present invention will be described below. It should be noted that the present invention is not limited to the following configurations, and may be modified as appropriate without departing from the gist of the present invention. The present invention also includes a combination of a plurality of individual preferred configurations described below.

Each embodiment shown below is an example, and it goes without saying that partial replacement or combination of configurations shown in different embodiments is possible. In the second and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and different points will be mainly described. In particular, similar actions and effects due to similar configurations will not be mentioned sequentially for each embodiment.

In the following description, when the embodiments are not particularly distinguished, they are simply referred to as "the heat diffusion device of the present invention" and "the electronic device of the present invention".

In each of the embodiments below, a vapor chamber is shown as an example of the heat diffusion device of the present invention. The heat diffusion device of the present invention can also be applied to heat diffusion devices such as heat pipes.

The drawings shown below are schematic diagrams, and their dimensions, aspect ratio scale, etc. may differ from the actual product.

[Heat diffusion device]
The heat spreading device of the present invention is described below.

<Embodiment 1>
The heat diffusion device of the present invention comprises a housing having, in an internal space, a liquid transporting section and an evaporating section connected to one end of the liquid transporting section in plan view from the thickness direction; an enclosed working medium; a first capillary structure provided in the internal space of the housing and overlapping the liquid transporting portion in plan view from the thickness direction; and provided in the internal space of the housing, and a second capillary structure that overlaps with the evaporator in plan view from the thickness direction.

FIG. 1 is a schematic perspective view showing an example of a heat diffusion device according to Embodiment 1 of the present invention. A schematic perspective view showing an example of a heat diffusion device according to another embodiment, which will be described later, is also the same as FIG.

A vapor chamber (heat diffusion device) 1a shown in FIG.

The housing 10 is hermetically sealed and has a hollow structure.

A heat source HS, which is a heating element, is attached to the outer wall surface of the housing 10 .

The heat source HS includes, for example, electronic components.

In this specification, the length direction, thickness direction, and width direction are defined by L, T, and W, respectively, as shown in FIG. The length direction L, the thickness direction T, and the width direction W are orthogonal to each other. Also, the dimension in the length direction L, the dimension in the thickness direction T, and the dimension in the width direction W are also referred to as length, thickness, and width, respectively.

The vapor chamber 1a is planar as a whole. That is, the housing 10 is planar as a whole.

In this specification, the planar shape includes a plate shape and a sheet shape, and in the vapor chamber 1a and the housing 10 shown in FIG. For example, it means a shape whose length and width are 10 times or more, preferably 100 times or more, the thickness.

The length, thickness, and width of the vapor chamber 1a, that is, the length, thickness, and width of the housing 10 are defined as the maximum dimensions in the length direction L, thickness direction T, and width direction W, respectively. be done.

The size of the vapor chamber 1a, that is, the size of the housing 10 is not particularly limited.

The length and width of the vapor chamber 1a, that is, the length and width of the housing 10 are preferably 5 mm or more and 500 mm or less, more preferably 20 mm or more and 300 mm or less, and still more preferably 50 mm or more and 200 mm or less. .

The length and width of the vapor chamber 1a, that is, the length and width of the housing 10 may be the same or different.

The thickness of the vapor chamber 1a, that is, the thickness of the housing 10 is preferably 50 µm or more and 500 µm or less.

The housing 10 is preferably composed of a first sheet 11 and a second sheet 12 whose outer edges are joined together.

The constituent materials of the first sheet 11 and the second sheet 12 are not particularly limited as long as they have properties suitable for the vapor chamber, such as thermal conductivity, strength, softness, and flexibility. The constituent materials of the first sheet 11 and the second sheet 12 are preferably metals such as copper, nickel, aluminum, magnesium, titanium, iron, alloys containing at least one of these metals as a main component, and the like. Copper is preferred.

The constituent materials of the first sheet 11 and the second sheet 12 may be the same or different, but are preferably the same.

Examples of methods for joining the outer edges of the first sheet 11 and the second sheet 12 include laser welding, resistance welding, diffusion bonding, brazing, TIG welding (tungsten-inert gas welding), ultrasonic bonding, and resin sealing. stop, etc. Among them, laser welding, resistance welding, or brazing is preferred.

The thicknesses of the first sheet 11 and the second sheet 12 are preferably 10 µm or more and 200 µm or less, more preferably 30 µm or more and 100 µm or less, and still more preferably 40 µm or more and 60 µm or less.

The thicknesses of the first sheet 11 and the second sheet 12 may be the same or different.

The thicknesses of the first sheet 11 and the second sheet 12 may be the same over the entire area, or may be partially different.

The shapes of the first sheet 11 and the second sheet 12 are not particularly limited.

For example, the first sheet 11 may have a flat plate shape with a constant thickness, and the second sheet 12 may have a shape in which the outer edge portion is thicker than the portions other than the outer edge portion.

In addition, the first sheet 11 has a flat plate shape with a constant thickness, and the second sheet 12 has a constant thickness, and has a shape in which a portion other than the outer edge portion is outwardly convex with respect to the outer edge portion. good too. In this case, the outer edge of the vapor chamber 1a, that is, the outer edge of the housing 10 is provided with a recess. If the outer edge of the vapor chamber 1a, that is, the outer edge of the housing 10 is provided with a dent, the dent of the outer edge can be used to facilitate mounting of the vapor chamber 1a on an electronic device. Other parts can be placed.

The planar shape of the vapor chamber 1a in a plan view from the thickness direction T, that is, the planar shape of the housing 10 includes, for example, polygons such as triangles and rectangles, circles, ovals, and combinations thereof. mentioned. Further, the planar shape of the vapor chamber 1a, that is, the planar shape of the housing 10 may be L-shaped, C-shaped (U-shaped), step-shaped, or the like. Further, a through hole may be provided in the thickness direction T of the housing 10 . The planar shape of the vapor chamber 1a, that is, the planar shape of the housing 10 may be a shape according to the use of the vapor chamber, may be a shape according to the mounting location of the vapor chamber, or may be a shape in the vicinity. It may also be shaped according to other parts present.

FIG. 2 is a schematic plan view showing the internal structure of an example of the heat diffusion device of Embodiment 1 of the present invention. More specifically, FIG. 2 shows a state in which the vapor chamber 1a shown in FIG. 1 is seen through from the second sheet 12 side. FIG. 3 is a schematic cross-sectional view showing a cross section along line segment A1-A2 of the heat diffusion device shown in FIG. FIG. 4 is a schematic cross-sectional view showing a cross section along line segment B1-B2 of the heat diffusion device shown in FIG. 3 and 4, the second sheet 12 shown in FIG. 1 is omitted.

The vapor chamber 1a shown in FIGS. 2, 3, and 4 has a housing 10, a working medium 20, a first capillary structure 30, and a second capillary structure 40.

The housing 10 has a liquid transporting part LP and an evaporating part EP in its internal space. Moreover, the working medium 20 is enclosed in the internal space of the housing 10 .

The liquid transporting part LP functions as a part that transports the liquid-phase working medium 20 to the evaporating part EP. In FIG. 2, a pair of wall portions 60 projecting in the thickness direction T from the inner surface 10a of the housing 10, here, a pair of wall portions 60 projecting in the thickness direction T from the inner surface 11a of the first sheet 11 are facing each other, It extends in the in-plane direction (direction including the length direction L and the width direction W) perpendicular to the thickness direction T, and the liquid transport part LP is provided in the region between the pair of wall parts 60 .

It is preferable that the liquid transport part LP extends linearly in plan view from the thickness direction T. In this case, when viewed from the thickness direction T, the liquid transporting portion LP may extend linearly like the three liquid transporting portions LP shown in FIG. 2, or may extend in a curved shape. Further, the liquid transporting portion LP may be curved in the middle like the left and right liquid transporting portions LP shown in FIG. It does not have to be bent in the middle like

The number of liquid transport parts LP may be only one, or may be plural (three in FIG. 2).

The evaporating part EP is a part that evaporates the transported liquid-phase working medium 20 to change it into a vapor-phase working medium 20 . More specifically, the evaporating part EP corresponds to a portion of the internal space of the housing 10 that is in the vicinity of the heat source HS shown in FIG. 1 and that is heated by the heat source HS.

The evaporating part EP is connected to one end of the liquid transporting part LP in plan view from the thickness direction T. In FIG. 2, in a plan view from the thickness direction T, one end of each of the three liquid transporting parts LP is connected to the evaporating part EP.

The position where one end of the liquid transporting part LP is connected to the evaporating part EP is not particularly limited.

Depending on the number of heat sources HS, the number of evaporators EP may be only one as shown in FIG. 2, or may be plural.

In the internal space of the housing 10, a vapor flow path VP is provided in a region other than the liquid transporting section LP and the evaporating section EP.

The working medium 20 is not particularly limited as long as it can cause a gas-liquid phase change in the environment inside the housing 10 . Examples of the working medium 20 include water, alcohols, CFC alternatives, and the like. The working medium 20 is preferably an aqueous compound, particularly preferably water.

The first capillary structure 30 and the second capillary structure 40 are provided in the internal space of the housing 10 .

In this specification, a capillary structure means a structure having a capillary structure that can move a working medium by capillary force, and is also called a wick.

The capillary structure may be a known structure used in conventional heat diffusion devices (vapor chambers, etc.), for example, fine structures having unevenness such as pores, protrusions, and grooves.

The first capillary structure 30 is provided in the internal space of the housing 10 and overlaps the liquid transporting part LP in plan view from the thickness direction T. In FIG. 2 , the first capillary structure 30 extends linearly from one end on the evaporating part EP side to the other end on the opposite side to the evaporating part EP so as to overlap the liquid transporting part LP in plan view from the thickness direction T. extended. In FIG. 3, the first capillary structure 30 is in contact with the wall portion 60 that defines the liquid transport portion LP.

The first capillary structure 30 functions as a liquid retaining section that sucks up and retains the liquid-phase working medium 20 transported by the liquid transporting section LP by capillary force, while the sucked-up liquid-phase working medium 20 is transferred to the evaporating section EP. It also functions as a liquid transport part that transports to.

In the heat diffusion device of the present invention, the ratio of the area of the arrangement region of the first capillary structure to the area of the internal space of the housing in plan view from the thickness direction is 50% or less.

In the vapor chamber 1a, the ratio of the area of the arrangement region CR1 of the first capillary structure 30 to the area of the internal space of the housing 10 in plan view from the thickness direction T is 50% or less.

The area of the internal space of the housing 10 in plan view from the thickness direction T corresponds to the area of the entire internal space of the housing 10 including the liquid transporting portion LP, the evaporating portion EP, and the vapor flow path VP.

Since the first capillary structure 30 is present in the vapor chamber 1a, the ratio of the area of the arrangement region CR1 of the first capillary structure 30 to the area of the internal space of the housing 10 in a plan view from the thickness direction T. is greater than 0%.

When a plurality of first capillary structures 30 exist as shown in FIG. 2, the area of the arrangement region CR1 of the first capillary structure 30 in plan view from the thickness direction T is the total area of these arrangement regions. Applicable.

When viewed from the thickness direction T, the ratio of the area of the arrangement region CR1 of the first capillary structure 30 to the area of the internal space of the housing 10 is 50% or less. , a wider vapor flow path VP is ensured than in the case where the first capillary structure 30 extends over the entire internal space of the housing 10 . As a result, the uniform heat performance of the vapor chamber 1a is improved.

The second capillary structure 40 is provided in the internal space of the housing 10 and overlaps the evaporating part EP in plan view from the thickness direction T. In FIG. 2 , in plan view from the thickness direction T, the entire second capillary structure 40 overlaps the evaporator EP.

The second capillary structure 40 functions as a liquid flow path that spreads the liquid-phase working medium 20 transported to the evaporator EP into the evaporator EP.

In the heat diffusion device of the present invention, the ratio of the area of the second capillary structure overlapping the evaporator to the area of the evaporator is 50% or more in plan view from the thickness direction.

In the vapor chamber 1a, in a plan view from the thickness direction T, the ratio of the area of the second capillary structure 40 overlapping the evaporator EP to the area of the evaporator EP is 50% or more.

The area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporating part EP in plan view from the thickness direction T corresponds to the area of the region overlapping the evaporating part EP in the second capillary structure 40 as a whole. . Therefore, in plan view from the thickness direction T, the ratio of the area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporator EP to the area of the evaporator EP is 100% or less.

In a plan view from the thickness direction T, the ratio of the area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporator EP to the area of the evaporator EP is 50% or more. The liquid-phase working medium 20 is easily spread over the entire evaporating part EP by the second capillary structure 40 . As a result, in the evaporating section EP, the heat transfer efficiency from the heat source HS to the liquid-phase working medium 20 is likely to be improved, and the evaporation heat resistance is likely to be reduced. As described above, the maximum heat transfer amount of the vapor chamber 1a is improved.

In plan view from the thickness direction T, the area of the entire second capillary structure 40 may be larger than the area of the evaporating part EP. In other words, in plan view from the thickness direction T, the ratio of the area of the entire second capillary structure 40 to the area of the evaporating portion EP may be greater than 100%.

In plan view from the thickness direction T, the area of the entire second capillary structure 40 may be smaller than the area of the evaporation part EP. In other words, in plan view from the thickness direction T, the ratio of the area of the entire second capillary structure 40 to the area of the evaporating portion EP may be less than 100%. However, as described above, since the ratio of the area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporation part EP to the area of the evaporation part EP in plan view from the thickness direction T is 50% or more, In plan view from the thickness direction T, the ratio of the area of the entire second capillary structure 40 to the area of the evaporating part EP is 50% or more.

In the heat diffusion device of the present invention, the area of the internal space of the housing, the area of the first capillary structure, the area of the evaporating section, and the area of the second capillary structure in plan view from the thickness direction are each: , is determined by image analysis of the internal structure of the vapor chamber as shown in FIG.

In the heat diffusion device of the present invention, the first capillary structure preferably contains a porous body.

The first capillary structure 30 preferably includes a porous body 31 in the vapor chamber 1a. 2 and 3, a porous body 31 is provided as the first capillary structure 30. In FIGS. In addition, in FIG. 2, the porous body 31 as the first capillary structure 30 is shown in a see-through state.

Examples of the porous body 31 include metal porous membranes, meshes, non-woven fabrics, sintered bodies, and other porous bodies formed by etching or metal processing. In this specification, meshes, non-woven fabrics, and sintered bodies are also included in porous bodies.

Examples of meshes include metal meshes, resin meshes, and surface-coated meshes of these. Among them, copper mesh, stainless steel (SUS) mesh, and polyester mesh are preferable.

Examples of sintered bodies include metal porous sintered bodies and ceramic porous sintered bodies. Among them, a porous sintered body of copper or nickel is preferable.

Examples of other porous bodies include metal porous bodies, ceramic porous bodies, resin porous bodies, and the like.

Instead of the porous body 31, the first capillary structure 30 may include a fiber bundle in which a plurality of fibers are linearly bundled. In this case, the first capillary structure 30 preferably includes a woven fiber bundle. In a woven fiber bundle in which a plurality of fibers are woven, irregularities are likely to exist on the surface. easier to transport to

Examples of fibers that make up the fiber bundle include metal wires such as copper, aluminum, and stainless steel, and non-metal wires such as carbon fibers and glass fibers. Among them, a metal wire is preferable because of its high thermal conductivity. For example, a fiber bundle can be obtained by bundling about 200 copper wires with a diameter of about 0.03 mm.

In the heat diffusion device of the present invention, it is preferable that the second capillary structure includes a plurality of protrusions provided on the inner surface of the housing.

In the vapor chamber 1a, the second capillary structure 40 preferably includes a plurality of protrusions 41a provided on the inner surface 10a of the housing 10.

The plurality of protrusions 41a protrude in the thickness direction T from the inner surface 10a of the housing 10, here, the inner surface 11a of the first sheet 11.

In the vapor chamber 1a, the second capillary structure 40 includes a plurality of protrusions 41a, so that the liquid-phase working medium 20 transported to the evaporator EP flows through the plurality of protrusions 41a into the evaporator EP. spread to Furthermore, when pressure is applied to the vapor chamber 1a in the thickness direction T, the plurality of protrusions 41a function as supports for maintaining the shape of the evaporator EP, resulting in a liquid flow path in the evaporator EP. is prevented from collapsing.

The plurality of protrusions 41a are preferably integrated with the housing 10, here the first sheet 11, as shown in FIG. In this case, the plurality of protrusions 41a are formed by etching the inner surface 11a of the first sheet 11, for example.

The constituent material of the plurality of projections 41 a is preferably the same as the constituent material of the housing 10 , here, the constituent material of the first sheet 11 .

The constituent materials of the plurality of protrusions 41a are preferably the same, but may be different from each other, or may be partially different.

The lengths of the plurality of protrusions 41a may be the same as each other, may be different from each other, or may be partially different.

The widths of the plurality of protrusions 41a may be the same as each other, may be different from each other, or may be partially different.

The areas of the plurality of projections 41a in plan view from the thickness direction T may be the same, different, or partly different.

The thicknesses of the plurality of protrusions 41a may be the same as each other, may be different from each other, or may be partially different.

The planar shape of the plurality of protrusions 41a in plan view from the thickness direction T includes, for example, a polygonal shape such as a rectangle, a circular shape, an elliptical shape, and a shape combining these.

The planar shapes of the plurality of protrusions 41a may be the same as each other, may be different from each other, or may be partially different.

In a plan view from the thickness direction T, it is preferable that the plurality of protrusions 41a be evenly arranged so that the distance between the plurality of protrusions 41a is constant. In this case, the plurality of protrusions 41a are preferably evenly arranged in a partial area of the second capillary structure 40, and more preferably evenly arranged over the entire area.

In the vapor chamber 1a, the second capillary structure 40 is present in addition to the plurality of protrusions 41a, on a portion of the inner surface 10a of the housing 10 present around each protrusion 41a, here present around each protrusion 41a. By combining a part of the inner surface 11a of the first sheet 11, a so-called microchannel is formed, which functions as a liquid flow path that spreads the liquid-phase working medium 20 into the evaporator EP. That is, in the vapor chamber 1a, the arrangement region CR2 of the second capillary structure 40 overlapping the evaporating part EP is composed of a plurality of projections 41a and a part of the inner surface 10a of the housing 10 around each projection 41a. corresponds to the area where a part of the inner surface 11a of the first sheet 11 existing around each projection 41a is arranged. Therefore, in the vapor chamber 1a, the ratio of the area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporating part EP to the area of the evaporating part EP in plan view from the thickness direction T is 100%. .

In the heat diffusion device of the present invention, it is preferable that a wall projecting from the inner surface of the housing in the thickness direction is present around the second capillary structure in plan view from the thickness direction.

In the vapor chamber 1a, it is preferable that a wall portion 61 protruding in the thickness direction T from the inner surface 10a of the housing 10 exists around the second capillary structure 40 in plan view from the thickness direction T. That is, in FIG. 2, it is preferable that a wall portion 61 protruding in the thickness direction T from the inner surface 10a of the housing 10 exists around the evaporating portion EP in plan view from the thickness direction T. As shown in FIG. In this case, the liquid-phase working medium 20 that has been transported to the evaporator EP is easily retained in the evaporator EP without spreading around the evaporator EP. As a result, in the evaporating section EP, the heat transfer efficiency from the heat source HS to the liquid-phase working medium 20 is more likely to be improved, and the evaporation heat resistance is more likely to be reduced. As described above, the maximum heat transfer amount of the vapor chamber 1a is further improved.

The thickness of the wall portion 60 and the wall portion 61 may be the same or different.

The thickness of the projection 41a (or the second capillary structure 40) and the wall portion 61 may be the same or different.

The wall portion 60 and the wall portion 61 may be integrated or joined.

The heat diffusion device of the present invention further includes a third capillary structure provided in the internal space of the housing and overlapping the evaporating section in a plan view from the thickness direction, wherein the third capillary structure comprises: Preferably, the capillary force is greater than that of the second capillary structure.

The vapor chamber 1a preferably further has a third capillary structure 50.

As shown in FIG. 2, the third capillary structure 50 is preferably provided in the internal space of the housing 10 and overlaps the evaporating part EP in plan view from the thickness direction T. In FIG. 2 , the third capillary structure 50 overlaps the entire second capillary structure 40 in plan view from the thickness direction T. In FIG. In FIG. 4, the third capillary structure 50 is in contact with the protrusion 41a that constitutes the second capillary structure 40. In FIG.

The third capillary structure 50 functions as a liquid retaining part that sucks up and retains the liquid-phase working medium 20 spread by the second capillary structure 40 by capillary force, and the sucked liquid-phase working medium 20 is absorbed by the evaporating part. It also functions as a liquid flow path extending in the EP. Therefore, by combining the second capillary structure 40 and the third capillary structure 50, the liquid-phase working medium 20 can be efficiently spread over the entire evaporation part EP.

The third capillary structure 50 preferably has a greater capillary force than the second capillary structure 40. In this case, the third capillary structure 50 can more easily suck up the liquid-phase working medium 20 spread by the second capillary structure 40, so that the liquid-phase working medium 20 is removed by the third capillary structure 50 to the evaporation part EP. Easier to spread inside.

The magnitude of the capillary force of the capillary structure is related to the size of the cross-sectional area of the liquid flow path through which the liquid-phase working medium passes in the capillary structure when viewed in cross section along the thickness direction of the heat diffusion device. That is, in a cross-sectional view along the thickness direction T of the vapor chamber 1a as shown in FIG. It is preferable that the cross-sectional area of the region is small.

In the heat diffusion device of the present invention, the third capillary structure preferably contains a porous body.

The third capillary structure 50 preferably includes a porous body 51 in the vapor chamber 1a. 2 and 4, a porous body 51 is provided as the third capillary structure 50. In FIGS. In addition, in FIG. 2, the porous body 51 as the third capillary structure 50 is shown in a see-through state.

As the porous body 51, for example, those similar to the porous body 31 can be used.

The constituent materials of the porous body 31 and the porous body 51 may be the same as each other, or may be different from each other.

The thickness of the porous body 31 (or the first capillary structure 30) and the thickness of the porous body 51 (or the third capillary structure 50) may be the same or different.

The porous body 31 (or the first capillary structure 30) and the porous body 51 (or the third capillary structure 50) may be integrated or joined.

Instead of the porous body 51, the third capillary structure 50 may include a fiber bundle obtained by linearly bundling the plurality of fibers described above.

In plan view from the thickness direction T, the ratio of the area of the arrangement region CR3 of the third capillary structure 50 overlapping the evaporator EP to the area of the evaporator EP is preferably 50% or more.

The area of the arrangement region CR3 of the third capillary structure 50 overlapping the evaporating part EP in plan view from the thickness direction T corresponds to the area of the region overlapping the evaporating part EP in the entire third capillary structure 50. . Therefore, in plan view from the thickness direction T, the ratio of the area of the arrangement region CR3 of the third capillary structure 50 overlapping the evaporator EP to the area of the evaporator EP is 100% or less.

In a plan view from the thickness direction T, the ratio of the area of the arrangement region CR3 of the third capillary structure 50 overlapping the evaporation part EP to the area of the evaporation part EP is 50% or more, so that the second capillary structure 40 combined with the action of , the liquid-phase working medium 20 transported to the evaporator EP is more likely to spread throughout the evaporator EP. As a result, in the evaporating section EP, the heat transfer efficiency from the heat source HS to the liquid-phase working medium 20 is more likely to be improved, and the evaporation heat resistance is more likely to be reduced. As described above, the maximum heat transfer amount of the vapor chamber 1a is further improved.

In plan view from the thickness direction T, the area of the entire third capillary structure 50 may be larger than the area of the evaporating part EP. That is, in a plan view from the thickness direction T, the ratio of the area of the entire third capillary structure 50 to the area of the evaporating portion EP may be greater than 100%. In this case, the ratio of the area of the entire third capillary structure 50 to the area of the evaporating portion EP in plan view from the thickness direction T is preferably 120% or less.

In plan view from the thickness direction T, the area of the entire third capillary structure 50 may be smaller than the area of the evaporating part EP. In other words, in a plan view from the thickness direction T, the ratio of the area of the entire third capillary structure 50 to the area of the evaporating portion EP may be less than 100%. In this case, in plan view from the thickness direction T, the ratio of the area of the entire third capillary structure 50 to the area of the evaporating portion EP is preferably 50% or more.

The vapor chamber 1a operates as follows.

The liquid-phase working medium 20 evaporates by absorbing heat from the heat source HS in the evaporating section EP, and changes into the gas-phase working medium 20 . Then, the vapor-phase working medium 20 generated in the evaporator EP passes through the vapor passage VP to a place away from the evaporator EP (for example, near the end of the liquid transporter LP opposite to the evaporator EP). It moves, is cooled there, and changes into the working medium 20 of a liquid phase. After that, the liquid-phase working medium 20 is transported to the evaporator EP by the liquid transporter LP and the first capillary structure 30 .

In the vapor chamber 1a, the working medium 20 circulates while undergoing a gas-liquid phase change by repeating the above process. At this time, the heat from the heat source HS is absorbed as latent heat of vaporization that changes the liquid-phase working medium 20 into the vapor-phase working medium 20 in the evaporator EP, and then the vapor-phase operation occurs at a location away from the evaporator EP. It is released as latent heat of condensation that transforms the medium 20 into a liquid phase working medium 20 . In this way, the vapor chamber 1a operates autonomously without the need for external power, and further utilizes the latent heat of vaporization and latent heat of condensation of the working medium 20 to transfer heat from the heat source HS two-dimensionally. can spread rapidly. Furthermore, in the vapor chamber 1a, the ratio of the area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporation part EP to the area of the evaporation part EP in plan view from the thickness direction T is 50% or more, Increases maximum heat transfer.

<Embodiment 2>
In the heat diffusion device of Embodiment 2 of the present invention, unlike the heat diffusion device of Embodiment 1 of the present invention, in a plan view from the thickness direction, the second capillary structure is provided in the region overlapping with the evaporator. It is not provided in the extending direction of the liquid transport section. The heat spreading device of Embodiment 2 of the present invention is the same as the heat spreading device of Embodiment 1 of the present invention except for this point.

FIG. 5 is a schematic plan view showing the internal structure of an example of the heat diffusion device of Embodiment 2 of the present invention.

In the vapor chamber 1b shown in FIG. 5, in a plan view from the thickness direction T, the second capillary structure 40, more specifically, a plurality of protrusions 41a, are located in the region overlapping the evaporating part EP in the liquid transporting part LP. Not provided in the extension direction.

The extending direction of the liquid transporting part LP is such that, in plan view from the thickness direction T, the liquid transporting part LP extends from one end of the liquid transporting part LP connected to the evaporating part EP to a region overlapping the evaporating part EP. It corresponds to the direction assumed in the case. That is, in FIG. 5, in a planar view from the thickness direction T, the second capillary structure 40 extends in the length direction L and the width direction W in the region overlapping the evaporation portion EP. not provided for.

Since the second capillary structure 40 is not provided in the extending direction of the liquid transporting part LP, the flow path resistance of the liquid flow path in the evaporating part EP tends to decrease. As a result, coupled with the action of the second capillary structure 40, the liquid-phase working medium 20 transported to the evaporator EP is more likely to spread throughout the evaporator EP.

In a planar view from the thickness direction T, even if the second capillary structure 40 is not entirely provided in the extending direction of the liquid transporting part LP as shown in FIG. Alternatively, it may not be provided partially in the extending direction of the liquid transporting portion LP.

When the second capillary structure 40 is not provided partially in the extending direction of the liquid transporting part LP, the second capillary structure 40 is provided from the viewpoint of reducing the flow resistance of the liquid flow path in the evaporating part EP. is preferably connected to one end of the liquid transporting part LP.

<Embodiment 3>
In the heat diffusion device of Embodiment 3 of the present invention, unlike the heat diffusion device of Embodiment 2 of the present invention, when viewed from above in the thickness direction, the plurality of protrusions constituting the second capillary structure are linear. shape. The heat spreading device of Embodiment 3 of the present invention is otherwise similar to the heat spreading device of Embodiment 2 of the present invention.

FIG. 6 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 3 of the present invention.

In the vapor chamber 1c shown in FIG. 6, in plan view from the thickness direction T, a plurality of protrusions 41b forming the second capillary structure 40 extend linearly. Thereby, the second capillary structure 40 constitutes a so-called microchannel. Since the capillary force of the microchannel is large, the second capillary structure 40 constitutes the microchannel, and in the vapor chamber 1c, the liquid-phase working medium 20 transported to the evaporator EP is spread throughout the entire evaporator EP. It becomes easier to get around.

Furthermore, in the vapor chamber 1c, in a plan view from the thickness direction T, it is preferable that the second capillary structure 40 is not provided in the extending direction of the liquid transporting part LP in the region overlapping the evaporating part EP. In this case, the flow path resistance of the liquid flow path in the evaporator EP is likely to be reduced, so that the liquid-phase working medium 20 transported to the evaporator EP can more easily spread throughout the entire evaporator EP.

From the viewpoint of spreading the liquid-phase working medium 20 over the entire evaporator part EP with the second capillary structure 40, the plurality of protrusions 41b are arranged in the region overlapping the evaporator part EP in a plan view from the thickness direction T, as shown in FIG. preferably extend radially as shown in FIG. More specifically, in a plan view from the thickness direction T, the plurality of projections 41b linearly extend from the region where the second capillary structure 40 is not provided to the edge in the region overlapping the evaporating portion EP. preferably.

The plurality of projections 41b preferably extends in a direction intersecting the length direction L and the width direction W as shown in FIG. , or may extend in the width direction W.

<Embodiment 4>
In the heat diffusion device of Embodiment 4 of the present invention, unlike the heat diffusion device of Embodiment 1 of the present invention, the second capillary structure constitutes a meandering flow path in plan view from the thickness direction. The heat spreading device of Embodiment 4 of the present invention is the same as the heat spreading device of Embodiment 1 of the present invention except for this point.

FIG. 7 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 4 of the present invention.

In the vapor chamber 1d shown in FIG. 7, in plan view from the thickness direction T, the second capillary structure 40 forms a meandering flow path. More specifically, the second capillary structure 40 includes a wall portion 62 protruding in the thickness direction T from the inner surface 10a of the housing 10, here, the inner surface 11a of the first sheet 11. The enclosed area is configured to meander. In the vapor chamber 1 d , the liquid-phase working medium 20 transported to the evaporator EP spreads in the evaporator EP through the meandering flow path formed by the second capillary structure 40 .

In the vapor chamber 1d, the arrangement region CR2 of the second capillary structure 40 that overlaps the evaporating section EP does not include the region R that does not contribute to forming the meandering flow path. That is, in the vapor chamber 1d, the ratio of the area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporator EP to the area of the evaporator EP in plan view from the thickness direction T is 50% or more. Yes, but not 100%.

The wall portion 61 and the wall portion 62 may be integrated or joined.

<Embodiment 5>
In the heat diffusion device of Embodiment 5 of the present invention, unlike the heat diffusion device of Embodiment 1 of the present invention, when viewed from above in the thickness direction, the inner surface of the housing is provided around the second capillary structure. There is no wall protruding from the thickness direction. The heat spreading device of Embodiment 5 of the present invention is the same as the heat spreading device of Embodiment 1 of the present invention except for this point.

FIG. 8 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 5 of the present invention. 9 is a schematic cross-sectional view showing a cross section along line A3-A4 of the heat diffusion device shown in FIG. 8. FIG. FIG. 10 is a schematic cross-sectional view showing a cross section along line segment B3-B4 of the heat diffusion device shown in FIG.

In the vapor chamber 1e shown in FIGS. 8, 9, and 10, in plan view from the thickness direction T, around the second capillary structure 40, there is a No wall exists. More specifically, in the vapor chamber 1e, in plan view from the thickness direction T, there are walls around the second capillary structure 40, such as the wall portion 61 present in the vapor chamber 1a and the like shown in FIGS. In addition, there is no wall portion protruding in the thickness direction T from the inner surface 10a of the housing 10 .

In the vapor chamber 1e, the liquid-phase working medium 20 transported to the evaporating part EP may spread around the evaporating part EP compared to the vapor chamber 1a or the like in which the wall part 61 is present. And compared to the vapor chamber 1f shown in FIG. 13, the liquid-phase working medium 20 spreads easily in the evaporation part EP.

<Embodiment 6>
In the heat diffusion device of Embodiment 6 of the present invention, unlike the heat diffusion device of Embodiment 1 of the present invention, the second capillary structure includes a porous body. The heat spreading device of Embodiment 6 of the present invention is the same as the heat spreading device of Embodiment 1 of the present invention except for this point.

FIG. 11 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 6 of the present invention. 12 is a schematic cross-sectional view showing a cross section along line A5-A6 of the heat diffusion device shown in FIG. 11. FIG. 13 is a schematic cross-sectional view showing a cross section along line B5-B6 of the heat diffusion device shown in FIG. 11. FIG.

In the vapor chamber 1f shown in FIGS. 11, 12, and 13, the second capillary structure 40 includes a porous body 41. 11 and 13, a porous body 41 is provided as the second capillary structure 40. In FIGS.

As the porous body 41, for example, the same as the porous body 31 can be used.

The constituent materials of the porous body 31 and the porous body 41 may be the same or different.

The total thickness of the porous body 31 (or the first capillary structure 30) and the wall portion 60 and the thickness of the porous body 41 (or the second capillary structure 40) may be the same, or can be different.

The porous body 31 (or the first capillary structure 30) and the porous body 41 (or the second capillary structure 40) may be integrated or joined.

Instead of the porous body 41, the second capillary structure 40 may include a fiber bundle obtained by linearly bundling the plurality of fibers described above.

The vapor chamber 1f may not have the third capillary structure, for example, the porous body 51 shown in FIGS. 2 and 4, or may further have the third capillary structure.

<Embodiment 7>
In the heat spreading device of Embodiment 7 of the present invention, unlike the heat spreading device of Embodiment 1 of the present invention, the second capillary structure includes grooves provided on the inner surface of the housing. The heat spreading device of Embodiment 7 of the present invention is the same as the heat spreading device of Embodiment 1 of the present invention except for this point.

FIG. 14 is a schematic plan view showing the internal structure of an example of a heat diffusion device according to Embodiment 7 of the present invention. 15 is a schematic cross-sectional view showing a cross section along line A7-A8 of the heat diffusion device shown in FIG. 14. FIG. 16 is a schematic cross-sectional view showing a cross section along line B7-B8 of the heat diffusion device shown in FIG. 14. FIG.

In the vapor chamber 1g shown in FIGS. 14, 15, and 16, the second capillary structure 40 preferably includes grooves 42 provided on the inner surface 10a of the housing 10.

The groove 42 is recessed in the thickness direction T from the inner surface 10 a of the housing 10 , here, the inner surface 11 a of the first sheet 11 . In FIG. 14 , the planar shape of the grooves 42 when viewed from the thickness direction T is mesh-like.

The grooves 42 are formed, for example, by processing the inner surface 10a of the housing 10, here, the inner surface 11a of the first sheet 11, by etching, pressing, machining, or the like.

In the vapor chamber 1g, the second capillary structure 40 includes the grooves 42, so that the liquid-phase working medium 20 transported to the evaporation part EP spreads through the grooves 42 into the evaporation part EP. Furthermore, the thickness of the region of the vapor chamber 1g that overlaps the evaporation part EP is smaller than the thickness of the region of the vapor chamber 1a that overlaps the evaporation part EP shown in FIG.

In the vapor chamber 1g, the second capillary structure 40 includes, in addition to the grooves 42, a portion of the inner surface 10a of the housing 10 that is not provided with the grooves 42, here the first sheet 11 that is not provided with the grooves 42. By combining a part of the inner surface 11a of the , a so-called microchannel is formed, which functions as a liquid flow path for spreading the liquid-phase working medium 20 in the evaporating part EP. That is, in the vapor chamber 1g, the arrangement region CR2 of the second capillary structure 40 overlapping the evaporating part EP consists of the groove 42 and a portion of the inner surface 10a of the housing 10 where the groove 42 is not provided. corresponds to the area where a part of the inner surface 11a of the first sheet 11 where the is not provided is arranged. Therefore, in the vapor chamber 1g, the ratio of the area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporation part EP to the area of the evaporation part EP in plan view from the thickness direction T is 100%. .

In the vapor chamber 1g shown in FIGS. 14 and 15, a plurality of grooves 72 recessed in the thickness direction T from the inner surface 10a of the housing 10, here, a plurality of grooves recessed in the thickness direction T from the inner surface 11a of the first sheet 11. 72 extends in the in-plane direction, and liquid transporting portions LP are provided in the plurality of grooves 72 .

In the vapor chamber 1g, since the liquid transporting portions LP are provided in the plurality of grooves 72, the thickness of the region overlapping the liquid transporting portions LP of the vapor chamber 1g is equal to that of the liquid transporting portions LP of the vapor chamber 1a shown in FIG. less than the thickness of the overlapping region.

In the vapor chamber 1g, compared to the vapor chamber 1a, the thickness of the region overlapping the liquid transporting part LP and the evaporating part EP is smaller, so it can be made thinner.

The depths (thicknesses) of the grooves 42 and the grooves 72 may be the same or different.

[Electronics]
Electronic equipment according to the present invention will be described below.

An electronic device of the present invention includes the heat diffusion device of the present invention and an electronic component attached to an outer wall surface of the housing of the heat diffusion device, and when viewed in plan from the thickness direction, the electronic component is , overlaps the evaporator section of the housing.

FIG. 17 is a schematic perspective view showing an example of the electronic device of the present invention.

An electronic device having the heat diffusion device of Embodiment 1 of the present invention will be described below as an example of the electronic device of the present invention. The same applies to electronic equipment having heat diffusion devices according to other embodiments of the present invention.

An electronic device 100 shown in FIG. 17 has a vapor chamber 1a and an electronic component 110. More specifically, electronic device 100 has vapor chamber 1 a and electronic component 110 in the internal space of device housing 120 .

The electronic component 110 is attached to the outer wall surface of the housing 10 of the vapor chamber 1a. The electronic component 110 corresponds to the heat source HS shown in FIG. In other words, the electronic component 110 is attached to the outer wall surface opposite to the inner surface 10a of the housing 10 shown in FIG. Furthermore, in plan view from the thickness direction T, the electronic component 110 overlaps the evaporation portion EP of the housing 10 .

The electronic component 110 may be attached directly to the outer wall surface of the housing 10, or may be attached via another member such as adhesive, sheet, or tape with high thermal conductivity.

Examples of the electronic device 100 include smartphones, tablet terminals, notebook computers, game machines, wearable devices, and the like.

Examples of the electronic components 110 include central processing units (CPUs), light emitting diodes (LEDs), and heating elements such as power semiconductors.

As described above with reference to FIGS. 1, 2, 3 and 4, the vapor chamber 1a operates autonomously without the need for external power and furthermore the latent heat of vaporization of the working medium 20 And by utilizing the latent heat of condensation, the heat from the heat source HS can be diffused two-dimensionally at high speed. Furthermore, in the vapor chamber 1a, the ratio of the area of the arrangement region CR2 of the second capillary structure 40 overlapping the evaporation part EP to the area of the evaporation part EP in plan view from the thickness direction T is 50% or more, Increases maximum heat transfer. As described above, the electronic device 100 having the vapor chamber 1a can effectively dissipate heat in a limited space inside the electronic device 100 .

The heat diffusion device of the present invention can be used for a wide range of applications in fields such as personal digital assistants. The heat diffusion device of the present invention can be used, for example, to lower the temperature of a heat source such as a central processing unit and extend the usage time of electronic equipment, and is used in smartphones, tablet terminals, laptop computers, game machines, wearable devices, etc. Available.

1a, 1b, 1c, 1d, 1e, 1f, 1g vapor chamber (thermal diffusion device)
10 housing 10a housing inner surface 11 first sheet 11a first sheet inner surface 12 second sheet 20 working medium 30

first capillary structures

31, 41, 51 porous body 40

second capillary structures

41a,

41b projection

42 , 72 groove 50

third capillary structure

60, 61, 62 wall 100 electronic device 110 electronic component 120 device housing CR1 arrangement region CR2 of first capillary structure arrangement region CR3 of second capillary structure third capillary structure Arrangement area EP Evaporation part HS Heat source L Length direction LP Liquid transport part R Area T Thickness direction VP Vapor flow path W Width direction

Claims

a housing having, in its internal space, a liquid transporting section and an evaporating section connected to one end of the liquid transporting section in plan view from the thickness direction;
a working medium enclosed in the internal space of the housing;
a first capillary structure provided in the internal space of the housing and overlapping the liquid transporting portion in plan view from the thickness direction;
a second capillary structure provided in the internal space of the housing and overlapping the evaporating section in plan view from the thickness direction;
In plan view from the thickness direction, the ratio of the area of the arrangement region of the first capillary structure to the area of the internal space of the housing is 50% or less,
The heat diffusion device, wherein the ratio of the area of the second capillary structure overlapping the evaporating portion to the area of the evaporating portion in plan view from the thickness direction is 50% or more. .
The thermal diffusion device according to claim 1, wherein the first capillary structure includes a porous body.
The heat diffusion device according to claim 1 or 2, wherein the second capillary structure includes a plurality of protrusions provided on the inner surface of the housing.
The heat diffusion device according to claim 1 or 2, wherein the second capillary structure includes grooves provided on the inner surface of the housing.
5. The heater according to any one of claims 1 to 4, wherein a wall protruding in the thickness direction from the inner surface of the housing is present around the second capillary structure in plan view from the thickness direction. diffusion device.
6. The second capillary structure according to any one of claims 1 to 5, wherein in a planar view from the thickness direction, the second capillary structure is not provided in the extending direction of the liquid transporting section in a region overlapping with the evaporating section. heat spreading device.
further comprising a third capillary structure provided in the internal space of the housing and overlapping the evaporating section in plan view from the thickness direction;
The heat spreading device according to any one of claims 1 to 6, wherein said third capillary structure has a greater capillary force than said second capillary structure.
The heat diffusion device according to claim 7, wherein the third capillary structure includes a porous body.
a heat diffusion device according to any one of claims 1 to 8;
an electronic component attached to an outer wall surface of the housing of the heat spreading device;
The electronic device according to claim 1, wherein the electronic component overlaps the evaporating portion of the housing when viewed in plan from the thickness direction.