HEAT DISSIPATION SHEET AND METHOD FOR MANUFACTURING HEAT DISSIPATION SHEET

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2017-165421 filed on Aug. 30, 2017 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND
1. Technical Field

The disclosure relates to a heat dissipation sheet that is suitable for dissipating heat generated from, for example, an electronic component generating heat to the outside and a method for manufacturing a heat dissipation sheet.

2. Description of Related Art

Electronic components that generate heat on their own, such as a central processing unit (CPU), are likely to operate improperly when the temperature increases excessively. In order to avoid such improper operation, an appropriate cooling device is used together with an electronic component. Examples of the cooling device as described above include the heat dissipation sheet described in Japanese Unexamined Patent Application Publication No. 2001-291810 (JP 2001-291810 A), the heat transport device described in Japanese Unexamined Patent Application Publication No. 2011-086753 (JP 2011-086753 A), and furthermore, the heat dissipation device described in Japanese Unexamined Patent Application Publication No. 2006-253601 (JP 2006-253601 A).

The heat dissipation sheet described in JP 2001-291810 A is configured of a thermally conductive adhesive layer including a matrix resin and a thermally conductive filler and an expanded sheet that supports the thermally conductive adhesive layer and is stretched in one direction. The heat transport device described in JP 2011-086753 A is configured of a working fluid enclosed in a housing, an expanded sheet that is provided in the housing and forms a flow path of the working fluid, and a capillary structure. The heat dissipation device described in JP 2006-253601 A includes a support frame formed of a flexible metal sheet material having a thermal conductive property and tubular rhombic fins formed of the same sheet material, a plurality of rhombic fins is disposed in a row in the support frame by coupling crests of the rhombic fins, and one crest of one rhombic fin in a central portion is bonded to the support frame.

In both of the heat dissipation sheet described in JP 2001-291810 A and the heat transport device described in JP 2011-086753 A, the expanded sheet has a function as a structural member for postural maintenance and the like and a function as a thermally conductive path that maintains a heat transfer property or a heat dissipation property. As described in JP 2001-291810 A and JP 2011-086753 A, in the related art, an expanded sheet 10 that is used for the above-described heat dissipation sheet and the like is formed by providing a plurality of incisions 2 in multiple rows in a zigzag shape at intervals of a width L in a thin plate-like metal sheet 1 and stretching (expanding) the metal sheet 1 in a direction orthogonal to the direction of the incisions 2 as illustrated in FIG. 13A. FIG. 13B illustrates an example of the expanded sheet 10 of the related art that is formed as described above, places of the incisions 2 are gradually opened broadly in a direction orthogonal to a formation direction of the incisions 2 due to the stretching, and the places of the incisions 2 transform to a plurality of rhombic opening portions 3 due to the broad openings.

The expanded sheet 10 in the above-described form is a sheet obtained by stretching the thin plate-like metal sheet 1, and, as illustrated in a sectional view of FIG. 13C that is in a direction of a line XIIIC-XIIIC in FIG. 13B, in a region of a coupling portion 4, a width (2L) that is twice a length L between adjacent incisions 2, 2 is provided; however, in a strand portion 5 that is between a coupling portion 4 and another coupling portion 4, a width of the length L between adjacent incisions is provided.

FIG. 14A is a plan view of a heat dissipation sheet 20 formed by loading a resin material 11 as a matrix into the opening portions 3 in the expanded sheet 10. FIG. 14B is a sectional view in a direction of a line XIVB-XIVB in FIG. 14A. FIG. 14C is a sectional view in a direction of a line XIVC-XIVC in FIG. 14A. As illustrated in the drawings, the expanded sheet 10 is entirely buried in the resin material 11, and the resin material 11 is loaded into the opening portions 3 in the expanded sheet 10. In the heat dissipation sheet 20 of the above-described form, the coupling portion 4 in the expanded sheet 10 that is the heat dissipation member regulates a thickness S of the heat dissipation sheet 20 so that the coupling portion 4 is located across the entire region between an upper surface 20a and a lower surface 20b of the heat dissipation sheet 20 as illustrated in FIG. 14B. In addition, an upper end portion 4a of the coupling portion 4 is located so as to be exposed on an upper surface 20a side of the heat dissipation sheet 20 or located extremely close to the upper surface side, and a lower end portion 4b of the coupling portion 4 is located so as to be exposed on a lower surface 20b side of the heat dissipation sheet 20 or located extremely close to the lower surface side.

Meanwhile, as illustrated in FIG. 14C, in the strand portion 5, the width L is half of the width 2L of the coupling portion 4, and thus an upper end portion 5a of a strand portion 5U that is located in an upper portion in the drawing is located so as to be exposed on the upper surface 20a side of the heat dissipation sheet 20 or located extremely close to the upper surface side, but a lower end portion 5b of the strand portion 5U is located in almost a middle portion of the heat dissipation sheet 20 in a thickness direction and does not reach the lower surface 20b side of the heat dissipation sheet 20. A lower end portion 5b of a strand portion 5D that is located in a lower portion in the drawing is located so as to be exposed on the lower surface 20b side of the heat dissipation sheet 20 or located extremely close to the lower surface side, but an upper end portion 5a of the strand portion 5D is located in almost a middle portion of the heat dissipation sheet 20 in the thickness direction and does not reach the upper surface 20a side of the heat dissipation sheet 20.

Therefore, in the heat dissipation sheet 20 of the form of the related art, it is not possible to avoid functioning as a thermally conductive path that becomes different between a portion in which the coupling portion 4 is located and a portion in which the strand portion 5 is located in the expanded sheet 10. As a result, inevitably, the formation of a thermally conductive path using the expanded sheet 10 that is the heat dissipation member becomes insufficient from the viewpoint of the entire heat dissipation sheet 20, and it is needed to increase the proportion of the expanded sheet 10 that is the heat dissipation member in the heat dissipation sheet 20 in order to make the heat dissipation member highly thermally conductive. What has been described above means a decrease in the ratio of the resin material, which, inevitably, sacrifices the flexibility of the heat dissipation sheet 20.

SUMMARY

The heat dissipation device described in JP 2006-253601 A has a configuration in which the tubular rhombic fins are provided in the rectangular support frame and has an advantage in which a number of thermally conductive paths with an equal length are formed between a top plate and a bottom plate that are heat dissipation surfaces or heat receiving surfaces using the rhombic fins. However, there is a disadvantage that the rectangular support frame is deficient in flexibility and sufficient flexibility cannot be obtained, particularly, in a depth direction. Therefore, it is difficult to satisfy both a high thermal conductive property and flexibility needed for heat dissipation sheets.

Aspects of the present disclosure provide a heat dissipation sheet capable of maintaining a higher thermal conductive property while holding needed flexibility and a method for manufacturing a heat dissipation sheet.

A first aspect of the disclosure relates to a heat dissipation sheet including a resin material and a heat dissipation member that is made of a material with a higher thermal conductivity than the resin material and has a predetermined thickness. The heat dissipation member is a bent product of a thin plate and has a plurality of elongated protrusion bands and a plurality of elongated recess bands that are alternately arranged in parallel with one another. Top surfaces of the respective protrusion bands are flush with each other, and are located in a first horizontal surface. Bottom surfaces of the respective recess bands are flush with each other, and are located in a second horizontal surface that is parallel to the first horizontal surface. A first slit including a first width that is narrower than a width of the top surface is provided between the top surfaces of the adjacent protrusion bands. A second slit including a second width that is narrower than a width of the bottom surface and is parallel to the first slit is provided between the bottom surfaces of the adjacent recess bands. Portions of the heat dissipation member other than both the top surfaces of the respective protrusion bands and the bottom surfaces of the respective recess bands are buried in the resin material.

In the heat dissipation sheet according to the first aspect, a plurality of third slits may be provided from the top surfaces of the protrusion bands to the bottom surfaces of the recess bands or from the bottom surfaces of the recess bands to the top surfaces of the protrusion bands in a direction orthogonal to the first slits and the second slits.

In the heat dissipation sheet according to the first aspect, insulating layers may be provided on front and rear surfaces of the heat dissipation sheet. In addition, in the heat dissipation sheet, the heat dissipation member may have insulating films on front and rear surfaces of the heat dissipation member.

In the heat dissipation sheet according to the first aspect, the heat dissipation member may be made of a single material or a complex material with a thermal conductivity of 10 W/m·K or more.

In the heat dissipation sheet according to the first aspect, the resin material may be made of any one or more of a silicone resin, an epoxy resin, a urethane resin, a polyamide resin, a polyphenylene sulfide resin, and a polyimide resin.

A second aspect of the disclosure relates to a method for manufacturing a heat dissipation sheet including a resin material and a heat dissipation member that is made of a material with a higher thermal conductivity than the resin material and has a predetermined thickness. The method includes bending a thin plate so that elongated protrusion bands having a top surface that is a flat surface and elongated recess bands having a bottom surface that is a flat surface are alternately formed, compressing the bent thin plate in a direction orthogonal to the formed protrusion bands and recess bands so that a first gap between the top surfaces of the adjacent protrusion bands and a second gap between the bottom surfaces of the adjacent recess bands become narrower than those before the thin plate is compressed; and burying the compressed thin plate in a molten resin material in a state in which the flat surfaces that are the top surfaces of the protrusion bands and the flat surfaces that are the bottom surfaces of the recess bands are left unburied and curing the resin.

The method for manufacturing a heat dissipation sheet according to the second aspect may further include forming slit rows each of which includes third slits arranged in a longitudinal direction of the third slit through non-slit portions with a predetermined length such that the silt rows are arranged parallel to one another in the thin plate at intervals in a direction orthogonal to the third slit. The thin plate in which the slit rows are formed may be bent.

With the aspect of the present disclosure, a heat dissipation sheet having higher flexibility and having a higher thermal conductive property without sacrificing the flexibility is provided (in the present specification, “being located in the first horizontal surface” also means “being substantially located in the first horizontal surface”).

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1A is a first view describing a heat dissipation member that is used in a heat dissipation sheet together with a manufacturing step thereof;

FIG. 1B is the first view describing the heat dissipation member that is used in the heat dissipation sheet together with the manufacturing step thereof;

FIG. 1C is the first view describing the heat dissipation member that is used in the heat dissipation sheet together with the manufacturing step thereof;

FIG. 2 is a view illustrating a second example of a raw sheet that forms the heat dissipation member;

FIG. 3 is a second view illustrating the manufacturing step;

FIG. 4 is a third view illustrating the manufacturing step;

FIG. 5 is a fourth view illustrating the manufacturing step;

FIG. 6 is a perspective view illustrating an example of a manufactured heat dissipation member;

FIG. 7 is a first view describing a step of manufacturing the heat dissipation sheet;

FIG. 8 is a second view describing the step of manufacturing the heat dissipation sheet;

FIG. 9 is a side view illustrating the manufactured heat dissipation sheet;

FIG. 10 is a side view illustrating another embodiment of the heat dissipation sheet;

FIG. 11 is a side view illustrating still another embodiment of the heat dissipation sheet;

FIG. 12 is a side view illustrating still another embodiment of the heat dissipation sheet;

FIG. 13A is a view for describing an expanded sheet that is a heat dissipation member used in a heat dissipation sheet of the related art;

FIG. 13B is a view for describing the expanded sheet that is a heat dissipation member used in a heat dissipation sheet of the related art;

FIG. 13C is a view for describing the expanded sheet that is a heat dissipation member used in a heat dissipation sheet of the related art;

FIG. 14A is a view for describing the heat dissipation sheet of the related art;

FIG. 14B is a view for describing the heat dissipation sheet of the related art; and

FIG. 14C is a view for describing the heat dissipation sheet of the related art.

DETAILED DESCRIPTION OF EMBODIMENTS

A first embodiment of a heat dissipation sheet according to the present disclosure will be described with reference to the drawings.

Heat Dissipation Member

First, an example of a heat dissipation member that is used in the heat dissipation sheet of an embodiment will be described together with a manufacturing step thereof.

A material of the heat dissipation member is not particularly limited, and examples thereof include metal, ceramic, and graphite. Examples of the metal include copper, aluminum, gold, silver, nickel, and zinc. Examples of the ceramic include alumina, silica, boron nitride, zinc oxide, and magnesium oxide. When ceramic is used, it is desirable to mold the ceramic in a state of a green sheet that is yet to be fired from the viewpoint of ease of molding. A single material or a complex material of the heat dissipation member with a thermal conductivity of 10 W/m·K or more is desirable. As the material, a 10 μm to 500 μm-thick thin plate-like raw sheet 50 is desirably used.

First, mountain fold locations and valley fold locations are set in the raw sheet 50 that is a rectangular thin plate as illustrated in FIG. 1A. In the example illustrated in the drawing, the mountain fold locations and the valley fold locations are indicated by mountain fold lines p (broken lines) and valley fold lines q (dot-and-dash lines) that extend in a Y direction of the raw sheet 50. The mountain fold lines p and valley fold lines q are all parallel to one another, the distances between a mountain fold line p and another mountain fold line p that are close to each other in an X direction are all set to a, the distances between a valley fold line q and another valley fold line q that are close to each other in the X direction are all set to a, and the distances between a mountain fold line p and a valley fold line q that are close to each other in the X direction are all set to b.

The raw sheet 50 is bent along the mountain fold lines p and the valley fold lines q. FIG. 1B illustrates a side surface of the bent raw sheet 50 when bending angles α in the bending are all 90 degrees. A region sandwiched by the mountain fold line p and the mountain fold line p forms a top surface 54 in a protrusion band, and a region sandwiched by the valley fold line q and the valley fold line q forms a bottom surface 55 in a recess band. The top surface 54 and the bottom surface 55 are both flat surfaces, and the shape in a planar view is a rectangular shape with a horizontal width (hereinafter, also referred to as the width in an X axis direction) of a. The top surfaces 54 are substantially located in a horizontal surface (hereinafter, also referred to as the first horizontal surface) H1, and the bottom surfaces 55 are also substantially located in a horizontal surface (hereinafter, also referred to as the second horizontal surface) H2. In addition, the first horizontal surface H1 and the second horizontal surface H2 are parallel to each other and are separated from each other in the vertical direction (hereinafter, also referred to as a Z axis direction) in the drawing by the distance b between the mountain fold line p and the valley fold line q in the X direction.

In the raw sheet 50 bent in the above-described form, a raw sheet portion between the mountain fold line p and the valley fold line q is present as a side surface in the vertical direction (the Z axis direction), is tolerant of a compressive force in the vertical direction (the Z axis direction), and is capable of easily following bending in a direction along an X axis (bending in a Kx direction in the drawing). However, when the bending angle α is 90 degree, as illustrated in FIG. 1B, in the first horizontal surface H1, an empty region with a distance a that is the horizontal width of the bottom surface 55 of the recess band is present between the adjacent top surfaces 54, 54, and, in the second horizontal surface H2 as well, an empty region with a distance a that is the horizontal width of the top surface 54 of the protrusion band is present between e the adjacent bottom surfaces 55, 55. Therefore, heat dissipation members having a shape including the sectional shape illustrated in FIG. 1B have a disadvantage that it is not possible to obtain a large contact area with a counterpart member on both a heat receiving surface and a heat dissipation surface.

FIG. 1C illustrates a sectional view of a heat dissipation member 100 according to the present disclosure that has solved the above-described disadvantage. Here, the bending angle α at a mountain fold portion (hereinafter, also referred to as the mountain fold line p) is set to an angle smaller than 90 degrees, that is, a sharp angle (for example, an angle of approximately 45 degrees to less than 90 degrees), and the bending angle α at a valley fold portion (hereinafter, also referred to as the valley fold line q) is also, similarly, set to an angle narrower than 90 degrees.

When bending is carried out under the above-described conditions, as illustrated in FIG. 1C, a distance c of a gap (to the gap can be regarded as a first slit 56) present between adjacent top surfaces 54, 54 in the first horizontal surface H1 becomes narrower than the distance a that is the horizontal width of the top surface 54, and, in the second horizontal surface H2 as well, the distance c of a gap (to the gap can be regarded as a second slit 57) present between adjacent bottom surfaces 55, 55 also becomes narrower than the distance a that is the horizontal width of the bottom surface 55. As a result, in the heat dissipation member 100 having a sectional shape illustrated in FIG. 1C, it becomes possible to maintain a larger contact area with a counterpart member on both the heat receiving surface and the heat dissipation surface than that of heat dissipation member having a form illustrated in FIG. 1B in the heat dissipation member 100 having the same width in the X axis direction while maintaining sufficient flexibility against bending in the direction along the X axis (the bending in the Kx direction in the drawing).

The thickness of the heat dissipation member 100, that is, a distance b1 between the first horizontal surface H1 and the second horizontal surface H2 in the Z axis direction is b1<b and changes depending on the bending angle α. As the bending angle α becomes sharper, the widths of the first slit 56 and the second slit 57 become narrower. The dimension of the bending angle α or the horizontal width a needs to be appropriately set depending on requirements in a place in which the heat dissipation member 100 is actually used.

In the description of the heat dissipation member 100 illustrated in FIGS. 1A to 1C, the top surface 54 in the protrusion band and the bottom surface 55 in the recess band have the same shape and dimension, and the distances b between the mountain fold line p and the valley fold line q in the X direction are all the same, but such conditions are for the convenience of using a bending machine such as a press machine for bending as described below, and the shape of the heat dissipation member 100 is not limited thereto. When the degree of freedom in work is high by manually bending the raw sheet, even in a case in which the heat dissipation member has a different shape, for example, the horizontal widths a of the top surface 54 and the bottom surface 55 are different from each other or the bending angles α are set to mutually different angles, it is possible to obtain a heat dissipation member capable of satisfying the conditions of a heat dissipation member according to the first aspect of the present disclosure, that is, a heat dissipation member satisfying conditions that a plurality of long protrusion bands and a plurality of long recess bands are alternately arranged in parallel with one another, the top surfaces 54 of the respective protrusion bands are flush with each other, the top surfaces 54 of the respective protrusion bands are substantially located in the first horizontal surface H1, the bottom surfaces 55 of the respective recess bands are flush with each other, the bottom surfaces 55 of the respective recess bands are located in the second horizontal surface H2 that is parallel to the first horizontal surface H1, the first slit 56 with the width c that is narrower than the width of the top surface 54 is provided between the top surfaces 54 of the adjacent protrusion bands, and the second slit 57 that is a gap with a width that is narrower than the width of the bottom surface 55 and is parallel to the first slit 56 is provided between the bottom surfaces 55 of the adjacent recess bands.

FIG. 2 is a view that illustrates another form of the raw sheet and corresponds to FIG. 1A. A raw sheet 50a illustrated in FIG. 2 is different from the raw sheet 50 in terms of having third slits 51, 52 that extend in the X axis direction. Hereinafter, the configuration will be described.

A plurality of third slits 51, 52 linearly arranged forms slit rows that are arranged through non-slit portions with a predetermined length, the third slits 51, 52 being linear slits with a predetermined length. The non-slit portion refers to a portion between the slit 51 and the slit 51 and a portion between the slit 52 and the slit 52. The slit rows are formed parallel to one another at intervals in a direction orthogonal to the third slits 51, 52.

The third slits 51, 52 are both formed in a direction orthogonal to the first slit 56 and the second slit 57, that is, in the X axis direction. The third slit 51 is formed across the top surface 54 of the protrusion band and both side wall portions thereof, that is, in FIG. 2, from a valley fold line q through two mountain fold lines p, p to the next valley fold line q in the X axis direction, and furthermore, on an extended line running toward the right, another third slit is formed from the next valley fold line q through two mountain fold lines p, p to the next valley fold line q, whereby the slit lines are formed. In other words, the slits are formed in portions other than regions between adjacent valley fold lines q, q (to the regions ca be regarded as the non-slit portions) in the X axis direction of the raw sheet 50 at intervals of a predetermined distance d in the Y axis direction.

The other third slit 52 is formed, in the middle location between the two third slits 51, 51, across the bottom surface 55 of the recess band and both side wall portions thereof, that is, in FIG. 2, from a mountain fold line p through two valley fold lines q, q to the next mountain fold line p in the X axis direction, and furthermore, on an extended line running toward the right, another third slit is formed from the next mountain fold line p through two valley fold lines q, q to the next mountain fold line p, whereby the slit lines are formed. In other words, the slits are formed in portions other than regions between adjacent mountain fold lines p, p (to the regions can be regarded as the non-slit portions) in the X axis direction of the raw sheet 50 at intervals of a predetermined distance d in the Y axis direction.

The intervals (d/2) between the third slit 51 and the third slit 52 are all desirably equal to one another, but all of the intervals do not need to be equal to one another at all times. The distance d may be approximately 0.1 mm to 10 mm. The raw sheet 50a illustrated in FIG. 2 is also bent in the same manner as the raw sheet 50 illustrated in FIG. 1A. For the third slits 51, 52, the slit length between the mountain fold line p and the valley fold line q may be the full width or a part thereof. The slit length is desirably ½ or more of the distance between the mountain fold line p and the valley fold line q.

A perspective view of a heat dissipation member 100a after the bending of the raw sheet 50a is illustrated in FIG. 6. In the heat dissipation member 100a after the bending of the raw sheet 50a illustrated in FIG. 6, portions that correspond to the same portions as portions in the heat dissipation member 100 illustrated in FIG. 1C will be given the same reference sign as in the heat dissipation member 100 and will not be described. In the heat dissipation member 100a, the protrusion bands and the recess bands have the third slits 51, 52 that extend in the X axis direction in the depth direction in FIG. 2, that is, in the Y axis direction in multiple stages, and thus the heat dissipation member has an advantage of becoming more flexible in the depth direction (the Y axis direction) than the heat dissipation member 100 illustrated in FIG. 1C. Even when any one of the third slits 51, 52 alone are formed due to the usage environment, it is possible to obtain needed flexibility.

An example of a case of producing the heat dissipation member 100 by bending the raw sheet 50 will be described with reference to FIG. 3 to FIG. 5. Here, a pressing machine 60 in which a plurality (three in the example illustrated in the drawing) of press apparatuses 63 made up of a movable press die 61 and a fixed press die 62 that are located to face each other in the Z axis direction is placed side by side in the X axis direction is used. As illustrated in the drawing, the three press apparatuses 63 are placed side by side in a posture in which the locations of the movable press dies 61 and the fixed press dies 62 in the vertical direction (the Z direction) are inverted. Each of the movable press dies 61 has a rectangular section, and a width A in the X axis direction is almost equal to the distance a in the raw sheet 50 (or the raw sheet 50a), that is, the distance between the two mountain fold lines p, p or between the two valley fold lines q, q. A distance B in the Z axis direction between a support surface of one of the fixed press dies 62 in the adjacent press apparatuses 63, 63 and a support surface of the other fixed press die 62 is almost equal to the distance b between the mountain fold line p and the valley fold line q that are adjacent to each other. The distance between the adjacent press apparatuses 63, 63 in the X axis direction is almost equal to the thickness of the raw sheet 50 to be bent. The lengths of the movable press die 61 and the fixed press die 62 in the depth direction, that is, in the Y axis direction are larger than the width in the Y axis direction of the raw sheet 50 to be bent.

At the time of initiating bending, the X axis direction and the Y axis direction are matched, and the raw sheet 50 is disposed between the movable press dies 61 and the fixed press dies 62 of the pressing machine 60 in an opened state. The state is illustrated in FIG. 3. In each of the press apparatuses 63, the movable press die 61 is moved toward the fixed press die 62. Therefore, the raw sheet 50 is bent in a shape in which the protrusion bands and the recess bands are alternately provided in parallel with one another. The shape is identical to the shape that has been described with reference to FIG. 1B, the top surfaces 54 of the protrusion bands and the bottom surfaces 55 of the recess bands are connected to one another through substantially vertical side walls, and the angles α formed by the top surface (or the bottom surface) and the side wall are 90 degrees.

After the bending, the press dies are opened, the bent raw sheet 50 is moved forward in a feed direction (the X axis direction) in FIG. 3, and the next stage of bending is carried out. In addition, as illustrated in FIG. 4, in this state, that is, in a state in which the raw sheet 50 is fixed by the press apparatuses 63 for the next stage of bending, a compressive force is applied in a direction opposite to the feed direction of the raw sheet 50 to a region that has been bent in the previous stage. Due to the application of the compressive force, the angles α formed by the top surface (or the bottom surface) and the side wall change so that the angles become a sharp angle. The state of the raw sheet 50 after the change is illustrated in FIG. 5.

After that, a work of the above-described press operation and the above-described compression operation is repeated as many times as needed, whereby it is possible to manufacture the heat dissipation member 100 or the heat dissipation member 100a illustrated in FIG. 6. In any case, the sectional view is as illustrated in FIG. 1C. When the raw sheet 50a illustrated in FIG. 2 is used, the third slits 51 facing toward the bottom surface 55 of the recess band from the top surface 54 of the protrusion band and the third slits 52 facing toward the top surface 54 of the protrusion band from the bottom surface 55 of the recess band are formed in a direction orthogonal to the first slits 56 and the second slits 57 as illustrated in FIG. 6, and thus the heat dissipation member 100a also becomes more flexible against bending in the Y axis direction.

Resin Material 300

A heat dissipation sheet 200 is obtained by burying the heat dissipation member 100 (or the heat dissipation member 100a) in a resin material 300. The resin material 300 may be a single resin body or a resin loaded with a filler in order to improve functions. Examples of the resin include moisture-curable or ambient temperature-curable thermosetting resins (any of a one-liquid type and a two-liquid-mixing type are available) such as a silicone resin, an epoxy resin, and a urethane resin and thermoplastic resins such as a polyamide resin, a polyphenylene sulfide resin, and a polyimide resin. Examples of the filler include metal fillers such as copper, aluminum, silver, nickel, and zinc and inorganic fillers such as alumina, silica, boron nitride, zinc oxide, magnesium oxide, and graphite. A mixed material obtained by grinding a material that is used to manufacture the heat dissipation member 100 (100a) in a particle form and mixing the particles into the resin material 300 can also be used.

Manufacturing of Heat Dissipation Sheet 200

The heat dissipation member 100 (100a) can be buried in the resin material 300 using a predetermined method. FIG. 7 and FIG. 8 illustrate an example thereof. As illustrated in FIG. 7, the formed heat dissipation member 100 is put into a mold 400, and the dimension is fixed by restraining the end portion with appropriate means such as a pin. In addition, the resin material 300 is poured from the above of the heat dissipation member 100 (100a). As illustrated in FIG. 8, the height is adjusted by covering the mold 400 with a lid 401, then, the mold is injected into a constant-temperature tank, and the resin material 300 is heated and cured. After cooling, the heat dissipation member is removed from the mold, whereby the heat dissipation sheet 200 having a side view illustrated in FIG. 9 is obtained.

Advantages of Heat Dissipation Sheet 200

As described above, the heat dissipation sheet 200 of the present embodiment is manufactured by using the heat dissipation member 100 (100a) obtained by bending the raw sheet 50 or one highly thermally conductive thin plate-like raw sheet 50a having the third slits 51, 52 formed in the X axis direction as a structural material and burying all of the heat dissipation member in the resin material 300.

The heat dissipation member 100 (100a) is one structure, has an area in a wide surface direction, and furthermore, is also continuously oriented in the thickness direction, and thus a thermally conductive path that is not cut in the middle in the thickness direction is formed. Parts (the top surfaces 54 and the bottom surface 55) of the heat dissipation member 100 (100a) are respectively located on the top and bottom surfaces of the heat dissipation sheet 200 in a wide area, and thus it is possible to efficiently conduct heat in the interface with an adherend (a heat generator or the like), and thermal resistance during actual use can be decreased. The first slits 56 and the second slits 57 that extend in the Y axis direction are provided, and the heat dissipation member is also capable of flexibly transforming in the X axis direction. In a case in which the heat dissipation member 100a illustrated in FIG. 6 is used, the heat dissipation member 100a includes the third slits 51, 52 and is also capable of flexibly transforming in the Y axis direction.

Since the first slits 56 and the second slits 57 are provided, a spatial region that is continuously connected in the three-axis directions is formed, and thus the property of allowing the resin material 300 to be loaded at the time of burying the heat dissipation member in the resin material 300 is excellent. When the heat dissipation member 100a including the third slits 51, 52 is employed, a superior loading property is maintained. Therefore, the resin material 300 does not drop off from the heat dissipation sheet 200 after being loaded, and the durability also improves.

In order to further improve the loading property of the resin material 300, it is also possible to form small pores with a diameter of approximately 0.05 mm in all or an appropriate portion of the raw sheet 50 or 50a to an extent in which the contact area with an adherend (a heat generator or the like) is not meaningfully impaired, for example, approximately 1 vol % or less of the entire raw sheet.

As described above, the heat dissipation member 100 (100a) is structurally strong and has a relatively high degree of freedom in bending and thus has an advantage of the increasing degree of freedom in being attached to an electronic component that generates heat for itself such as CPU. The heat dissipation member is capable of following a work shape such as an uneven surface or an R surface in addition to a flat surface and is thus being used in a broadening scope of places. Regarding the aspects of use, not only the use of the heat dissipation sheet 200 that has been loaded with the resin but also an aspect of use in which solely the heat dissipation member 100 (100a) is attached to a work side and then loaded with the resin material 300, thereby producing the heat dissipation sheet 200 become possible.

Other Configurations of Heat Dissipation Sheet

The volume fraction of the heat dissipation member 100 (100a) in the total volume of the heat dissipation sheet 200 is not particularly limited, but is desirably 5% or more and 80% or less. At a volume fraction of less than 5%, it is not possible to increase the thermal conductivity, and thus the heat dissipation sheet is not useful as a heat dissipation material. A region that does not contribute to heat dissipation broadens, and thermal conduction unevenness becomes significant in the heat dissipation sheet, and thus there is likelihood that an unpredictable high-temperature portion may be generated in the product. When the volume fraction exceeds 80%, the thermal conductivity of the heat dissipation sheet becomes high, but the heat dissipation sheet becomes too hard, the interface thermal resistance with a product increases, and there is a likelihood that desired heat dissipation performance cannot be obtained.

The ratio between the thickness of the raw sheet 50 (50a) that configures the heat dissipation member 100 (100a) and the thickness of the heat dissipation sheet 200 is desirably 1:3 or more and 1:10 or less. When the ratio between the thickness of the raw sheet 50 (50a) and the thickness of the heat dissipation sheet 200 is less than 1:3, the flexibility of the heat dissipation member against a compressive stress in the thickness direction decreases, and the flexibility as a heat dissipation sheet is impaired, and thus the interface thermal resistance with a product increases, and there is a likelihood that desired heat dissipation performance cannot be obtained. When the ratio between the thickness of the raw sheet 50 (50a) and the thickness of the heat dissipation sheet 200 exceeds 1:10, it is not possible to increase the volume fraction of the heat dissipation member, and an increase in the thermal conductivity is not possible.

Second Embodiment-1

FIG. 10 illustrates a second embodiment of the heat dissipation sheet. A heat dissipation sheet 200a of the second embodiment is different from the heat dissipation sheet 200 in terms of insulating layers 101 that are provided on the front and rear surfaces of the heat dissipation member 100 (100a). The rest of the configuration is the same as that of the heat dissipation sheet 200. As a material of the insulating layer 101, it is possible to use a material such as a thermosetting resin such as a silicone resin, an epoxy resin, or a urethane resin, a resin material such as a polyamide resin, a polyphenylene sulfide resin, or a polyimide resin, or a ceramic material such as alumina, silica, or boron nitride. When the insulating layers 101 are provided, the heat dissipation sheet 200a maintaining both a higher thermal conductivity and a higher insulating property can be obtained.

Third Embodiment

FIG. 11 illustrates a third embodiment of the heat dissipation sheet. In a heat dissipation sheet 200b of the third embodiment, the heat dissipation member 100 (100a) is formed using a material having insulating films 102 on the front and rear surfaces as the raw sheet 50 (50a). As a material of the insulating film 102, it is possible to use a material such as a thermosetting resin such as a silicone resin, an epoxy resin, or a urethane resin, a resin material such as a polyamide resin, a polyphenylene sulfide resin, or a polyimide resin, or a ceramic material such as alumina, silica, or boron nitride. In the heat dissipation sheet 200b as well, the heat dissipation member 100 has insulating performance, and thus it is possible to maintain both a higher thermal conductivity and a higher insulating property.

Fourth Embodiment

FIG. 12 illustrates a fourth embodiment of the heat dissipation sheet. In a heat dissipation sheet 200c of the fourth embodiment, as a heat dissipation member 100c, a heat dissipation member obtained by forming multiple stages of bent portions 103 in portions that extend in the thickness direction of the heat dissipation sheet 200c (the portions present between the mountain fold line p and the valley fold line q in the raw sheet 50 (50a)) is used. In the above-described configuration, the heat dissipation sheet 200c having an improved compression characteristic in the thickness direction can be obtained.

Hereinafter, the superiority of the heat dissipation sheet 200 according to the present disclosure will be described using examples and comparative examples.

Example Products

0.2 mm-thick pure Cu foils that were the thin plate-like raw sheet 50a illustrated in FIG. 2 were bent as described based on FIG. 3 to FIG. 5, thereby producing a plurality of heat dissipation members 100a having the shape illustrated in FIG. 6 with different dimensions and a different angle α. Specific dimensions were shown in the columns of Examples 1, 2, and 3 in Table 1. The produced heat dissipation members 100a were buried in a liquid-phase silicone resin that served as the resin material 300 as illustrated in FIG. 7 and FIG. 8 and then heated and cured in a constant-temperature tank, thereby producing heat dissipation sheets 200.

As shown in Table 1, in Examples 1, 2, and 3, the heat dissipation members 100a were made to differ in dimensions or shape, thereby providing different volume fractions of the heat dissipation member (Cu) in the heat dissipation sheet 200. The used silicone resin was KE-1870 (addition reaction-type resin) manufactured by Shin-Etsu Chemical Co., Ltd., the curing conditions were 150° C.×30 minutes, the viscosity was 400 mPa·s, and the hardness after curing was 15 (durometer A).

Comparative Example Products

Heat dissipation members 10 and heat dissipation sheets 20 were produced using the same materials and the method of the related art that has been previously described based on FIGS. 13A to 13C and FIGS. 14A to 14C. The stretching amount was varied during the production of the heat dissipation members 10, thereby producing heat dissipation sheets of Comparative Examples 1 to 3 having different volume fractions of the heat dissipation member (Cu) that are shown in Table 1. The inclination angles α of Comparative Examples 1 to 3 are an inclination angle A° illustrated in FIG. 14B.

Characteristic Test

For Example Products 1 to 3 and Comparative Example Products 1 to 3, the thermal conductivity and the thermal resistance were measured using the steady method. The results are shown in Table 1.

TABLE 1

Example
Comparative Example

1
2
3
1
2
3

Volume fraction
Heat dissipation member
17
22
26
10
20
30

Resin
83
78
74
90
80
60

Dimensions
Thickness of Cu foil [mm]
0.2
0.2
0.2
0.2
0.2
0.2

Inclination angle α[°]
60
45
45
120
120
120

[Note 1]

Width a of top surface 54 and
6
6
5
—
—
—

bottom surface 55 [mm]

Final thickness of heat dissipation
2
2
2
2
2
2

sheet [mm]

Thermal
Thermal conductivity [W/mk]
9
14
19
3
7
10

characteristics
Thermal resistance [° C./W]
0.75
0.50
0.37
2.81
1.42
0.86

[Note 2]

[Note 1]

The inclination angle α in the comparative examples is the angle A° in FIG. 14B.

[Note 2]

The thermal conductivity is the heat dissipation performance of the heat dissipation sheet alone, and the thermal resistance is the estimated heat dissipation performance of the heat dissipation sheet sandwiched by members in actual use. The produced heat dissipation sheet was cut to a predetermined size (φ20 mm), and the thermal characteristics were measured using the steady method.

Evaluation

In Example Products 1, 2, and 3 and Comparative Example Products 1, 2, and 3, the final thicknesses were all equal to one another (2 mm), and the volume fractions of the heat dissipation member and the resin were also almost equal to one another. However, in Example Products 1, 2, and 3, the thermal conductivity improved more significantly compared with those in Comparative Example Products 1, 2, and 3. The thermal resistance became smaller in Example Products 1, 2, and 3 compared with in Comparative Example Products 1, 2, and 3. This results from the fact that the heat dissipation members that were used in the present examples basically had the shape illustrated in FIG. 6, and thus the thermally conductive paths substantially increased compared with those in the comparative example products.

HEAT DISSIPATION SHEET AND METHOD FOR MANUFACTURING HEAT DISSIPATION SHEET

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