Heat dissipating device

A heat dissipating device which dissipates heat generated by a heat generating object mounted on a base includes a heat sink body, a heat-conducting area, a tip portion, an inclined surface, and a fastener. The heat-conducting area includes the tip portion, which is a substantially middle portion of the heat-conducting area and is arranged substantially closest to the heat generating object among the other areas of the heat-conducting area, and the inclined surface which is a part of the heat-conducting area and inclines outwardly from the tip portion such that a distance between the inclined surface and the heat generating object gradually increases. The fastener includes an attaching portion to mount the heat dissipating device to the base, and the attaching portion is arranged substantially radially outside of an outer peripheral portion of the heat generating object. When the attaching portion is secured to the base, the tip portion of the heat-conducting area is pressed to the heat generating object.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a heat dissipating device which dissipates heat generated by an electronic component (e.g., a microprocessing unit).

2. Background of the Related Art

With recent technological advances, a microprocessing unit (MPU) has a high speed. Such an MPU, however, generates considerable heat. Since an overheated MPU may malfunction, a technique for effectively dissipating the heat generated by the MPU is in great demand.

Generally, a heat dissipating device is arranged on the MPU of an electronic device to dissipate heat generated by the MPU. The heat dissipating device generally includes a heat sink having a plurality of heat sink fins and a cooling fan. The heat generated by the MPU is diffused to the plurality of heat sink fins of the heat sink, and a cooling fan provides air flow to the heat sink fins. Thereby, the heat is dissipated actively from the heat sink fins.

For effectively dissipating heat, it is preferable that the heat sink is retained in close contact with the MPU and has a wide heat-conducting area through which the heat is diffused from the MPU to the heat sink. However, it is difficult to arrange the heat sink and the MPU without a minor gap left therebetween. Generally, a bottom surface of the heat sink is pressed to the MPU, and a thermal conductive member (e.g., a thermal tape or thermal-conductive silicone grease) is arranged between the MPU and the heat sink to fill in the gap.

It is known that the thermal conductive member should be as thin as possible for effectively dissipating the heat. It is also generally known that the bottom surface of the heat sink that is pressed to the MPU preferably has a substantially flat surface.

SUMMARY OF THE INVENTION

According to various preferred embodiments of the present invention, a heat dissipating device which dissipates heat generated by a heat generating object mounted on a base includes a heat sink body, a plurality of heat sink fins, a heat-conducting area, a tip portion, an inclined surface, and a fastener. The plurality of heat sink fins is integral with the heat sink body. The heat-conducting area is a portion of the heat dissipating device which is pressed to a substantially flat surface of the heat generating object. The tip portion is a substantially middle portion of the heat-conducting area and is arranged substantially closest to the heat generating object among other areas of the heat-conducting area. The inclined surface is a portion of the heat-conducting area and inclines outwardly from the tip portion such that a distance between the inclined surface and the heat generating object gradually increases. The fastener includes an attaching portion arranged to mount the heat dissipating device to the base, and the attaching portion is arranged substantially radially outside of an outer peripheral portion of the heat generating object.

According to another preferred embodiment of the present invention, the vertical distance between the tip portion and a distal end portion of the heat-conducting area in the radial direction is about 200 μm or less.

According to yet another preferred embodiment of the present invention, the distance between the attaching portion and the base is greater than a distance between the tip portion and the heat generating object in a state when the heat dissipating device is placed on the heat generating object.

With the configurations mentioned above, when the attaching portion is secured to the base, moments of force pressing the tip portion to the heat generating object are generated. At the same time, the tip portion acts as a fulcrum, and the base and the heat generating object is bent. As a result, the heat generating object and the contact surface are arranged closely, and therefore, thermal resistance therebetween is lowered.

According to yet another preferred embodiment of the present invention, the heat dissipating device further includes a cooling fan. With the cooling fan providing air flow to the heat sink fins, the heat generated by the heat generating object is actively dissipated.

According to yet another preferred embodiment of the present invention, the heat-conducting area of the heat dissipating device is shaped by a cutting process. By shaping the heat-conducting area by cutting process, it is possible to process the heat-conducting area precisely into a desirable shape.

Other features, elements, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring toFIGS. 1 to 15, a heat dissipating device according to a first preferred embodiment of the present invention will be described in detail. It should be understood that in the explanation of the preferred embodiments of the present invention, when positional relationships among and orientations of the different components are described as being up/down or left/right, ultimate positional relationships and orientations that are in the drawings are indicated and positional relationships among and orientations of the components once having been assembled into an actual device are not indicated.

First Preferred Embodiment

(1) Heat Dissipating Device Having Heat Sink Pressed Against MPU with Thermal Conductive Member Arranged Between Heat Sink and MPU

Referring toFIGS. 1 to 3, a first preferred embodiment of the present invention will be described in detail.FIG. 1is a side view illustrating a heat sink according to the first preferred embodiment of the present invention.FIG. 2is a perspective view illustrating the heat sink according to the first preferred embodiment of the present invention.FIG. 3is an exploded view illustrating the heat sink and a core to be press-fitted into a through hole arranged on the heat sink.

A heat sink1preferably includes a substantially cylindrical heat sink body11and a plurality of heat sink fins12protruding radially outwardly from the heat sink body11to widen a superficial area of the heat sink1. The heat sink1is preferably made of a material with high thermal conductivity (e.g., aluminum, copper, and copper alloy). In the first preferred embodiment of the present invention, the heat sink body11and the heat sink fins12are preferably made of aluminum, for example. The plurality of heat sink fins12are arranged on an outer circumferential surface of the heat sink body11, as shown inFIG. 2. The plurality of heat sink fins12may curve in a circumferential direction to further widen the superficial area. It should be noted, however, the shapes of the heat sink fins12are not limited to those described above, and a number of modifications may be made thereon.

As shown inFIG. 3, the heat sink body11includes a through hole111, penetrating axially through the heat sink body11along a center axis thereof. A core13made of a material with high thermal conductivity (e.g., aluminum, copper, copper alloy) is press-fitted to the through hole111such that residual pressure (i.e., contact pressure between the core13and the heat sink body11) becomes great. In this preferred embodiment of the present invention, the core13is preferably made of copper. With the great contact pressure between the core13and the heat sink body11, thermal resistance between the core13and heat sink body11is lowered. By virtue of this configuration, heat generated by a heat generating object (e.g., an MPU3) is diffused to the heat sink fins12, through the core13and the heat sink body11, and then the heat is dissipated into the air. Alternatively, a concave portion may be provided at the bottom of the heat sink body11, and the core13may be press-fitted to the concave portion. Alternatively, the core13may be integral with the heat sink body11.

As shown inFIG. 2, the core13includes a heat-conducting area131(a bottom surface of the core13in this preferred embodiment of the present invention) and a fastener14. As shown inFIG. 13B, the fastener14is secured to a base (e.g., a mother board31) such that the heat sink1is arranged on the MPU3, and the heat-conducting area131is pressed against the MPU3with a thermal conductive member4(e.g., a thermal tape or thermal conductive silicone grease) arranged therebetween such that the core13is thermally connected with the MPU3. In this preferred embodiment, a base to which the fastener14is secured is the mother board31. It should be noted, however, the base may be any other suitable member, such as an MPU socket or any other suitable device.

In this preferred embodiment of the present invention, the fastener14includes an attaching portion attached to the mother board31and a connecting portion at which the fastener14is connected to the core13of the heat sink1. It should be noted, however, the fastener14may be connected to any other preferred portion of the heat dissipating device. Alternatively, the fastener14may be provided as a member completely separated from the heat dissipating device.

The thermal conductive member4preferably is mainly defined by a material having a high thermal conductivity. In this preferred embodiment of the present invention, the thermal conductive member4is a tape-shaped member (e.g., the thermal tape). The tape-shaped member is defined by a supporting base (e.g., aluminum foil, polyimide film, or fiberglass mat) and a pressure-sensitive adhesive with a filler applied on the supporting base. The thermal conductive member4may be a thermal-conductive-silicone grease including silicone oil and a material having a high thermal conductivity (e.g., alumina powder). With the thermal conductive member4being in a grease state, the thermal conductive member4may closely contact with both the heat-conducting area131and a heat spreading portion, i.e., an upper surface of the MPU3, without gaps left therebetween. It should be noted, however, other forms of the thermal conductive member4may be used as long as it has a high thermal conductivity.

The heat generated by the MPU3is diffused to the heat sink1through the thermal conductive member4and the heat-conducting area131. In diffusing the heat from the MPU3to the heat sink1, the thermal contact resistance between the MPU3and the heat sink1(i.e., the thermal contact resistance between the thermal conductive member4, and each of the top surface of the MPU3and the heat-conducting area131of the heat sink1) is a critical factor for effectively dissipating the heat. By lowering the thermal contact resistance between the heat sink1and the MPU3, the heat is more effectively dissipated from the MPU3to the heat sink1. The thermal contact resistance is determined based on various factors, e.g., contact pressure, width of the heat-conducting area, surface roughness of the heat-conducting area, thermal conductivity of each member, thermal conductivity of the thermal conductive member4, thickness of the thermal conductive member4, and the hardness of each member surface. In this preferred embodiment of the present invention, the heat spreading portion and the core13are preferably made of a copper having a high thermal conductivity to lower the thermal contact resistance. In the present preferred embodiment of the present invention, the thermal contact resistance is further lowered by changing a form of the heat-conducting area131of the heat sink1. In the following description, the form of a contacting surface of the heat-conducting area131according to the present preferred embodiment will be described in detail.

FIG. 4illustrates a bottom portion of the core13and a vertical cross section thereof, which is along a line x-x′ and a line y-y′. The line x-x′ is a horizontal line passing a center of the heat-conducting area131, and the line y-y′ is a vertical line passing a center of the heat-conducting area131as shown inFIG. 4.FIGS. 5 to 11illustrate profile curves of various modified examples of the core13. The core13is preferably made of copper and includes the heat-conducting area131having a substantially circular shape as shown inFIG. 4.FIG. 5illustrates a profile curve of the core13along the line x-x′ and the line y-y′ shown inFIG. 4. The x-axis onFIG. 5indicates a horizontal scale of the cross section (e.g., the scale along the line x-x′ shown inFIG. 4), and the y-axis indicates a vertical scale of the cross section (e.g., the scale along the line y-y′ shown inFIG. 4, passing the center131a). The point labeled 0 mm on the x-axis represents the center131aof the heat-conducting area131. The vertical height of the peripheral portion of the heat-conducting area131is 0 μm.

As shown inFIG. 5, the heat-conducting area131according to the present preferred embodiment of the present invention protrudes vertically downwardly about 60 μm at the center131a(i.e., the heat-conducting area131includes a tip point132, protruding the lower most in the vertical direction, and an inclined surface133which inclines from the tip point132in a radial outer direction).

FIG. 12illustrates the core13pressed to the MPU3with the thermal conductive member4arranged therebetween. InFIG. 12, the vertical scale is magnified for illustrative purposes. The thermal conductive member4is in close contact with both the heat-conducting area131and the MPU3so that air or a gap does not remain therebetween. Since the heat-conducting area131has a cone shape, the vertical thickness of the thermal conductive member4becomes thinner below the tip point132when the heat sink1is pressed against the MPU3. Upon further pressing the heat sink1against the MPU3, the tip point132of the heat-conducting area131may come in contact with a center portion of the MPU3. It should be noted, however, the tip point132may not come into contact with the MPU3depending on the pressure pressing the heat-conducting area131against the MPU3.

The center portion of the MPU3generates the most heat among the portions of the MPU3. In this preferred embodiment of the present invention, the tip point132of the heat-conducting area131comes into contact with or is arranged closely to the center portion of the MPU3. Therefore, the thermal contact resistance between the MPU3and the heat-conducting area131is lowered, and the heat generated by the MPU3is effectively dissipated.

FIGS. 13A and 13Bare side views illustrating the MPU3and the heat sink1installed on the mother board31. The vertical scale ofFIG. 13Ais magnified for illustrative purposes.

During the installation of the heat sink1, the fastener14is secured to the mother board31such that a middle portion of the heat-conducting area131is pressed against the MPU3. Screws or the like are inserted into the attaching portions of the fastener14(e.g., mounting holes15, as shown inFIG. 2), and are secured to the mother board31. In the present preferred embodiment of the present invention, the connecting portion of the fastener14is arranged radially outside of an outer periphery of the MPU3. In addition, when the heat sink1is placed on the MPU3, the vertical height between the attaching portion and the mother board31is greater than that between the tip portion132and the MPU3. By securing the attaching portion to the mother board31, the tip point132is pressed downwardly against the MPU3and acts as a fulcrum. As a result, the first moment of force directed downward is generated at the middle portion of the heat-conducting area131and the second moment of force directed upward is generated at a portion of the fastener14is attached to the mother board31. InFIG. 13B, each of the moments of force is illustrated by an arrow. Therefore, the MPU3and the mother board31are bent as shown inFIG. 13A. In this preferred embodiment of the present invention, since the heat-conducting area131has a cone shape, the inclined surface133is closely arranged along the bent heat spreading portion of the MPU3. By virtue of this configuration, the thickness of the thermal conductive member4arranged between the heat sink1and the MPU3is reduced, and the thermal contact resistance therebetween is lowered as well.

On the other hand, when a conventional heat sink having a flat heat-conducting area131B, as shown inFIG. 19, is pressed against the MPU3, the gap between a core13B of the heat sink and the MPU3becomes a maximum below a center of the heat-conducting area131B. Therefore, the thickness of the heat conductive member4becomes thicker above the center portion of the MPU3, at which the most heat is generated among the other portions of the MPU3. As a result, the thermal resistance between the MPU3and the core13B increases and the efficiency of the heat dissipating device is degraded. In the present preferred embodiment of the present invention, since the heat-conducting area131of the heat sink body11has a protruding shape, it is possible to dissipate heat more effectively compared with the conventional heat sink.

FIG. 14is a graph describing the relationship of the thermal resistance and the vertical height. When the heat-conducting area131is flat as shown inFIG. 19(i.e., when the vertical height A is about 0 μm), the thermal resistance is about 0.300° C./W. When the heat-conducting area is concave (i.e., when the vertical height A ranged from about −30 μm to about −60 μm), the thermal resistance ranges from about 0.319° C./W to about 0.350° C./W. The result shows that the concave heat-conducting area less effectively dissipates heat compared with the flat heat-conducting area. With the concave heat-conducting area, the thermal conductive member4arranged above the center of the MPU becomes thicker, and therefore, the thermal contact resistance becomes higher.

With the convex heat-conducting area131(i.e., when the vertical height A ranges from about 30 μm to about 60 μm), the thermal resistance ranges from about 0.282° C./W to about 0.271° C./W. When the vertical height A ranges from about 100 μm to about 150 μm, the thermal resistance ranges from about 0.280° C./W to about 0.290° C./W. When the vertical height A ranges from about 200 μm, the thermal resistance is about 0.300° C./W, which is substantially equal to the thermal resistance when the heat-conducting area131is flat. Therefore, in this preferred embodiment of the present invention, the heat-conducting area131is formed such that the tip point132protrudes in the range from about 0 μm to 200 μm.

The shape of the heat-conducting area131is not limited to a cone shape as described inFIG. 5. It may be any other preferred shape such as those shown inFIGS. 6 to 11. As shown inFIGS. 6 and 7, the heat-conducting area131may have a curved slope133a,133band the tip point132at the middle portion131aof the heat-conducting area. As shown inFIG. 8, the heat-conducting area131may have the tip point132at the middle portion131a, the inclined surface133downwardly inclined in the radial outward direction, and a curved edge connecting the middle portion131aand the inclined surface133. Instead of a tip point132, a top surface132a, which is arranged to be substantially parallel with a top surface of the MPU3, may be formed on the heat-conducting area131as shown inFIGS. 9 to 11. As shown inFIG. 9, the heat-conducting area131may include a top surface132aand the inclined surface133inclined downwardly outwardly. As shown inFIG. 10, the heat-conducting area131may include a top surface132aand a substantially arc-shaped slope133ainclined downwardly outwardly. As shown inFIG. 11, the heat-conducting area131includes a curved edge connecting the top surface132aand the inclined surface133. The shape of the heat-conducting area131is not limited to the given examples; various alterations and modifications are possible as long as it has a substantially convex shape. With a CNC (Computer Numerical Control) lathe, various kinds of modified examples of the heat-conducting area are easily formed.

(2) Heat Dissipating Device Having Cooling Fan Mounted on Heat Sink To Actively Dissipate Heat

FIG. 15is a perspective view illustrating the heat dissipating device having the heat sink1described above and a cooling fan mounted on the heat sink1.

A cooling fan5includes an impeller52to generate air flow by rotation thereof, a motor to rotationally drive the impeller52, a supporting portion51supporting the motor, and at least three spokes512.

As shown inFIG. 15, the cooling fan5is arranged on the heat sink1in a manner that the center axis of the heat sink body11is concentric to a rotational axis of the impeller52. The cooling fan5provides axially downwardly directed air flow to the heat sink1. The heat generated by the MPU3is diffused to the heat sink1through the thermal conductive member4and the heat-conducting area131. With the air flow generated by the cooling fan5, the heat is actively dissipated in the air. The heat sink fins12may be inclined or bent along the same direction as a rotation direction of the impeller52. By virtue of this configuration, the air effectively flows between the plurality of heat sink fins12, and therefore, the heat is more actively dissipated in the air.

As described above, cooling characteristics of the heat dissipating device is further improved with the cooling fan5mounted on the heat sink1.

Second Preferred Embodiment

(1) Heat Dissipating Device Having Heat Sink Pressed Against MPU with Thermal Conductive Member Arranged Between Heat Sink and MPU

Referring toFIGS. 16 to 17, a heat sink1A according to a second preferred embodiment of the present invention will be described.FIG. 16is a plan view illustrating the heat sink1A according to the second preferred embodiment of the present invention.FIG. 17is a perspective view illustrating the heat sink1A according to the second preferred embodiment of the present invention. The members having substantially the same functions as the counterparts of the first preferred embodiment are identified by the same reference numerals inFIGS. 16 and 17.

As shown inFIG. 16, a heat sink1A includes a heat sink body11A and a plurality of heat sink fins12A protruding axially from the heat sink body11A to widen a superficial area of heat sink1A. The heat sink1A is preferably made of material with a high thermal conductivity (e.g., aluminum, copper, and copper alloy). In this preferred embodiment of the present invention, the heat sink body11A and the heat sink fins12A are preferably made of aluminum. The heat sink fins12A protrude axially from the heat sink body11A in an equally spaced manner. In addition, the heat sink fins12A may be arranged on sides of the heat sink body11A to further increase the superficial area of the heat sink1A.

The heat sink body11A includes a concave portion, and the core13made of material with a high thermal conductivity (e.g., aluminum, copper, and copper alloy) is press-fitted to the concave portion. In this preferred embodiment of the present invention, the core13is preferably made of copper. The core13is press-fitted to the concave portion such that residual pressure (i.e., contact pressure between the core13and the heat sink body11A) becomes great to lower contact thermal resistance therebetween. By virtue of this configuration, the heat generated by the MPU3is diffused to the heat sink fins12A through the core13and the heat sink body11A, and then the heat is dissipated into the air. Alternatively, the core13may be integral with the heat sink body11A.

The core13includes the heat-conducting area131. The heat-conducting area131protrudes axially at the middle portion thereof as described in the first preferred embodiment of the present invention. The heat-conducting area131is pressed against the MPU3with a thermal conductive member4(e.g., a thermal tape or thermal conductive silicone grease) arranged therebetween such that the core13is thermally connected with the MPU3. When the heat sink1A is pressed against the MPU3, the vertical thickness of the thermal conductive member4becomes thinner or the heat-conducting area131comes into contact with the MPU3at the middle portion. As a result, the thermal contact resistance between the heat sink1A and the MPU3is lowered, and the heat generated by the MPU3is effectively diffused to the heat sink1A.

(2) Heat Dissipating Device Having Cooling Fan Mounted on Heat Sink To Actively Dissipate Heat

Referring toFIG. 18, a heat dissipating device according to the second preferred embodiment of the present invention will be described in detail.FIG. 18is a perspective view illustrating the heat dissipating device having the heat sink1A and the cooling fan arranged thereon.

A cooling fan5A includes an impeller52A to generate air flow by rotation thereof, a motor to rotationally drive the impeller52A, a housing511A surrounding the impeller52A and defining a passage of air flow, a supporting portion51A supporting the motor, and at least three spokes512A connecting the supporting portion51A and the housing511A. An outer shape of the housing511A has a substantially rectangular shape, and a mounting hole to mount the cooling fan5A on the heat sink1A is arranged at each of the four corners of the substantially rectangular housing511A.

As shown inFIG. 18, the cooling fan5A and the heat sink1A are positioned and secured to casing6such that the cooling fan5A provides air flow along the heat sink fins12A to actively dissipate the heat. The casing6includes on one side surface an intake through which the cooling fan5A intakes air, and includes on another side surface an outlet through which the air flowing along the heat sink fins12A is discharged. The casing6further includes an attaching portion62to secure the heat dissipating device to the mother board31. The casing6is secured on the mother board31such that the heat-conducting area131of the heat sink1A is pressed to the MPU3with the thermal conductive member4arranged therebetween. With the cooling fan5A mounted on the heat sink1A, cooling characteristics of the heat dissipating device are further improved.