Heat-radiating structure of electronic apparatus

In a heat-radiating structure HRS1 in which heat generated in a heat-generating component built in a housing of an electronic apparatus is conducted to the outside, the central portion of a flexible graphite sheet that is folded and shaped so as to be elastic is thermally connected to the heat-generating component, and a flexible conductive member is applied to a portion in which the central portion is thermally connected to the heat-generating component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat-radiating mechanism of a portable electronic apparatus, for example, a notebook-type personal computer. More specifically, the present invention relates to a heat-radiating structure.

2. Description of the Background Art

Referring toFIG. 7, a heat-radiating mechanism of a conventional portable electronic apparatus will be described by taking a notebook-type personal computer as an example. In notebook-type personal computers, a heat-radiating plate53made of copper or aluminum having a thickness from about 0.5 mm to 2.0 mm is tightly attached to a CPU2, which is a heat-generating component mounted in a print wiring board51to release and radiate heat generated in the CPU2to the outside via a heat-radiating plate53. When sufficient heat radiation is not expected with such a structure, a portion of the heat-radiating plate53is brought in contact with an aluminum keyboard supporting plate6on the back of the keyboard so that the heat in the CPU2is also radiated to the keyboard supporting plate6.

However, metal such as copper and aluminum used for the heat-radiating plate53or the keyboard supporting plate6is highly rigid, and is hardly deformed by an external stress, thus its shape including its height is fixed. Furthermore, the CPU2, the heat-radiating plate53, and the keyboard supporting plate6are not completely smooth, because of, for example, fabrication tolerance or a change in shape over time or due to heat.

Therefore, when the height from the CPU2to the keyboard supporting plate6is structurally fixed, a space (clearance) is inevitably generated between the CPU2and the heat-radiating plate53and between the heat-radiating plate53and the keyboard supporting plate6, so that they cannot be attached tightly to each other. This space functions as a contact thermal resistance between the CPU2and the heat-radiating plate53and between the heat-radiating plate53and the keyboard supporting plate6, and prevents heat from moving, that is, being radiated, from the CPU2to the heat-radiating plate53and the keyboard supporting plate6.

A space (clearance) between the CPU2and the heat-radiating plate53is referred to as “thermal conduction resistance space IS”. The distance in which the heat-radiating plate53is spaced apart from the CPU2is referred to as “resistance distance Dis”, and the area in which the thermal conduction resistance space IS is present in the direction parallel to the CPU2and the heat-radiating plate53is referred to as “resistance area Ais” (not shown). The size of the thermal conduction resistance space IS is referred to as “thermal resistance space size Vis”.

In order to reduce this contact thermal resistance, Japanese Laid-Open Patent Publication No. 2001-142574 discloses a method of providing a flexible thermal conductive member such as a heat-radiating grease56(not shown) or elastic heat-radiating elastomer57between the CPU2and the heat-radiating plate53and between the heat-radiating plate53and the keyboard supporting plate6to eliminate the thermal conduction resistance space IS. In this method, it is attempted to improve the heat transfer properties by replacing the air in the thermal conduction resistance space IS generated between the CPU2and the heat-radiating plate53and between the heat-radiating plate53and the keyboard supporting plate6with a flexible thermal conductive member or material having a larger thermal conductivity than that of air. In other words, the flexible conductive member in an amount corresponding to the thermal resistance space size Vis is filled in the thermal conduction resistance space IS.

In practice, each of the CPU2, the heat-radiating plate53and the keyboard supporting plate6each exhibit a dimensional tolerance of 0.5 mm or more. Therefore, when the CPU2, the heat-radiating plate53and the keyboard supporting plate6are brought in contact, they are spaced apart at a gap of 0.5 mm or more, and the thermal conduction resistance space IS is generated there. In other words, in order to eliminate the thermal conduction resistance space IS with a resistance distance Dis of 0.5 mm, it is necessary to fill with heat-radiating grease56or the heat-radiating elastomer57to a thickness of 0.5 mm or more. It is also necessary to determine the amount of the heat-radiating grease56or the heat-radiating elastomer57to be filled, in view of variation in the thermal resistance space size Vis of the thermal conduction resistance space IS due to thermal expansion or thermal contraction of the components caused in the process of absorbing and radiating heat from the CPU2.

However, the thermal conductivity of the heat-radiating grease56or the heat-radiating elastomer57is larger than the thermal conductivity of air, but smaller than the thermal conductivity of copper or aluminum. Therefore, the heat transfer properties are poorer than when the CPU2, the heat-radiating plate53and the keyboard supporting plate6are in direct contact. From this point of view, it is necessary to reduce the amount of the flexible thermal conductive member to be filled, that is, to reduce thermal conduction resistance space IS as much as possible. However, a slightly excessive amount of flexible thermal conductive member is provided to accommodate a change in the thermal resistance space size Vis of the thermal conduction resistance space IS.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a heat-radiating mechanism and a heat-radiating structure that accommodates a variation in size due to component tolerance when conducting and radiating heat from a heat-generating component in an electronic apparatus to the outside and to provide improved heat-radiating performance.

The present invention has the following features to attain the object mentioned above.

The present invention is directed to a heat-radiating structure in which heat generated in a heat-generating component built in a housing of an electronic apparatus is conducted to the outside, including a flexible first graphite sheet shaped so as to be elastic by including both end portions positioned substantially on the same plane, both rising portions that cross those two end portions at a predetermined angle, and a central portion positioned on a plane substantially in parallel to the two end portions; and a flexible thermal conductive member. In the first graphite sheet, the central portion is thermally connected to the heat-generating component, and at least one of the two end portions is thermally connected to at least one of the housing and a heat-radiating component that is fixed to the housing. The flexible conductive member is applied to a portion in which the first graphite sheet is thermally connected to the heat-generating component.

In the heat-radiating mechanism of an electronic apparatus of the present invention, a graphite sheet is pressed elastically against a heat-generating component such as CPU and a heat-radiating component such as a keyboard supporting plate on the back of a keyboard. The arrangement utilizes the flexibility of the graphite sheet, so that a clearance generated therebetween can be minimized. As a result, the contact thermal resistance between the heat-generating component and the graphite sheet and between the graphite sheet and the keyboard supporting plate is reduced, and thus the heat-radiating performance of the electronic apparatus can be improved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A heat-radiating mechanism and a heat-radiating structure of an electronic apparatus of the first embodiment of the present invention will be described with reference toFIG. 1.FIG. 1shows a state viewed from the side of a heat-radiating mechanism provided inside a notebook-type personal computer as an example of an electronic apparatus. It should be noted that members that are irrelevant to the heat-radiating mechanism such as a housing and a power source, are not shown.

In the notebook-type personal computer of this example, a heat-radiating grease3is applied to a CPU2, which is a heat-generating component mounted in a print wiring board1. Thereafter, a flexible graphite sheet4having a high thermal conductivity in the plane direction is thermally connected thereto in a such a manner that the lower surface of its central portion4cthat is obtained by folding the sheet with steps is attached in a non-fixed manner, and the upper surface of both end portions4eof the graphite sheet4is tightly attached and thermally connected to a keyboard supporting plate6made of aluminum on the back side of a keyboard (not shown). The rising portions4sconnecting the two end portions4eto the central portion4callow the graphite sheet4to be shaped into an elastic structure. In other words, the heat-radiating plate53and the heat-radiating elastomer57in the conventional heat-radiating mechanism shown inFIG. 7are replaced by the graphite sheet4.

In other words, in this embodiment, the graphite sheet4is used as heat-radiating means for conducting heat in the CPU2to the keyboard, instead of the heat-radiating plate53. Therefore, a space (clearance) between the graphite sheet4and the CPU2is referred to as “thermal conduction resistance space IS1”. The distance at which the graphite sheet4is spaced apart from the CPU2is referred to as “resistance distance Dis1”, and the area in which the thermal conduction resistance space IS1is present in the direction parallel to the graphite sheet4and the CPU2is referred to as “resistance area Ais1”. The size of the thermal conduction resistance space IS1is referred to as “thermal resistance space size Vis1”.

The graphite sheet4is folded and thus is shaped so as to include two end portions4e, two rising portions4sand one central lower surface4c, as shown inFIG. 1. More specifically, the two end portions4eare positioned substantially in the same plane, the central portion4cis positioned in a plane substantially parallel to the end portions4e, and the two rising portions4sare formed so as to cross the end portions4eand the central portion4cat predetermined angles. Consequently, the graphite sheet4can support elastically the central portion4cwith the rising portions4s.

The upper surfaces of the two end portions4eof the graphite sheet4are tightly fixed to the keyboard supporting plate6reliably with mechanical joining means such as screws (not shown). Since the heat-radiating plate53made of a metal in the conventional heat-radiating mechanism is highly rigid, a large clearance (thermal conduction resistance space IS) between the heat-radiating plate and the CPU2due to manufacturing tolerance of the components, a temporary deformation or thermal expansion is generated. On the other hand, the graphite sheet4of the present invention is bonded by the adsorptive power of the heat-radiating grease3applied to the CPU2and due to the spring effect induced by its flexibility and the folding, is pressed elastically to the CPU2so that the clearance generated between the CPU2and the graphite sheet4is accommodated.

In other words, the graphite sheet4is deformed more easily than the heat-radiating plate53and accommodates a variation in the size of the components due to fabrication tolerance, temporary deformation or temperature change. As a result, the resistance distance Dis1of the thermal conduction resistance space IS1generated between the CPU2and the graphite sheet4is much smaller than the resistance distance Dis of the thermal conduction resistance space IS in the conventional heat-radiating mechanism, which is 0.5 mm. The minimum resistance distance Dis1is reduced to that caused by the surface roughness of the graphite sheet4and the CPU2. Consequently, the resistance area Ais1and the thermal resistance space size Vis1of the thermal conduction resistance space IS1are also much smaller than the resistance area Ais and the thermal resistance space size Vis of the thermal conduction resistance space IS in the conventional heat-radiating mechanism.

Thus, in the present invention, the thermal conduction resistance space IS1that is generated between the graphite sheet4and the CPU2acts as a contact thermal resistance. By bending the graphite sheet4so as to accommodate the fabrication tolerance of the components, the thermal conduction resistance space is reduced to the surface roughness of the graphite sheet4and the CPU2. Furthermore, the graphite sheet4can accommodate a change in the size of the components due to temporary deformation and thermal change with its flexibility.

However, the amount of the heat-radiating grease3applied in the thermal conduction resistance space IS1generated between the graphite sheet4and the CPU2is small, corresponding to the thermal resistance space size Vis1. More specifically, the heat-radiating grease3is applied to a thickness of up to 0.3 mm and a thickness of at least the resistance distance Dis1, which is a thickness to which the grease can be applied in practice.

Thus, the contact thermal resistance between the CPU2and the graphite sheet4is provided in an area smaller than the area in which the graphite sheet4and the keyboard supporting plate6are provided. Therefore, the heat in the CPU2can be absorbed and moved effectively. The graphite sheet4and the keyboard supporting plate6are tightly attached mechanically to each other in a reliable manner, so that the heat in the CPU2is conducted to the keyboard supporting plate6efficiently via the graphite sheet4. In this manner, in the heat-radiating mechanism of the present invention, the contact thermal resistance between the heat-generating portion, the heat-absorbing portion and the heat-radiating portion is reduced more than in the conventional heat-radiating mechanism and thus the overall heat-radiating performance can be improved.

As described above, in the present invention, the flexible graphite sheet having a high thermal conductivity in the plane direction is folded with steps and utilized as a heat-radiating plate. Thus, even in the case where a clearance may be formed between the heat-generating component and the heat-radiating plate, or between the heat-radiating plate and the keyboard supporting plate because of the tolerance of the components, the flexibility of the graphite sheet is utilized so that the graphite sheet is deformed and thus a clearance can be prevented from being formed between the heat-generating component and the graphite sheet, or between the graphite sheet and the keyboard supporting plate without generating residual stress. Furthermore, the graphite sheet has good heat transfer properties, so that the heat-radiating performance of an entire electronic apparatus can be improved.

In order to improve the workability for forming the heat-radiating mechanism, a thin heat-radiating elastomer having a strong adsorptive power may be used, instead of the heat-radiating grease3, or they can used in combination. It is preferable that the graphite sheet4used as a means for absorbing and moving the heat in the CPU2has a thermal conductivity in the plane direction of 100 (W/mK) or more and a thickness of 0.5 to 2.0 mm and is also flexible. However, the graphite sheet4can be selected as appropriate, depending on the shape and the size of the components constituting the heat-radiating mechanism used, the fabrication tolerance, the amount of heat generated in the CPU2, the necessary amount of heat to be radiated, and the like.

In this embodiment, the graphite sheet4and the heat-radiating grease3constitute the minimum unit constituting a heat-radiating structure HRS1that realizes the function of capturing (absorbing) heat generated in the CPU2. Furthermore, the keyboard supporting plate6is provided as one component of the heat-radiating structure HRS1so that the heat captured from the CPU2is released to the outside of the personal computer.

In this example, as shown inFIG. 1, the graphite sheet4is folded such that the rising portions4sof the graphite sheet4cross the central lower surface4cand the two end portions4eat predetermined angles to assume approximately a shape of a trapezoid. As a result, the graphite sheet4provides a spring effect and thus serves to press the central lower surface4cagainst the CPU2. Therefore, the graphite sheet4may have, for example, a rectangular shape or a curved shape, as long as the shape allows the central lower surface4cof the graphite sheet4to be pressed against the CPU2stably with a desired spring effect.

The heat-radiating mechanism of an electronic apparatus of a second embodiment of the present invention will be described with reference toFIG. 2. Similarly to inFIG. 1,FIG. 2shows a state viewed from the side of the heat-radiating mechanism configured inside a notebook-type personal computer as an example of an electronic apparatus. A heat-radiating structure HRS2of this embodiment is configured by adding an elastic member8to the heat-radiating structure HRS1shown inFIG. 1. In this embodiment, a space (clearance) between the graphite sheet4and the CPU2is referred to as “thermal conduction resistance space IS2”. The distance in which the graphite sheet4is spaced apart from the CPU2is referred to as “resistance distance Dis2”, and the area in which the thermal conduction resistance space IS2is present in the direction parallel to the graphite sheet4and the CPU2is referred to as “resistance area Ais2”. The size of the thermal conduction resistance space IS2is referred to as “thermal resistance space size Vis2”.

The elastic member8is provided in a space formed between the graphite sheet4and the keyboard supporting plate6. The elastic member8is formed of an elastic material such as urethane foam or melamine foam, and its length L8can be expressed by an equation (1) below, taking the thickness of the graphite sheet4as Tg, and the distance from the lower surface of the keyboard supporting plate6to the upper surface of the CPU2as L,
L8=L−Tg−Dis2+ΔLEquation (1)

where ΔL is the compression length of the elastic member8and is a predetermined length necessary to apply a predetermined pressure to the CPU2. More specifically, ΔL is determined as appropriate, based on the bending amount of the graphite sheet4, the elastic modulus of the elastic member8, the area in which the elastic member8is in contact with the CPU2and the graphite sheet4, and the required pressing force of the graphite sheet4against the CPU2.

The elastic member8is compressed between the graphite sheet4and the keyboard that are tightly fixed to each other reliably with screws or the like, and this reaction force presses the lower surface of the central portion of the folded graphite sheet4against the CPU2. As a result, the graphite sheet4is attached more tightly to the CPU2with the pressing force of the elastic member8, in addition to the spring effect by the folding structure of the graphite sheet4itself, than in the heat-radiating structure HRS1.

It is understood from the above equation (1) that if the compression length ΔL is increased, the resistance distance Dis2can be reduced. In other words, the CPU2and the graphite sheet4are attached to each other more tightly than in the case of the heat-radiating structure HRS1, so that the resistance distance Dis2, the resistance area Ais2and the thermal resistance space size Vis2can be smaller than the resistance distance Dis1, the resistance area Ais1and the thermal resistance space size Vis1, respectively. In other words, the thermal conduction resistance space IS2is also smaller than the thermal conduction resistance space IS1, so that the amount of the heat-radiating grease3to be applied can be reduced.

Thus, the amount of the flexible thermal conductive member applied between the CPU2and the graphite sheet4can be reduced, so that the contact thermal resistance between the graphite sheet4and the keyboard supporting plate6can be reduced, and thus the heat-radiating performance of the heat-radiating structure HRS2can be increased more than in the heat-radiating structure HRS1.

Referring toFIG. 3, a first variant example of the heat-radiating structure HRS2of the second embodiment will be described. In the heat-radiating structure HRS2A of this variant example, the elastic member8in the heat-radiating structure HRS2is replaced by a plate spring8A, and the graphite sheet4is replaced by a graphite sheet4A. The graphite sheet4A is obtained by coating the surface of the graphite sheet4with a thin film resin such as a polyester foil in order to protect the graphite sheet4from damages caused by a contact with the plate spring8A. In this variant example, the plate spring8A is provided in the keyboard supporting plate6, but when this causes a problem in the strength, the plate spring8A can be provided in another portion of the personal computer, for example, the housing.

The above-described elastic member8and the plate spring8A can have any shape, instead of the shapes shown inFIG. 2andFIG. 3, respectively, as long as they can press the central lower surface4cof the graphite sheet4against the CPU2stably with a desired compressing force.

Referring toFIG. 4, a second variant example of the heat-radiating structure HRS2of the second embodiment will be described. In the heat-radiating structure HRS2B of this variant example, the graphite sheet4in the heat-radiating structure HRS2is replaced by a graphite sheet4B. The graphite sheet4B is not shaped into an elastic structure by being bended, unlike the graphite sheet4and the graphite sheet4A, and one graphite sheet is used with the original state kept. That is to say, the graphite sheet4B does not have portions directly corresponding to each of the two end portions4e, the rising portions4sand the central portion4cin the graphite sheet4and the graphite sheet4A. However, for convenience for description, positionally approximately corresponding portions are denoted by both end portions4eB, rising portions4sB and a central portion4cB, respectively.

In the heat-radiating structure HRS2B, both the end portions4eB are fixed mechanically to the keyboard supporting plate6in such a manner that the central portion4cB of the graphite sheet4B can be suspended and can be in contact with the CPU2in at least a predetermined area. The position at which both the end portions4eB are fixed to the keyboard supporting plate6may be about the same as the position at which both the end portions4eare fixed to the keyboard supporting plate6. However, the graphite sheet4B does not have an elastic structure, so that the thermal conduction resistance space IS2generated between the graphite sheet4B and the CPU2cannot be eliminated, and also it is difficult for the lower surface of the central portion4cB to be in surface contact with the surface of the CPU2.

Therefore, the elastic member8provided between the keyboard supporting plate6and the graphite sheet4B presses the lower surface of the central portion4cB to the CPU2for tight attachment. The graphite sheet4B that is fixed to the keyboard supporting plate6while being bended is also a kind of elastic structure. However, the graphite sheet4B cannot be expected to have adherence with the CPU2by the pressing force stemming from the elastic structure by folding as in the graphite sheet4and the graphite sheet4A. Therefore, in order to ensure that the lower surface of the central portion4cB is tightly attached to the entire surface of the CPU2, it is preferable that the cross-sectional area of the elastic member8used in the heat-radiating structure HRS2B is larger than the surface area of the CPU2. Instead of the elastic member8, the above-described plate spring8A may be used. Furthermore, in the case where the plate spring8A is used, it is preferable that the graphite sheet4B is configured such that the surface of the graphite sheet4B is covered with a thin film resin such as a polyester foil in order to protect it from damages due to a contact with the plate spring8A, as in the case of the graphite sheet4A.

As described above, in the heat-radiating structure HRS2B, it is not necessary to bend the graphite sheet4B, so that this structure is better in terms of the workability than in the case of the graphite sheet4, the graphite sheet4A or the like. Furthermore, in the graphite sheet4, the graphite sheet4A or the like, it is necessary to bend and shape the graphite sheet into a predetermined shape in accordance with the shape or the size of a portion to which it is to be attached. In addition, the graphite sheet4or the graphite sheet4A that has been bended and shaped in advance significantly limits the portion to which it can be attached and therefore cannot be used for radiation in the other portions. On the other hand, the graphite sheet4B can be used without being bended and therefore is more economical since the degree of limitation regarding the location in which it is to be attached is smaller.

The heat-radiating mechanism of an electronic apparatus of a third embodiment of the present invention will be described with reference toFIG. 5. Similarly toFIG. 1,FIG. 5shows a cross section of the heat-radiating mechanism configured inside a notebook-type personal computer as an example of an electronic apparatus. A heat-radiating structure HRS3of this embodiment is obtained by replacing the graphite sheet4in the heat-radiating structure HRS1shown inFIG. 1by a graphite multilayered sheet14. In this embodiment, a space (clearance) between the graphite multilayered sheet14and the CPU2is referred to as “thermal conduction resistance space IS3” (not shown). The distance in which the graphite multilayered sheet14is spaced apart from the CPU2is referred to as “resistance distance Dis3” (not shown), and the area in which the thermal conduction resistance space IS3is present in the direction parallel to the graphite multilayered sheet14and the CPU2is referred to as “resistance area Ais3”. The size of the thermal conduction resistance space IS3is referred to as “thermal resistance space size Vis3”.

The graphite multilayered sheet14is formed by sandwiching a flexible graphite sheet14ahaving a thermal conductivity in the plane direction of 100 (W/mK) or more and a thickness of 0.5 to 2.0 mm by thin metal foils14bsuch as aluminum foils or copper foils having a thickness of 0.01 mm to 0.2 mm. Similarly to the heat-radiating structure HRS1, the upper surfaces of both ends of the graphite multilayered sheet14are tightly fixed to the keyboard supporting plate6with mechanical means such as screws.

In this embodiment, the graphite multilayered sheet14is constituted by the flexible graphite sheet14and the thin metal foils14aand14b, so that the graphite multilayered sheet14is bonded by the adsorptive power of the heat-radiating grease3applied to the CPU2, and therefore no clearance is generated between the CPU2and the graphite multilayered sheet14.

Thus, the thermal resistance between the CPU2and the graphite multilayered sheet14and between the graphite multilayered sheet14and the keyboard supporting plate6can be reduced. In addition, the metal foils14bon the surface of the graphite multilayered sheet14have a volume specific heat higher than and a thermal conductivity equal to or higher than the graphite sheet14ain the middle portion of the graphite multilayered sheet14. Therefore, the overall heat-radiating performance when radiating the heat in a heat-generating component in a notebook-type personal computer can be increased by a greater amount than when the heat-radiating plate is constituted only by a graphite sheet.

The heat-radiating mechanism of an electronic apparatus of a fourth embodiment of the present invention will be described with reference toFIG. 6. Similarly to inFIG. 1,FIG. 6shows a cross section of the heat-radiating mechanism configured inside a notebook-type personal computer as an example of an electronic apparatus. A heat-radiating structure HRS4of this embodiment is configured by additionally providing a graphite sheet17having a thickness of 0.1 mm to 1.0 mm between the graphite sheet4and the keyboard supporting plate6in the heat-radiating structure HRS1shown inFIG. 1.

The graphite sheet17is attached to the keyboard supporting plate6. The upper surfaces of both ends of the graphite sheet4are tightly fixed and thermally connected to the keyboard supporting plate6with mechanical means such as screws via the graphite sheet17.

In this embodiment, a space (clearance) between the graphite sheet4and the CPU2is referred to as “thermal conduction resistance space IS4” (not shown). The distance in which the graphite sheet4is spaced apart from the CPU2is referred to as “resistance distance Dis4” (not shown), and the area in which the thermal conduction resistance space IS4is present in the direction parallel to the graphite sheet4and the CPU2is referred to as “resistance area Ais4”. The size of the thermal conduction resistance space IS4is referred to as “thermal resistance space size Vis4”.

The contact thermal resistance between the graphite sheet17and the graphite sheet4is smaller than the contact thermal resistance between the graphite sheet4and the keyboard supporting plate6. Therefore, the heat-radiating performance in the plane direction can be improved more than in the case of the heat-radiating structure HRS1, and the temperature of the surface of the keyboard can be reduced by utilizing the high thermal conductivity in the plane direction and the low thermal conductivity in the cross sectional direction of the graphite sheet17to release the heat from the graphite sheet4to the graphite sheet17attached to the keyboard supporting plate6.

While the embodiments have been individually described as above, the configuration can be obtained by any combination thereof. As described above, the present invention can be utilized to radiate heat out of a portable electronic apparatus such as a notebook-type personal computer.