Title:
ELECTRONIC APPARATUS
Kind Code:
A1


Abstract:
In one embodiment, an electronic apparatus is provided. The electronic apparatus is equipped with an electronic device and a cooling device for cooling the electronic device. A heat pipe is provided with a wick and an operating liquid. The electronic device is disposed inside the heat pipe, and a heat spreader for thermally connecting the electronic device and the wick is provided inside the heat pipe. The electronic device further has a connector for connecting the electronic device to an outside of the heat pipe.



Inventors:
Shimizu, Masayuki (Kawasaki, JP)
Application Number:
12/174210
Publication Date:
01/22/2009
Filing Date:
07/16/2008
Assignee:
FUJITSU LIMITED (Kawasaki-shi, JP)
Primary Class:
International Classes:
F28D15/00
View Patent Images:
Related US Applications:



Primary Examiner:
THOMPSON, GREGORY D
Attorney, Agent or Firm:
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP (TYSONS, VA, US)
Claims:
What is claimed is:

1. An electronic apparatus equipped with an electronic device and a cooling device for cooling the electronic device, comprising: a heat pipe provided with a wick and an operating liquid, the electronic device being disposed inside the heat pipe; a heat spreader thermally connected with the electronic device and the wick provided within the heat pipe; and a connector connecting the electronic device to an outside of the heat pipe.

2. The electronic apparatus according to claim 1, wherein the heat spreader is provided on both sides of the electronic device.

3. The electronic apparatus according to claim 1, wherein the heat spreader has a buffer plate, and uneven parts or fins.

4. The electronic apparatus according to claim 1, wherein the connector has optical connection means.

5. The electronic apparatus according to claim 1, wherein the connector has electric connection means.

6. The electronic apparatus according to claim 1, wherein the heat pipe has an opening for mounting the electronic device, the electronic device is disposed on a blocking member airtightly blocking the opening, and the electronic device is disposed inside the heat pipe by the blocking member being disposed in the opening.

7. The electronic apparatus according to claim 6, wherein the connection means is provided on the blocking member.

8. A heat pipe provided with a wick and an operating liquid inside a closed vessel and a pipe part, wherein an electronic device and a heat spreader are provided inside the closed vessel.

9. The heat pipe according to claim 8, wherein the heat spreader is constructed of a buffer plate and uneven parts or fins.

10. The heat pipe according to claim 8, wherein the heat spreader is provided on both sides of the electronic device.

11. The heat pipe according to claim 8, further comprising connection means for connecting the electronic device to an outside of the closed vessel.

12. An electronic apparatus comprising: a circuit board; an electronic device mounted on the circuit board; a heat pipe provided with a wick and an operating liquid therein; and a heat spreader placed between the electronic apparatus and the wick, mounted on one side of the electronic apparatus, and arranged so as to be in contact with the wick.

13. The electronic apparatus according to claim 12, wherein the heat pipe has an opening formed therein, the opening is configured to be blocked by the circuit board, and the electronic device and the heat spreader are provided inside the opening.

14. The electronic apparatus according to claim 12, wherein the circuit board is joined to a mounting board in the electronic apparatus.

15. The electronic apparatus according to claim 12, wherein a surface of the heat spreader in contact with the wick is formed on an uneven surface.

Description:

BACKGROUND

The present invention relates to an electronic apparatus, and in particular, relates to an electronic apparatus using a heat pipe as a cooling device.

In recent years, increasingly higher functionality and faster speed of electronic devices such as semiconductor devices have been pursued. However, if the clock frequency is increased to speed up semiconductor devices, power consumption of the semiconductor devices increases, leading to an increase in calorific value.

Electronic equipment in which semiconductor devices are mounted, on the other hand, is becoming increasingly more compact and thinner. This makes it more difficult to provide a radiation area of heat produced by semiconductor devices inside the electronic equipment, and thus, the heat more likely remains inside the electronic equipment. If such heat is left alone, the temperature of the semiconductor devices rises, disabling normal operation. Thus for example, as disclosed in a publicly known technique, a cooling device for cooling a semiconductor device using a heat pipe is proposed, for example see Japanese Laid-Open Patent Application No. 2002-261216.

SUMMARY

The object described above is achieved by an electronic apparatus equipped with an electronic device and a cooling device for cooling the electronic device, wherein a heat pipe provided with a wick and an operating liquid is used as the cooling device, the electronic device is disposed inside the heat pipe, a heat spreader for thermally connecting the electronic device and the wick is provided inside the heat pipe, and connection means for connecting the electronic device to an outside of the heat pipe is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for illustrating a cooling structure of a semiconductor device using a heat pipe;

FIG. 2 is an enlarged view of a pyramid buffer thermally connecting a semiconductor chip and the heat pipe;

FIG. 3 is a longitudinal sectional view showing the configuration of an electronic apparatus in a first embodiment;

FIG. 4 is a bottom view showing the configuration of the electronic apparatus in the first embodiment;

FIG. 5 is an enlarged view of a buffer plate and fins applied to the electronic apparatus in the first embodiment;

FIG. 6 is a view showing a modification of the fins shown in FIG. 5;

FIG. 7 is a bottom view of a configuration of an electronic apparatus in a second embodiment; and

FIG. 8 is an enlarged view of a buffer plate and fins applied to the electronic apparatus in the second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Next, preferred embodiments of an electronic apparatus will be described together with the drawings.

FIGS. 3 and 4 show an electronic apparatus 20A in a first embodiment. FIG. 3 is a longitudinal sectional view of the electronic apparatus 20A and FIG. 4 is a bottom view of the electronic apparatus 20A. FIG. 3 is a sectional view taken along an A-A line in FIG. 4.

In the present embodiment, a semiconductor chip 21 is used as an electronic device and a heat pipe 22 is used as a cooling device. The semiconductor chip 21 is a high-density, fast device and therefore produces heat while operating. The semiconductor chip 21 is mounted on a closure plate 23A in a bear chip state without being packaged by, for example, a sealing resin.

The closure plate 23A is a ceramic substrate in a multilayer structure. The semiconductor chip 21 is mounted on a top surface (an upper surface in FIG. 3) of the closure plate 23A, and solder balls 24 serving as external connection terminals are disposed on an undersurface of the closure plate 23A. An internal wire 34 is laminated inside the closure plate 23A, and the semiconductor chip 21 and the solder balls 24 are electrically connected by the internal wire 34. FIG. 3 shows a state in which the solder balls 24 are joined to a mounting substrate 25.

In addition, a heat spreader 50A is provided on a rear side (an upper surface in FIG. 3) of the semiconductor chip 21. The heat spreader 50A is formed of copper with thermal conductivity and, as shown in FIG. 5 as an enlarged view, the heat spreader 50A has a buffer plate 26 and fins 27A. The buffer plate 26 is thermally connected to the semiconductor chip 21 and the fins 27A comes into contact with a wick 31 of the heat pipe 22.

The heat spreader 50A may be in various shapes and, in the present embodiment, the buffer plate 26 has a rectangular parallelepiped shape with a plurality of uneven parts (fins) 27A made of triangle poles formed on the buffer plate 26.

The buffer plate 26 has a base area about twice the area of the semiconductor chip 21 in the present embodiment, but a buffer plate is not limited to the size of twice the area of the semiconductor chip 21. Further, instead of the uneven parts 27A in the shape of triangle poles, fins may also be used and, if fins are used, costs can be reduced in return for a slight increase in thermal resistance. For convenience of description, a detailed structure of the heat spreader 50A will be described later.

The heat pipe 22 has a closed vessel 28 and a plurality of pipe parts 30. Both the closed vessel 28 and the pipe parts 30 are formed of copper with high thermal conductivity. The closed vessel 28 has a cabinet-like shape. Each pipe part 30 is disposed, as shown in FIG. 4. An opening 35 is formed at the bottom of the closed vessel 28 and the semiconductor chip 21 mounted on the closure plate 23A is inserted into the closed vessel 28 through the opening 35.

The pipe part 30 is communicatively connected with the closed vessel 28, and the plurality of pipe parts 30 project outward from the closed vessel 28. By using the plurality of pipe parts 30 in this manner, the amount of heat transport can be increased. The wick 31 is disposed inside each pipe part 30. In the present embodiment, a felt material made of, for example, polyester fitted to the shape of the heat spreader 50A is used as the wick 31.

However, the wick 31 is not limited to the felt material and, a mesh material or a metallic thin line such as a copper thin line may also be used. Further, instead of the felt material, a fine groove may be formed in the pipe part 30, which can be used as a wick. It is desirable than the interval between the uneven parts 27A or fins forming the heat spreader 50A be sufficiently larger than the groove utilizing surface tension of an operating liquid. It is also possible to form a groove on the surface of the uneven parts 27A or fins, thereby flowing back the operating liquid fitly.

Chlorofluorocarbon HFC152a (CH3-CHF2) is used in the present embodiment as the operating liquid of the heat pipe 22. However, the operating liquid is not limited to chlorofluorocarbon and, water, methanol, naphthalene and the like may also be used.

The semiconductor chip 21 is mounted on the heat pipe 22 according to the procedure shown below. First, the heat spreader 50A is fixed to the top surface of the semiconductor chip 21 mounted on the closure plate 23A. The heat spreader 50A is fixed to the semiconductor chip 21 by using, for example, an adhesive with high thermal conductivity.

Subsequently, the semiconductor chip 21 with the heat spreader 50A fixed thereto is inserted into the closed vessel of the heat pipe 22 through the opening 35. At this point, the closed vessel 28 and the pipe parts 30 are filled with the operating liquid in advance.

The area of the closure plate 23A is set to be larger than that of the opening 35. Thus, the closure plate 23A comes into contact with an outer circumferential edge of the opening 35 of the closed vessel 28 by the semiconductor chip 21 being inserted into the closed vessel 28. The opening 35 is airtightly blocked with the closure plate 23A by the position of contact between the closure plate 23A and the closed vessel 28 being hermetically sealed by an adhesive or the like and thus, the closed vessel 28 is hermetically sealed from the outside.

In a hermetically sealed state, the semiconductor chip 21 is in a state of being disposed inside the closed vessel 28 (the heat pipe 22) (a sealed state). Thus, the heat pipe 22 functions also as a package to protect the semiconductor chip 21.

While the semiconductor chip 21 is disposed inside the heat pipe 22, the semiconductor chip 21 is connected to the solder balls 24 via the internal wire 34 formed in the closure plate 23A. That is, the closure plate 23A functions as a connection unit for connecting the semiconductor chip 21 (electronic device) to the outside of the closed vessel 28 (the heat pipe 22). Thus, even if the semiconductor chip 21 is disposed inside the closed vessel 28, the semiconductor chip 21 can reliably be connected electrically to an external device (the mounting substrate 25 in the present embodiment).

The position of contact between the closure plate 23A and the closed vessel 28 is configured so that the surface of ceramic having insulating properties comes into contact with the closed vessel 28. Thus, even if the closure plate 23A has a multilayer wiring substrate structure having the internal wire 34, the semiconductor chip 21 and the heat pipe 22 will not short-circuit.

Further, since the heat spreader 50A is fixed to the semiconductor chip 21 in the present embodiment, the buffer plate 26 and the fins 27A of the heat spreader 50A are engaged in the wick 31 when the semiconductor chip 21 is mounted inside the closed vessel 28. The contact area between the heat spreader 50A and the wick 31 can thereby be made wider, reducing thermal resistance between the semiconductor chip 21 and the wick 31.

Next, operations of the electronic apparatus 20A in the above configuration will be described.

When the semiconductor chip 21 operates and heat is produced, heat from the semiconductor chip 21 reaches the wick 31 via the heat spreader 50A (the buffer plate 26 and the uneven parts 27A). The wick 31 is in a state of being penetrated by the operating liquid through capillarity and, as described above, the heat spreader 50A is engaged in the wick 31. Thus, the operating liquid is evaporated by the heat of the semiconductor chip 21 to receive the heat of the semiconductor chip 21 as latent heat.

The evaporated operating liquid moves to a cooling unit 32 due to a difference of vapor pressure. The evaporated operating liquid is liquefied by the cooling unit 32, giving off heat to the cooling unit 32 as latent heat. The liquefied operating liquid is transported to near the semiconductor chip 21 and the heat spreader 50A by surface tension with the wick 31 and the closed vessel 28. Since the operating liquid is transported regardless of gravity as described above, the semiconductor chip 21 can be arranged at any position of the heat pipe 22. In the present embodiment, the semiconductor chip 21 is arranged in the middle position of the heat pipe 22 in consideration of cooling efficiency. Arrows in broken lines in FIG. 3 indicate the flow of the gaseous operating liquid and those in solid lines indicate the flow of the liquefied operating liquid moving inside the wick 31.

Here, the electronic apparatus 20A according to the present embodiment and a cooling device shown in FIGS. 1 and 2 will be compared. The cooling device described with reference to FIGS. 1 and 2 has a pyramid buffer 6, which is a pyramid-shaped buffer plate. In the comparison described below, a configuration in which the pyramid buffer 6 is assembled in the electronic apparatus 20A is assumed in place of the heat spreader 50A used in the present embodiment to make the comparison simpler. This configuration and a cooling device of FIGS. 1 and 2 will be compared.

In the example shown in FIG. 1, a semiconductor chip 1 is cooled by a heat pipe 2. The semiconductor chip 1 is disposed inside a package 3 and connected to solder balls 4 via a wire provided inside the package 3. The package 3 is mounted on a mounting substrate 5, thereby connecting the semiconductor chip 1 electrically to the mounting substrate 5.

The heat pipe 2 has a wick 9, and an operating liquid provided inside a closed vessel 8. The semiconductor chip 1 is thermally connected to the middle position of the heat pipe 2 and thus, both side parts of the heat pipe 2 become cooling units 10 for re-liquefying the operating liquid evaporated by heat generated by the semiconductor chip 1. In the example in FIG. 1, the semiconductor chip 1 and the heat pipe 2 are thermally connected by the pyramid buffer 6 made of copper. As shown in FIG. 2 as an enlarged view, the pyramid buffer 6 has a first surface 6a, and a second surface 6b whose area is larger than that of the first surface 6a. The first surface 6a is thermally connected to the semiconductor chip 1 and the second surface 6b is thermally connected to the heat pipe 2. With this configuration, heat generated by the semiconductor chip 1 is conducted to a wider area of the heat pipe 2 via the pyramid buffer 6.

In the cooling device shown in FIGS. 1 and 2, only the second surface 6b of the pyramid buffer 6 comes into contact with the heat pipe 22, so that the area of the second surface 6b becomes an area to be thermally connected to the heat pipe 2 (the wick 9). In contrast, according to the present embodiment, the whole surface of the pyramid buffer 6 is engaged in the wick 31 and thus, sides 6c of the pyramid buffer 6 are also in contact with the wick 31. Therefore, the area of contact of the pyramid buffer 6 with the wick 31 becomes larger compared with that of the example in FIG. 1, which allows more efficient cooling. Particularly the heat spreader 50A of the present embodiment, which is equivalent to the pyramid buffer 6 in the above example, has a configuration in which the plurality of uneven parts 27A in the shape of triangle poles is provided. Accordingly, the surface area can further be increased, allowing still more efficient cooling.

The semiconductor chip 21 is directly disposed inside the closed vessel 28 in the present embodiment and therefore, thermal connection between the semiconductor chip 21 and the wick 31 can be realized fitly via the heat spreader 50A even if the size or weight of the heat spreader 50A is reduced. In addition, as described above, the area of contact between the heat spreader 50A (the buffer plate 26 and the uneven parts 27A) and the wick 31 can be made larger. If a groove is used as the wick 31, the area in which the groove is cut can be increased, thereby allowing efficient cooling.

Further, in the example in FIG. 1, the semiconductor chip 1 is sealed inside the package 3 in order to protect the semiconductor chip 1. Since the package 3 is formed of resin, thermal resistance from the semiconductor chip 1 to the heat pipe 2 increases. In contrast, in the present embodiment, as described above, the semiconductor chip 21 is disposed inside the closed vessel 28. Thus, thermal resistance by the package present in the example in FIG. 1 can be eliminated and the semiconductor chip 21 can also thereby be cooled efficiently.

Next, a detailed structure of the heat spreader 50A will be described.

The heat spreader 50A attempts to improve cooling capacities by increasing the effective area of contact with the wick 31. The heat spreader 50A disperses heat by causing the semiconductor chip 21 to thermally bind to the buffer plate 26 having a thickness of several millimeters.

By dispersing heat as described above, the area where the uneven parts 27A in the shape of triangle poles are set up can be increased compared with that of the top surface of the semiconductor chip 21. The effective area of contact with the wick 31 increases as the interval at which the uneven parts 27A in the shape of triangle poles are set up becomes narrower. However, due to necessity to bring the wick 31 into contact with the surface of the uneven parts 27A of triangle poles and to cut a groove, it is desirable to set up the uneven parts 27A of triangle poles at intervals of about several millimeters.

The total of surface areas of the heat spreader 50A increases as the height of the uneven parts 27A in a triangular shape in cross section becomes higher. However, due to saturation caused by saturation of thermal resistance of copper, the effective surface area will gradually not increase even if the height of the uneven parts 27A is increased. In terms of the cost/performance ratio, it is suitable to determine the height of the triangle in cross section of the uneven parts 27A so that effective efficiency of the uneven parts 27A becomes about 0.7, that is, near a value satisfying the formula (1).


2IIh/bλ=1 (1)

wherein I denotes the height of the sectional triangle: h denotes the thermal conductivity to the operating liquid; b denotes the interval of setting up triangle poles; and λ denotes the thermal conductivity of copper.

FIG. 6 shows a heat spreader 50B, which is a modification of the heat spreader 50A shown in FIG. 5. The heat spreader 50B is a modification obtained by reducing the weight of the cooling device shown in FIGS. 1 and 3.

The heat spreader 50B according to the present modification and the pyramid buffer 6 shown in FIG. 2 will be compared. Assume, for example, that the area where uneven parts 27B in the shape of triangle poles of the heat spreader 50B are set up is 16 mm×16 mm, which is equal to the area of the semiconductor chip 21.

Since the area where the uneven parts 27B are set up is not larger than the area of the semiconductor chip 21 under this assumption, the buffer plate 26 may be thin. More specifically, the buffer plate 26 has a thickness of about 1 mm. If the uneven part 27B has a shape of a triangle pole with the height of about 13 mm, it is suitable to set up the uneven parts 27B at intervals of 4 mm in four rows.

If the above configuration is adopted, the total of effective surface areas of the uneven parts 27B in the shape of triangle poles will be about 1200 mm2. If thermal conductivity to the operating liquid is 5000 W/m2K, thermal resistance to the operating liquid will be about 0.17 K/W. The weight of the buffer plate in the present modification is approximately 22 g including pyramid portions 33 of 4 mm.

If, on the other hand, thermal resistance to the operating liquid should be made equal to that using the pyramid buffer 6 in FIG. 2, an area of 16 mm×16 mm to 38 mm×38 mm will be needed for the pyramid buffer 6 with the height of about 10 mm. The weight of the pyramid buffer 6 in this case will be about 67 g, which is significantly heavier than the weight (approximately 22 g) of the heat spreader 50A according to the present modification. Therefore, the weight of the electronic apparatus 20A can be reduced by using the heat spreader 50B in the present modification.

FIGS. 7 and 8 are views for illustrating an electronic apparatus 20B of a second embodiment. The same reference numerals are attached to components in FIGS. 7 and 8 as those of corresponding components in FIGS. 3 to 6, and a description thereof is omitted.

As shown in FIG. 3, the above-described electronic apparatus 20A according to the first embodiment shows a configuration in which the heat spreader 50A comes into contact with only one side (the top surface in FIG. 3) of the semiconductor chip 21. In contrast, the electronic apparatus 20B according to the present embodiment is characterized in that a heat spreader 50C is provided on both sides of the semiconductor chip 21. By adopting this configuration, heat can be transported not only from the front side of the semiconductor chip 21, but also from the rear side thereof and further, the effective area of contact with the wick 31 can be increased.

The heat spreader 50C is provided on both sides of the semiconductor chip 21 in the present embodiment, as shown in FIG. 8. With this configuration, the arrangement position of the semiconductor chip 21 inside the closed vessel 28 becomes higher than that in the first embodiment. More specifically, the semiconductor chip 21 is arranged in substantially the middle position of the closed vessel 28.

Thus, the present embodiment provides, in addition to a closure plate 23B, an intermediate substrate 37 as connection means for connecting the semiconductor chip 21 to the outside of the closed vessel 28. The closure plate 23B is provided with an electric connection terminal 38 and an optical connection terminal 41, as well as the solder balls 24 for external connection disposed thereon.

The intermediate substrate 37 is provided with electric connection terminals 39 and optical connection terminals 42, as well as the semiconductor chip 21 mounted thereon. Further, electric connection pins 40 are disposed between the electric connection terminals 38 and the electric connection terminals 39, and optical fibers 43 are disposed between the optical connection terminals 41 and the optical connection terminals 42.

Thus, the closure plate 23B and the intermediate substrate 37 are electrically connected by the electric connection terminals 38 and 39 and the electric connection pin 40, and the closure plate 23B and the intermediate substrate 37 are also optically connected by the optical connection terminals 41 and 42 and the optical fiber 43. Further, a material of high rigidity is selected for the electric connection pin 40 and the intermediate substrate 37 is thereby supported above the closure plate 23B.

Therefore, if the closure plate 23B is disposed in the closed vessel 28 so that the opening 35 is blocked, the semiconductor chip 21 is located in the middle position of the closed vessel 28 by being supported by the electric connection pin 40 and the like. The heat spreader 50C has fins 27C (in a rectangular shape in cross section) formed thereon, instead of the uneven parts 27A and 27B in the triangular shape in cross section, and is constructed so that the electric connection pin 40 and the optical fiber 43 can pass between a predetermined pair of the fins 27C.

According to the above-described electronic apparatus 20B in the present embodiment, the effective area of contact with the wick 31 can be increased by the heat spreader 50C being provided on both sides of the semiconductor chip 21, so that cooling efficiency of the semiconductor chip 21 can still be enhanced. Further, the distance between other coupling parts and a radiator can be made longer by the optical connection means (the optical connection terminals 41 and 42 and the optical fiber 43) being provided and therefore, the radiator can be designed more flexibly.

Electronic apparatuses according to an example of embodiments have been described above, but the present invention is not limited to the above specific embodiments and may be variously modified or altered.