JP2010216676A - Cooling substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cooling substrate having a flow passage capable of reducing a pressure loss in the flow passage by relatively increasing the cross sectional area of the flow passage at a heat transport side, and suppressing the generation of dryout in a heat absorbing part by relatively reducing the cross sectional area of the flow passage at a return side, easily making a refrigerant in the flow passage flow in one direction and having an improved heat transport capacity. <P>SOLUTION: In the cooling substrate, at least the one heat absorbing part 30 and one heat release part 40 are provided in the substrate 10, and the heat absorbing part and heat release part communicate with each other to form a loop shape by the refrigerant flow passage 50. The refrigerant is circulated in the refrigerant flow passage and heat transport is performed by the evaporation-condensation latent heat of the refrigerant. The refrigerant flow passage comprises a heat transport side flow passage 60 for sending the vaporized refrigerant from the heat absorbing part to the heat release part and a return side flow passage 70 for sending the liquefied refrigerant from the heat release part to the heat absorbing part. The cross sectional area of the return side flow passage is set smaller than that of the heat transport side flow passage. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a cooling substrate that cools an element to be cooled such as a heating element by flowing a coolant through a flow path provided inside the substrate.

In recent electronic devices, the amount of heat generated by the CPU, other elements, etc. has increased, and the heat generation density tends to increase due to the miniaturization of the semiconductor process. Therefore, a high-performance heat sink with excellent heat dissipation efficiency is required. . Further, in order to meet the demands for downsizing and cost reduction of devices, not only high performance heat sinks but also small and low cost heat sinks are required.

As a conventionally known heat sink, there is a heat sink in which a heating element is thermally connected to one surface of a metal heat receiving plate and a radiation fin is formed on the other surface. An electric fan such as a centrifugal fan is attached to the side or top surface of the radiating fin, and the heat transmitted from the heating element is dissipated into the atmosphere by forcibly sending cooling air between the radiating fins by the rotation of the electric fan. It was.

There is also a heat sink using a heat pipe for improving the performance of the heat sink. One end of the heat pipe is thermally connected to the heat receiving plate, a heat radiating fin is attached to the other end, heat is moved away from the heat receiving plate, and heat is dissipated into the atmosphere by an electric fan. It is a method. Thereby, the heat density of a heat radiating part can be reduced and the heat dissipation efficiency of a heat sink improves.
However, even with the above-described method, it has become difficult to effectively dissipate heat generated by a heating element having a particularly high heat generation density in recent years.

In order to cope with the increase in the heat generation amount and the heat generation density, a method of dissipating heat by providing a flow path inside the substrate and circulating the refrigerant is proposed. Patent Document 1 discloses a technique in which a flow path is provided inside a base body of a cooling device with which a CPU or the like contacts, and a refrigerant is allowed to flow through the flow path to dissipate heat. Patent Document 2 discloses a technique for dissipating heat by providing a micro flow path in an insulating layer of a mounting substrate and flowing a coolant in the flow path.

Patent Literature 3 and Patent Literature 4 disclose a technique for connecting a heat absorbing portion and a heat radiating portion with a flow path.

JP 2004-134742 A JP-A-2005-33162 JP 2005-229033 A JP 2005-300038 A

However, in order to improve the heat dissipation performance, if a method of circulating the refrigerant between the heat absorbing portion and the heat radiating portion while evaporating and condensing and transporting heat by latent heat is actually performed, there are the following problems.

In the refrigerant transport channel from the heat absorbing part to the heat radiating part, when the refrigerant evaporates in the heat absorbing part to form a two-phase flow, the pressure loss increases and the refrigerant may not flow easily. In the refrigerant transport flow path from the heat radiating section to the heat absorbing section, the refrigerant containing the vapor that could not be condensed in the heat radiating section may be supplied again to the heat absorbing section, so that a so-called local dryout may occur easily.

Furthermore, if the cooling substrate is made smaller and thinner in response to downsizing of the device, the above problem becomes more prominent, and cooling using latent heat due to evaporation / condensation of the refrigerant becomes difficult.

The configuration of the cooling substrate of the present invention for solving the above-described problems is as follows. The invention according to claim 1 includes at least one heat absorbing portion and at least one heat radiating portion in the substrate, wherein the heat absorbing portion and the heat radiating portion communicate with each other in a loop shape by a refrigerant flow path, and the refrigerant flow path In the cooling substrate in which the refrigerant circulates and heat transports by latent heat of evaporation and condensation of the refrigerant, the refrigerant flow path includes a heat transport side flow path for sending the vaporized refrigerant from the heat absorption part toward the heat dissipation part. A reflux side flow path for sending the liquefied refrigerant from the heat radiating section toward the heat absorption section, wherein the cross sectional area of the reflux side flow path is smaller than the cross sectional area of the heat transport side flow path. It is a cooling substrate.

In the heat transport side flow path from the heat absorbing section to the heat radiating section, by increasing the cross-sectional area of the refrigerant flow path, the refrigerant does not partially evaporate in the heat transport side flow path and the two-phase flow of the gas phase liquid phase Even in this case, the pressure loss in the flow path can be reduced. In addition, since the steam flows preferentially to the lower pressure loss, the refrigerant flow tends to be unidirectional. Thereby, the steam generated in the heat absorbing part can be efficiently moved to the heat radiating part, so that the heat transport capability is improved.

Furthermore, the pressure loss is relatively increased by reducing the cross-sectional area of the refrigerant flow path on the reflux side from the heat radiating portion to the heat absorbing portion. For this reason, it becomes difficult for the vapor | steam which was not able to condense in a thermal radiation part to flow into a reflux side flow path with a liquid phase. Thereby, it is possible to prevent the steam that has not been condensed from being supplied to the heat absorption part, and to reduce the occurrence of dryout in the heat absorption part.

Further, even if there is a large heat input in the heat absorption part, the vapor does not flow backward to the reflux side flow path and the liquid phase refrigerant is not scattered, and the refrigerant flow tends to be unidirectional. Thereby, since the liquid phase condensed in the heat radiating part can be efficiently moved to the heat absorbing part, the heat transport capability is improved.

In the invention according to claim 2, in the cooling substrate, a ratio of a cross-sectional area of the reflux side flow path to a cross-sectional area of the heat transport side flow path is in a range of 0.0002 to 0.77. The cooling substrate according to claim 1, wherein:

The effects of this configuration are as follows. When the ratio of the cross-sectional area of the reflux side channel to the cross-sectional area of the heat transport side channel is in the range of 0.0002 to 0.77, the vapor of the refrigerant generated in the heat absorption part is more effectively returned to the reflux side flow. While flowing preferentially in the heat transport flow path without flowing back to the path, the liquid phase of the refrigerant condensed in the heat radiating section is sufficiently transported in the reflux flow path.

If the ratio of the cross-sectional area of the reflux side channel to the cross-sectional area of the heat transport side channel is 0.0002 or less, the cross-sectional area of the reflux side channel becomes too small, and the liquid phase of the condensed refrigerant is refluxed. Resistance increases. In addition, when the ratio of the cross-sectional area of the reflux side channel and the cross-sectional area of the heat transport side channel exceeds 0.77, the refrigerant vapor generated in the heat absorption part may flow backward to the reflux side channel.

According to a third aspect of the present invention, in the cooling substrate, the return-side flow path is provided with a check structure that prevents the liquefied refrigerant from flowing backward from the heat absorbing portion toward the heat radiating portion. The cooling substrate according to claim 1, wherein the cooling substrate is characterized by that.

The effects of this configuration are as follows. By providing a check device such as a check valve, it is possible to completely prevent the refrigerant from flowing back through the flow path. As a result, the flow of the refrigerant is completely unidirectional, and even when the endothermic amount is particularly high, it is possible to prevent the vapor flow from overcoming the pressure loss and backflowing in the return side flow path. Even the heat transport capacity is more stable.

According to a fourth aspect of the present invention, in the cooling substrate, the return-side flow path is provided with a capillary structure that generates a capillary force. It is a cooling substrate as described in above.

The effects of this configuration are as follows. By providing the capillary structure in the reflux side flow path, the flow of the condensed liquid phase refrigerant is promoted, and the liquid phase can be efficiently moved to the heat absorption part, so that the heat transport capability is further improved. As the capillary structure, a porous body or a laminate of meshes is preferable. The capillary structure exhibits excellent capillary force against the liquid phase of the refrigerant, and is easy and inexpensive to manufacture.

In the cooling substrate according to the fifth aspect of the present invention, in the cooling substrate, the liquefied refrigerant is forcibly sent from the heat radiating portion toward the heat absorbing portion using power in the reflux side flow path. The cooling substrate according to any one of claims 1 to 4, further comprising a refrigerant transport mechanism.

The effects of this configuration are as follows. By providing the refrigerant transport mechanism in the reflux side channel, the liquid phase refrigerant can be forcibly transported and the circulation amount of the refrigerant can be increased, so that the heat transport capability is further improved. As the refrigerant transport mechanism, a piezoelectric pump is preferable, and it is small and consumes little power, and can be embedded in the substrate. In addition, by embedding the piezoelectric pump in the flow path on the return side, the cooling circuit board can be made smaller and reliable without taking out the flow path from the substrate and installing a separate pump or forming a seam in the flow path. Will also improve.

  According to the present invention, in the cooling substrate provided with the flow path, the pressure loss in the flow path is reduced by relatively increasing the cross-sectional area of the flow path on the heat transport side, and Since the cross-sectional area can be made relatively small, it is possible to suppress the occurrence of dry-out in the heat absorption part, so that the flow of the refrigerant in the flow path is likely to be unidirectional and a cooling substrate with improved heat transport capability is obtained. be able to.

It is a perspective view which shows the cooling substrate which is the 1st Embodiment of this invention. It is a three-plane figure which shows the cooling substrate which is the 1st Embodiment of this invention. It is AA sectional drawing in FIG. It is BB sectional drawing in FIG. It is CC sectional drawing in FIG. It is DD sectional drawing in FIG. It is EE sectional drawing in FIG. It is a top view of the 1st copper plate in which the pattern used for the cooling substrate which is the 1st Embodiment of this invention was formed. It is a top view of the 2nd copper plate in which the pattern used for the cooling substrate which is the 1st Embodiment of this invention was formed. It is a side view which shows an example of the state which mounted the cooling substrate which is the 1st Embodiment of this invention. It is a side view which shows another example of the state which mounted the cooling substrate which is the 1st Embodiment of this invention. It is the graph which measured the thermal resistance of the cooling substrate which is the 1st Embodiment of this invention. It is a fragmentary sectional view which shows the return side flow path of the cooling substrate which is the 2nd Embodiment of this invention. It is the elements on larger scale which show the return side flow path of the cooling substrate which is the 3rd Embodiment of this invention. It is a fragmentary sectional view which shows the return side flow path of the cooling substrate which is the 4th Embodiment of this invention. It is a graph which shows the relationship between the heat input and thermal resistance in the cooling substrate which is embodiment of this invention. It is a graph which shows the relationship between the heat input in the cooling substrate which is embodiment of this invention, and a cooling water flow rate. It is a perspective view which shows the cooling substrate which is the 5th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 are schematic views of a cooling substrate 10 according to the first embodiment of the present invention. 1 is a perspective view, FIG. 2 is a three-side view, FIG. 2 (a) is a plan view, FIG. 2 (b) is a front view, and FIG. 2 (c) is a side view.
The cooling substrate 10 is a copper plate and has an outer shape of 100 mm × 200 mm × 1 mm. Although it is a substantially flat plate in appearance, a space 20 shown by a broken line is provided inside. FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2, that is, the cooling substrate 10 cut in the thickness direction.

The space 20 is a thin cavity sealed in the substrate, and includes a heat absorbing part 30, a heat radiating part 40, and a coolant channel 50. The refrigerant flow path 50 is a heat transport side flow path 60 that sends the vaporized refrigerant from the heat absorption part 30 toward the heat dissipation part 40, and a reflux that sends the liquefied refrigerant from the heat dissipation part 40 toward the heat absorption part 30. And a side flow path 70. The heat absorption part 30, the heat transport side flow path 60, the heat radiation part 40, and the reflux side flow path 70 are arranged in a loop in the order described above, and a refrigerant (not shown) made of pure water is enclosed therein, and FIG. It can be circulated in a loop shape in the direction indicated by the thick arrow. The refrigerant is sealed in such an amount that the liquid phase occupies a part of the space 20 at room temperature. The remainder of the space 20 is occupied by the refrigerant gas phase. Further, non-condensable gas such as air is degassed in the operating temperature range.

The direction indicated by the thick arrow in FIG. 3 is the moving direction of the refrigerant, and this is defined as the flow direction in each part. Moreover, the direction substantially orthogonal to the flow path direction in the plane formed by the cooling substrate 10 is defined as the width direction at each portion.

As shown in FIG. 3, when comparing the heat absorbing portion 30 and the heat radiating portion 40, the heat radiating portion 40 is longer than the heat absorbing portion 30 in both the flow direction and the width direction, and the cross-sectional area is wide. Further, when the heat transport side flow path 60 and the reflux side flow path 70 are compared, the reflux side flow path 70 is longer in the flow path direction and narrower in the width direction than the heat transport side flow path 60. In FIG. 3, fine channels 32 and 42 described later are omitted.

FIG. 4 shows a partially enlarged view of the cross section taken along the line B-B in FIG. The heat-absorbing part 30 is composed of a fine channel 32 composed of a plurality of grooves 31, 31... Arranged in parallel along the channel direction in FIG. 3, and the upper half communicates in the width direction in FIG. A composite flow path 34 composed of the communication flow path 33 is formed. In other words, the lower half of the heat absorbing portion 30 is partitioned by a plurality of walls 35, 35.

FIG. 5 shows a partially enlarged view of the CC cross section in FIG. 2, that is, the cross section in the width direction of the heat radiating portion 40. Similarly to the heat absorbing part 30, the heat radiating part 40 is also composed of a fine flow path 42 composed of a plurality of grooves 41, 41... In the lower half in FIG. A composite flow path 44 is formed which includes a communication flow path 43 half of which communicates in the width direction. In other words, the lower half of the heat radiating portion 40 is partitioned by a plurality of walls 45, 45.

4 and 5 are partially enlarged views, and therefore, the heat absorbing portion 30 and the heat radiating portion 40 are not widened in the width direction, but the heat radiating portion 40 is wider than the heat absorbing portion 30. The heat absorption part 30 and the heat radiation part 40 have substantially the same height.

FIG. 6 shows a partially enlarged view of the DD cross section in FIG. 2, that is, the cross section in the width direction of the heat transport side channel 60. The heat transport channel 60 is a simple flat space. Moreover, the EE cross section in FIG. 2, ie, the partial expanded view of the cross section in the width direction of the reflux side flow path 70, is shown in FIG. The reflux side channel 70 is also a simple flat space like the heat transport side channel 60, but is narrower than the heat transport side channel 60. The heat transport side flow path 60 and the reflux side flow path 70 have substantially the same height, and these have substantially the same height as the heat absorption part 30 and the heat dissipation part 40. In this figure, for example, the width of the reflux side channel 70 is 2 mm, the width of the heat transport side channel 60 is 10 mm, and the channel ratio is 0.2.

Here, the ratio of the channel widths in the heat transport side channel 60 and the reflux side channel 70 will be described. The maximum value of the channel width ratio (cross-sectional area ratio) can be expressed as follows as a condition for the vapor to block in the coolant channel 50.

At this time, a ₁ is the width of the heat transport side channel 60, _ac is the width of the reflux side channel 70, P 1 is the saturated vapor pressure in the heat radiating unit 40, P 2 is the saturated vapor pressure in the heat absorbing unit 30, and κ is water vapor Specific heat ratio. Here, temperature 40 ° C. of the heat radiating portion 40, the temperature 70 ° C. The heat absorbing portion 30, and when each saturated vapor pressure, 6.2KPa, since the 27.2KPa, the ratio of the width of the channel _{(a c} The maximum value of / a ₁ ) is 0.77.

Further, the minimum value of the ratio of the widths of the flow paths is the refrigerant gas-phase to liquid-phase volume ratio if the mass flow rate does not change in the refrigerant flow path 50. Since the density of the gas phase and liquid phase of the refrigerant at the endothermic part 30 (temperature 70 ° C.) is 0.11 g / l and 985 g / l, the minimum value of the ratio of the width of the flow path is 0.0002. It will be about.
From the above, it is preferable that the ratio of the channel widths in the heat transport channel 60 and the reflux channel 70 is in the range of 0.0002 to 0.77.

Next, the manufacturing method of the cooling substrate 10 which becomes embodiment of this invention is demonstrated.
Two copper plates having an outer diameter of 100 mm × 200 mm and a thickness of 0.5 mm were prepared. One is a first copper plate 11 (first plate material), and the other is a second copper plate 12 (second plate material). The first copper plate 11 is a plate material arranged on the lower side in FIG. 1, and the second copper plate 12 is a plate material arranged on the upper side in FIG.

A first recess 21 having a pattern as shown in FIG. 8 was formed on the first copper plate 11 by etching. The depth of the first recess 21 is 0.15 mm. The first recess 21 corresponds to the lower part of each of the heat absorbing unit 30, the heat radiating unit 40, the refrigerant channel 50, the heat transport side channel 60, and the reflux side channel 70.

In addition, a plurality of walls 35 and 45 are provided in portions corresponding to the heat absorbing portion 30 and the heat radiating portion 40 of the first recess 21, respectively. The height of the top portions of the walls 35 and 45 is the same as that of the flat portion 11a. In FIG. 8, the walls 35 and 45 are appropriately omitted.

On the second copper plate 12, a second recess 22 having a pattern as shown in FIG. 9 was formed by etching. The depth of the second recess 22 is 0.15 mm. The second recess 22 corresponds to the upper part of each of the heat absorbing unit 30, the heat radiating unit 40, the refrigerant channel 50, the heat transport side channel 60, and the reflux side channel 70. The second copper plate 12 is provided with a through hole 12 b in a portion corresponding to the reflux side flow path 70.

The first recess 21 and the second recess 22 are formed so as to coincide with the same shape and position on a plane when the first copper plate 11 and the second copper plate 12 are stacked face to face. ing.

Silver brazing material was plated on the flat portions 11a and 12a of the first copper plate 11 and the second copper plate 12, which are the peripheral portions of the recesses 21 and 22, respectively.
Next, the 1st copper plate 11 and the 2nd copper plate 12 were piled up so that each plane part 11a and 12a might face each other, and the 1st recessed part 21 and the 2nd recessed part 22 might overlap. Next, this was heated and pressed in a vacuum to melt the silver brazing material, thereby integrating the first copper plate 11 and the second copper plate 12 to obtain the cooling substrate 10. As a result, the first recess 21 and the second recess 22 are combined to form a space 20 inside the cooling substrate 10.

Through the above steps, the composite flow paths 34 and 44 of the heat absorbing portion 30 and the heat radiating portion 40 as shown in FIGS. 4 and 5 can be formed. By changing the ratio of the depths of the concave portions 21 and 22, it is possible to manufacture the composite flow passages 34 and 44 in which the height ratio P of the grooves 31 and 41 is changed. The total height of the composite flow paths 34 and 44 is determined by the sum of the depths of the first recess 21 and the second recess 22.

In the cooling substrate 10 of the present invention, when the check valve 71, the capillary structure 72, and the piezoelectric pump 75 are provided in the middle of the reflux side flow path 70, the following is performed. At least one of the first copper plate 11 and the second copper plate 12 is provided with a member installation hole (not shown) in a part of the reflux side flow path 70. Then, when brazing is completed, the reflux-side flow path 70 is exposed to the outside through the member installation hole. A member can be installed by embedding the check valve 71, the capillary structure 72, and the piezoelectric pump 75 and closing them with an adhesive or the like.

Next, the inside of the space 20 is evacuated through the through-hole 12b, and pure water in an amount occupying 30% of the volume in the space is injected, and the through-hole 12b is closed in the deaerated state, 20 was sealed. Through the steps as described above, the cooling substrate 10 of the present invention can be manufactured.

Below, the effect | action of cooling in the 1st Embodiment of this invention is demonstrated. As shown in FIG. 10, an element to be cooled 90 such as a CPU is disposed on the outer surface 36 of the heat absorbing portion 30 of the cooling substrate 10 and brought into thermal contact therewith. The element 90 to be cooled is not limited to a CPU, and may be any element that generates heat by Joule heat and requires cooling, such as a laser diode or a power transistor.
The element 90 to be cooled is surface-mounted by solder 230 on a circuit 220 formed on a normal insulating substrate 210.

As shown in FIG. 10, the element to be cooled 90 is disposed on the outer surface 36 of the heat absorbing unit 30 by bringing the package 91 of the element into close contact with the outer surface 36 of the heat absorbing unit 30 through thermal conductive grease 240 or the like. Alternatively, as shown in FIG. 11, the circuit 220 may be formed on the cooling substrate 10 via the insulating film 250, and the element to be cooled 90 may be surface-mounted on the circuit 220. In this case, the element 90 to be cooled is in thermal contact with the cooling substrate 10 through the electrode 92, but thermal conduction grease 240 or the like may be injected between the package 91 and the insulating film 250 to make thermal contact. .

The heat generated in the element to be cooled 90 is transmitted to the heat absorbing unit 30 through the outer surface 36 of the heat absorbing unit 30. In the heat absorption part 30, the refrigerant evaporates due to heat and changes from the liquid phase to the gas phase. At this time, the refrigerant absorbs heat from the outside by the latent heat of vaporization in the heat absorbing section 30. Since the refrigerant becomes a gas phase and the volume rapidly expands, the refrigerant passes through the heat transport side channel 60 and spreads to the heat radiating unit 40.

The gas-phase refrigerant spread to the heat radiating section 40 releases the latent heat of condensation in the heat radiating section 40 and returns to the liquid phase. Here, the amount of heat input to the heat absorbing portion 30 is equal to the amount of heat dissipated by the heat radiating portion 40, but the heat radiating portion 40 has a larger area than the heat absorbing portion 30, so the heat density is the heat absorbing portion 30. Therefore, the heat can be radiated from the outer surface 46 of the heat radiating portion 40 to the atmosphere or the like by another heat radiating means such as the fin 100 described later.

The refrigerant that has become a liquid phase enters the reflux side flow path 70 and returns to the heat absorption unit 30. The refrigerant liquid phase that has returned to the heat-absorbing portion evaporates in the same manner as described above, thereby depriving the cooled element 90 of heat. By repeating the above cycle, the cooling substrate 10 can cool the element 90 to be cooled.

Next, the effect | action of the composite flow paths 34 and 44 of the heat absorption part 30 and the thermal radiation part 40 is demonstrated. A plurality of types of cooling substrates 10 having the same external shape were produced. The bottom area, the width, and the flow path height are the same for the heat absorption part 30, the heat radiation part 40, the heat transport side flow path 60, and the reflux side flow path 70, respectively. Here, the overall height of the composite flow paths 34 and 44 of the heat absorbing section 30 and the heat radiating section 40 is fixed to 0.3 mm, and the width of the fine flow paths 31 and 41 varies between 0.2 mm and 0.5 mm. I let you.

Here, the ratio P of the height of the communication flow paths 33 and 43 to the total height of the composite flow paths 34 and 44 is changed between 0 and 1, and the outer surface 36 of the heat absorption part and the outer surface 46 of the heat dissipation part The thermal resistance R (K / W) was measured. The thermal resistance R is obtained by dividing the temperature difference ΔT (K) between the outer surface 36 of the heat absorbing portion 30 and the outer surface 46 of the heat radiating portion 40 by the heat generation amount W (W) of the element 90 to be cooled, and R = ΔT / W I can express.

The measurement result of thermal resistance is shown in FIG. As can be seen from FIG. 12, the influence of the widths of the grooves 31 and 41 of the fine channels 32 and 42 was not observed. On the other hand, when compared with the height ratio P of the communication channels 33 and 43, P is 1 (that is, the whole is a communication channel) than when P is 0 (that is, the whole is a fine channel and there is no communication part). The thermal resistance R was larger in the case of no groove). This is because the heat transfer area is increased in the heat absorbing part 30 and the heat radiating part 40 due to the fine flow path, and the heat transfer distance from the refrigerant to the heat absorbing part 30 or the flow path wall of the heat radiating part 40 is reduced. Alternatively, the heat transfer coefficient in the heat radiating section 40 is improved.

Furthermore, the thermal resistance R decreases when P is between 0.3 and 0.6, and is a minimum value near 0.4. This is because if P is small, the heat transfer coefficient is improved, but on the other hand, the pressure loss increases and the refrigerant does not flow easily. The pressure loss is reduced by the communication flow paths 33 and 43, and the flow rate of the refrigerant can be increased. However, when the whole is composed of the communication flow paths 33 and 43 (P = 1), the heat transfer coefficient is reduced, and thus the heat transfer rate is reduced. The resistance R increases.

The heat transport amount of the cooling substrate 10 is a combination of these two factors, which determines the thermal resistance R, so that R is minimized within a certain range. When P is in the range of 0.3 to 0.6, R is preferably small.

In the cooling substrate 10 according to the second embodiment of the present invention, as shown in the partially enlarged view in FIG. 13A, the refrigerant moves from the heat absorption part 30 toward the heat radiation part 40 in the middle of the reflux side flow path 70. Therefore, a check valve 71 is provided to prevent backflow. The check valve 71 is a thin-film copper foil projecting obliquely from one wall surface of the reflux side flow channel toward the flow channel direction, the base end portion 71a is fixed to the wall surface, and the distal end portion 71b is free (movable). )It has become. FIG. 13 is a cross-sectional view of the reflux side flow path 70 taken along a plane perpendicular to the cooling substrate and parallel to the flow path direction.

When the flow of the refrigerant is in the direction (forward direction) from the heat radiating unit 40 to the heat absorbing unit 30 in the reflux side flow path 70, the check valve 71 does not disturb the refrigerant flow as shown in FIG. 13B. Deflection. When the flow of the refrigerant is in the direction (reverse direction) from the heat absorbing unit 30 to the heat radiating unit 40, the check valve 71 blocks the recirculation-side flow path 70 to prevent the reverse flow of the refrigerant as shown in FIG. .
The check valve 71 works as a pump that transports the refrigerant only in one direction due to the check action of the check valve 71 and the pressure increase due to the evaporation of the refrigerant in the heat absorbing section 30.

In the cooling substrate 10 according to the third embodiment of the present invention, as shown in a partially enlarged view in FIG. 14A, a capillary structure 72 made of a copper porous body 73 is provided in the middle of the reflux side flow path 70. Was provided. The capillary structure 72 promotes the flow of the liquid phase, and the liquid phase can efficiently move to the heat absorption part. Moreover, since it becomes resistance with respect to a gaseous phase, a liquid phase can pass the reflux side flow path 70 preferentially. Therefore, it works as a pump that transports the refrigerant only in one direction. FIG. 14 is a cross-sectional view of the reflux side flow path 70 cut by a plane perpendicular to the cooling substrate and parallel to the flow path direction.

As shown in FIG. 14B, the copper porous body 73 is obtained by gently sintering copper powder so as to leave a continuous air hole. The capillary structure 72 may be a copper mesh laminate 74 as shown in FIG.

In the cooling substrate 10 according to the fourth embodiment of the present invention, as shown in a partially enlarged view in FIG. 15, a piezoelectric pump 75 is embedded in the middle of the reflux side flow path 70. Since the transportation of the refrigerant is assisted by the external force by the piezoelectric pump 75, the transportation amount of the refrigerant can be increased and the heat transportation amount can be improved as compared with the first to third embodiments. FIG. 15 is a cross-sectional view of the reflux side flow path 70 taken along a plane perpendicular to the cooling substrate and parallel to the flow path direction.

FIG. 16 shows the result of measuring the thermal resistance R while producing a cooling substrate with P of 0.5 and a cooling substrate with P of 0 and using the same piezoelectric pump 75 and changing the amount of heat input. In all cases where the heat input was between 0W and 240W, P = 0.5 showed a lower thermal resistance than P = 0. Further, when the transport amount of the refrigerant at that time is measured, as shown in FIG. 17, even when the output of the piezoelectric pump 75 is the same, the transport amount of the refrigerant is larger at P = 0.5 than at P = 0. It appears as a difference in resistance.

In the cooling substrate 10 according to the fifth embodiment of the present invention, as shown in FIG. 18, a plurality of heat transfer columns 101 made of copper round bars are joined to the outer surface 46 of the heat radiating portion 40, and the heat transfer columns are formed. A plurality of fin plates 102 made of an aluminum plate are inserted into 101 to form a laminated fin 100.

Thereby, heat is conducted from the heat radiating portion 40 to the fin plate 102 via the heat transfer column 101 and can be radiated to the atmosphere by the fin plate 102, so that the heat radiating capability can be further improved. Further, when air is blown between the fin plates 102 by a fan (not shown), the heat radiation amount is further increased and the heat radiation capability is further improved.

Moreover, you may comprise the heat-transfer pillar 101 with a heat pipe instead of a copper round bar. By using a heat pipe, the heat conduction is further improved as compared with a copper round bar, and the heat dissipation capability can be further improved.

Alternatively, the heat transfer column 101 may be formed of a pipe whose upper end is closed and whose lower end is open, and the lower end communicates with the space of the heat radiating unit. Thereby, since the refrigerant circulates to the inside of the heat transfer column 101, the area of the heat radiating portion 40 is increased, and the heat resistance of the heat transfer column 101 is reduced, so that the heat dissipation capability can be further improved. it can.

The plate members 11 and 12 used for the cooling substrate 10 of the present invention may not be copper. Other metals such as aluminum, alloys, silicon, ceramics, and the like may be used, and it is preferable to use a material that is excellent in heat conduction and that can be finely processed and bonded.

The method for forming the recesses 21 and 22 on the surfaces of the plate members 11 and 12 is not limited to etching, and methods such as cutting, sandblasting, forging, and transfer can be applied. Or, conversely, a portion other than the recess may be raised by plating, sputtering, or the like, and the remaining portion may be used as the recess.

Joining is not limited to brazing, and methods such as diffusion joining and welding can be applied, and mechanical joining such as caulking may be used in combination. Even in the case of brazing, in addition to forming a solder by plating, it is also possible to apply a paste-like solder or sandwich a foil-like solder between plate materials.

The through hole 12b may be opened on the first copper plate side. The through hole 12b may be opened after brazing. Moreover, you may open in the side surface instead of the surface of the 2nd copper plate 12. FIG. A pipe (not shown) may be formed outside the through hole 12b. Thereby, processing of deaeration, water injection, and sealing is facilitated.

In addition to pure water, the refrigerant may be any substance that has a large latent heat, can be evaporated and condensed within the temperature and pressure ranges to be used, and does not cause a chemical reaction with the plate material forming the cooling substrate. As such a refrigerant, substances such as chlorofluorocarbon, alternative chlorofluorocarbon, hydrocarbon, alcohol, and ether can be applied.

DESCRIPTION OF SYMBOLS 10 Cooling board 11 1st copper plate 11a, 12a Plane part 12 2nd copper plate 12b Through-hole 20 Space 21 1st recessed part 22 2nd recessed part 30 Endothermic part 31, 41 Groove 32, 42 Fine flow path 33, 43 Communication Channels 34 and 44 Composite channels 35 and 45 Walls 36 and 46 Outer surface 40 Heat radiation portion 50 Refrigerant channel 60 Heat transport side channel 70 Return side channel 71 Check valve 71a Base end portion 71b Tip end portion 72 Capillary structure 73 Porous Mass 74 Laminated body 75 Piezoelectric pump 90 Cooled element 100 Laminated fin 101 Heat transfer column 102 Fin plate

Claims (5)

Provided with at least one heat absorbing part and at least one heat radiating part in the substrate,
The heat absorbing part and the heat radiating part communicate with each other in a loop shape by a refrigerant flow path,
In the cooling substrate in which the refrigerant circulates in the refrigerant flow path and thermally transports by latent heat of evaporation and condensation of the refrigerant,
The refrigerant flow path includes a heat transport side flow path for sending the refrigerant vaporized from the heat absorption part toward the heat dissipation part, and a recirculation side flow path for sending the refrigerant liquefied from the heat dissipation part toward the heat absorption part. Consists of
The cooling substrate according to claim 1, wherein a cross-sectional area of the reflux side flow path is smaller than a cross-sectional area of the heat transport side flow path. The ratio of the cross-sectional area of the reflux side flow path and the cross-sectional area of the heat transport side flow path is in the range of 0.0002 to 0.77,
The cooling substrate according to claim 1. The reflux side flow path is provided with a check structure that prevents the liquefied refrigerant from flowing backward from the heat absorption part toward the heat dissipation part,
The cooling substrate according to claim 1 or 2. The reflux channel is provided with a capillary structure that generates a capillary force,
The cooling substrate according to any one of claims 1 to 3. The reflux side flow path is provided with a refrigerant transport mechanism for forcibly sending the liquefied refrigerant from the heat radiating portion toward the heat absorbing portion using power.
The cooling substrate according to any one of claims 1 to 4.

Images