COOLING DEVICE FOR ELECTRONIC PARTS

Abstract: A cooling device located between a cooling plate (3) hav­ ing a first coolant (9) circulating therein, and an electronic part (2) to be cooled, mounted on a printed-wiring board (1), com­ prising a hollow part (6C) being thermally conductive, having a hollow chamber (6B) through which the first coolant circu­ lates, and connected to the cooling plate (3) by a flange part (6A) being thermally conductive, a thermal conductive plate (4) attached to a surface of the electronic part (2) and connec­ ted to the flange part (6A) by a bellows (5) providing a space among the hollow part (6C) the bellows (5) and the thermal conduction plate (4), and a second liquid coolant (7) filling the space for transferring heat from the thermal conduction plate (4) to the hollow part (6C) by a convection current of the second coolant (7). The second coolant (7) is made of alloy being chemically inactive to the bellows (5) and having a low melting point so as to be liquid at ordinary temperatures.

Description: The invention relates to a cooling device located between a cooling plate and thermal conduction means, the thermal conduction means being attached to a surface of a heat producing electronic part, which is to be cooled. Recently, high density packaging and high speed operation have been required for electronic parts such as Large Scale Integrated circuit (LSI) elements widely applied to electronic apparatus, so that the temperature of electronic parts tends to rise disproportionately. Therefore, it becomes very important that electronic parts are cooled with high efficiency to obtain a stable operation of those electronic parts. In the EP-A-151068, a cooling device is disclosed to be used for the cooling of electronic circuit parts mounted on a printed circuit board. This cooling device is located between a cooling plate and thermal conduction means in thermal contact with a surface of a heat producing electronic part, which is to be cooled, the cooling plate comprising a hole provided on a surface of the cooling plate, this hole providing a fluid passage between the cooling plate and a hollow chamber of bellows means, whereby this hole allows a coolant which circulates in the cooling plate to also circulate in the hollow chamber of the bellows means without leakage from it, the bellow means connecting said thermal conduction means to the cooling plate and pressing said thermal conduct-ion means to the surface of the electronic part. Fig. 1 is a general perspective view of a prior art cooling device. In Fig. 1, a cooling plate 3 is provided in such a way as being stacked as indicated by an arrow mark F on a printed-wiring board 1 on which a plurality of electronic parts 2 are mounted. A bellows 5 engaged with the predetermined surface of the cooling plate 3 presses a surface of the electronic part 2, and cooled water is capable of circulating in the direction of an arrow mark A from the one opening 10 of the cooling plate 3 and in the direction of the arrow mark B from the other opening 100, thereby cooling the electronic parts 2. The extruding height of the electronic part 2 from the printed-wiring board 1 is not always equal to the specified value. Therefore, in view of absorbing "dispersion" of extruding heights of the electronic parts 2, a flexible bellows 5 is provided between the surfaces of the cooling plate 3 and the electronic part 2 and the bellows 5 is placed in certified close contact with the surfaces keeping a pressure not giving adverse effect on the respective electronic part 2. Therefore, the bellows 5 is formed using a very thin sheet made of copper or stainless steel so that the bellows 5 may be damaged if corroded or rusted after use for a long period of time. Accordingly, extended duration of bellows has been expected in order to assure stabilized cooling effect for long time operation. Fig. 2 is a cross-sectional view of a prior art cooling device similar to that disclosed in the EP-A-0151068. As shown in Fig. 2, the cooling structure of the prior art cooling device comprises a flange 11 attached to a cooling plate 3 through an O-ring 13, a thermal conduction plate 4 attached with pressure to the electronic part 2 through a thermal conduction sheet 12 and the bellows 5 which combines the flange 11 and the thermal conduction plate 4. A coolant 9 flowing in the direction of arrow mark A1, passing through the one circulating path 3A of the cooling plate 3, is injected in the direction of arrow mark A2 from a nozzle 3B, provided on the cooling plate 3. Moreover it is caused to flow in the direction of arrow mark A3 into the other circulating path 3A, thereby cooling the electronic part 2 through the thermal conduction plate 4 and the thermal conduction sheet 12. The bellows 5 is provided in the cooling device for making thermal conduction and pressure contact appearing and performed between the electronic part 2 and the thermal conduction plate 4 high and tightly respectively. Accordingly, the bellows 5 is made of very thin sheet, such as 80 µm of copper or stainless steel, using a spring nature of the sheet. However, this structure results in such a problem if the coolant 9 circulates for a long time that the bellows 5 may be rusted, so that the coolant 9 leaks out from the bellows 5 and thereby the electronic part 2 will be damaged. Moreover, the problem arises that, when the flow rate of the coolant 9 is required to be increased in order to raise the cooling capability, an increased pressure due to the flow rate is applied to the surface of the electronic part. Thereby, the thermal conduction plate 4 may be broken. Therefore, an object of the present invention is to improve the prior art cooling device so that the bellows is not corroded (rusted) by the coolant circulating through the cooling plate to stabilize the operation of the cooling device and to extend the operation life of the device. The object of the present invention is achieved by a device as defined in claim 1. The present invention improves the prior art cooling device so that an electronic part is not damaged by the pressure applied from a part of the cooling device due to increased pressure of the coolant, even if the flow rate of the circulating coolant is increased. According to claim 1, the heat-transferring cooling device of the present invention comprises a hollow means, i. e. a hollow part, inside of the bellows. The hollow means has a hollow chamber opened to the circulating path in the cooling plate so as to circulate the coolant of the cooling plate through the hollow chamber of this hollow means. The coolant of the cooling plate (now called the first coolant) flows into the hollow chamber for cooling the hollow means. The hollow chamber is completely separated from the exterior of the hollow part so that the first coolant does not leak out from the hollow part. The space between the hollow part and the bellows is filled with another coolant (called the second coolant), so that the electronic part can be cooled by convection of the second coolant,cooled by the hollow part. Accordingly, metal rust which has been produced in the prior art can be prevented, and the operation life of the cooling device can be extended by using a liquid which does not result in metal corrosion by the second coolant and moreover. since influence on the electronic part by the flowing pressure of the first coolant can be eliminated, the flow rate can be increased and the cooling capability can also be improved. Fig. 1 is a perspective illustration indicating the working condition of a cooling device incorporated with the present invention, Fig. 2 is a schematic vertical sectional view of a cooling device of the prior art, and Fig. 3 is a schematic vertical sectional view of an embodiment of the present invention. The present invention is explained in detail with reference to Fig. 3, which is a vertical sectional view of an embodiment of the present invention. In Fig. 3, the same reference numerals as those in Figs. 1 and 1 designate the similar parts to those in Figs. 1 and 2. In the embodiment, a cooling device located between the cooling plate 3 and the electronic part 2, comprises a block 6, comprising a flange 6A and a hollow part 6C; the cooling device further comprising a bellows 5, a hollow chamber 6B and a second coolant 7, filling the space existing between the hollow part 6C and the bellows 5, i. e. provided in the interior of the bellows 5. The flange 6A is attached to the cooling plate 3 through an O-ring 13. Inside the hollow chamber 6B of the hollow part 6C, the first coolant 9 circulates. The external side of the hollow part is in contact with the second coolant 7. The thermal conduction plate 4 is in contact with the surface of the electronic part 2 through the thermal conduction sheet 12. The block 6 and the thermal conduction plate 4 are made of copper when these are formed thick or made of stainless steel when these are formed thin. Since ordinary water is used as the first coolant 9, when the block 6 is formed with copper, particular rust-preventing processing is not required for the surface which is in contact with the first coolant 9. However, the surface which is in contact with the second coolant 7 requires the surface processing such as a coating of Teflon in order to prevent chemical variations caused by the copper and the second coolant 7. Also, in the case of forming the thermal conduction plate 4 with copper, the surface processing is necessary for the surface to be in contact with the second coolant 7. When the block 6 and the thermal conduction plate 4 are formed by stainless steel, such surface processings are no longer necessary. As described in the prior art, the bellows 5 is formed by very thin metal material, for example, as thin as 80 microns, in order to have a very delicate spring force which presses the electronic part 2 to the cooling device but does not give any damage thereto. Therefore, when the Teflon coating is carried out as described above, flexibility is lost and when thin Teflon coating is executed, the coating is easily damaged. In any case, the Teflon coating results in various disadvantages. Accordingly, stainless steel or nickel material which does not generate rust with the second coolant 7 is used as the raw material. The second coolant 7 is preferably liquid for the purpose that the thermal conduction plate 4 is closely placed in contact with the surface of the electronic part 2 through a thermal conduction sheet 12. Raised heat of electronic part 2 is transferred to the second coolant 7 and moreover it is effectively transferred to the first coolant. The thermal conduction sheet 12 is provided for absorbing difference of parallelism between the surface of the electronic part 2 and the thermal conduction plate 4 fixed to the bellows 5 and assuring close contact and is usually composed of a flexible good thermal conduction member, for example, BFG-20 or BFG-30 manufactured by DENKA chemical Industrial Corp. However, since it is difficult from the point of view of manufacture to fill the bellows 5 with liquid, it is preferable to use a low melting point metal, for example, the INDALLOY Number 51 or 60 of INDIUM CORP. OF AMERICA which is in a solid at a low temperature when cooling is not required and is a liquid at a high temperature when cooling is required and is formed by the alloy of gallium (Ga), indium (In), tin (Sn) and is fused within temperature ranging from 5°C to 50°C. When a fin 8 is provided to the external or internal circumference of the hollow part 6C (to the external circumference in Fig. 3), the heat exchange area respectively for the first and second coolants 9 and 7 can be increased and thermal conduction efficiency can be raised. Because of such structure and temperature rise of the electronic part 2, heat produced from the electronic part 2 is transferred to the second coolant 7 through the thermal conduction sheet 12 and thermal conduction plate 4 and thereby the second coolant 7 is fused. Next, heat is transferred to the first coolant 9 through the hollow part 6C by a convection current of the fused second coolant 7. The first coolant 9 is caused to flow into the nozzle 3B from the one circulating path 3A of the cooling plate 3 as indicated by an arrow mark A11, the first coolant 1 is then injected to the hollow chamber 6B from the nozzle 3B as indicated by an arrow mark A12 and moreover the injected second coolant 9 is caused to flow to the other circulating path 3A as indicated by an arrow mark A13. In this case, since the injected first coolant 9 is received by the hollow part 6C, even when the flow rate is increased, flowing pressure is not applied directly on the bellows 5 and it does not press the surface of electronic part 2. As a result, the flow rate can be increased easily. In addition, since rusting of metal does not occur on the thin bellows 5, the bellows 5 is now free from damage due to metal rusting. As explained above, according to the present invention, damage by metal rusting of the bellows can be prevented and thereby reliability of bellows can be improved so as to obtain a longer operation life. Moreover, since the contact pressure at the surface of the electronic part is not influenced by variations of flow rate of the first coolant, a specified contact pressure can always be maintained, assuring stabilized cooling and allowing an increased flow rate of the first coolant, namely resulting in such a large practical effect that the cooling capability can be enhanced by an increase of the flow rate.

Claims: A heat-transferring cooling device located between a cooling plate (3) and thermal conduction means (4, 12) which are attached to a surface of a heat producing electronic part (2); which is to be cooled, the cooling plate comprising a hole provided on a surface of the cooling plate (3), this hole providing a fluid passage between the cooling plate (3) and a hollow chamber (6B) of a hollow chamber means (6C), whereby this hole allows a coolant which circulates in the cooling plate (3) to also circulate in this hollow chamber (6B) without leakage from it, the heat-transferring cooling device further comprising: thermally conductive hollow chamber connection means (6A) connecting the hollow chamber means, to the surface of the cooling plate, the hollow chamber containing the cooling plate's (3) coolant as a first coolant (9), bellows means (5) connecting said thermal conduction means to said thermally conductive hollow chamber connection means and pressing said thermal conduction means to the surface of the electronic part, whereby a space between said hollow chamber means and said bellows means and between said hollow chamber means and said thermal conduction means is provided, a second heat transferring coolant (7) filling this space, this second coolant (7) being liquid at ordinary temperatures and being chemically inactive to the bellows means (5). A cooling device according to claim 1, wherein this hollow chamber connection means (6A) comprise a flange part (6A), and further comprise an O-ring (13) which is inserted into a joint of the cooling plate (3) and this flange part (6A) for preventing the first coolant (9) leaking out from the joint. A cooling device according to claim 2, wherein this O-ring (13) consists of rubber. A cooling device according to claim 1, 2 or 3, wherein, the hollow chamber means (6C) comprises a plurality of fins (8) for increasing the efficiency of heat exchange, performed between the first coolant (9) and said second coolant (7). A cooling device according to anyone of claims 1 to 4, wherein the hollow chamber connection means (6A) and the hollow chamber means form a block part (6) which consists of copper, having a coating on a surface which faces to said second coolant (7), said coating being chemically inactive to said second coolant (7). A cooling device according to claim 5, wherein this coating is a tetrafluoroethylene coating. A cooling device according to anyone of the claims 1 to 4 wherein this hollow chamber connection means (6A) and the hollow chamber means form a block part (6) which consists of stainless steel. A cooling device according to anyone of the preceding claims 1 to 7 wherein this bellows means (5) consists of stainless steel. A cooling device according to anyone of the preceding claims 1 to 7, wherein this bellows means (5) consists of nickel. A cooling device according to anyone of the preceding claims 1 to 9, wherein this second coolant (7) comprises an alloy having a low melting point ranging from 5°C to 50°C. A cooling device according to claim 10, wherein this alloy consists of gallium and indium. A cooling device according to claim 10, wherein, this alloy consists of gallium, indium and tin.

Inventors: ONO, IZUMI
Applicants: FUJITSU LIMITED
Application year: 1986
Main classification: H01L23
IPC codes: H05K7, H01L23