Abstract:
An electronic apparatus includes a fan, a circuit board which is positioned downstream in an airflow to which the fan generates, at least one processer mounted on the circuit board, a radiator which is positioned downstream in the airflow which the fan generates, the radiator cooling a liquid coolant, a pipe unit which includes a heat receiving member in which the coolant flows and coolant piping, the heat receiving member being mounted on the processer, and the coolant piping circulating the liquid coolant between the radiator and the heat receiving member, and at least one memory board on which memory package is mounted, the memory board being mounted on the circuit board, and the memory board and the pipe unit being arranged along a direction perpendicular to a direction to which the fan blows the airflow.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from, and incorporates by reference the entire disclosure of, Japanese Patent Application No. 2012-197918, filed on Sep. 7, 2012. 
     FIELD 
     The present application relates to an electronic apparatus which is able to cool high heat generating components, which are arranged aligned, with a high efficiency and to a cooling module which is mounted in that electronic apparatus. 
     BACKGROUND 
     In recent years, servers and other electronic apparatuses have been made higher in speed and more advanced in functions. Such electronic apparatuses mount large numbers of electronic devices. These electronic devices generate heat along with their operation. One of these electronic devices, the CPU (central processing unit), is now consuming increased power due to its higher speed and more advanced functions. The amount of heat generated by a CPU tends to increase the greater the supplied power. Further, in general, a server mounts a plurality of CPUs. The amount of heat which is generated from these becomes tremendous. If the heat causes the inside of the server to become high in temperature, the functions of the electronic devices will become impaired and malfunction of the server will be caused. Therefore, to maintain the functions of the electronic devices and avoid malfunction of the server, the heat generating electronic devices need to be cooled. 
     As a radiator which takes heat from heat generating electronic devices and discharges it to the outside, there is known a liquid cooling system which runs coolant through coolant piping and uses its passage so as to take heat from the electronic devices and discharges the heat to the outside (for example, Japanese Laid-Open Patent Publication No. 5-109798 and Japanese Laid-Open Patent Publication No. 2005-381126). A liquid cooling system in general is provided with heat receiving units, a radiator, pumps, a manifold, and a plurality of pipes which connect these with each other to form a closed path. The heat receiving unit takes heat from the CPUs using the coolant, while the radiator discharges the heat of the coolant which has become high in temperature due to the taken heat to the air or other outside part. The coolant which flows through the channels which are formed by the piping is supplied with the force for running through the channels by the pumps. The manifold divides and merges the coolant which flows through the channels. 
     In this regard, since a liquid cooling system has such a plurality of components, when applying the liquid cooling system to a server, since there is a limit to the space inside of the server, the layout of the components inside the server has to be considered or else mounting is not possible. Further, in a server, an air cooling system which uses fans is mounted for cooling the electronic components other than the CPUs. The fans are used to take in outside air as the cooling air so as to cool the electronic components and to discharge to the outside the cooling air which has become high in temperature due to the taken heat. For this reason, if mounting a liquid cooling system in addition to the existing air cooling system, there is the problem that the flow of the cooling air which is supplied by the air cooling system will be blocked by the components of the liquid cooling system and cooling will be obstructed. Mounting has therefore been difficult. 
     Furthermore, a server or other electronic apparatus is installed in a data center or computer room or other cramped location, so the places where it can be installed are limited. To enable a large number of servers to be installed in such limited locations, reduction of the server size and reduction of the area occupied at the time of installation are sought. In this regard, in recent years, servers have been expanded in functions and performance, so the work, calculations, etc. which used to be performed by a large number of servers can now be performed by a smaller number of servers. Also, individual servers have also been improved in performance, so the area which the hardware occupies has been reduced. This improvement of the functions which the servers can perform and improvement of the performance of the servers have led to higher density mounting of electronic components in the servers. When mounting electronic components in servers at such a higher density, the issue arises of how to efficiently cool the heat generating electronic components. 
     SUMMARY 
     The present application provides an electronic apparatus includes a fan, a circuit board which is positioned downstream in an airflow to which the fan generates, at least one processer mounted on the circuit board, a radiator which is positioned downstream in the airflow which the fan generates, the radiator cooling a liquid coolant, a pipe unit which includes a heat receiving member in which the coolant flows and coolant piping, the heat receiving member being mounted on the processer, and the coolant piping circulating the liquid coolant between the radiator and the heat receiving member, and at least one memory board on which memory package is mounted, the memory board being mounted on the circuit board, and the memory board and the pipe unit being arranged along a direction perpendicular to a direction to which the fan blows the airflow. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a perspective view which illustrates the appearance of a server which mounts a plurality of server modules which are provided with cooling modules according to the present application. 
         FIG. 1B  is a partially enlarged view which illustrates a state of pulling out one server module from a rack cabinet of the server which is illustrated in  FIG. 1A . 
         FIG. 1C  is a perspective view which illustrates a general internal configuration of one server module which mounts an air cooling system. 
         FIG. 2A  is an assembled view which illustrates a state of mounting a liquid cooling module according to the present application in a server module of a first embodiment of the present application which is provided with an air cooling system. 
         FIG. 2B  is a plan view which illustrates a state of a cooling module mounted in a server module which is provided with an air cooling system which is illustrated in  FIG. 2A . 
         FIG. 3A  is an assembled perspective view which illustrates a state of mounting the cooling module according to the present application at a main board in a server module which is provided with the cooling module which is illustrated in  FIG. 2A . 
         FIG. 3B  is a perspective view of the server module which is illustrated in  FIG. 2B . 
         FIG. 4  is an enlarged perspective view of principal parts which illustrates a tank and pumps in the cooling module which is illustrated in  FIG. 3A . 
         FIG. 5A  is a vertical cross-sectional view which illustrates one example of the internal structure of the tank which is illustrated in  FIG. 4 . 
         FIG. 5B  is a cross-sectional view along the line B-B of  FIG. 5A . 
         FIG. 6A  is a perspective view which illustrates one embodiment of the structure of a connecting part of fins and coolant piping of a radiator which is illustrated in  FIG. 3 . 
         FIG. 6B  is a front view of the radiator which is illustrated in  FIG. 6A . 
         FIG. 7A  is an explanatory view which explains a flow of coolant in the cooling module which is illustrated in  FIG. 2A  and  FIG. 3A . 
         FIG. 7B  is a circuit diagram which illustrates one embodiment of the configuration of a control circuit of pumps in the cooling module which is illustrated in  FIG. 7A . 
         FIG. 8  is a flow chart which illustrates an embodiment of a control routine of the pumps which is illustrated in  FIG. 7B . 
         FIG. 9  is an explanatory view which illustrates the layout of heat generating components and memories in a server module according to the present application and the layout of a cooling module which cools the heat generating components. 
         FIG. 10  is a disassembled perspective view which illustrates specific component members of a cooling module according to the present application. 
         FIG. 11A  is a comparative view which compares the flow of the cooling air which flows through the inside of a server module which is provided with an air cooling system and the flow of the cooling air in the case of providing a wall at a center part inside of the server module. 
         FIG. 11B  is a cross-sectional view which illustrates an embodiment where the wall is covered by a ceiling part. 
         FIG. 11C  is an explanatory view which illustrates the flow of the cooling air in the case of providing a curved part at an upstream side of the wall. 
         FIG. 11D  is an explanatory view which illustrates the flow of the cooling air in the case of providing a tapered part at an upstream side of the wall. 
         FIG. 12  is an assembled perspective view which illustrates an embodiment which arranges a leakage tray between a cooling module and a main board which are illustrated in  FIG. 3A . 
         FIG. 13A  is a perspective view which illustrates the state of mounting a leakage tray and a water cooling system on the main board which is illustrated in  FIG. 12 . 
         FIG. 13B  is a cross-sectional view of principal parts of the server module which is illustrated in  FIG. 13A . 
         FIG. 14A  is a cross-sectional view of principal parts of the server module which is illustrated in  FIG. 13 . 
         FIG. 14B  is a schematic cross-sectional view which illustrates the structure of the leakage tray which illustrates a second embodiment of the leakage tray which is illustrated in  FIG. 14A . 
         FIG. 14C  is a schematic cross-sectional view which illustrates the structure of the leakage tray which illustrates a third embodiment of the leakage tray which is illustrated in  FIG. 14A . 
         FIG. 14D  is a schematic cross-sectional view which illustrates the structure of the leakage tray which illustrates a fourth embodiment of the leaking water prevention structure of the cooling module which is illustrated in  FIG. 14A . 
         FIG. 15A  is a partially enlarged perspective view which illustrates the configuration of six pumps and heat receiving members which are arranged at the two sides of the tank of the cooling module. 
         FIG. 15B  is a partially enlarged perspective view which illustrates a holding structure which holds at a slant the six pumps which are illustrated in  FIG. 15A . 
         FIG. 16  is a plan view which illustrates a second embodiment of a server module  1  which mounts an air cooling system and the cooling module of the present application. 
         FIG. 17  is a plan view which illustrates the state of cooling air of the air cooling system being supplied to a connection mechanism of top and bottom server modules which are provided at the rear surface side of the server module of the second embodiment which is illustrated in  FIG. 16 . 
         FIG. 18  is an assembled perspective view which illustrates a third embodiment of the present application where a single server module mounts two main boards on which cooling modules are mounted. 
         FIG. 19  is a perspective view which illustrates the structure of a bottom surface of a top side main board which is illustrated in  FIG. 18 . 
         FIG. 20  is a perspective view of principal parts of the server module in the state where a first system unit which is illustrated in  FIG. 18  has a second system unit laid over it. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, the attached drawings will be used to explain modes of working the present application in detail based on specific embodiments. Note that in the embodiments which are explained below, as the electronic apparatus, a server module which forms a server is explained as an example, but the electronic apparatus is not limited to this. Further, in the following embodiments, component members which are provided with the same functions will be assigned the same reference numerals for the explanations. 
       FIG. 1A  is a perspective view which illustrates the appearance of a rack mount server  100  in which a server module  1  which is provided with a liquid cooling system according to the present application is mounted in a rack cabinet  9 . The rack mount server  100  is one type of data processing system. Inside the rack cabinet  9 , one or more server modules  1  are mounted. The cooling air for cooling the server module  1  is sucked in from the front surface, cools the internal devices of the server module  1 , and is exhausted from the rear surface. 
       FIG. 1B  is a partially enlarged view which illustrates the state when pulling out one server module  1  from the rack cabinet  9  which is illustrated in  FIG. 1A . Further,  FIG. 1C  is a perspective view which illustrates the configuration of the air cooling system which is mounted in one server module  1 . Inside the server module  1 , the first heat generating components  2  are at the upstream side of the fans  5  with respect to the flow of the cooling air, while at the downstream side of the fans  5 , CPUs (second heat generating components)  3 , electronic components  4 , etc. are arranged. The first heat generating components  2  are, for example, hard disks or SSDs (solid state devices) or other electronic components. The cooling air from the fans  5  is used to cool the CPUs  3  and electronic components  4  and other heat generating components and electronic components. 
       FIG. 2A  illustrates the server module  1  of one embodiment of the present application and is an assembled view which illustrates by a plan view the state of the server module  1  which is provided with an air cooling system and mounts the liquid cooling system  10 . Note that, after this, the liquid cooling system  10  will sometimes also be referred to as the “cooling module  10 ”. Further,  FIG. 2B  is a plan view which illustrates the state of the server module  1  which is provided with an air cooling system which is illustrated in  FIG. 2A  and mounts the liquid cooling system  10 . The air cooling system is provided with a plurality of fans  5  which generate cooling air. The main board  6  at the upstream side of the fans  5  is provided with the first heat generating components (hard disk, SSD, etc.) which were explained in  FIG. 1C , but here their illustration is omitted. 
     In the present application, the region on the main board  6  at the downstream side from the fans  5  of the server module  1  is divided by lines which run in the direction of flow of the cooling air CA into a first region A 1  and second regions A 2 . The first region A 1  is a region in which a plurality of heat generating components (here, the heat generating components  3 A and  3 B) are arranged. The plurality of heat generating components  3 A and  3 B are arranged aligned along the direction of flow of the cooling air CA. The heat generating components  3 A and  3 B are, for example, the CPUs  3 A and  3 B. These are large heat generating components which require strong cooling. In this embodiment, the CPU  3 B is arranged at the downstream side of the CPU  3 A. Accordingly, the heat generating components  3 A and  3 B are subsequently also referred to as the “CPUs  3 A and  3 B” or “the components which require strong cooling  3 A and  3 B”. The second regions A 2  are regions which are positioned at the two sides of the first region A 1  (sometimes at one side of the first region A 1 ) and contain electronic components which can be cooled by cooling air. 
     The CPUs  3 A and  3 B which are arranged at the first region A 1  may not be cooled sufficiently by cooling air, that is, are components which require strong cooling, so are cooled by the liquid cooling system  10 . The part at which the liquid cooling system  10  is arranged also has components which do not require cooling air, that is, have  1 W or less heat generating characteristics. If the CPUs  3 A and  3 B are arranged in the region at which the liquid cooling system  10  is arranged, the direction of flow of the cooling air need not be straight. The electronic components  4  which are arranged at the second regions A 2  are electronic components  4  which can be cooled by the supply of cooling air or which can be cooled by the supply of cooling air and the attachment of a heat sink or other radiator and which have 1W to 100W or so heat generating characteristics. They are also called “components which require weak cooling”. As such electronic components  4 , there are DIMMs (memory modules), power components, etc. 
     The above-mentioned first region A 1  and second regions A 2  are elongated rectangular regions. Non-tapering regions are secured. This is because if the regions on the main board  6  are finely divided by the components etc. of the liquid cooling system  10 , the distance between air cooled components will be limited by the liquid cooling system  10  and realization of the circuit configuration which the system requires will become difficult. The position of the first region A 1  on the main board  6  is determined by the sizes and positions of the second regions A 2 , but in general is a position slightly offset from the center part of the main board  6 . Further, the second regions A 2  which are positioned at the two sides of the first region A 1  may not be the same. 
     In the present application, the region on the main board  6  at the downstream side of the cooling air CA of the air cooling system is divided into the first region A 1  and the second regions A 2 . In this server module  1 , a liquid cooling system  10  designed not to interfere with the cooling air CA to the second regions A 2  is mounted at the first region A 1 . The liquid cooling system  10  is in general provided with a radiator which cools the coolant, heat receiving members which take heat from the heat generating components (absorb heat from them), coolant piping which runs coolant from the radiator to the heat receiving members, and pumps which make the coolant in the coolant piping move. The heat receiving members are also called “cooling jackets”. 
     In the embodiment which is illustrated in  FIGS. 2A and 2B , the radiator  11  is provided at the downstream side of the fans  5  so that it is sufficiently cooled by the cooling air CA. Usually, it is provided in the direction vertical to the direction of flow of the cooling air CA. It is arranged so that all of the cooling air CA which is supplied by the fans  5  can be supplied to it. The length of the radiator  11  is shorter than the total length of the plurality of aligned fans  5 . The heat receiving members  12  are provided on the CPUs  3 . The coolant piping  13  which supplies coolant to the heat receiving members  12  from the radiator  11  is provided on the main board  6  so as not to enter the second regions A 2 . The radiator  11  has a plurality of channels. The coolant piping  13  is connected by the manifold  16  to the plurality of channels of the radiator  11 . Further, between the coolant piping  13  and the heat receiving member  12 , tanks  15  which temporarily store the coolant and pumps  15  which move the coolant are provided. The configuration of the pumps  14  will be explained in detail later, but pluralities are provided at the two sides of the tanks  15 . Note that, if the pumps  14  are large in capacity, the pumps  14  may also be provided at just single sides of the tanks  15 . 
     Due to this structure, the heat receiving members  12  has the pumps  14  and the tanks  15  arranged concentrated on them in adjoining manners, so the coolant piping  13  which connects these can be shortened and space can be saved. Further, the channel resistance when the coolant flows through the inside of coolant piping  13  depends on the length of the coolant piping  13 , so by making the coolant piping  13  shorter, the channel resistance of the coolant which flows through the inside of the liquid cooling system  10  can be made smaller. Further, by the amount of movement of the coolant becoming greater, heat is efficiently transferred from the heat receiving units  12  to the radiator  11 , so the liquid cooling system  10  can be improved in performance. 
     Furthermore, the components which require strong cooling are concentrated at the first region A 1  while avoiding the second regions, so the components of the liquid cooling system  10  can also be concentrated at the first region A 1 . As a result, the second regions A 2  can be secured wide without being made narrow. On top of this, the liquid cooling system  10  does not inhibit the flow of cooling air CA to the second regions A 2  and can sufficiently supply cooling air CA to the electronic components  4  which are mounted at the second regions A 2 . Due to these advantages, the performance of the liquid cooling system  10  is improved and it becomes possible to mount at the server a liquid cooling system  10  which cools heat generating components  3 A and  3 B which have  300 W or so high heat generating characteristics while not interfering with the cooling of electronic components  4  which use cooling air CA for cooling. 
       FIG. 3A  is an assembled perspective view which illustrates the state of mounting the liquid cooling system  10  on the main board  6  which is illustrated in  FIG. 2A , while  FIG. 3B  is a perspective view of the server module  1  which is illustrated in  FIG. 2B . As will be understood from these figures, the electronic components  4  include a large number of electronic components which are mounted on one or both surfaces of a sub board  4 A. The sub board  4 A is attached to a socket  4 B which is provided on the main board  6 . Further, a single tank  15  has six pumps  14  connected to it in parallel, so the flow rate of the coolant can be increased. 
     Here,  FIG. 9  will be used to explain the features of the layout of sub boards  4 A on which the electronic components  4  are mounted and the connection with the CPUs  3 A and  3 B. Here, the electronic components  4  are memories (DIMM). The DIMMs  4  are structured as sub boards  4 A on both or one side of which a plurality of DRAM devices are mounted. Below, the electronic components  4  will also be referred to as “memories  4 ” or “DIMMs  4 ”. Pluralities of the sub boards  4 A are arranged in parallel with the flow of the cooling air CA at the two sides of the CPUs  3 A and  3 B. For this reason, the physical wiring lengths between the DIMMs  4  and the CPUs  3 A and  3 B can be made the shortest. 
     Inside of the CPUs  3 A and  3 B, there are system controllers  3 S and memory access controllers  3 M. The memories  4  transfer data with the CPUs  3 A and  3 B through the memory access controllers  3 M and the system controllers  3 S. Data transfer between devices takes time corresponding to the length of wiring between the devices (physical distance). During that time, the data processing at the CPUs is stopped. In the present embodiment, as explained above, the physical length of wiring between the memories  4  and the CPUs  3 A and  3 B can be made the shortest, so the time until completion of transfer of data (memory latency) is small and the time required for data processing in the system as a whole can be shortened. 
     That is, in the present embodiment, the layout of the CPUs  3 A and  3 B and the memories  4  is given the greatest priority to in the design of the main board  6 . The liquid cooling system  10  is arranged in accordance with the layout of the components which require strong cooling  3  on the main board  6 . For this reason, in the present embodiment, the liquid cooling system  10  is arranged at a location offset from the center of the main board  6 , while the air cooling system has a left-right asymmetric area ratio. 
       FIG. 4  is an enlarged perspective view which illustrates the principal parts of structures of the coolant piping  13 , pumps  14 , and a tank  15  in the liquid cooling system  10  which is illustrated in  FIG. 3A . The coolant piping  13  is provided with a cold water pipe  13 C through which low temperature coolant which was cooled at the radiator flows and a warm water pipe (not illustrated) through which high temperature coolant which had absorbed the heat of the heat generating components and risen in temperature flows. The cold water pipe  13 C is connected to the tank  15 . The tank  15  is provided with six pumps  14 . The pumps  14  suck in coolant which was temporarily stored inside the tank  15  by the suction pipes  14 S and return it through the discharge pipes  14 D to the inside of the tank  15 . The six pumps  14  are attached to the tank  15  in diagonally slanted states so as to lower the heights from the heat receiving members  12 . The coolant which is returned from the six pumps  14  to the inside of the tank  15  merges, passes through the cold water pipe  13 C, and is supplied to the not illustrated heat receiving members. The structure of the heat receiving members will be explained later. At the inside of the pump  14 , while not illustrated, backflow of coolant at the time of pump breakdown is prevented. 
       FIG. 5A  is a vertical cross-sectional view which illustrates one example of the internal structure of a tank  15  which is illustrated in  FIG. 4 , while  FIG. 5B  is a cross-sectional view along the line B-B of  FIG. 5A . As will be understood from these figures, the tank  15  is divided internally into two chambers by a partition wall  15 W. One chamber is a storage chamber  15 S to which the coolant piping  13  which is connected to the radiator and the suction pipes  14 S of the pumps  14  are connected. The other chamber is a mixing chamber  15 M to which the cooling piping  13  which is connected to the heat receiving members and the discharge pipes  14 D of the pumps  14  are connected. The storage chamber  15 S receives and temporarily stores the coolant which flows in from the radiator. At this time, the air which is contained in the coolant builds up at the ceiling part of the storage chamber  15 S. The suction pipes  14 S of the pumps  14  are connected to parts close to the bottom surface of the storage chamber  15 S so as to suck out coolant, so air which has built up at the ceiling part of the storage chamber  15 S will never enter the pumps  14 . The mixing chamber  15 M receives and mixes coolant from the pumps  14  flowing in through the discharge pipe  14 D and discharges the mixture from the coolant piping  13 . The partition wall  15 W is not limited in shape to this embodiment. 
       FIG. 6A  is a perspective view which illustrates the configuration of one embodiment of the radiator  11  in the present application, while  FIG. 6B  is a front view of the radiator  11  which is illustrated in  FIG. 6A . The radiator  11  of this embodiment is provided with four radiating channels at the left side and four radiating channels at the right side centered about a manifold  16 . The channels are shaped from flat channels which are bent back in a U-shape. Between the facing channels, corrugated fins  11 F are provided for raising the radiating efficiency. 
     The channels are connected to the manifold  16 . The manifold  16  has a coolant inlet part  16 H and a coolant outlet part  16 C. The coolant inlet part  16 H is connected inside of the manifold  16  to first end parts of the four radiating channels at the left side of the manifold  16 , while the coolant outlet part  16 C is connected inside of the manifold  16  to first end parts of the four radiating channels at the right side of the manifold  16 . The other end parts of the left side and right side radiating channels which are not connected to the coolant inlet part  16 H and the coolant outlet part  16 C are connected inside of the manifold  16 . 
     The coolant (warm water) which flows to the coolant inlet part  16 H from not illustrated coolant piping flows into the four radiating channels at the left side of the manifold  16 , makes U-turns at the end parts, returns to the manifold  16 , then flows into the four radiating channels at the right side of the manifold  16 . The coolant which flows into the four radiating channels at the right side of the manifold  16  makes U-turns at the end parts to again return to the manifold  16 , is discharged from the coolant outlet part  16 C, and flows into not illustrated coolant piping. The coolant which flows in from the coolant inlet part  16 H is warm water, but the coolant which is discharged from the coolant outlet part  16 C is cooled by the radiating channels of the radiator  11 , so is cold water. 
       FIG. 7A  is an explanatory view which explains the flow of coolant in the liquid cooling system  10  which is illustrated in  FIG. 2A  and  FIG. 3A , while  FIG. 7B  is a circuit diagram which illustrates an embodiment of the configuration of the control circuit of the pump in the liquid cooling system  10  which is illustrated in  FIG. 7A . As explained above, the coolant is cooled by the radiator  11 , flows through the cold water pipe  13 H into the tank  15 , and is sent by the pumps  14  to the heat receiving member  12  to cool the heat generating components. The raised temperature coolant is then returned through the warm water pipe  13 H to the radiator  11 . 
     The pumps  14 , while not illustrated, have speed detection sensors attached to them. The operations of the pumps  14  are monitored by a control circuit (service processor)  20  to which the speed signals (pulse signals) are input. The control circuit  20  includes conversion circuits  21  which convert pulse signals to speed signals, threshold value judgment circuits  22  which compare the speeds of the pumps  14  against a threshold value, and a component judgment circuit  23  and system judgment circuit  24  which use the outputs from the threshold value judgment circuits  22  to judge if the pumps  14  are normal. 
     For example, when, among the six pumps  14 , just one pump  14  has broken down, the speed signal from that one pump  14  is not input to the control circuit  20 , but the control circuit  20  judges that with breakdown of just one pump, the cooling of the heat generating components by the liquid cooling system  10  is not hindered. Further, the component judgment circuit  23  outputs a notification of breakdown of one of the pumps  14 , but the system judgment circuit  24  outputs a command for continuation of operation (OK) of the liquid cooling system so the cooling of the heat generating components by the liquid cooling system  10  is continued. By giving redundancy to control of the pumps  14  in this way, even when a pump  14  breaks down, if the cooling ability can be secured, the liquid cooling system  10  does not stop and the CPUs can continue to be cooled, so the reliability can be secured. 
       FIG. 8  is a flow chart which illustrates one embodiment of a control routine of the control circuit  20  of the pumps  14  which is illustrated in  FIG. 7B . At step  801 , the operation of the liquid cooling system is started. At step  802 , the control circuit  20  reads the speeds x of the pumps. While the server module is operating, the speeds of the pumps are constantly monitored by the control circuit. Further, at step  803 , it is judged if the speeds x of the pumps have reached the threshold value (2050 rpm) or more. When the speeds x of all of the pumps have reached the threshold value or more (YES), the routine returns to step  802  where the speeds x of the pumps continue to be read. 
     On the other hand, if the judgment at step  803  is that there is a pump where the speed x has not exceeded the threshold value (NO), the routine proceeds to step  804  where breakdown of that pump is notified, then the routine proceeds to step  805 . At step  805 , it is judged if just one pump has broken down. If just one pump has broken down (YES), as explained above, it is judged that the cooling of the heat generating components by the liquid cooling system is not hindered and the routine returns to step  802  where the speeds x of the pumps continue to be read. In this regard, when it is judged at step  805  that several pumps have broken down (NO), it is judged that the cooling of the heat generating components by the liquid cooling system is hindered and the routine proceeds to step  806  where the operation of the cooling system is stopped and this routine is ended. 
       FIG. 10  is a disassembled perspective view which illustrates in detail the configuration of members under the pumps  15  and the tanks  15  in the liquid cooling system  10  according to the present application. Under the pumps  14  and the tanks  15 , there are pump support mechanisms  50  and heat receiving members  12 . The heat receiving members  12  are fastened by heat receiving member fastening parts  17  to the top of a not illustrated main board. At the inside of the heat receiving member fastening parts  17 , female threads are formed. These engage with male screws  19  which are illustrated in  FIG. 12 . The pump support mechanisms  50  are provided with pump placers  51 , base plates  52 , mounts  54 , and brackets (pump mounting fittings)  55 . Further, each heat receiving member  12  is provided with a metal plate  40 , CPU-use metal plate  60 , and cold plate  90 . 
     The metal plate  40  has a step part  41 , a CPU power source-use metal plate part  42 , a CPU-use metal plate part  43 , a hole  44  for avoiding interference with the mounted components, a recessed part  45 , and holes  46  for insertion of the heat receiving member fastening parts  17 . The CPU-use metal plate  60  has a base plate  61  and mounting holes  62  for insertion of the heat receiving member fastening parts  17 . The cold plate  90  has a cold water inlet  91 , coolant channel  92 , CPU-use cold plate  93 , U-turn channel  94 , and CPU power source-use cold plate  95 . The members which form the metal plate  40 , CPU-use metal plate  60 , and the cold plate  90  will be explained in detail later using enlarged drawings. 
     Here, the air barrier wall and the leakage tray which are provided at the server module of the present application will be explained.  FIG. 11A  is a comparative view which compares the flow of cooling air CA which flows through the inside of the server module  1  which is provided with the air cooling system and the flow of cooling air CA in the case of setting an air barrier wall  7  at the center part of the inside of the server module  1 . When the server module  1  does not have the air barrier wall  7  inside it, the cooling air CA which is generated by the fans mainly flows over the main board  6  at which the low height heat generating components  3  (CPUs  3 A and  3 B) are mounted since the parts where the electronic components  4  are concentrated have channel resistance. 
     Channel resistance is generated due to the narrow interval between components on the main board  6  due to high density mounting and the high height of the components which are mounted at such regions. That is, the electronic components  4  are DIMMs, power modules, and other components which are formed by circuits on sub boards which are mounted vertically on the main board  6 , so are high in height. Therefore, the channels of the cooling air CA end up being blocked by the DIMMs, power modules, etc., so channel resistance occurs. As opposed to this, the CPUs  3 A and  3 B are directly mounted on the main board  6 , so are lower in height compared with DIMMs, power modules, etc. DIMMs have a height from the board  6  of, for example, 33 mm. Further, the leakage tray  8  has a height from the board  6  of, for example, 26.5 mm. The lower limit value of the height of the leakage tray  8  for preventing leakage is about half of that or 13 mm, while the upper limit value of the height of the leakage tray  8  for preventing contact with the ceiling of the housing is 35 mm. If in this range of height, there will be no leakage and higher efficiency of cooling of the DIMMs and power source can be expected. 
     Even if the main board  6  on which low height heat generating components  3  are mounted is provided which an above-mentioned such liquid cooling system  10  as illustrated by the broken lines, the cooling air CA flows to around the liquid cooling system, so the cooling ability of the electronic components  4  by the cooling air CA falls. That is, in the region inside the broken lines, only components which require strong cooling which are covered by liquid cooling and components which require weak cooling which have a low heat generating characteristic (including no heat generation) of an extent not requiring air cooling are mounted. Despite the fact that the supply of cooling air is not required, the cooling air flows into this region. Therefore, the cooling air which is supplied to the electronic components  4  which relatively require the supply of cooling air is reduced, so the cooling performance of the electronic components  4  falls. 
     Therefore, to prevent the cooling air CA from flowing to around the heat generating components  3 , the area around the liquid cooling system  10  which is mounted over the heat generating components  3  is covered by an air barrier wall  7 . Therefore, the cooling air CA is prevented from flowing to the components which require strong cooling  3 . As a result, the inflow of cooling air to the region which does not require the supply of cooling air can be prevented and all of the cooling air can be supplied to the components which require weak cooling  4  where the cooling air is required, so the cooling ability of the electronic components  4  by the cooling air CA is improved. 
     Furthermore, as illustrated in  FIG. 11B , if forming a ceiling part  70  above the air barrier wall  7  which is provided around the heat generating components  3  and the liquid cooling system  10  which are mounted on the main board  6  and covering the heat generating components  3  and the liquid cooling system  10  as a whole by these, the cooling ability of the electronic components  4  by the cooling air CA is improved much more. Further, when providing the air barrier wall  7  around the heat generating component  3  and the liquid cooling system  10 , as illustrated in  FIG. 11C , if providing a curved part at the upstream side of the air barrier wall  7  or, as illustrated in  FIG. 11D , if providing a tapered part at the upstream side of the air barrier wall  7 , the cooling air CA more easily flows to the electronic component sides. 
     In this regard, in the liquid cooling system  10  which has been explained up to here, the coolant for performing the cooling is a liquid (for example, water), so there is a possibility of coolant leaking from the coolant piping  13  or connecting parts of the coolant piping  13  and the heat receiving members  12 , pumps  14 , or tanks  15 . Further, if coolant leaks from the liquid cooling system  10 , the leaked coolant is liable to overflow on to the main board  6  whereby the electronic components  4  are liable to be flooded and the circuits to short. Therefore, it is considered to place a leakage tray which prevents leakage of leaked coolant to other locations below the heat receiving members, pumps  14 , and tanks  15  of the liquid cooling system  10 . 
       FIG. 12  is an assembled perspective view which illustrates the state of insertion of the leakage tray  8  between the main board  6  which is illustrated in  FIG. 3A  and the liquid cooling system  10  which is mounted on the main board  6 , while  FIG. 13A  is a perspective view which illustrates the state of mounting the leakage tray  8  and the liquid cooling system  10  on the main board  6 . On the main board  6 , assume that the CPUs  3 A and  3 B, sockets  4 B for attaching sub boards, and power circuits  30 A and  30 B for CPU use are mounted. Further, the liquid cooling system  10 , as explained above, includes a radiator  11 , heat receiving members  12 , coolant piping  13 , pumps  14 , tanks  15 , and the manifold  16 . 
     The leakage tray  8  is provided with a base plate  80 , CPU contact-use holes  8 A and  8 B, power circuit contact-use holes  8 HA and  8 HB, and the air barrier wall  7  which sticks out from the periphery of the base plate  80 . The CPU contact-use holes  8 A and  8 B are holes for insertion of the CPUs  3 A and  3 B on the main board  6 , while the power circuit contact-use holes  8 HA and  8 HB are holes for insertion of CPU-use power circuits  30 A and  30 B. Further, the base plate  80  between the CPU contact-use holes  8 A and  8 B is provided with a sleeve  8 S. The sleeve  8 S will be explained later. 
     The air barrier wall  7  is formed by extending and bending upward the outer edge part of the base plate  80  of the leakage tray  8 . This is because the outer edge part of the base plate  80  of the leakage tray  8  requires a bent part for keeping leakage from the liquid cooling system  10  inside the leakage tray  8 , so this bent part is extended upward to increase the wall height and serve also as an air barrier wall  7 . If attaching the leakage tray  8  on the main board  6  and attaching the liquid cooling system  10  over that, as illustrated in  FIG. 13A , the air barrier wall  7  sticks out around the pumps  14  and the tanks  15  and therefore the cooling air no longer enters the region where the pumps  14  and the tanks  15  are provided. 
       FIG. 13B  is a cross-sectional view of the liquid cooling system  10  which is illustrated in  FIG. 13A  in the direction vertical to the flow of the cooling air. The heat receiving member fastening parts  17  are screw components with springs  17 B wound around their top parts. They are inserted from the metal plate  40  side through the metal plates  40 , CPU-use metal plates  60 , leakage tray  8 , and main board  6  and screwed into the fastening plate  18  which is attached to the rear side of the main board  6 . The springs  17 B are inserted between the heads  17 H of the heat receiving member fastening parts  17  and the metal plates  40  and bias the metal plates  40  to the main board  6  side. From this figure, it will be understood that the air barrier wall  7  holds inside it all of the components in the range from the cold water pipe  13 C and warm water pipe  13 H to the coolant channel  92  of the cold plate and that the cooling air will not enter inside the liquid cooling system  10 . 
     On the other hand,  FIG. 14A  is a partial cross-sectional view of the liquid cooling system  10  which is illustrated in  FIG. 13A  in the direction along the flow of the cooling air.  FIG. 14A  illustrates only the part of the CPU  3 A. The cross-section of the CPU  3 B side is omitted. From this figure as well, it will be understood that the heat receiving member fastening parts  17  are screwed by the male screws  19  with the fastening plate  18  at the rear side of the main board  6  and that the springs  17 B bias the metal plate  40  from the head  17 H side to the main board  6  side. 
     Here, the engaged state of the metal plate  40 , CPU-use metal plate  60 , and the cold plate  90  which are illustrated in  FIG. 10  and the main board  6  and leakage tray  8  which are illustrated in  FIG. 12  will be explained using  FIG. 14A . The main board  6  mounts as the CPU-use power circuit  30 A a first component  30 A 1  and a second component  30 A 2  and a CPU  3 A. In the state of the main board  6  having the leakage tray  8  attached, the CPU-use power circuit  30 A enters the power contact-use hole  8 HA of the leakage tray  8 , while the CPU  3 A enters the CPU contact-use hole  8 A of the leakage tray  8 . At the surface of the base  80  of the leakage tray  8  on the main board  6  side, the CPU contact-use holes  8 A and  8 B may be surrounded by packing. The packing is adhered around the CPUs  3 A and  3 B whereby the water-stemming effect is enhanced. 
     The cold plate  90  which is illustrated in  FIG. 10  includes the CPU-use cold plate  93  and the CPU power source-use cold plate  95 . The CPU-use cold plate  93  has two channels. The end of one channel is connected to the cold water inlet  91 , while the other end is connected to the U-turn channel  94 . The other channel has one end connected to the U-turn channel  94 , while has the other end connected to the coolant channel  92 . The coolant channel  92  is divided inside it into two channels. The coolant channel  92  with the cold water inlet  91  and the coolant channel  92  through which coolant which has passed the U-turn channel  94  returns are not communicated. Therefore, the entire amount of the coolant which has passed through the U-turn channel  94  and returned to the coolant channel  92  flows into the CPU power source-use cold plate  95  and flows into the warm water pipe  13 H of the coolant piping  13 . The flow of the coolant is illustrated by the arrow marks in  FIG. 10 . 
     If the liquid cooling system  10  is attached over the leakage tray  8 , the CPU-use cold plate  93  of the cold plate  90  which forms the heat receiving member  12  is positioned right above the CPU  3 A, while the CPU power source-use cold plate  95  is positioned right above the CPU-use power circuit  30 A. At this time, the CPU  3 A is laid over the CPU-use cold plate  93  through a heat conducting sheet  31 , but the first component  30 A 1  of the CPU-use power circuit  30 A is low in height, so is not laid over the CPU power source-use cold plate  95 . Therefore, the first component  30 A 1  of the CPU-use power circuit  30 A has provided on it a metal rod  32  for contact with the CPU power source-use cold plate  95  through the heat conducting sheet  31 . 
     The CPU metal plate  60  is provided with mounting holes  62  at the four corners of the base plate  61 . The heat receiving member fastening parts  17  which are inserted through the mounting holes  62  are used to lay the base plate  61  over the CPU-use cold plate  93 . 
     The metal plate  40  is provided with a CPU-use metal plate part  43 . This CPU-use metal plate part  43  is provided with holes  46  which overlap the mounting holes  62  which are formed at the four corners of the base plate  61 . One end part of the metal plate  40  has a step part  41 . This step part  41  is provided with springiness. Further, the CPU power source-use metal plate part  42  which follows the step part  41  is much lower than the CPU-use metal plate part  43  and is formed to approach the main board  6  at the time of mounting. In the state where the metal plate  40  is attached by the heat receiving member fastening parts  17 , the CPU-use metal plate part  43  is laid over the base plate  61  of the CPU metal plate  60  and the CPU power source-use metal plate part  42  is laid over the CPU power source-use cold plate  95 . Further, in the state where the CPU-use metal plate part  43  of the metal plate  40  is laid over the base plate  61  of the CPU metal plate  60 , the height of the bottom surface of the CPU power source-use metal plate part  42  from the main board  6  is lower than the height of the top surface of the CPU power source-use cold plate  95  from the main board  6 . For this reason, in the state where the metal plate  40  is attached by the heat receiving member fastening parts  17  and the CPU power source-use metal plate part  42  is laid over the CPU power source-use cold plate  95 , the springiness of the step part  41  causes the CPU power source-use cold plate  95  to be biased by the CPU power source-use metal plate part  42 . 
     Due to the above such configuration, the heat which is generated by the CPUs  3 A and  3 B and components in the CPU-use power source component  30 A which are arranged in the first region A 1  of the main board  6  is absorbed by the CPU-use cold plate  93  and the CPU power source-use cold plate  95 . 
     Note that, if making the bottom plate of the leakage tray  8  for preventing leakage from the liquid cooling system  10 , as illustrated in  FIG. 14B  and  FIG. 14C , a double layer structure, it becomes harder for the coolant which has leaked from the liquid cooling system  10  to escape.  FIG. 14B  illustrates an embodiment wherein a drain  83  is provided at a double layer bottom  84 .  FIG. 14C  illustrates the configuration of an embodiment which is provided with two slanted bottom plates  85 ,  86 . Further, it is possible to not make the leakage tray  8  a double layer bottom but, as in another embodiment which is illustrated in  FIG. 14D , insert a water absorbing sheet  87  at the bottom plate of the leakage tray  8  so as to make it difficult for the coolant which has leaked from the liquid cooling system  10  to escape. 
       FIG. 15A  is a partially enlarged perspective view which illustrates the mounting state of the six pumps  14  which are arranged at the two sides of a tank  15  of the liquid cooling system  10 . As explained above, the tank  15  has six pumps  14  connected to it. The tank  15  is supplied with coolant from the cold water pipe  13 C of the coolant piping  13 . Between the pumps  14  and the tank  15 , suction pipes  14 S and discharge pipes  14 D are connected. The coolant inside the tank  15  is sucked out by the pumps  14 , pressurized, and returned to the tank  15 . The coolant which is pressurized by the pump  14  runs from the end of the tank  15  at the opposite side to the feed side through the cold water pipe  13 C and is supplied to the heat receiving members  12 . The structure of the heat receiving members  12  has already been explained, so the same component members will be assigned the same reference signs and explanations omitted. The heat absorbing coolant is returned from the CPU power source-use cold plate  95  of the heat receiving members  12  to the warm water pipe  13 H. 
       FIG. 15B  is a partially enlarged perspective view which removes the six pumps  14  from the structure which was illustrated in  FIG. 15A  so as to explain the structure of the pump support mechanism  50 . A tank  15  is fastened to the base plate  52  of the pump support mechanism by screws  53  at the mounting tabs  15 A which are provided at the coolant piping  13  side. Further, the base plate  52  has mounts  54  which are present at the two end parts of brackets  55  which are provided with three pump placers  51  fastened to it by screws  53 . To place the pumps  14  at a slant from the tank  15 , the pump placers  51  are made V-grooves. At the side surfaces of the tank  15 , discharge ports  15 T for discharging coolant to the pumps  14  and suction ports  15 K for the inflow of coolant from the pumps are provided. The brackets  50  are, for example, comprised of SUS (stainless steel sheet). Further, the pump placers  51  are provided with buffer plates between the brackets  55  and the pumps  14 . These buffer plates enable any offset which occurs due to deformation of the heat receiving members  12  and the tank  15  or dimensional tolerance at the time of manufacture to be absorbed. 
       FIG. 16  is a plan view which illustrates a second embodiment of the server module  1  in which an air cooling system and the liquid cooling system  10  of the present application are mounted. The server module  1  of the second embodiment differs from the above-mentioned embodiment in the point that at the rear surface side of the server module  1 , a connection unit (hereinafter referred to as an “XB unit”)  71  is provided which connects the main boards  6  at the server module  1  which are stacked in the vertical direction. The XB unit  71  is provided at the second region A 2  at one side of the first region A 1  which is provided with the liquid cooling system  10  and at the downstream side in the flow of the cooling air. The configuration of the liquid cooling system  10  at the first region A 1  and the configurations of the second regions A 2  which are arranged at the two sides of the first region A 1  are similar to the already explained embodiments, so the same component members will be assigned the same reference signs and their explanations will be omitted. 
     Like in the second embodiment of the server module  1 , when the server module  1  is provided with the XB unit  71 , at the inside of the XB unit  71 , as illustrated in  FIG. 17 , there is an XB chip  73  which generates a large amount of heat at the time of operation. Further, this XB chip  73  is a weak cooling component which requires cooling by cooling air. For this reason, in the second embodiment of the server module  1 , the first region A 1  and the two second regions A 2  are shifted to one side with respect to the housing of the server module  1 . Cooling air CA is sent through the part opened by the shift to the XB unit  71 . 
       FIG. 18  is an assembled perspective view which illustrates a third embodiment of the server module  1  of the present application which provides the server module  1  of the second embodiment which was explained in  FIG. 16 ,  FIG. 17  with the liquid cooling system  10  and which attaches two main boards  6 . Here, the main board  6  which is provided with the first and the second regions A 1 , A 2 , which mounts on those regions the already explained heat generating components or electronic components, and is provided with the liquid cooling system  10  will be called a “system unit”. This being the case, in the server module  1  of the third embodiment, the first system unit U 1  is first attached on the housing, then the second system unit U 2  is attached laid over the top side of the first system unit U 1 . The positions of the electronic components at the main board  6  of the first system unit U 1  and the positions of the electronic component at the main board  6  of the second system unit U 2  are exactly the same. 
     In this case, the bottom surface of the main board  6  of the second system unit U 2  has a connector  70  which is illustrated in  FIG. 19  attached to it. The connector  70  is for connecting a circuit at the second system unit U 2  to the circuit at the first system unit U 1  when the second system unit U 2  is attached laid over the top side of first system unit U 2 . If the first system unit U 1  and the second system unit U 2  are electrically connected through the connector  70 , the CPUs  3 A,  3 B which are at one main board  6  can use the data of the DIMMs  4  at the other main board  6 . 
     The position of the connector  70  which is provided at the bottom surface of the second system unit U 2  is the same as the position of the sleeve  8 S at the leakage tray  9  which is attached to the main board  6  of the first system unit U 1 . In this case, the main board  6  of the first system unit U 1  mounts a connector (pair connector) which mates with the connector  70  which is provided at the bottom surface of the main board  6  of the second system unit U 2  inside the sleeve  8 S of the leakage tray  8 . Therefore, if the second system unit U 2  is attached laid over the top side of the first system unit U 1 , the connector  70  which is at the second system unit U 2  is inserted into the sleeve  8 S at the first system unit U 1  and connected to the pair connector. 
       FIG. 20  is a perspective view of principal parts of the server module  1  which illustrates the state with the first and the second system units U 1 , U 2  which are illustrated in  FIG. 18  stacked together. Illustration of the fans will be omitted. As will be understood from this figure, even in the state with the second system unit U 2  attached over the top side of the first system unit U 1 , a path for cooling air to the XB unit  71  is secured. Note that, as illustrated in  FIG. 18 , the size of the fans  5  is a size which enables sufficient cooling air to be sent to radiators  11  which are stacked in two levels. 
     In this way, according to the present application, it is possible to provide a liquid cooling system which has the ability to radiate off a high amount of generated heat, which can be mounted at a high density at a predetermined device while saving space, and, furthermore, which enables a mountable area of components other than those for cooling to be broadly secured. Further, it is possible to provide a liquid cooling system which has pumps for transport of coolant redundantly configured and redundantly controlled and thereby secures a high reliability and does not obstruct cooling of other components besides the ones being cooled and to provide an electronic apparatus which mounts the same. 
     The liquid cooling system of the present application enables cooling of two 300 W CPUs by a pump flow rate of 0.9 liter/min in the case of a radiator of a size of a height of 36 mm, a depth of 59 mm, and a width of 350 mm. Further, the path of the cooling air which cools the DIMMs only has a radiator in it, so the cooling air efficiently hits the DIMMs and therefore 256 W of DIMMs (32 8W DIMMs) becomes possible. Further, if assuming notification of abnormalities in the pumps and replacements being installed in a short time from the occurrence of the abnormalities, the possibility of two pumps simultaneously breaking down is eliminated and the possibility of system trouble occurring in the liquid cooling system can be eliminated. 
     Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciated that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.