Patent Publication Number: US-2012026693-A1

Title: Cooling Apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     The application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-169639 filed on Jul. 28, 2010; the entire content of which are incorporated herein by reference. 
     FIELD 
     The present invention relates to a cooling apparatus for cooling semiconductor modules. 
     BACKGROUND 
     A high-speed (serial) channel is used as means for improving communication speed between devices. For example, a channel having eight-bit links with a data transmission rate of 5 Gbps at both TX and RX is used. 
     In the high-speed channel, a temperature fluctuation range is stipulated as a condition for guaranteeing the AC characteristics between TX and RX. However, if the stipulated range is lower than an operation temperature range of a device in a trade-off with its performance, it is necessary to control the temperature of the device. 
     When temperature control for a micro processing unit (MPU) and a south bridge chip (SBC) is taken as an example, since the MPU has a high operation frequency, a large die area and a large self-leakage current, its power consumption is high at the time of power-on operation and in its standby state due to clock mesh activity. Hence, the temperature of the die of the MPU can be raised by self power consumption before calibration is carried out. On the other hand, since the SBC has a low operation frequency, a small die area and a small self-leakage current, the temperature of the die of the SBC is not raised sufficiently at the time when calibration is carried out. 
     Furthermore, the high-speed channel has a characteristic in which eye pattern drifts occur due to temperature change. If the temperature fluctuations at both ends of the channel are shifted in the opposite directions, the drifts of the two devices are eventually synergized. 
     Wiring crosstalk and operation voltage are taken as parameters, other than temperature, significantly affecting an operation margin of the high-speed channel. However, if the temperature environment is not optimized, it is necessary to take countermeasures in which wiring space is made wider to reduce crosstalk (cost increases due to increase in the area of a circuit board), a power supply circuit and components being high in grade are used to stabilize the operation voltage, and the power supply lines on the circuit board are made thicker (the area of the circuit board is made larger, and Decoupling-C and the number of components increases, whereby the cost of hardware increases). 
     Accordingly, the channel circuit provided in a semiconductor module is ingeniously contrived to perform communication normally even if the temperature of the semiconductor module fluctuates. 
     Furthermore, there are demands for reducing the temperature fluctuation range in the high-speed channel and for guiding the temperature fluctuations at both ends of the high-speed channel in the same direction. However, means for satisfying these demands are not yet known. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an example of a system configuration of an information-processing apparatus according to the embodiment. 
         FIG. 2  is a flowchart showing an initialization processing flow according to the embodiment. 
         FIG. 3  is a view showing a configuration example of a cooling apparatus according to the embodiment. 
         FIG. 4  is a diagram of a thermal radiation equivalent circuit using concentrated constants according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one exemplary embodiment, a cooling apparatus includes: a cooling fin which cools heat-generating components by radiating heat of the heat-generating components; a first semiconductor module which serves as one of the heat-generating components; a second semiconductor module which serves as another one of the heat-generating components; a first heat sink which cools the first semiconductor module; a second heat sink which cools the second semiconductor module; a first heat pipe which thermally couples the cooling fin to the first heat sink; and a second heat pipe which thermally couples the first heat sink to the second heat sink. A functional upper limit of a junction temperature of the first semiconductor module is lower than a functional upper limit of a junction temperature of the second semiconductor module, and a heat generation of the first semiconductor module is larger than a heat generation of the second semiconductor module. 
     An embodiment according to the present invention will be described below referring to  FIGS. 1 to 4 . 
       FIG. 1  is a block diagram showing an example of a system configuration of an information processing apparatus according to the embodiment. 
     As shown in  FIG. 1 , the information processing apparatus is equipped with a processor module  100  serving as a first semiconductor module, a bridge controller  110  serving as a second semiconductor module, a system controller  120 , a temperature controller  130 , a cooling fan  140 , a power supply controller  150 , a main memory  160 , etc. 
     The processor module  100  includes a processor circuit  101 , a first high-speed channel circuit  102  serving as a first high-speed channel circuit, a first initialization circuit  103 , and a linear temperature sensor  104 . The operation guarantee temperature of the processor module  100  is in the range of 5 to 85° C. Furthermore, the temperature range in which the high-speed channel circuit operates is 5 to 85° C. However, a temperature fluctuation range in which the AC characteristics of the I/O section of the first high-speed channel circuit  102  are guaranteed is ΔT_c=55° C. 
     The processor circuit  101  is a processor provided to control the operation of the information processing apparatus and executes an OS, application programs, etc. loaded into the main memory  160  from an external storage unit. 
     The first high-speed channel circuit  102  is a circuit for communicating with the second high-speed channel circuit  111  of the bridge controller  110 . The first initialization circuit  103  is a circuit for executing the initialization (calibration) of the first high-speed channel circuit  102 . 
     The linear temperature sensor  104  is a sensor for monitoring the average temperature of a die at high accuracy (approximately ±1 to 2° C.). The linear temperature sensor  104  is formed of a single analog (diode) cell, and the average temperature of a silicon die of the processor module  100  is read using the temperature controller  130  provided externally. 
     The bridge controller  110  connected to the processor module  100  includes a video output circuit for outputting video data calculated by the processor module  100  to a display device, audio input/output circuits, digital video input/output interfaces, a network controller, an ATA controller, etc. (these are not shown). 
     Furthermore, the bridge controller  110  includes the second high-speed channel circuit  111  serving as a second high-speed channel circuit for communicating with the high-speed channel circuit  102  of the processor module  100  and a second initialization circuit  112  for initializing the second high-speed channel circuit  111 . Eight-bit parallel communication is performed between the first high-speed channel circuit  102  and the second high-speed channel circuit  111  at a communication speed of 5 Gbps. 
     The system controller  120  includes an initialization controller  121 , a temperature controller control module (temperature ctl control module)  122 , a power supply controller control module (power supply ctl control module)  123 , and a temperature acquisition module  124 . The system controller  120  has a function of monitoring the starting and abnormality for the processor module  100  and the bridge controller  110 . 
     The initialization controller  121  has a function of performing initialization of the entire system. The temperature ctl control module  122  sets and controls with respect to the temperature controller  130 . Furthermore, the power supply ctl control module  123  sets and controls with respect to the power supply controller  150 . The temperature acquisition module  124  has a function of acquiring temperature read from the linear temperature sensor  104  using the temperature detection circuit  133  of the temperature controller  130 . 
     First, the initialization of the channel circuits  102  and  111  will be described below. A data signal is transmitted from the second high-speed channel circuit  111  to the first high-speed channel circuit  102 . The first high-speed channel circuit  102  sweeps sample points for receiving the data signal transmitted from the second high-speed channel circuit  111 . When the sample points are swept, there occur two cases: one case wherein the data signal can be received, and the other case wherein the data signal cannot be received. Furthermore, the first high-speed channel circuit  102  is set so that data can be received optimally from the sample points at which the data signal was able to be received. For example, the first high-speed channel circuit  102  is set depending on the center sample point of the sample points at which the data signal was able to be received. After the setting of the first high-speed channel circuit  102  is completed, the setting of the second high-speed channel circuit  111  is performed. 
     The temperature controller  130  includes a control circuit  131 , the temperature detection circuit  133  and a fan control circuit  132 . The temperature detection circuit  133 , reads the die temperature of the processor module  100  measured using the linear temperature sensor  104 . In addition, the fan control circuit  132  controls a rotational speed of the cooling fan  140  for cooling the processor module  100 . The control circuit  131  controls the fan control circuit  132  so that the die temperature is maintained in the temperature range specified by the temperature ctl control module  122  depending on the temperature read using the temperature detection circuit  133 . 
     The operation guarantee temperature range of the processor module  100  is ΔT — 1=80° C., and the temperature fluctuation range in which the AC characteristics of the I/O section of the first high-speed channel circuit  102  are guaranteed is ΔT_c=55° C. Hence, the temperature fluctuation range of the first high-speed channel circuit  102  is narrower than the operation guarantee temperature range of the processor circuit  101 . Because of this difference in the temperature ranges, if the temperature of the processor module  100  becomes higher than the temperature of the first high-speed channel circuit  102  at the time of the initialization thereof, the first high-speed channel circuit  102  cannot perform communication normally. 
       FIG. 2  shows an initialization processing flow for normally performing communication in the first high-speed channel circuit  102  even if the temperature of the processor module  100  rises. In this flow, the system controller  120  controls the initialization controller  121 , the temperature ctl control module  122 , the power supply ctl control module  123  and the temperature acquisition module  124  in the order described below. This flow is an example in which the initialization processing flow is completed. 
     First, when the user performs power-on operation, the initialization controller of the system controller  120  starts initialization. The temperature ctl control module  122  first sets the temperature controller  130  to a state for initialization processing (at step S 11 ). By the setting of the temperature controller  130  to the state for initialization processing, the temperature controller  130  sets the cooling fan  140  to a stopping state. Since the cooling fan  140  is not rotated, the processor module  100  is not cooled and the temperature of the processor module  100  can be raised. 
     Furthermore, the power supply ctl control module  123  sets the power supply controller  150  to a state for initialization processing and enables the output of drive power (at step S 12 ). By the setting of the power supply controller to the state for initialization processing and by the enabling of the output of the drive power, the power supply controller  150  starts to supply the drive power to the processor module  100 . At the setting of the state for initialization processing, the voltage value of the drive power may be the maximum voltage value in the operation voltage range of the processor module  100 . The self-heating of the processor module  100  becomes maximum by applying the maximum voltage value to the processor module  100 . 
     Next, the initialization controller  121  executes processing up to the processing precedent to the initialization processing of the high-speed channel circuits  102  and  111  (at step S 13 ). The processing up to the processing precedent to the initialization processing means the processing to be executed after the activation of the processor module  100  and the bridge controller  110  themselves, that is, preparation for the initialization (calibration) processing of the high-speed channels, such as the setting of the sweeping range and the stepping width for the calibration. 
     Furthermore, the temperature acquisition section  124  acquires the temperature of the processor module  100  measured using the linear temperature sensor  104  and read using the temperature controller  130  from the temperature controller  130  (at step S 14 ). 
     Moreover, the initialization controller  121  determines whether the temperature acquired using the temperature acquisition section  124  has become equal to or higher than a preset temperature (at step S 15 ). It is desirable that the preset temperature should be, for example, the difference between the upper limit of the operation guarantee temperature of the processor module  100  and the temperature fluctuation range in which the AC characteristics of the first high-speed channel circuit  102  are guaranteed. In the case of the embodiment, since the upper limit of the operation guarantee temperature is 85° C. and the temperature fluctuation range in which the AC characteristics are guaranteed is 55° C., the preset temperature is 30° C. 
     The initialization controller  121  periodically acquires the temperature of the processor module  100  and executes the determination of step S 15  until the temperature becomes equal to or higher than the preset temperature. When the temperature has become equal to or higher than the preset temperature (YES at step S 15 ), the initialization controller  121  issues an initialization instruction for executing the initialization processing of the first high-speed channel circuit  102  and the second high-speed channel circuit  111  described above to the processor module  100  and the bridge controller  110 , respectively (at step S 16 ). 
     The first initialization circuit  103  of the processor module  100  and the second initialization circuit  112  of the bridge controller  110  execute the above-mentioned initialization processing (the initialization (calibration) processing of the high-speed channels in the initialization processing of the processor module  100  and the bridge controller  110 ) (at step S 17 ). 
     After the initialization is completed, the temperature ctl control module  122  resets the setting of the temperature controller  130  to a state for normal system operation according to the instruction from the initialization controller  121 . The cooling fan  140  can be rotated by the resetting, and the temperature controller  130  controls the rotation of the cooling fan  140  so that the temperature of the processor module  100  becomes equal to or lower than the upper limit of its operation temperature. 
     After the initialization is completed, the power supply ctl control module  123  resets the power supply controller  150  to the state for the normal system operation according to the instruction from the initialization controller  121  (at step S 19 ). 
     Next, the initialization controller  121  executes the initialization processing subsequent to the initialization processing of the high-speed channel circuits (at step S 20 ). When the initialization processing is completed, an OS and application programs are loaded into the main memory  160  from the external storage unit, and the OS and the application programs are executed by the processor circuit  101 . 
     According to the embodiment, since the initialization processing of the first high-speed channel circuit  102  is executed after the temperature of the processor module  100  has become 30° C., the communication between the processor module  100  and the bridge controller  110  can be performed normally even if the temperature of the processor module  100  has become the upper limit of the operation guarantee temperature. A case in which the initialization processing of the first high-speed channel circuit  102  is executed when the temperature of the processor module  100  is 20° C. is herein taken as an example. In this case, since the temperature fluctuation range in which the AC characteristics of the first high-speed channel circuit  102  are guaranteed is 55° C., the upper limit of the temperature at which the first high-speed channel circuit  102  can perform communication normally is 75° C. 
     Hence, if the temperature of the processor module  100  has become the upper limit (85° C.) of the operation guarantee temperature, the first high-speed channel circuit  102  cannot perform communication normally. However, when the initialization processing of the first high-speed channel circuit is performed after the temperature of the processor module  100  has become 30° C., the upper limit of the temperature at which the first high-speed channel circuit  102  can perform communication normally becomes 85° C. Hence, the first high-speed channel circuit  102  can perform communication normally even if the temperature of the processor module  100  becomes the upper limit (85° C.) of the operation guarantee temperature. 
     In the case of the embodiment, since the initialization processing of the first high-speed channel circuit  102  is executed after the temperature of the processor module  100  has become 30° C., the starting time of the system may become long. In the case that the starting time is the first priority, it is desirable that power should be supplied to the processor module  100  at all times. Furthermore, a heater may be mounted on the processor module  100  so that the processor module  100  is heated using the heater. Moreover, the temperature rising may be accelerated by causing the processor circuit  101  to execute a program capable of executing processing only within the processor circuit  101  at the time of the power-on operation by the user. 
     In the case that power is supplied to the processor module  100  at all times or the processor module  100  is heated using the heater, a disadvantage of increasing the standby power of the system occurs in compensation for the advantage of being capable of shortening the period between the power-on operation by the user and the start of the execution of software. Accordingly, in a system wherein a period in which the high-speed channels cannot be used temporarily is allowed to exist after the execution of the software, for the purpose of shortening the apparent starting time of the system, the processor module  100  is started once while the temperature of the system is maintained at its initial temperature. When the temperature of the silicon of the processor module has exceeded 30° C. after the start of the execution of the software, the initialization processing of the high-speed channels is executed again. As a result, the wait time for the rising of the temperature of the silicon can be suppressed, and the increase in the standby power can be eliminated. 
     An example in which the setting temperature for the cooling operation performed conventionally is 30° C. is described above. However, it is possible to perform operation so that the temperature fluctuation amount across both ends of a channel is restrained further positively by changing the setting temperature to 5° C. as described below. 
       FIG. 3  is a view illustrating a configuration example of the cooling apparatus according to the embodiment. 
     An MPU (processor module  100 ) is a first object to be cooled and serves as one end of a high-speed channel. An SBC (bridge controller  110 ) is a second object to be cooled and serves as the other end of the high-speed channel. In addition, a cooling fin is a fin (for example, a cooling fin equipped with the cooling fan  140 ) for cooling both the MPU and SBC. 
     Heat pipes  1  are first heat pipes for thermally coupling the cooling fin to a heat sink base  1   a  (a heat sink base for the MPU), and the heat sink base  1   a  is a first heat sink base for cooling a package  1   b  of the MPU. In addition, the package  1   b  is a first package serving as the lid (a heat radiating surface) of the MPU, and a die  1   c  is a first die serving as the silicon of the MPU. 
     In the case that the MPU is package-less or lid-less, the package  1   b  does not exist, and the heat sink base  1   a  directly cools the die  1   c.    
     A heat pipe  2  is a second heat pipe for thermally coupling the heat sink base la to a heat sink base  2   a  (a heat sink base for the SBC), and the heat sink base  2   a  is a second heat sink base for cooling a package  2   b  of the SBC. In addition, the package  2   b  is a second package serving as the lid (a heat radiating surface) of the SBC, and a die  2   c  is a second die serving as the silicon of the SBC. 
     In the case that the SBC is package-less or lid-less, the package  2   b  does not exist, and the heat sink base  2   a  directly cools the die  2   c.    
       FIG. 4  is a diagram of a thermal radiation equivalent circuit in which concentrated constants according to the embodiment are used. 
     The following are available as points to be controlled as the temperatures [deg C] (° C.) at the various sections. 
     Ta: the operation temperature range of the set (the ambient temperature for the cooling apparatus)
 
Tfin: the temperature of the cooling fin
 
Ths 1 : the temperature of the first heat sink base  1   a  
 
Tpkg 1 : the temperature of the package  1   b  of the MPU
 
Tdie 1 : the temperature of the die  1   c  of the MPU
 
Ths 2 : the temperature of the second heat sink base  2   a  
 
Tpkg 2 : the temperature of the package  2   b  of the SBC
 
Tdie 2 : the temperature of the die  2   c  of the SBC
 
     Furthermore, the following constituent elements are available as the thermal resistances [deg C/W] of the various sections. 
     Rex-a: the thermal resistance between the cooling fin and the atmosphere
 
Rhp 1 : the thermal resistance of the first heat pipes  1 
 
Rhs 1 : the thermal resistance of the first heat sink
 
Rjc 1 : the thermal resistance between the junction (die) and the case (package) of the MPU
 
     In the case that the MPU is package-less or lid-less, Rjh 1  (the thermal resistance between the junction and the heat sink) is used instead of Rjc 1 . 
     Rhp 2 : the thermal resistance of the second heat pipe  2 
 
Rhs 2 : the thermal resistance of the second heat sink
 
Rjc 2 : the thermal resistance between the junction (die) and the case (package) of the SBC
 
     In the case that the SBC is package-less or lid-less, Rjh 2  (the thermal resistance between the junction and the heat sink) is used instead of Rjc 2 . 
     (Verification of Operation Temperature) 
     The operation temperatures for the below-mentioned four examples (1) to (4) will be described below under the following settings. 
     First, it is assumed that the operation temperature range of the information-processing apparatus set is Ta=5 to 40 [deg C] and that the temperature specifications of the MPU/SBC and the high-speed channel are as described below. 
     PKG thermal resistance Rjc (inversely proportional to the die area): Rjc of MPU (Rjc 1 )&lt;Rjc of SBC (Rjc 2 ) 
     For example, (Rjc 1 =0.20 [deg C/W])&lt;(Rjc 2 =0.40 [deg C/W]) 
     Case temperature: the case temperature of MPU (Tpk 1 )&lt;the case temperature of SBC (Tpk 2 ) 
     For example, (Tpk 1 =70 [deg C]&lt;(Tpk 2 =75 [deg C]) 
     Junction temperature: the junction temperature of MPU (Tjc 1 )&lt;the junction temperature of SBC (Tjc 2 ) 
     For example, (Tjc 1 =80 [deg C])&lt;(Tjc 2 =85 [deg C]) 
     Operation temperature range of high-speed channel: +55 [deg C] 
     In the embodiment, the following thermal design and setting values are applied. 
     Thermal resistance of waste heat from the cooling fin to Ta: Rex-a=0.20 [deg C/W]
 
Thermal resistance of the first heat pipes  1 : Rhp 1 =0.10 [deg C/W] (two heat pipes are connected between the fin and the MPU)
 
Thermal resistance of the second heat pipe  2 : Rhp 2 =0.20 [deg C/W] (one heat pipe is connected between the MPU and the SBC)
 
Thermal resistance of the first heat sink: Rhs 1 =0.05 [deg C/W] (the same component is used if the MPU and the SBC have equivalent sizes)
 
Thermal resistance of the second heat sink: Rhs 2 =0.05 [deg C/W] (the same component is used if the MPU and the SBC have equivalent sizes)
 
Initialization power: initialization power of MPU (Pmpu)&gt;initialization power of SBC (Psbc)
 
     For example, (Pmpu=30 [W])&gt;(Psbc=15 [W]) 
     Unloaded power: unloaded power of MPU (Pmpu)&gt;unloaded power of SBC (Psbc) 
     For example, (Pmpu=40 [W])&gt;(Psbc=20 [W]) 
     Maximum power consumption: maximum power consumption of MPU (Pmpu)&gt;maximum power consumption of SBC (Psbc) 
     For example, (Pmpu=50 [W])&gt;(Psbc=25 [W]) 
     Since the SBC is heated by the heat generation of the MPU at the time of power-on operation, the temperature difference at the silicon (die) at each of both ends of the high-speed channel can be restrained within a desired range (the temperature fluctuation amount at each of both ends can be restrained within 55 [deg C] and the temperature fluctuation amount between both ends can be restrained within ±10 [%] in the embodiment). The following shows the temperature states at the various sections in the operation states (1) to (4) of the set (system). 
     (1) An example of temperature fluctuation at both ends of the MPU/SBC in the case that the system is started at Ta=5 [deg C] 
     The following are the temperatures at various sections of the common sections. 
       Tfin= Ta +(Rex-a×(Pmpu+Psbc))=5+(0.2×(30+15))=14.0[deg C]
 
       Ths1=Tfin+(Rhp1×(Pmpu+Psbc))=14+(0.1×(30+15))=18.5[deg C]
 
     The following are the temperatures at various sections on the side of the MPU. 
       Tpkg1=Ths1+(Rhs1×Pmpu)=18.5+(0.1×30)=21.5[deg C]
 
       Tdie1−0=Tpkg1+(Rjc1×Pmpu)=21.5+(0.2×30)=27.5[deg C],
 
     wherein the reference (calibration execution) temperature on the side of the MPU is obtained at the minimum temperature of the die of the MPU. 
     The following are the temperatures at the various sections on the side of the SBC. 
       Ths2=Ths1+(Rhp2×Psbc)=18.5+(0.2×15)=21.5[deg C]
 
       Tpkg2=Ths2+(Rhs2×Psbc)=21.5+(0.1×15)=23.0[deg C]
 
       Tdie2−0=Tpkg2+(Rjc2×Psbc)=23.0+(0.4×15)=29.0[deg C],
 
     wherein the reference (calibration execution) temperature on the side of the SBC is obtained at the minimum temperature of the die of the SBC. 
     The following is the temperature difference between the SBC and the MPU. 
       dT12=Tdie2−0−Tdie 1−0=29.0−27.5=1.5[deg C] 
 
     (2) An example of temperature fluctuation at both ends of the MPU/SBC in the case that both the MPU and the SBC are under high-load operation at Ta=40 [deg C] 
     The following are the temperatures at various sections of the common sections. 
       Tfin=Ta+(Rex-a×(Pmpu+Psbc))=40+(0.2×(50+25))=55.0[deg C]
 
       Ths1=Tfin+(Rhp1×(Pmpu+Psbc))=55+(0.1×(50+25))=62.5[deg C]
 
     The following are the temperatures at various sections on the side of the MPU. 
       Tpkg1=Ths1+(Rhs1×Pmpu)=62.5+(0.1×50)=67.5[deg C]
 
       Tdie1−1=Tpkg1+(Rjc1×Pmpu)=67.5+(0.2×50)=77.5[deg C],
 
     the maximum temperature of the die of the MPU 
       dT1−1=Tdie1−1−Tdie1−0=77.5−27.5=50.0[deg C],
 
     whereby the maximum temperature difference on the side of the MPU is restrained within 55 [deg C]. 
     The following are the temperatures at the various sections on the side of the SBC. 
       Ths2=Ths1+(Rhp2×Psbc)=62.5+(0.2×25)=67.5[deg C]
 
       Tpkg2=Ths2+(Rhs2×Psbc)=67.5+(0.1×25)=70[deg C]
 
       Tdie2−1=Tpag2+(Rjc2×Psbc)=70.0+(0.4×25)=80.0[deg C],
 
     the maximum temperature of the die of the SBC 
       dT2−1=Tdie2−1−Tdie2−0=80.0−29.0=51.0[deg C],
 
     whereby the maximum temperature difference on the side of the SBC is restrained within 55 [deg C]. 
     The following is the temperature difference between the SBC and the MPU. 
       dT12=Tdie2−1−Tdie1−1=51.0−50.5=1.0[deg C]
 
     The following is the temperature fluctuation ratio at both ends while the temperature at the starting time is used as the reference. 
         R _diff=|dT2−1−dT1−1|/Min.(dT1−1,dT2−1)×100=1/50×100=2.0[%],
 
     whereby the temperature difference between the MPU and the SBC is restrained within 10 [%].
 
(3) An example of temperature fluctuation at both ends of the MPU/SBC in the case that the MPU is under high-load operation and the SBC is under low-load operation at Ta=40 [deg C]
 
     The following are the temperatures at various sections of the common sections. 
       Tfin=Ta+(Rex-a×(Pmpu+Psbc)=40+(0.2×(50+20))=54.0[deg C]
 
       Ths1=Tfin+(Rhp1×(Pmpu+Psbc)=54+(0.1×(50+20))=61.0[deg C]
 
     The following are the temperatures at various sections on the side of the MPU. 
       Tpkg1=Ths1+(Rhs1×Pmpu)=61.0+(0.1×50)=66.0[deg C]
 
       Tdie1−2=Tpkg1+(Rjc1×Pmpu)=66.0+(0.2×50)=76.0[deg C],
 
     the maximum temperature of the die of the MPU 
       dT1−2=Tdie1−2−Tdie1−0=76.0−27.5=48.5[deg C],
 
     whereby the maximum temperature difference on the side of the MPU is restrained within 55 [deg C]. 
     The following are the temperatures at the various sections on the side of the SBC. 
       Ths2=Ths1+(Rhp2×Psbc)=61.0+(0.2×20)=65.0[deg C]
 
       Tpkg2=Ths2+(Rhs2×Psbc)=65.0+(0.1×20)=67.0[deg C]
 
       Tdie2−2=Tpag2+(Rjc2×Psbc)=67.0+(0.4×20)=75.0[deg C],
 
     the maximum temperature of the die of the SBC 
       dT2−2=Tdie2−2−Tdie2−0=75.0−29.0=46.0[deg C],
 
     whereby the maximum temperature difference on the side of the SBC is restrained within 55 [deg C]. 
     The following is the temperature difference between the SBC and the MPU. 
       dT12=Tdie2−2−Tdie1−2=46.0−48.5=−2.5[deg C]
 
     The following is the temperature fluctuation ratio at both ends while the temperature at the starting time is used as the reference. 
         R _diff=|dT2−2−dT1−2|/Min.(dT1−2,dT2−2)×100=2.5/46×100=5.5[%],
 
     whereby the temperature difference between the MPU and the SBC is restrained within 10 [%].
 
(4) An example of temperature fluctuation at both ends of the MPU/SBC in the case that the MPU is under low-load operation and the SBC is under high-load operation at Ta=40 [deg C]
 
     The following are the temperatures at various sections of the common sections. 
       Tfin=Ta+(Rex-a×(Pmpu+Psbc))=40+(0.2×(40+25))=53.0[deg C]
 
       Ths1=Tfin+(Rhp1×(Pmpu+Psbc))=53+(0.1×(40+25))=59.0[deg C]
 
     The following are the temperatures at various sections on the side of the MPU. 
       Tpkg1=Ths1+(Rhs1×Pmpu)=59.5+(0.1×40)=63.5[deg C]
 
       Tdie1−3=Tpkg1+(Rjc1×Pmpu)=63.5+(0.2×40)=71.5[deg C],
 
     the maximum temperature of the die of the MPU 
       dT1−3=Tdie1−3−Tdie1−0=71.5−27.5=44.0[deg C],
 
     whereby the maximum temperature difference on the side of the MPU is restrained within 55 [deg C]. 
     The following are the temperatures at the various sections on the side of the SBC. 
       Ths2=Ths1+(Rhp2×Psbc)=59.5+(0.2×25)=64.5[deg C]
 
       Tpkg2=Ths2+(Rhs2×Psbc)=64.5+(0.1×25)=67.0[deg C]
 
       Tdie2−3=Tpkg2+(Rjc2×Psbc)=67.0+(0.4×25)=77.0[deg C],
 
     the maximum temperature of the die of the SBC 
       dT2−3=Tdie2−3−Tdie2−0=77.0−29.0=48.0[deg C],
 
     whereby the maximum temperature difference on the side of the SBC is restrained within 55 [deg C]. 
     The following is the temperature difference between the SBC and the MPU. 
       dT12=Tdie2−3−Tdie1−3=77.0−71.5=5.5[deg C]
 
     The following is the temperature fluctuation ratio at both ends while the temperature at the starting time is used as the reference. 
         R _diff=|dT2−3−dT1−3|/Min.(dT1−3,dT2−3)×100=3.5/44×100=7.9[%],
 
     whereby the temperature difference between the MPU and the SBC is restrained within 10 [%]. 
     Heat sinks for high-power devices have been usually separated individually to avoid mutual influence. In the embodiment, however, the heat sink bases being separated are coupled to each other using a heat pipe. 
     In addition, a high-speed channel being point-to-point connected has a characteristic in which its operable range drifts depending on the temperature difference between both ends thereof, and the amount of the drift can be reduced by decreasing the temperature difference between both ends (by changing the temperatures at both ends in the same direction). Hence, the high-speed channel can be maintained in its stable operation range or can support a higher transmission rate by sharing the heat sinks so as to decrease the temperature difference between the devices at both ends of the high-speed channel. 
     Due to use of the cooling apparatus according to the embodiment, the heat generated at the MPU (micro processing unit) having large power consumption is used to heat the SBC (south bridge chip) having small power consumption, whereby the temperature fluctuation range at the high-speed channel of the SBC is reduced. Furthermore, the temperature fluctuations of the MPU and SBC are guided in the same direction, whereby, for example, eye pattern drifts at the high-speed channels are canceled each other. Hence, it is possible to securely obtain an operation margin relating to the temperature fluctuation in the high-speed channel. As a result, it is possible to ease constraints on the design relating to the crosstalk (in the wiring) and the voltage fluctuation (in the power supply circuit and decoupling-C) adversely affecting the operation margin of the high-speed channel, thereby being possible to reduce cost. 
     As in the case of the embodiment as shown in  FIG. 2 , the processor modules are self-heated at the time of power-on operation and the system waits for temperature rise due to use of the heater to reduce the temperature difference across the high-speed channel. Furthermore, in addition to the above-mentioned effect, the embodiment is effective in shifting the temperature fluctuations at both ends of the channel in the same direction (effective in not allowing the temperature fluctuations to become independent). 
     For the purpose of increasing the operation margin of the high-speed channel by minimizing the temperature fluctuations at both ends and the temperature difference between both ends of the “high-speed channel” point-to-point connected between the MPU and the SBC as described above, the following configuration is adopted under the conditions of Tj 1 ≦Tj 2  (Tjc 1 =80 [deg C] and Tjc 2 =85 [deg C] in the embodiment) and P 1 ≧P 2  (Pmpu max=50 [W] and Psbc max=25 [W] in the embodiment). 
     In other words, the cooling apparatus is configured so that the heat sinks and the cooling fin are arranged so as to have the above-mentioned positional relationship with respect to thermal resistance. More specifically, the cooling apparatus has a configuration in which two heat pipes are used to thermally couple the cooling fin to the heat sink base on the side of the device (MPU) having high power consumption, and one heat pipe is used to thermally couple the heat sink base on the side of the device (MPU) having high power consumption to the heat sink base on the side of the device (SBC) having low power consumption, whereby the cooling apparatus functions so that the device (SBC) having low power consumption is heated by the device (MPU) having high power consumption at the time of power-on operation and so that the temperature difference between the devices (the MPU and the SBC) is reduced during the operation of system. 
     However, the present invention is not limited to the above-mentioned embodiment, but can be modified variously within a range not departing from the gist of the invention. For example, it is possible to make a configuration effective in which the heat sink bases of the MPU (CBE) and the SBC (SCC) are connected intentionally to each other. 
     While certain embodiment has been described, the exemplary embodiment has been presented by way of example only, and is not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.