Abstract:
It is intended to provide a heat sink unit and an electronic apparatus capable of efficiently cooling a plurality of semiconductor devices and taking action for unnecessary electromagnetic waves. There are provided a plurality of fan units and electromagnetic shielding means for cutting off electromagnetic waves on a heat sink substrate. It is also provided a heat sink substrate, a unit having a fan for supplying fluid to the heat sink substrate and driving means for rotating the fan, and electromagnetic shielding means provided for the heat sink substrate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a heat sink unit for cooling a semiconductor device such as an IC and to an electronic apparatus. 
     2. Description of the Prior Art 
     Conventionally, a heat sink unit is used to cool a semiconductor producing a high temperature. Particularly, a fan-motor integrated heat sink unit having a high cooling effect in which a small fan is built in a heat sink is recently used in order to correspond to a high temperature produced by an MPU. 
     A conventional heat sink unit is described below. FIG. 6 is a perspective view showing a conventional heat sink unit. In FIG. 6, numeral  1  denotes a substrate and a plurality of semiconductor devices  2 ,  3 ,  4 ,  5 , and  6  are set on the substrate  1 . Numeral  7  denotes a heat sink unit which is set on a semiconductor device  6  producing a relatively large amount of heat. The heat sink unit  7  comprises a plurality of fins  8 , a fan  9 , and a motor  10  for rotating the fan  9 . 
     An air flow is generated by rotating the fan  9  by the motor  10  and the semiconductor device  6  is prevented from being abnormally heated by applying the air flow to the fins  8 . That is, the heat produced by the semiconductor device  6  is transmitted to the fins  8  and cooled by the air flow. Moreover, the air flow coming out of the heat sink  7  contacts the semiconductor devices  2 ,  3 ,  4 , and  5  to cool the semiconductor devices  2 ,  3 ,  4 , and  5 . 
     However, the above conventional heat sink unit  7  has a limit in its cooling capacity. In addition to the heat produced by the semiconductor device  6  serving as a CPU, the amount of heat produced by the semiconductor devices  2 ,  3 ,  4 , and  5  is increased because operation speeds of the semiconductor devices  2 ,  3 ,  4 , and  5  are increased (clock acceleration) and a computer having two CPUs appears. Therefore, a problem occurs that adequate cooling cannot be made only by the air flow discharged from the heat sink unit  7 . 
     Moreover, because electromagnetic waves are inevitably generated due to clock acceleration, a problem occurs that an action must be taken for electromagnetic waves in order to cut off unnecessary electromagnetic waves emitted from a lead  6   a  of the semiconductor device  6 . 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a heat sink unit and an electronic apparatus capable of efficiently cooling a plurality of semiconductor devices and taking action for unnecessary electromagnetic waves. 
     To achieve the above object of the present invention, the present invention has a plurality of fan units and electromagnetic shielding means for cutting off electromagnetic waves on a heat sink substrate. 
     Moreover, a function capable of controlling unnecessary electromagnetic waves emitted from a semiconductor device and the like is obtained because of using a heat sink substrate, a fan unit having a fan for supplying fluid to the heat sink substrate and driving means for rotating the fan, and electromagnetic shielding means provided for the heat sink substrate. 
     Furthermore, a function capable of controlling unnecessary electromagnetic waves emitted from a semiconductor device and the like is obtained by providing electromagnetic shielding means for a heat sink substrate by at least one of ways of constituting the heat sink substrate with an electromagnetic shielding material, forming a film made of the electromagnetic shielding material on the heat sink substrate, and attaching a plate made of the electromagnetic shielding material to the heat sink substrate and moreover, has a function capable of improving the productivity because the electromagnetic shielding means can be easily set. 
     Furthermore, a function capable of efficiently transmitting the heat discharged from semiconductor devices with different heights to a heat sink substrate is obtained by setting a sheet having at least either of elasticity and plasticity to the heat sink substrate or forming a recess on the heat sink substrate. 
     Furthermore, in the case of an electronic apparatus of the present invention provided with a substrate, a plurality of exothermic elements set on the substrate, and a heat sink unit set on the exothermic elements, the heat sink unit is provided with a heat sink substrate, a fan for supplying fluid to the heat sink substrate, and driving means for rotating the fan. Therefore, a function capable of securely and efficiently cooling the exothermic elements is obtained by setting the exothermic elements to the heat sink substrate and cooling the exothermic elements by one heat sink substrate and moreover, a function capable of improving the productivity is obtained because the number of parts is decreased so that the structure is simplified. 
     Furthermore, a function capable of improving the cooling efficiency is obtained by setting a plurality of fan units on a heat sink substrate. 
     Furthermore, a function capable of controlling unnecessary electromagnetic waves emitted from a semiconductor device and the like is obtained by setting electromagnetic shielding means to a heat sink substrate. 
     Furthermore, a function capable of improving the productivity is obtained because electromagnetic shielding means can be easily set by providing the electromagnetic shielding means for a heat sink substrate by at least one of ways of constituting the heat sink substrate with an electromagnetic shielding material, forming a film made of the electromagnetic shielding material on the heat sink substrate, and attaching a plate made of the electromagnetic shielding material to the heat sink substrate. 
     Furthermore, a function capable of efficiently leading the heat produced by exothermic elements with different heights to a heat sink substrate is obtained because a plurality of exothermic elements are a plurality of semiconductor devices, at least one of the exothermic elements has a setting height from the substrate different from that of other elements, and moreover means to be brought into contact with the semiconductor devices is set to the heat sink substrate. 
     Furthermore, a function capable of improving the productivity is obtained because a heat sink substrate can be easily brought into contact with a plurality of semiconductor devices at a low cost by setting a sheet having at least either of elasticity and plasticity to the heat sink substrate as means to be brought into contact with the semiconductor devices or forming a recess on the heat sink substrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view showing the heat sink unit of an embodiment of the present invention; 
     FIG. 2 is a top view showing the heat sink unit of an embodiment of the present invention; 
     FIG. 3 is a side view showing the heat sink unit of an embodiment of the present invention; 
     FIG. 4 is a side view showing the heat sink unit of an embodiment of the present invention; 
     FIG. 5 is a side view showing the heat sink unit of an embodiment of the present invention; and 
     FIG. 6 is a perspective view showing a conventional heat sink unit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     An embodiment of the present invention is described below. 
     FIGS. 1 and 2 are a side view and a top view of the heat sink unit of an embodiment of the present invention. 
     In FIGS. 1 and 2, numeral  11  denotes a heat sink substrate made of a material having a high heat conductivity such as aluminum or iron and a plurality of fins  12  are vertically set to the heat sink substrate  11 . In the case of an embodiment of the present invention, the heat sink substrate  11  is made of aluminum and its alloy. However, it is possible to constitute the substrate  11  with a resin and ceramic having a high heat conductivity. When constituting the heat sink substrate  11  with a metal such as aluminum or the like, the mechanical strength is increased because aluminum has a very high heat conductivity and thereby, the cooling efficiency is greatly improved and moreover, the stiffness of the heat sink substrate  11  is increased. Moreover, when constituting the heat sink substrate  11  with a resin, the productivity is improved because the substrate  11  can be easily made. Moreover, when the heat sink substrate  11  is constituted by ceramic, it is possible to greatly improve the dimensional accuracy because the machining accuracy is very high. Further, in FIG. 2, each of arrows shows the direction of an air flow. 
     Furthermore, in the case of an embodiment of the present invention, the fins  12  vertically set to the heat sink substrate  11  are constituted by integrally forming plates. However, it is also possible to vertically set pin-like fins. Moreover, in the case of an embodiment of the present invention, the fins  12  are integrally formed with the heat sink substrate  11 . However, it is also possible to separately form the fins  12  and bond them to the heat sink substrate  11  by an adhesive or the like or mechanically fit them into the substrate  11 . 
     Numeral  13  denotes a fan unit. The fan unit  13  comprises a motor mount  14 , a motor  15  set to the motor mount  14 , and a fan  16  to be rotated by the motor  15 . The motor mount  14  is secured to the fins  12  by using means such as an adhesive or screws. Power is supplied to the motor  15  from an external unit by not-illustrated lead wires. 
     Moreover, the heat sink substrate  11  is provided with another fan unit  17  in addition to the fan unit  13 . The fan unit  17  comprises a motor mount  18 , a motor  19 , and a fan  20  similarly to the case of the fan unit  13  and the motor mount  18  is set to the heat sink substrate  11  by an adhesive or screws. These fan units  13  and  17  are stored in storing sections  11   a  and  11   b  provided for the heat sink substrate  11 . 
     The motors  15  and  19  can respectively use driving means such as an AC motor or DC motor. Moreover, in the case of an embodiment of the present invention, it is possible to lengthen the service life of a bearing and the like because heat can be prevented from being directly added to the bearings of the motors  15  and  19  by setting the motors  15  and  19  to the heat sink substrate  11  through the motor mounts  14  and  18 . Furthermore, to downsize a heat sink unit, it is possible to set the motors  15  and  19  directly onto the heat sink substrate  11  by omitting the motor mounts  14  and  18 . In this case, the motors  15  and  19  are set between the heat sink substrate  11  on one hand and the fans  16  and  20  on the other respectively. 
     Furthermore, in the case of an embodiment of the present invention, the fan unit  13  is set in order of the fan  16 , motor  15 , and motor mount  14  from the heat sink substrate  11  side and the fan unit  17  is similarly set in order of the fan  20 , motor  19 , and motor mount  18  from the heat sink substrate  11  side. However, it is also possible to set the fan unit  13  in order of the motor mount  14 , motor  15 , and fan  16  from the heat sink substrate  11  side and similarly set the fan unit  17  in order of the motor mount  18 , motor  19 , and fan  20  from the heat sink substrate  11  side. 
     Furthermore, it is possible to use cross-flow fan units instead of the fan units  13  and  17 . 
     Numeral  21  denotes a substrate. Semiconductor devices  22 ,  23 , and  24  are set to the substrate  21 . The semiconductor devices  22 ,  23 , and  24  are brought into contact with a plane  11   c  opposite to the plane to which the fan units  13  and  17  of the heat sink substrate  11  are set. It is enough that the semiconductor devices  22 ,  23 , and  24  are merely brought into contact with the heat sink substrate  11 . To further improve the heat radiation effect, however, it is preferable to connect the heat sink substrate  11  with the semiconductor devices  22 ,  23 , and  24  by an adhesive or the like and it is more preferable to use an adhesive superior in heat conductivity (e.g. adhesive obtained by dispersing metallic particles in a polymeric material). 
     In the case of a heat sink unit constituted as described above, when the power supply of an electronic apparatus is turned on, the fan units  13  and  17  rotate to supply air to the heat sink substrate  11  and discharge the heat produced by the semiconductor devices  22 ,  23 , and  24  together with the air through the heat sink substrate  11 . Therefore, the semiconductor devices  22 ,  23 , and  24  are completely cooled and therefore, no thermal damage is added to the devices  22 ,  23 , and  24 . 
     In the case of an embodiment of the present invention, when the power supply of an electronic apparatus is turned on, the same power is supplied to the fan units  13  and  17  to make the units  13  and  17  generate the same air flow. However, because the semiconductor devices  22 ,  23 , and  24  do not greatly produce heat immediately after the power supply is turned on, it is possible to reduce the power consumption by driving only the fan unit  13  and stopping the fan unit  17  or keeping the numbers of revolutions of the fan units at a low level. 
     Moreover, though not illustrated, it is possible to securely cool the semiconductor devices  22 ,  23 , and  24  by setting temperature detection means such as a temperature sensor onto or nearby the heat sink substrate  11  and controlling the numbers of revolutions of the fan units  13  and  17  in accordance with the information supplied from the temperature detection means. Furthermore, when the semiconductor devices  22 ,  23 , and  24  do not greatly produce heat, it is possible to reduce the power consumption by decreasing the power to be supplied to the fan units  13  and  17 . 
     Furthermore, though not illustrated, it is possible to securely cool the semiconductor devices  22 ,  23 , and  24  and reduce the power consumption as described above by setting a plurality of temperature detection means onto or nearby the heat sink substrate  11 , measuring the difference of produced amount of heat between the semiconductor devices  22 ,  23 , and  24  and the imbalance of the temperature distribution of the heat sink substrate  11 , and controlling the numbers of revolutions of the fan units  13  and  17  in accordance with the temperature information on the devices  22 ,  23 , and  24  and the substrate  11 . 
     Furthermore, in the case of an embodiment of the present invention, though the air supply directions of the fan units  13  and  17  are the same direction, it is possible to improve the cooling efficiency by making the air supply direction of the fan unit  13  different from that of the fan unit  17 . That is, as shown in FIG. 1, it is possible to efficiently convect the air on the heat sink substrate  11  by rotating the fan unit  13  so that an air flow occurs in the direction of arrow A and rotating the fan unit  17  so that an air flow occurs in the direction of arrow B. Therefore, it is possible to greatly improve the efficiency for cooling the heat sink substrate  11 . 
     By using the above structure, the heat produced by the semiconductor devices  22 ,  23 , and  24  is led to the heat sink substrate  11  and the temperature of the heat sink substrate  11  is raised but the heat sink substrate  11  is cooled by the air flows produced by the fan units  13  and  17 . Therefore, it is possible to prevent the semiconductor devices  22 ,  23 , and  24  from abnormally producing heat and improve the reliability of the apparatus. 
     Because an embodiment of the present invention makes it possible to cool the semiconductor devices  22 ,  23 , and  24  at the same time, it is unnecessary to set a fan unit to each semiconductor device like the case of the prior art and therefore, the cost is greatly decreased. 
     Moreover, because an embodiment of the present invention makes it possible to increase an air flow rate by using two fan units, it is possible to sufficiently cool a plurality of semiconductor devices at the same time. 
     Though an embodiment of the present invention uses three semiconductor devices, it is also possible to use two or more than three semiconductor devices. When using a lot of semiconductor devices to be cooled are used, it is preferable to use three fan units or more. In general, it is very advantageous from the aspect of cost to use the number of fan units less than the number of semiconductor devices. For example, when five semiconductor devices or more are used, it is preferable to use substantially three fan units. 
     Moreover, as shown in FIG. 3, it is possible to firmly secure the substrate  21  and heat sink substrate  11  by forming a through-hole lid on the heat sink substrate  11  and inserting a screw  25  into the through-hole lid. According to the above structure, the substrates  21  and  11  can be firmly secured without using any adhesive and moreover, easily removed. Therefore, it is possible to easily set the heat sink substrate  11  to other substrate and improve the availability. Though only the screw  25  is shown in FIG. 3, it is actually preferable to secure the substrates  21  and  11  with a plurality of screws. 
     Furthermore, as shown in FIG. 4, it is possible to bring the heat sink substrate  11  into contact with the semiconductor devices  22 ,  23 , and  24  by holding the heat sink substrate  11  and substrate  21  with elastic clips  26  and  27  having a U-shaped cross section. According to the above structure, it is possible to bring the heat sink substrate  11  into contact with the semiconductor devices  22 ,  23 , and  24  without using any adhesive or screw and therefore, the availability is improved because the heat sink substrate  11  can be very easily removed. Moreover, though an embodiment of the present invention uses simple elastic clips  26  and  27 , it is possible to use other type of hardware as long as the hardware is elastic and makes it possible to bring the heat sink substrate  11  into contact with the semiconductor devices  22 ,  23 , and  24 . 
     Furthermore, because the semiconductor devices  22 ,  23 , and  24  may have different heights H 1 , H 2 , and H 3  in general, a semiconductor device not being contact with the heat sink substrate  11  may be present and the semiconductor device may not be preferably cooled if the planes of the heat sink substrate  11  to be brought into contact with the semiconductor devices  22 ,  23 , and  24  are flat. In this case, as shown in FIG. 5, it is preferable to set a sheet  28  having at least either of elasticity and plasticity to the planes of the heat sink substrate  11  to be brought into contact with the semiconductor devices  22 ,  23 , and  24 . According to the above structure, it is possible that the semiconductor devices  22 ,  23 , and  24  is in good contact with the heat sink substrate  11  through the sheet  28  even if the semiconductor devices  22 ,  23 , and  24  have different heights. Therefore, the semiconductor devices  22 ,  23 , and  24  are efficiently cooled. Moreover, the sheet  28  can use a resin such as polyester or plastic or an alloy as a specific material. 
     Furthermore, instead of using the sheet  28  as described above, by forming recesses corresponding to the heights of the semiconductor devices  22 ,  23 , and  24  on the planes of the heat sink substrate  11  to be brought into contact with the devices  22 ,  23 , and  24  and storing the devices  22 ,  23 , and  24  in their corresponding recess respectively, it is possible to securely bring the heat sink substrate  11  into contact with the devices  22 ,  23 , and  24 . Specifically, when the heights of the semiconductor devices  22 ,  23 , and  24  meet an inequality H 1 &gt;H 2 &gt;H 3 , recesses are formed on the portions of the heat sink substrate  11  facing the semiconductor devices  22 ,  23 , and  24  respectively. Then, in this case, because the height H 1  is the largest, the depth of the recess formed on the portion facing the semiconductor device  22  is made the largest and the recess facing the semiconductor device  24  is made the smallest. According to the above structure, it is possible to securely bring the heat sink substrate  11  into contact with the semiconductor devices  22 ,  23 , and  24  and moreover, easily position the heat sink substrate  11 . 
     Furthermore, by accelerating the clock of the semiconductor devices  22 ,  23 , and  24 , unnecessary electromagnetic waves may be generated by leads  22   a ,  23   a , and  24   a  of the semiconductor devices  22 ,  23 , and  24 . Therefore, to prevent the electromagnetic waves, it is preferable to constitute the heat sink substrate  11  by an electromagnetic shielding material. The electromagnetic shielding material uses, for example, a magnetic material such as ferrite or permalloy, conductive elastomer, or metallic mesh. Thus, by constituting the heat sink substrate  11  by an electromagnetic shielding material so as to cover the semiconductor devices  22 ,  23 , and  24 , it is possible to cut off the unnecessary electromagnetic waves generated by the leads  22   a ,  23   a , and  24   a . Furthermore, it is possible to form an electromagnetic shielding material on the surface of the heat sink substrate  11  by means of vacuum evaporation, sputtering, thermal spraying, or coating. In this case, because the main material of the heat sink substrate  11  can be determined by considering the workability and cost, it is possible to improve the productivity. Moreover, because an electromagnetic shielding material to be formed on the heat sink substrate  11  can be easily changed in accordance with the purpose or using environment, it is possible to select the type of a semiconductor device to be cooled and a material corresponding to unnecessary electromagnetic waves. Furthermore, it is possible to form an electromagnetic shielding material like a sheet (metallic tape, metallic mesh, conductive elastomer, etc.) and attach it to the planes of the heat sink substrate  11  facing the semiconductor devices  22 ,  23 , and  24 . It is particularly preferable to form a structure so as to cool a plurality of semiconductor devices and simultaneously cover the lead portions of the semiconductor devices like an embodiment of the present invention. 
     Though the semiconductor devices  22 ,  23 , and  24  described in the embodiment of the present invention use an LSI, memory, or IC, it is also possible to use other exothermic element (such as laser diode or transistor). Moreover, in the case of the embodiment of the present invention, the semiconductor devices  22 ,  23 , and  24  are directly set to the heat sink substrate  11  or they are bonded to the substrate  11  through an adhesive. However, it is also possible to indirectly set the devices  22 ,  23 , and  24  to the substrate  11  through a member having a high heat conductivity.