Abstract:
A heat sink, which comprises a plurality of flat fins erected on a surface of a base portion, and an air passage defined by the flat fins. In the heat think, at least one of the side end portions of one of the flat fins protrudes outwardly from a peripheral edge of the base portion.

Description:
[0001]     This application claims priority from Provisional Application Ser. No. 60/543,906, filed Feb. 13, 2004, pending, incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention deals with a heat sink comprising a plurality of flat fins erected on a surface of a base portion.  
         [0004]     2. Discussion of the Related Art  
         [0005]     Generally, a heat sink is contacted with an exothermic member or a heat source to enlarge the substantial heat radiation area of the exothermic member or the heat source. For this reason, it is preferable to arrange the fins or the heat radiation faces as many as possible in the heat sink of this kind. However, in order to secure the applicability to any kind of cooling objects having various shapes, heat sink having the heat radiation fins on its base portion is used generally. In the prior art, there is known a heat sink, in which flat heat radiation fins are erected integrally on one of a surface of a base portion in a parallel manner.  
         [0006]     The heat sink of this kind has a large heat radiation area in total so that large quantity of heat can be radiated. However, in order to further enhance the heat radiation capacity, it is preferable to carry out a compulsory cooling by blowing air. In this case, the cooling air is flown through a clearance between radiation fins to facilitate heat radiation from the surface of each radiation fins. In consideration of the heat radiation efficiency and the flexibility of installation, for example, an air blowing means such as a fan may be arranged above the radiation fins, in other words, on the opposite side of the base portion.  
         [0007]     In the above mentioned heat sink, the heat transmitted to the base portion is further transmitted to the flat fins while sending the cooling air into the clearance between the fins by the air blowing means such as a fan, therefore, the heat of the heat radiation fin is carried away by the cooling air. As a result of this, an exothermic member being contacted to the base member is cooled by the cooling air indirectly. In this case, the substantial heat radiation area of the exothermic member is enlarged by the fins. Moreover, heat transfer rate between the fin and the cooling air contacting thereto can be raised by widening temperature difference between those; therefore, the heat can be radiated efficiently and temperature raise in the exothermic member is prevented or suppressed. One example of the heat sink having this kind of structure is disclosed in Japanese Patent Laid-Open No. 2001-319998.  
         [0008]     In the heat sink thus far described, the heat radiation area can be enlarged by increasing the number of the fins. However, if the base portion is relatively large compared to the cooling object, i.e., to the exothermic member, the thermal resistance of the base portion is increased so that the heat radiation efficiency (i.e., cooling performance) is degraded. Moreover, the heat sink is desirable to be reduced in its size and weight, so that flow paths of the cooling air are narrowed if the number of the fins is increased. For this reason, it is difficult for the air flow to get into the clearance between the fins even if the compulsory cooling is carried out. Furthermore, flow of the cooling air is hindered. Due to those factors, the heat radiating effect of the heat sink may be deteriorated. In other words, the substantial heat radiation area will not be enlarged even if the number of the fins is increased. Therefore, the heat radiating performance of the heat sink is limited.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention has been conceived in view of the aforementioned technical problems, and it is an object of the present invention to improve heat radiating characteristics of a heat sink comprising a plurality of flat fins.  
         [0010]     An exemplary heat sink according to the present invention comprises a plurality of flat fins erected on a surface of a base portion, and clearances between those fins function as air passages. In the heat sink of the invention, at least one of the side end portions of at least one of the flat fins protrudes outwardly from a peripheral edge of the base portion.  
         [0011]     In the heat sink of the invention, an air passage is formed between a pair of adjoining flat fins, and at least one of the side end portions thereof protrudes outwardly from the peripheral edge of the base portion. Consequently, the lower end portion of the air passage protruding from the base portion functions as a flow outlet.  
         [0012]     According to the invention, therefore, both top and bottom portions of the air passage being defined by the flat fins are opened. In other words, the air passage is opened on the base portion side and the upper side. For this reason, in case of arranging an air blowing means above the base portion and fins and sending cooling air into the air passage, the airflow vertical to the base portion is discharged from the lower end of the air passage. As a result, airflow resistance in the air passage is reduced and the flow of the cooling air is thereby facilitated. This improves the heat radiating characteristics of the heat sink entirely.  
         [0013]     According to the invention, moreover, there is provided a heat sink, which has: a plurality of flat fins erected on the surface of the base portion; air passages being defined by the flat fins, and an air blowing means for establishing airflow toward the base portion, which is arranged above the flat fins. This heat sink is characterized by comprising an exhaust slot portion for discharging the airflow established by the air blowing means and flowing through the air passage toward the base portion.  
         [0014]     The exhaust slot portion includes a lower end opening of the air passage protruding from the base portion. As mentioned above, the air passage is defined by the flat fins, and at least one of the side end portions thereof protrudes outwardly from the peripheral edge of the base portion.  
         [0015]     The exhaust slot portion may also be a through hole portion penetrating the base portion from top to bottom.  
         [0016]     According to the invention, therefore, the airflow established by the air blowing means flows through the air passage to the base portion, and then flows through the base portion from top to bottom. For this reason, the flow of the air is smoothened in the air passage. Consequently, the heat radiating characteristics of the heat sink is improved entirely.  
         [0017]     The exemplary heat sink according to the present invention further comprises a pedestal portion, which is arranged on the surface of the base portion opposite to the surface where the flat fins are erected. The pedestal portion has heat conductivity higher than that of the base portion, and an exothermic member is contacted thereto in a heat transmittable manner.  
         [0018]     According to the invention, therefore, the heat generated by the exothermic member is transferred to the base portion through the pedestal portion. This facilitates thermal diffusion and heat transfer from the exothermic member to the base portion. Consequently, a thermal resistance of the heat transfer route from the exothermic member to the flat fins is reduced, and the heat radiating characteristics of the heat sink is thereby improved entirely.  
         [0019]     The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a front view showing one example of a heat sink according to the invention.  
         [0021]      FIG. 2  is a side view showing the heat sink shown in  FIG. 1 .  
         [0022]      FIG. 3  is an enlarged view showing exhaust slots of the heat sink shown in  FIG. 1 .  
         [0023]      FIG. 4  is a perspective view showing another example of a heat sink according to the invention.  
         [0024]      FIG. 5  is a perspective view showing the heat sink shown in  FIG. 4  from different angle.  
         [0025]      FIG. 6  is a side view showing the heat sink shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     Here will be described the exemplary embodiment of the invention.  FIG. 1  shows one example of a heat sink according to the invention. The construction of the heat sink  1  will be described first of all. The heat sink  1  comprises a flat fin  3 , an external wall  4  having a function as a radiation fin, a base portion  7  and a heat spreader  8 . The flat fin  3 , the external wall  4  and the base portion  7  are formed integrally of aluminum or aluminum alloy, for example. On the other hand, the heat spreader  8  is made of copper.  
         [0027]     The flat fin  3  and the external wall  4  are elected on the surface of the base portion  7  at a regular interval in a parallel manner. The longitudinal lengths of the flat fin  3  and the external wall  4  are longer than that of the base portion  7 .  
         [0028]     Here will be described the arrangement of the flat fins  3  and the external walls  4 . A plurality of the flat fins  3  is arranged at the regular interval in parallel manner on the surface of the base portion  7 , and the external walls  4  are arranged on both outer ends. In other words, the flat fins  3  are sandwiched between two external walls  4  in the arranging direction. Consequently, an air passage  5  is formed linearly in each clearance between flat fins  3 , and between the flat fin  3  and the external wall  4 . Airflow is to be flown through each air passage  5 . Additionally, both end portions of the air passage  5  in the longitudinal direction are flow outlets  5 C.  
         [0029]     As shown in  FIG. 3 , an exhaust slot  10  is composed of the side end portions of the flat fins  3 , or composed of side end portions of the flat fin  3  and the external wall  4 . Specifically, the exhaust slot  10  is composed of the side end portions of the flat fin  3  and the external wall  4  protruding from the base portion  7 . The exhaust slots  10  are formed on both side ends of the fin  3  and the external wall  4 . Accordingly, the lower end portion of the exhaust slot  10  is a flow outlet  5 D opening in the thickness direction of the base portion  7  (i.e., the vertical direction).  
         [0030]     An axial-flow fan  2  facing the base portion  7  (i.e. facing downwardly) is arranged above the flat fins  3  and the external wall  4 . Accordingly, a clearance between the upper end portions of the flat fins  3 , and a clearance between the fin  3  and the external wall  4 , are flow inlets  5 A of the air passage  5  and a slit  6 .  
         [0031]     A plurality of the slits  6  is formed in the flat fins  3  as well as in the external wall  4 , at the predetermined positions in the longitudinal direction. The slit  6  is formed from the upper end of the flat fin  3  and the external wall  4  to the vicinity of the surface of the base portion  7 . Additionally, the position of each slit  6  is deviated away from one another little by little. As a result, a plurality of flow passages is formed so as to cross the air passage  5  diagonally. Therefore, the slit  6  of the external wall  4  is a flow outlet  5 B for discharging the airflow.  
         [0032]     As shown in  FIG. 2 , the external wall  4  is provided with a hook portion  4 A on its leading end opposite to the base portion  7 . Here, the axial-flow fan  2  is eliminated from FIG.  2 . This hook portion  4 A is coupled with the peripheral edge of a housing of the axial-flow fan  2 . As a result, the axial-flow fan  2  is joined integrally with the heat sink  1 . In Addition, a height of the flat fin  3  next to the external wall  4  is shorter than that of the other flat fins  3 , so as not to interfere with the peripheral edge of the axial-flow fan  2  when the axial-flow fan  2  is joined with the heat sink  1 .  
         [0033]     An exothermic member  8 A is attached to the heat spreader  8  in a heat transferable manner. The heat spreader  8  is shaped rectangular, and fitted into a recess portion  7 A formed on the bottom of the base portion  7 . The recess portion  7 A and the heat spreader  8  are fixed by soldering.  
         [0034]     Here will be described the action of the heat sink  1 . As described above, the air passage  5  is formed between the flat fins  3 , or between the flat fin  3  and the external wall  4 . Moreover, both top and bottom ends of the protruding portion of the air passage  5  are opened to form the exhaust slot  10 . Therefore, the cooling air in the air passage  5  sent by the axial-flow fan  2  is then flown through the exhaust slot  10 . Since the exhaust slot  10  is formed vertically with respect to the axial-flow fan  2 , the flow resistance is reduced in the air passage  5  and the flowage of the cooling air is thereby facilitated. Consequently, the heat radiating characteristics of the heat sink  1  is improved entirely.  
         [0035]     Moreover, the heat generated at the exothermic member  8 A is transmitted to the base portion  7  through the heat spreader  8 , so that the heat transfer and the heat radiation between the exothermic member  8 A and the base portion  7  are facilitated. As a result, a thermal resistance of the heat transfer route from the exothermic member  8 A to the flat fin  3  or to the external wall  4  is reduced, and the heat radiating characteristics of the heat sink  1  is thereby improved entirely.  
         [0036]     Furthermore, flow outlets  5 B and  5 D are formed on both end portions of the flat fin  3 , in addition to the flow outlet  5 C. Therefore, the discharge amount of the cooling air flowing through the air passage  5  is increased.  
         [0037]     According to the aforementioned heat sink  1 , both side ends of the air passage  5  being defined by the fins  3  and protruding from the base portion  7  are the flow outlets  5 C. Consequently, the heat radiating area of the heat sink  1  is thereby enlarged with respect to the dimensions of the base portion  12 . Therefore, it is possible to improve the heat radiation efficiency of the heat sink  1 .  
         [0038]     On the other hand, the axial-flow fan  2  can be fixed easily to the heat sink  1  by means of the hook portion  4 A of the external wall  4 . This allows a body portion of the conventional heat sink to function as the external wall  4 . As a result, the heat radiating area of the heat sink  1  can be enlarged and the heat radiating capacity of the heat sink  1  is therefore improved. Moreover, the number of parts can be reduced to lower the manufacturing cost.  
         [0039]     The airflow is also discharged from the flow outlet  5 B formed in the slit  6 . This increases the flow amount of the cooling air passing through the air passage  5 , so that the heat exchange efficiency is improved. For this reason, the cooling performance of the heat sink  1  is enhanced.  
         [0040]     Since the heat spreader  8  is fitted into the recess portion  7 A formed on the bottom of the base portion  7 , moreover, the contacting dimensions between the base portion  7  and the heat spreader  8  can be enlarged. Consequently, the heat transferred to the heat spreader  8  can be efficiently transmitted to the base portion  7 , and the cooling performance of the heart sink  1  is thereby improved.  
         [0041]     Here will be described another specific embodiment according to the invention. Here, further description of the constructions identical or similar to those of the foregoing specific embodiment will be omitted by allotting common reference numerals. In FIGS.  4  to  6 , there is shown a heat sink  11  as another specific embodiment of the invention. The heat sink  11  comprises the flat fins  3 , the external wall  4 , the base portion  12  and the heat spreader  8  made of copper. In the heat sink  11 , the flat fin  3 , the external wall  4  and the base portion  12  are made of aluminum or aluminum alloy, and those are formed integrally by, e.g., the die-casting process. Moreover, both side end portions of the flat fins  3  and the external wall  4  function as the exhaust slots  10 . Accordingly, the lower end of the exhaust slots  10  composed of the flat fins  3  or of the flat fin  3  and the external wall  4  is the flow outlet  5 D.  
         [0042]     An axial-flow fan  13  is arranged above the external wall  4 . The axial-flow fan  13  is fixed with the base portion  12  by a pair of clips  14 . Specifically, each clip  14  has bent arm portions  15 , and the base portion  12  and the axial-flow fan  13  are clamped integrally between the end portions of the arm portions  15 . Moreover, the arm portion  15  is equipped with a fastening tool  16  for tightening the arm portions  15 . The base portion  12  and the axial-flow fan  13  are clamped by adjusting the fastening tool  16 .  
         [0043]     Moreover, there are formed slits  17  vertically from the top end of the external wall  4  to the bottom end of the base portion  12 . Consequently, there are formed openings on the bottom face of the base portion  12  underneath the slits  17 . Those openings function as exhaust slots  18  for discharging the cooling air from the air passage  5  being defined by the flat fins  3 . Moreover, the slit  17  penetrates the several flat fins  3  from the external wall  4 . This allows the cooling air in the air passage  5  to be discharged from the openings of the external wall  4 . Namely, the openings of the external wall  4  are flow outlets  5 E for discharging the cooling air.  
         [0044]     Furthermore, there are formed through holes  19  penetrating the base portion  12  in the thickness direction. Accordingly, the cooling air in the air passage  5  being defined by the flat fins  3  can also be discharged from the through hole  19  of the base portion  12 . Namely, the through hole  19  of the bottom face of the base portion  12  functions as an exhaust slot  20  for discharging the cooling air.  
         [0045]     Next, the action of the heat sink  11  will be explained hereinafter. When the cooling air is sent to the air passage  5  by the axial-flow fan  13  arranged above the fins  3  and the external walls  4 , the cooling air is flown into the slit  17  and the through hole  19 . For this reason, the cooling air is discharged not only from the exhaust slot  10  but also from the exhaust slots  18  and  20 . As a result, the flow of the cooling air is smoothened in the heat sink  11  so that the flow amount of the cooling air in the heat sink  11  is increased. Specifically, the heat sink  11  comprises not only the exhaust slot  10  positioned at both side ends of the flat fin  3 , but also the exhaust slot  18  or the slit  17  and the exhaust slot  20  or the through hole  19 . Moreover, those exhaust slots are opposed to the axial-flow fan  13 . According to the heat sink  11 , therefore, the flowability of the cooling air in the air passage  5 , and the heat radiating characteristics or the cooling performance of the heat sink  11  itself are improved, in addition to the action of achieved by the heat sink  1  shown in FIGS.  1  to  3 .  
         [0046]     Here will be briefly described the corresponding relation between the aforementioned embodiments and the invention. The heat spreader  8  corresponds to a pedestal portion of the invention; the slit  17  and the through hole  19  correspond to a through hole portion of the invention; and the slit  17  corresponds to a slit portion.  
         [0047]     Here, in the aforementioned embodiment, the flat fins and the base portion are made of aluminum or aluminum alloy, and the heat spreader is made of cooper. However, the materials of the flat fin, the base portion and the heat spreader are not limited to aluminum, aluminum alloy or copper. For example, the base portion may be made of copper, and the heat spreader may be made of aluminum. Otherwise, the base portion and the heat spreader may be made of same material.  
         [0048]     Here will be synthetically described the advantages to be attained by the invention. According to the invention, both top and bottom portions of the air passage being defined by the flat fins are opened; therefore, the airflow vertical to the base portion is partially discharged from the lower opening end of the air passage. As a result, the flow resistance is reduced in the air passage so that the flowage of the cooling air is facilitated. The heat radiating characteristics of the heat sink is thereby improved entirely.  
         [0049]     According to the invention, moreover, the airflow established by the air blowing means and flowing toward the base portion through the air passage is discharged from the exhaust slot. Therefore, the airflow in the air passage is smoothened so that the heat radiating characteristics of the heat sink can be improved entirely.  
         [0050]     According to the invention, furthermore, the heat generated at the exothermic member is transferred to the base portion through the pedestal portion, thereby facilitating thermal diffusion and the heat transfer from the exothermic member to the base portion. As a result, the heat resistance of the heat transfer route from the exothermic member to the flat fin is reduced. Therefore, the heat radiating characteristics of the heat sink is improved entirely.