Abstract:
A heatsink of the present invention has a column having a heat conducting plate with a heat receiving face contacting a heat producing element. On the side faces of the column are a plurality of first slits disposed parallel to the heat receiving face and a plurality of second slits disposed transversely to the heat receiving face. These slits form a plurality of pillar-type protrusions functioning as fins for cooling. At least one of cross sections of the column has a shape of a rectangle, a trapezoid, a triangle or a shape which tapers off as it goes away at right angle from the heat receiving face. A method of manufacturing the heatsink of the present invention includes first and second processes. In the first process, the first slits are formed by providing a plurality of metallic plate fins on the column along its length by the methods including the extrusion molding using a metallic mold. In the second process, the second slits are formed in a direction approximately transverse to the length direction of the plate fins. By using a specialized jig for the machining of the second slits, many fins can be formed remarkably efficiently. A cooling apparatus for the present invention includes a cooling means mounted on the heatsink of the present invention. The cooling apparatus for the present invention enjoys a high cooling capability and reduced size.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a heatsink which is used to cool heat producing semiconductor elements such as integrated circuits (IC), central processing units (CPU), micro processing units (MPU) and electronic components including heating sections. The present invention also relates to manufacturing methods of a heatsink, and to a cooling apparatus using the heatsink. The cooling apparatus uses the heatsink combined with cooling means such as a fan for cooling the heat producing elements.  
         BACKGROUND OF THE INVENTION  
         [0002]    Integration of the electronic components such as semiconductors and increasing frequencies of operation clocks have been raising the heat produced by such components in recent years. Under such circumstances, maintaining temperatures at contact points of the electronic components within the range of the operation temperature has become a critical issue for the normal functioning of the electronic components. Increases in integration and frequency of the micro processing units (MPU) has been remarkable. Thus, dissipation of the heat produced by MPUs is particularly important for stabilizing their function and securing their operational longevity.  
           [0003]    Heat emitted from the electronic components is , in general, dissipated by a cooling apparatus comprising a heatsink and a fan.  
           [0004]    An example of a conventional heatsink will now be described referring to FIGS. 12, 13 and  14 .  
           [0005]    [0005]FIG. 12 shows a perspective view of a conventional heatsink. FIG. 13 shows a top view and sectional views of a conventional cooling apparatus. FIG. 14 shows a perspective view and a side view of another conventional heatsink. These heatsinks can be categorized into a plate-type heatsink where a plurality of plate fins  1   c  made of thin plates are disposed on a base plate  2   b  or a heat conduction section as shown in FIG. 12 ( a ), a pin-type heatsink where a plurality of fins  1  are disposed on the plate  2   b  as shown in FIG. 12 ( b ) , and a tower-type heatsink where a plurality of plate fins  1   c  made of thin plates are disposed at right angle to the axis of column  2  as shown in FIG. 14 ( a ). These heatsinks are generally constructed of materials with high heat conductivity such as aluminum and copper, and produced by the extrusion molding (otherwise called pultrusion molding) method, the cold forging method, the die casting method, or the thin plates accumulating method.  
           [0006]    The heatsinks are mounted either directly onto a heat producing element  3  as illustrated in FIG. 13 ( a ), or indirectly by inserting a heat diffusion plate  2   c  between the heat producing element  3  and the heatsink as illustrated in FIG. 13 ( b ) in the case of the pin-type heatsink. The heat diffusion plate conducts heat emitted from the heat producing element  3  to the heatsink, and helps to diffuse the heat and protect the heat producing element. The cooling mechanism of the cooling apparatus in use , is described as follows: heat produced by the heat producing element  3  is conducted to the pin-shaped fins  1  via the heat-conductive base plate  2   b  made of a highly heat conductive material such as aluminum, and, over the surface of the fins  1 , convectively conducted to the air blown by a cooling fan  4  thus dissipated into the air and cooled.  
           [0007]    In order to improve the capability of the cooling apparatus, heat is most desirably diffused throughout the heat conductive section evenly, and dissipated from all of the dissipation fins. However, in the case of the plate-type and pin-type heatsinks, heat emitted from the heat producing element  3  tends to be conducted intensively to the dissipation fins disposed right above the heat producing element  3 . It is relatively hard for the heat to be conducted to the peripheral dissipation fins. The reason for this is that the heat producing element is much smaller than the heat conducting section, thus contact area between them is very limited. Consequently, with the plate-type and the pin-type heatsinks, the heat dissipation fins as a whole often fail to function effectively.  
           [0008]    It could be argued that if the amount of air flow around the heat dissipation fins is the same, the heat dissipating capability can be increased by expanding the surface area by increasing the number of fins. In reality however, considering unit area, when the sectional area of the heat dissipation fins is increased, the area where air can flow into, such as an air flow area  7   e  (marked with diagonal lines in FIG. 13 ( a )) decreases, as does the total volume of air flow. Therefore, in some cases, the heat dissipation capability lowers as a result. In other words, a mere increase in the number of dissipation fins does not bring about an improvement.  
           [0009]    The most important aspect for the dissipation of heat is to effectively conduct heat produced by the heat producing element  3  to the dissipation fins to the largest possible area.  
           [0010]    To solve the foregoing problems the tower-type heatsink shown in FIG. 14 has been introduced. In this kind of heatsink, heat produced in the heat producing element is conducted directly to the upper part of the heatsink by a central column, and spread flatly by the plate fins  1   c  formed at a right angle to the axis of the column. The heat which has been spread flatly on the both faces of the thin plates is generally dissipated into the air by natural air cooling. In this tower-type heat sink, improvements have been proposed to increase the dissipation capability. For example, Japanese Patent Laid Open Publication No. S62-182600 discloses a heatsink where through-hole vents are formed on the surface of the thin plates by cutting and standing the cut edges of the thin plates in the process of producing the plate fins. Through these vents, air is permitted to convect more easily in the direction parallel to the axis of the column.  
           [0011]    However, development of electronic components used in high speed processing such as semiconductors has been resulted in a relative increase in the amount of heat produced. As a result, conventional cooling apparatus are now facing difficulties in cooling electronic components sufficiently, especially when it comes to electronic components such as MPU which produce significant amount of heat, the conventional cooling apparatus fail to reach their full capability. In some cases, temperature rise in MPUs led to thermal runaway and caused electronic apparatus to malfunction. To deal with increases in heat generation, it is possible to enhance the cooling capability by making the cooling apparatus itself larger. However, the size of the electronic apparatus itself inevitably limits the size and weight of the cooling apparatus.  
           [0012]    Compared with other types, the construction of the tower-type heatsink realizes a better heat conductivity, however, it also tends to trap air. Furthermore, it is difficult to dispose a cooling fan on the top of the tower-type heatsink, therefore, the cooling fan must be disposed on a side face of the heatsink. However, if the cooling fan is disposed in such a manner, the heatsink is required to be as high as the cooling fan. Thus, the cooling apparatus as a whole becomes remarkably large. Despite its size, however, the dissipation efficiency can not be improved satisfactorily.  
           [0013]    The present invention aims to address the foregoing problems, and to provide a compact and highly efficient heatsink and a small cooling apparatus with high cooling ability using the heatsink. The present invention further aims at providing a manufacturing method of the heatsink which achieves the production of a highly effective heatsink in a productive and inexpensive manner.  
         SUMMARY OF THE INVENTION  
         [0014]    A heatsink of the present invention has a column having a heat conducting plate with a heat receiving face in contact with a heat producing element. On the side faces of the column are a plurality of first slits disposed parallel to the heat receiving face and a plurality of second slits disposed transversely to the heat receiving face. These slits form a plurality of pillar-type protrusions functioning as cooling fins. Hereinafter, the pillar-type protrusions are called fins.  
           [0015]    Another heatsink of the present invention includes a heat conducting plate section having a heat receiving face and a column which acts as a heat conducting section by protruding opposite the heat receiving face of the heat conducting plate section. At least one cross section of the column has a shape of a rectangle, a trapezoid, a triangle or some shape which tapers off as it goes away at right angle from the heat receiving face. On the side faces of the column are a plurality of fins formed along the heat receiving face.  
           [0016]    Although the heatsink of the present invention is compact it can effectively lead the heat produced by the heat producing element throughout the heatsink, thus realizing high heat dissipating properties. The heatsinks which have especially superior heat dissipating properties include the following types:  
           [0017]    a heatsink in which fins are disposed such that their central lines are disposed transversely at a right angle to the base line which is substantially vertical to the heat receiving face,  
           [0018]    a heatsink in which fins are disposed such that their central lines are disposed transversely at a predetermined angle to the base line vertical to the heat receiving face; and  
           [0019]    a heatsink in which fins are disposed such that their central lines are disposed transversely at a predetermined angle to the base line vertical to the heat receiving face, and the tips of the plurality of fins extend as high as the top face of the column.  
           [0020]    When the plurality of fins have recesses or protrusions on the surface thereof, the dissipation effect of heat into air is especially enhanced.  
           [0021]    The manufacturing method of the heatsink of the present invention includes first and second processes. In the first process, the first slits are formed by providing a plurality of metallic plate fins in the column and its length directions by the methods including extrusion molding using a metallic mold. In the second process, the second slits are formed in a direction approximately transverse to the length direction of the plate fins. By using a specialized jig for the process of producing the second slits, many fins can be formed remarkably effectively.  
           [0022]    This manufacturing method achieves productive and inexpensive production of high-performance heatsinks.  
           [0023]    A cooling apparatus of the present invention includes a cooling means mounted on the heatsink of the present invention. Mounting a wind blowing means such as a fan opposite the heat receiving face allows the cooling apparatus of the present invention to enjoy a high cooling capability and to be reduced in size. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 shows a perspective view and side views of the main part of a heatsink in accordance with a first preferred embodiment of the present invention.  
         [0025]    [0025]FIG. 2 shows a perspective view illustrating the external shape of a heatsink and sectional views of columns of the heat sinks in accordance with the first preferred embodiment of the present invention.  
         [0026]    [0026]FIG. 3 shows plan views and side views of a heatsink in accordance with a second preferred embodiment of the present invention.  
         [0027]    [0027]FIG. 4 shows plan views and side views of a heatsink in accordance with the second preferred embodiment of the present invention.  
         [0028]    [0028]FIG. 5 shows a perspective view of fins of the heatsink in accordance with the first and second preferred embodiments of the present invention.  
         [0029]    [0029]FIG. 6 shows front views and side views of the heatsink and the cooling apparatus in accordance with the first and second preferred embodiments of the present invention.  
         [0030]    [0030]FIG. 7 shows side views which illustrate air flow of the heatsink and the cooling apparatus in accordance with the first and second preferred embodiments of the present invention.  
         [0031]    [0031]FIG. 8 shows a perspective view illustrating a manufacturing method of the heatsink in accordance with the first and second preferred embodiments of the present invention.  
         [0032]    [0032]FIG. 9 shows perspective views illustrating an extrusion process of a manufacturing method of the heatsink in accordance with the first and second preferred embodiments of the present invention.  
         [0033]    [0033]FIG. 10 shows a perspective view of the heatsink and side views of the heatsink placed on a jig during a cutting process of the manufacturing method of the heatsink in accordance with the first and second preferred embodiments of the present invention.  
         [0034]    [0034]FIG. 11 shows perspective views of the cooling apparatus having cooling fans mounted on the top of the heatsink in accordance with the first and second preferred embodiments of the present invention.  
         [0035]    [0035]FIG. 12 shows perspective views illustrating construction of a conventional heatsink.  
         [0036]    [0036]FIG. 13 shows a plan view and sectional views of a conventional cooling apparatus.  
         [0037]    [0037]FIG. 14 shows a perspective view and a side view illustrating construction of a conventional heatsink. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0038]    The preferred embodiments of the present invention are described hereinafter with reference to the drawings.  
         [0039]    The First Embodiment  
         [0040]    [0040]FIG. 1 shows a perspective view and side views of the main part of a heatsink in accordance with a first preferred embodiment of the present invention. FIG. 1 ( a ) is a perspective view of the heatsink according to the first preferred embodiment of the present invention. FIG. 1 ( b ) is a sectional view of a cooling apparatus of the present invention disposed right on the top of a heat producing element  3  viewed from the perspective of the length direction of a column  2  (hereinafter, Y axis direction) when a cooling fan  4  is mounted. FIG. 1 ( c ) is a side view of a cooling apparatus of the present invention viewed from the perspective of the width direction of the column  2  (hereinafter, X axis direction) when the cooling fan  4  is mounted.  
         [0041]    [0041]FIG. 2 shows a perspective view illustrating the external shape of a heatsink and sectional views of columns of the heatsink in accordance with the first embodiment of the present invention. FIG. 2 ( a ) is a perspective view of the external shape (drawn by broken line) of the heatsink of the first embodiment of the present invention. FIGS.  2  ( b )-( e ) show plan views and side views of the heatsink of the first embodiment of the present invention with different sectional shapes.  
         [0042]    In FIGS.  1  ( a )-( c ), a plurality of fins  1  are disposed on the column  2  (or heat conducting section). The heat producing element  3  is disposed under the column  2  (hereinafter, negative Z axis direction). On the top of the heatsink is the cooling fan  4 .  
         [0043]    In sum, in this embodiment, the heatsink comprises the fins  1  and the column  2 . The heat producing element  3  here is an electronic component which produces heat including semiconductors and transistors such as IC, LCI and MPU.  
         [0044]    For the sake of convenience of description, width, length and height directions of the column are, in some cases, expressed as X axis, Y axis and Z axis directions as mentioned previously.  
         [0045]    In FIG. 1, the column  2  is a prism of which a cross section through Y axis direction is a triangle. Creating the shape of the column  2  in this manner improves contact between the column  2  and the heat producing element  3  and reduces waste of the materials. It especially contributes to providing a heatsink with superior mountability and heat conductivity. The column  2  has fins  1  disposed thereon. The fins  1  in FIG. 1 are disposed on both faces of the column.  
         [0046]    The construction of the heatsink of the present invention can realize a compact cooling apparatus having superior heat conductivity and heat dissipation properties.  
         [0047]    In the heatsink of the first preferred embodiment shown in FIG. 1, heat produced by the heat producing element  3  is received on the bottom surface of the prism column  2  (or heat receiving face) which contacts with the heating surface of the heat producing element  3 . The heat is then diffused three-dimensionally to in the directions of the X, Y and Z axes from the bottom surface of the column  2 . In this case, since the column  2  is a prism, a stable hemispherical temperature distribution can be achieved over a much larger area inside the column compared with the plate heat conducting section of the conventional plate-type and pin-type heatsinks. The heat emitted from the heat producing element  3  is conducted over the hemispherical temperature distribution range and to the fins  1  which function as heat dissipating fins. As a result, the heatsink of this embodiment achieves significantly higher heat dissipation properties than the conventional heatsinks of the same size. Furthermore , even in the vicinity of both ends of the heatsink where such hemispherical temperature distribution is hard to obtain, fins  1  can sufficiently function as heat dissipation fins since the sectional area of the column  2  is large enough to maintain a low heat resistance associated with the transfer of heat.  
         [0048]    FIGS.  2  ( b ) and ( c ) shows constructions of a plurality of other embodiments where the sectional shapes of column  2  of the heatsink illustrated in FIG. 1 are changed. In FIGS.  2  ( b ) and ( c ), differences in sectional shapes of the column  2  produces difference in the sectional area of the column  2  and the sectional area of an air flow section of which opening is placed on the cooling fan side at the top. FIG. 2( a ) shows the condition of the column  2  when the cross section of the column shown in FIG. 1 is triangular. The sectional area of the column  2  which directly affects the diffusion of the heat , becomes progressively smaller according to its shape in the following order; square shown in FIG. 2 ( e ) , trapezoid, in FIG. 2 ( c ), triangle, in FIG. 2 ( d ), and bell-shape (or a shape having a curved face with a curvature radius of “R”) in FIG. 2 ( e ). In order to conduct (or diffuse) heat to the largest possible area, it is desirable to ensure that the column  2  has the largest possible sectional area.  
         [0049]    On the contrary, the sectional area of the air flow section which is concerned with the volume of air which dissipates heat outside, becomes larger as the length of a side A and a side B having an opening on the top of the heatsink becomes longer. Thus, the sectional area of the air flow section expands according to the shape of the column in the following order; square, shown in FIG. 2 ( e ), trapezoid, in FIG. 2 ( c ), triangle, in FIG. 2 ( d ), and bell-shape, in FIG. 2 ( e ). It is desirable to provide the air flow section with the largest possible sectional area so as to obtain sufficient volume of air flow.  
         [0050]    Therefore, ideally the sectional area of the column  2  which conducts heat produced by the heat producing element  3  as well as the area of the air flow section are the largest possible so as to obtain the maximum air flow necessary for dissipating heat. The two have in some ways a conflicting relationship. However, what is needed is to select the shape of the column  2  with the largest possible sectional area while maintaining the maximum air flow area to ensure sufficient volume of air to dissipate heat. Among the constructions illustrated in FIGS.  2  ( b )-( e ), ones in FIGS.  2  ( d ) and ( e ) are desirable since the air flow sections have sufficient width (the total length of the sides A and B) and the sectional area of the column  2  is large.  
         [0051]    In these heatsinks, end faces of the fins  1  and the bottom corners of the column  2  are desirably chamfered. The chamfering prevents chipping and generation of undesirable material. If a corner is sharp, the heatsink may contact with other components when it is being mounted onto an electronic component and break the component. When material is generated from a chipped corner and falls on wiring, it might trigger a short circuit and cause the electronic apparatus to malfunction.  
         [0052]    The column  2  and the fins  1  can be integrally formed, or the fins can be adhered to the column  2  as separate parts with adhesives. As another method, the fins  1  can be press fitted into holes provided on the column  2 .  
         [0053]    When the column  2  and the fins  1  are integrally formed, productivity improves. Furthermore, heat conductivity improves as no heat-resistance part exists between the column  2  and the fins  1 . When the fins  1  are fixed to the column  2  by the adhesive or press-fitting method, appropriate materials can be used for the column  2  and the fins  1 , thereby promoting ease of design of the heatsink.  
         [0054]    For the construction of the fins  1 , a square pole as shown in FIG. 1, a cylinder, a polygonal pole, a elliptic cylinder and the like can be used. By forming the fins  1  to have a shape of square pole, the mounting density of the fins  1  can be enhanced, thereby improving the heat dissipation.  
         [0055]    In this embodiment, thickness of the fins  1  was set approximately the same. However, the fins  1  can be designed such that they have a taper of which either the thickest or thinnest part is fixed to the column  2 . The fins  1  can also be designed so that the center of it is thinner or thicker than the other parts.  
         [0056]    Chamfering of the corners of the fins  1  prevents generation of the undesirable material caused by chipping as previously mentioned.  
         [0057]    Furthermore, when the fins  1  are disposed at regular intervals, heat dissipation and productivity are desirably improved. In other words, by disposing the fins  1  at regular intervals, the convection of air improves, and the manufacturing of the heatsink is faciliated.  
         [0058]    Desirable materials for the heatsinks are ones which have a heat conductivity at 100° C. of 100 k/W·m −1 ·K −1  or more. Such materials can be selected from zinc, aluminum, brass, gold, silver, tungsten, copper, beryllium, magnesium, and molybdenum (hereinafter, material group), and used in their pure form. These materials can also be used in an alloy form. In the latter case it is possible to either select a plurality of alloys from the above-mentioned group or select at least one from the material group and alloying it with materials not included in the above group. In this embodiment, aluminum and an aluminum alloy and at least one other material selected from the material group were used because of its ease of processing and low cost.  
         [0059]    The Second Embodiment  
         [0060]    [0060]FIGS. 3 and 4 show plan views and side views of the second embodiment of the present invention in which the construction of the column and fins of the heatsink is changed.  
         [0061]    In FIG. 3 ( a ), the axis of the fins  1  are set at right angle against a base line  9   a  which is vertical to the heating face of the column  2 . By disposing the fins  1  on both side faces of the column  2  placed in the middle, the surface area as a heat dissipating surface can be securely provided by the fins  1  while keeping the height of the heatsink low.  
         [0062]    The cooling fan is mounted on the top of the heatsink. Air blown by the cooling fan travels through an air flow section  7   a  (gap between fins) marked with diagonal lines and the heatsink from the top to the bottom similar to an air current  5   a  to radiate heat of the fins  1 .  
         [0063]    The only possible disadvantageous point is that the air flow area per unit area is smaller than that of the conventional heatsink shown in FIG. 13 ( a ) when size of the top part of which is the same. In other words , in the case of the air flow area  7   e  of the conventional heatsink which is marked with diagonal lines in FIG. 13 ( a ) , the area is calculated by subtracting the total area of all of the fins  1  from the total area on the top surface of the heatsink. In the case of the construction of the present invention, however, approximately 50% of the area on the top surface of the heatsink is covered with the side faces of the fins  1 . Therefore, the air flow area is reduced by that amount.  
         [0064]    Even though the air flow area is reduced, when the fins  1  are disposed on both sides of the approximately prism-shaped column, the column can achieve a sufficient heat diffusion effect and air can be convected very smoothly. Thus, significantly increased heat dissipation properties can be achieved compared with the conventional heatsink.  
         [0065]    In the heatsink shown in FIG. 3 ( b ), the axis of the fins  1  are set such that it has a predetermined angle θ against the base line  9   a . By positioning the fins  1  on both side faces of the column  2  at a predetermined angle θ in such a manner that the end faces of the fins  1  are parallel to the base line  9   b  on the top surface of the heatsink, the air flow section  7   b  can be extended even wider than the conventional heatsink shown in FIG. 13 ( a ) while maintaining the surface area of the fins and height of the heatsink at the same level as the heatsink described in FIG. 3.  
         [0066]    The heatsink illustrated in FIG. 3 ( b ) has the air flow section twice as large as the air flow section  7   a  illustrated in FIG. 3 ( a ), thus realizing even higher heat dissipation properties. Furthermore, since the fins  1  are tilted by an angle θ and positioned, air flow coming in from the top of the heatsink becomes an air flow  5   b . The air flow  5   b  then is led along the top surface of the fins  1  to the surface of the column  2  in addition to the air flow  5   a , thereby further improving the heat dissipation properties.  
         [0067]    [0067]FIG. 4 ( a ) shows a heatsink which has the fins  1  disposed radially with one point on the base line  9   a  as base point. In this case, the air flow area can be increased as in the case of FIG. 3 ( b ) compared with FIG. 3 ( a ), further enhancing the heat dissipation properties.  
         [0068]    [0068]FIG. 4 ( b ) shows the heatsink of FIG. 3 ( a ) in which the fins  1  are bent at right angles. Such heatsinks can also achieve the same performance properties as the heatsinks illustrated in FIG. 3 ( b ) and FIG. 4 ( a ).  
         [0069]    The Third Embodiment  
         [0070]    [0070]FIG. 5 shows a perspective view of the fins of the heatsink in accordance with the first and second preferred embodiments of the present invention. As the external shape of the fins  1  in FIG. 5 illustrates, by forming protrusions and recesses on the surface of the fins  1  of the heatsink, the surface area increases enhancing the heat dissipating capability. The protrusions and recesses can be formed only on a part of the fins  1 . Furthermore, even if they are formed on some of the fins, the same effect can be obtained. The surface of the fins  1  can be provided with dimples. The fins  1  can be formed such that the width near the bottom and the top end are the same as shown in FIG. 5  1   a . The fins  1  can also be formed such that they have diminishing taper either from bottom to top or top to bottom as shown in FIG. 5  1   b.    
         [0071]    The Fourth Embodiment  
         [0072]    The cooling apparatus of the present invention is described below with reference to FIGS. 6 and 7.  
         [0073]    FIGS.  6  ( a ) and ( b ) show front views and side views of the heatsink and the cooling apparatus in accordance with the first and second preferred embodiments of the present invention. FIGS.  7  ( a ), ( b ) and ( c ) show side views which illustrate air flow of the cooling apparatus.  
         [0074]    In this embodiment, as FIGS.  6  ( a ) and ( b ) show, the whole face or part of the face where the heat producing element is mounted, has a protuberant heat conducting plate section  2   a  formed thereon. In forming the plate section  2   a , some space can be provided in between the heat receiving face and the fins  1  disposed in the vicinity of the plate section  2   a . Therefore, air flow created by the cooling fan  4  can be effectively led to the surface of the fins  1  near the heat receiving face. A heat receiving face is formed on the heat producing element mounting section of the plate section  2   a.    
         [0075]    Specific air flow is described hereinafter with reference to FIGS.  7  ( a ), ( b ) and ( c ). As shown in FIG. ( a ), the existence of the plate section  2   a  of the column  2  allows the air flow  5   a  from the cooling fan  4  to be led directly from the top to the bottom of the heatsink. In other words, as the air flow  5   a  can be led to the surface of the fins  1  near the heat receiving face as previously mentioned, the function of the heat dissipating fins is enhanced, thus the heat dissipating properties of the heatsink are improved.  
         [0076]    In FIGS.  7  ( b ) and ( c ), a comparison is made between the columns  2  with and without the plate section  2   a  on condition that the heat diffusion plate  2   c  and the heat producing element  3  are provided. In the construction shown in FIG. 7 ( b ), the fins  1  near the heat receiving face contact directly with the heat diffusing plate  2   c  because of the absence of the plate section  2   a . Therefore, air can not be sent to the fins  1  disposed on the lower part. Compared with this, in the construction illustrated in FIG. 7 ( c ), the plate section  2   a  is provided on the column  2 . By setting a width L 1  of the heat conducting plate section  2   a  narrower than a width L 2  of the heat sink , space is created between the plate section  2   a  and the heat diffusing plate  2   c , thereby allowing air to reach the fins  1  placed at the lower part near the heat receiving face.  
         [0077]    The Fifth Embodiment  
         [0078]    The manufacturing method of the heatsink of the present invention is described below with reference to FIGS. 8, 9 and  10 .  
         [0079]    [0079]FIG. 8 ( a ) shows the initial condition of a heat conductive material  6 . FIG. 8 ( b ) shows a first process in which a plurality of plate fins  1   c  are formed along the length of the column  2  by a cutting, extrusion or pultrusion method. FIG. 8 ( c ) shows a second process in which a plurality of fins  1  are formed on both side faces of the column  2  by providing slits at right angle to the length of the plate fins  1   c.    
         [0080]    The first process is conducted by a cutting, extrusion or pultrusion method. The example below refers to the extrusion method.  
         [0081]    In FIG. 9 ( a ), a high-temperature heat conductive material is pressed into an extrusion die  10  in the direction marked by an arrow. Successively, the material  6  is pressed out and plastically deformed into the same shape as the mold cavity. At this point, the column  2  and the plate fins  1   c  are formed simultaneously as shown in FIG. 8 ( b ). The first process is completed by cutting at a predetermined length the material  6  which is pressed out from the mold cavity as shown in FIG. 9 ( c ).  
         [0082]    In the second process, the shape of the heatsink having a plurality of fins shown in FIG. 10 ( a ) is formed by the cutting process. In this embodiment, as shown in FIG. 10 ( b ), a cutting tool  11  is used to slit a plurality of heatsinks which are placed parallel to one another on a tilted jig  12   a , so as to convert plate fins on one side to a plurality of fins  1 . Successively, as FIG. 10 ( c ) shows the plate fins  1   c  on the other side are processed to modify them to the fins  1 .  
         [0083]    If a plurality of cutting tools are placed parallel to one another and the heatsinks are machinedat a time in the above-mentioned second process, the process requires less time.  
         [0084]    Furthermore, the second process can be processed by the laser cutting method.  
         [0085]    This embodiment achieves efficient and low cost manufacture of compact and high-performance heatsinks with a plurality of fins. The heatsinks produced by the manufacturing method of this embodiment have thoroughly one-piece construction, therefore they can achieve a remarkably superior heat dissipation capability.  
         [0086]    The Sixth Embodiment  
         [0087]    [0087]FIG. 11 shows perspective views of the cooling apparatus having cooling fans mounted on the top of the heatsink in accordance with the first and second preferred embodiments of the present invention. FIGS.  11  ( a ) and ( b ) show the cooling apparatus where one cooling fan and two cooling fans are respectively disposed on the heatsink of the present invention. The cooling fan  4  can be mounted on top of the heatsink with screws, adhesives, clips, belt, or clip pins.  
         [0088]    The height of the heatsink of the present invention can be lowered while maintaining high cooling capability. Therefore, the overall height can be kept low even when the cooling fan  4  is mounted, thereby achieving a compact cooling apparatus.  
         [0089]    As a cooling means for the cooling apparatus, the cooling fan  4  was used in this embodiment, however, heat exchange elements such as Peltier elements can alternatively be used as a cooling means. As yet another cooling means, a heat pipe can be used to transfer the heat of the heatsink to an other place to cool it down. It is also possible to immerse the heatsink into liquid to cool it down.  
         [0090]    As described above, the heatsink of the present invention, which forms part of the cooling apparatus of this embodiment has fins on both side faces of the column  2  functioning as a heat conducting section. The cooling apparatus of this embodiment will allow superior cooling capability compared with a conventional cooling apparatus of the same volume. In other words, when the performance is set to be the same as that of the conventional cooling apparatus, the cooling apparatus of this embodiment can be the smaller and the lighter.  
         [0091]    As described thus far, the heatsinks of the present invention improve the diffusing effect of the heat produced by the heat producing element by introducing a heat conducting section of a pole-type column. Furthermore, sufficient heat dissipating area can be secured since the fins are provided on both faces of the column, thereby realizing high heat dissipation capability and a reduction in size.  
         [0092]    Introduction of the heatsink of the present invention allows the cooling apparatus of the present invention to achieve higher performance and smaller size compared with the conventional apparatus.  
         [0093]    The manufacturing method of the heatsink of the present invention provides productive and low-cost manufacturing of high performance heatsinks.