Abstract:
A heat sink comprising a body made of a metallic material with good thermal and electricity conduction properties having a surface intended to support an electronic power component forming a heat source. The body comprises a plurality of openings axially crossed by tubes of circulation of a cooling liquid. Each tube being formed of a material with a good thermal conductivity and being separated from the body by a ring-shaped electric isolation layer formed of a compressed powder of at least one material with good electric isolation and thermal conduction properties.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a heat sink for an electronic power component, for example, a thyristor, a triac, a MOS power transistor, or an insulated gate bipolar transistor (IGBT). More specifically, the present invention relates to a heat sink in which a cooling liquid is circulated to carry off calories provided by the electronic power component.  
         [0003]     2. Discussion of the Related Art  
         [0004]     The heat sink must ensure three main functions: 
        mechanically mounting the component to be cooled down;     carrying off calories provided by the component; and     electrically isolating the component from the cooling liquid.        
 
         [0008]     A conventional heat sink generally comprises a parallelepipedal body on which is mounted the component to be cooled down, and which is formed of a material with a good thermal conductivity. To ease the component assembly on the component and avoid generation of thermal resistances, the material forming the heat sink body generally also is a good electric conductor. It generally is metal, for example, copper or aluminum. The body is crossed by parallel cylindrical openings containing tubes conducting the cooling liquid.  
         [0009]     French application 2,729,044 filed by Atherm Company describes a heat sink in which each tube is formed of an electric isolator to electrically isolate the cooling liquid from the electronic power component. Each tube is separated from the corresponding opening of the heat sink body by a gap filled with a metal alloy, to optimize the thermal exchange between the electronic power component and the cooling liquid.  
         [0010]     It may however be difficult to find for all tubes a material which provides a convenient compromise between a good electric isolation and a good thermal conductivity. Indeed, each tube must have walls of a thickness greater than a minimum thickness to obtain a sufficient electric isolation and to have a sufficient mechanical hold, especially to simplify the tube handling and assembly. This tends to decrease the thermal conductivity properties of the tube.  
         [0011]     Further, the manufacturing of such a heat sink is relatively complex, especially to ensure a good mounting of the tubes with respect to the heat sink body.  
         [0012]     Further, according to French application 2,729,044, the heat sink may comprise, in each tube, means for guiding the cooling liquid flow in the tube, called a “turbulator”. Turbulators enable increasing the local Reynolds coefficient of the cooling liquid flowing in the tubes to increase thermal exchanges between the cooling liquid and the tubes. The turbulators are maintained in the associated tubes via screws, which increases the complexity of the assembly of such a heat sink.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention aims at obtaining a heat sink for an electronic power component comprising a heat sink body, on which the component is assembled, crossed by tubes conducting a cooling liquid flows, the heat sink enabling increasing thermal exchanges between the cooling liquid and the heat sink body.  
         [0014]     Another object of the present invention consists of improving the electric isolation of the cooling liquid with respect to the component.  
         [0015]     Another object of the present invention consists, in the case where the cooling tubes are equipped with turbulators, of easing the turbulator assembly.  
         [0016]     To achieve these objects, the present invention provides a heat sink comprising a body made of a metallic material having a surface intended to support an electronic power component, the body comprising a plurality of openings axially crossed by tubes of circulation of a cooling liquid, each tube being formed of a material with a good thermal conductivity and being separated from the body by a ring-shaped electric isolation layer formed of a compressed powder of at least one material with good electric isolation and thermal conduction properties.  
         [0017]     According to an embodiment of the present invention, each tube is made of metal.  
         [0018]     According to an embodiment of the present invention, the compressed powder is a boron nitride and/or aluminum nitride powder.  
         [0019]     According to an embodiment of the present invention, the heat sink further comprises, at least in a tube, guiding means intended to accelerate the cooling liquid flow in contact with the tube are made of a material with a good thermal conductivity.  
         [0020]     According to an embodiment of the present invention, the guiding means is only maintained by contact with the tube.  
         [0021]     According to an embodiment of the present invention, the guiding means comprise a cylindrical portion on the circumference of which extend grooves separated by teeth, the grooves being adapted to the flowing of the cooling liquid, the teeth being in contact with the tube.  
         [0022]     The present invention also provides a method for manufacturing a heat sink, comprising the steps of: 
        a) providing a heat sink body made of a metallic material having a surface intended to support an electronic power component, the body being crossed by a plurality of openings;     b) placing in each opening a tube separated from the opening by a ring-shaped gap;     c) filling each ring-shaped gap with a powder of at least one material with good electric isolation and thermal conduction properties; and     d) compressing the powder in each gap.        
 
         [0027]     According to an embodiment of the present invention, step b) comprises, for each opening, the arrangement of a tubular jointing sleeve crossed by an orifice at one end of the opening, the tube being maintained in the orifice of the jointing sleeve distantly from the body, the powder being then introduced, at step c), through the ring-shaped gap at the level of the axial end of the opening opposite to the jointing sleeve.  
         [0028]     According to an embodiment of the present invention, step d) is followed by the arrangement of an additional tubular sleeve at the level of the end of the opening through which the powder has been introduced.  
         [0029]     According to an embodiment of the present invention, the method comprises before step c), the arrangement of guiding means in at least one tube, the powder compression being performed to deform the tube so that it comes into contact with and maintains in place the guiding means.  
         [0030]     The foregoing objects, features, and advantages of the present invention, as well as others, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is a simplified perspective view of an example of the forming of a heat sink according to the present invention on which is assembled an electronic power component to be cooled down;  
         [0032]      FIG. 2  is a top view of the heat sink of  FIG. 1 ;  
         [0033]      FIG. 3  is a cross-section view of  FIG. 2  along line III-III;  
         [0034]      FIG. 4  is an enlargement of a portion of  FIG. 3 ;  
         [0035]      FIG. 5  is a cross-section view of  FIG. 4  along line V-V; and  
         [0036]      FIG. 6  is a simplified perspective view of an example of the forming of a turbulator. 
     
    
     DETAILED DESCRIPTION  
       [0037]      FIG. 1  schematically shows an example of the forming of a heat sink  10  according to the present invention, comprising a parallelepipedal body  12 , formed of a material which is both a good thermal conductor and a good electric conductor, for example, copper or aluminum, on which is attached an electronic power component  14  to be cooled down.  
         [0038]      FIG. 2  is a top view of heat sink  10 . Body  12  is crossed by parallel openings, not visible in  FIG. 2 , of circular cross-section, in which flows a cooling liquid, for example, glycol water. The circulating of the liquid is ensured by an intake manifold  16  and an exhaust manifold  18 . Isolating connections  20 ,  21 , for example, made of silicon, are provided between body  12  and manifold  16 ,  18 .  
         [0039]      FIG. 3  is a cross-section view of  FIG. 2  along line III-III formed at the level of an opening  22  crossing body  12  of the heat sink. The structure described hereafter is identical for each opening  22  of body  12  of the heat sink. Opening  22  contains a metal tube  24 , for example, made of copper or aluminum, corresponding to a good thermal conductor, which is separated from opening  22  by a gap  26 . As an example, tube  24  has a radial thickness on the order of 0.5 mm and the gap has a radial thickness on the order of 2 mm. Gap  26  contains a compressed powder formed of a material which corresponds to a good electric isolator and to a good thermal conductor. The powder may also be formed of a mixture of materials that each correspond to a good electric isolator and to a good thermal conductor. It is for example boron nitride or aluminum nitride. Tube  24  comprises a first end portion  28  which prolongs out of opening  22  and which is mounted to intake manifold  16  and a second end portion  30  which prolongs out of opening  22  and which is mounted to exhaust manifold  18 . The connection between each end portion  28 ,  30  of tube  24  and intake manifold  16  and exhaust manifold  18  may be formed by any known method, for example, by welding or by soldering. On either side of body  12  of the heat sink, a portion of end portions  28 ,  30  of tube  24  protruding out of body  12  is surrounded with an isolating jointing sleeve  32 ,  34 , for example, made of glass fiber, slightly penetrating into opening  24  of body  12 , between tube  24  and body  12 . Isolating connections  20 ,  21  surround end portions  28 ,  30  of tube  24  and a portion of isolating sleeves  34  between body  12  and manifolds  16 ,  18  to prevent the forming of electric arcs between body  12  and tube  24 . A turbulator  36 , having the shape of a full profile, is arranged in tube  24 . Turbulator  36  delimits with the tube ducts  38 , extending along the entire length of opening  22 , conducting the cooling liquid.  
         [0040]     Inlet and exhaust manifolds  16  and  18  comprise internal openings, not shown, arranged to obtain a specific type of flow of the cooling liquid in body  12  of the heat sink. According to a first example, intake manifold  16  and exhaust manifold  18  may each comprise an opening into which all tubes  24  emerge so that the cooling liquid simultaneously flows in each tube  24  from intake manifold  16  to exhaust manifold  18 . According to a second example, intake manifold  16  and exhaust manifold  18  comprise orifices connecting tubes  24  in pairs so that the cooling liquid zigzags successively from a tube to an adjacent tube.  
         [0041]      FIG. 4  is an enlarged view of a portion of  FIG. 3  at the level of an end of tube  24 . Opening  22  divides into a main opening  39  of constant circular cross-section which prolongs at each end in an end opening  40 , of larger diameter, connected to main opening  39  by a shoulder  41 . Each isolating end sleeve  34  comprises a main tubular portion  42  having its external diameter corresponding to the inner diameter of end opening  40  and having its inner diameter corresponding to the outer diameter of tube  24 . Main tubular portion  42  prolongs in a secondary tubular portion  43  having its outer diameter corresponding to the inner diameter of end opening  40  and having its inner diameter substantially corresponding to the inner diameter of main opening  39 . Secondary tubular portion  43  abuts against shoulder  41 , a portion of main tubular portion  42  then extending out of opening  22 .  
         [0042]      FIG. 5  is a cross-section view of  FIG. 4  along line V-V and  FIG. 6  is a perspective view of turbulator  36 . Turbulator  36  has the shape of a cylindrical tree of axis D on the circumference of which are distributed teeth  45  which extend parallel to axis D along the entire length of turbulator  36 . Passages  38  delimited between turbulator  36  and tube  24  correspond to the grooves between two adjacent teeth  45 . Turbulator  36  enables locally increasing the speed of the cooling liquid and thus increasing the local Reynolds coefficient of the cooling liquid which is representative of the thermal exchanges between the cooling liquid and tube  24  and between the cooling liquid and turbulator  36 .  
         [0043]     Turbulator  36  is in contact with tube  24  at the level of the ends of teeth  45 , which causes thermal exchanges between turbulator  36  and tube  24 . Turbulator  36  is then advantageously formed of a material with a good thermal conductivity and takes part in the carrying off of the calories provided by the component to be cooled down. As an example, turbulator  36  may be formed of the same material as tube  24 . The cross-section shown in  FIG. 5  is particularly advantageous since it enables obtaining a significant thermal exchange surface area between turbulator  36  and tube  24 .  
         [0044]     More generally, the cross-section of turbulator  36  is defined according to the flow rate and to the head loss which is desired to be obtained for tube  24  while attempting to bring the thermal exchanges between turbulator  36  and tube  24  to a maximum. In the case where it is necessary to have a relatively large flow rate run through tube  24 , a hollow turbulator  36  may be provided, the cooling liquid being then able to flow through turbulator  36  and around it.  
         [0045]     Further, it is possible for turbulator  36  not to have a constant cross-section. As an example, teeth  45  may have a helical shape wound around axis D.  
         [0046]     An example of a method for manufacturing heat sink  10  according to the present invention comprises the steps of: 
        forming openings  22  in body  12  of the heat sink;     arranging isolating sleeves  32  at the level of end openings  40  of openings  22  located on a same side of body  12 ;     arranging tubes  24  in openings  22  by inserting an end of each tube  24  into the corresponding isolating sleeve  32 ,  34 , which automatically centers tube  24  with respect to opening  22  and defines gap  26 ;     arranging a turbulator  36  in each tube  24 . The diameter of tube  24  is then slightly greater than the maximum diameter of turbulator  36  so that turbulator  36  is not in contact with tube  24 , or very slightly in contact with tube  24 . This eases the insertion of turbulator  36  into tube  24  but requires the use of a system for temporarily holding turbulator  36 ;     for each opening  22 , filling gap  26  with a powder, for example, boron nitride, through the end of opening  22  opposite to previously-arranged isolating sleeve  32 ,  34 ;     compressing the powder with a piston to obtain a compact structure exhibiting the desired thermal conductivity and electric isolation properties. The compression causes a slight deformation of tube  24  which then contacts turbulator  36 ; and     arranging isolating sleeves  32 ,  34  at the ends of openings  22  used for the powder introduction.        
 
         [0054]     Inlet and exhaust manifolds  16  and  18  are then fixed to the ends of tubes  24  and isolating connections  20 ,  21  are arranged.  
         [0055]     The present invention has many advantages.  
         [0056]     First, the thermal conductivity criterion is the main criterion to be taken into account in the selection of the material forming tubes  24 . The electric isolation criterion is then not to be taken into account. This enables using metal tubes  24  which keep remarkable thermal conductivity properties even for significant thicknesses. The radial thickness of the tubes then no longer is a constraint and may be determined only according to the mechanical hold that the tube must have, especially to enable its mounting on the manifolds. The compromise between a good electric isolation and a good thermal conductivity concerns the compressed powder arranged between tubes  24  and body  12  of the heat sink. However, since it is a compressed powder, there is no specific mechanical hold constraint as in the case of a conventional heat sink where the tube itself ensures the electric isolation. The radial thickness of the gap containing the compressed powder may correspond to the minimum thickness ensuring a proper electric isolation. This enables degrading as little as possible the thermal conductivity of the electric isolation layer formed by the compressed powder. In particular, for equivalent electric isolation performances, the radial thickness of the gap containing the compressed powder of a determined material is smaller than the thickness of a cooling liquid flow tube formed with the same electric isolating material implemented in a conventional heat sink.  
         [0057]     Second, when turbulators  36  are used, they are in direct contact with associated tubes  24 . Each turbulator  36  may then advantageously be formed of a material with a good thermal conductivity to take part in the thermal exchange between the cooling liquid and body  12  of the heat sink. In particular, turbulators  36  may be metallic.  
         [0058]     Third, when turbulators  36  are used, they are maintained by the contact forces between the turbulators and the associated tubes, such contact forces being created on compression of the powder. It is thus not necessary to provide an additional turbulator hold system, which simplifies the structure of the heat sink according to the present invention.  
         [0059]     Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. In particular, the thickness examples mentioned for the tubes and the gaps are given as an example and are to be adapted by those skilled in the art according to the envisaged application.  
         [0060]     Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.