Abstract:
A power module with heat sources wherein the heat is dissipated by a heat sink. The heat sink includes a manifold with coolant flowing therein. An opening on the manifold enables the coolant to come in direct contact with a base plate of the power module. The power module being retained on the heat sink by a plurality of spring clips.

Description:
TECHNICAL FIELD 
     The present invention relates generally to a method and apparatus for mounting a power module and, more particularly, to clip fasteners for securely mounting a power module to a heat sinking surface or medium. 
     BACKGROUND OF THE INVENTION 
     The usual hybrid power modules (HPM) in power inverter for motor drives is well known. The power modules include associated power switches and other related functions. A common method of mounting these devices is by inserting a screw in each of the mounting holes provided at each corner thereof with the screw engaging threaded holes in a chassis. These power modules generate excessive heat and therefore include a thermally conductive baseplate to dissipate the excessive heat. The baseplate is typically a metallic plate in thermal communication with the power switches of the module. 
     It is also known for a hybrid power module to be mounted over an opening of a fluid manifold so that liquid coolant flowing through the manifold comes into direct contact with the coolant for cooling the power module. This arrangement has the advantage of a more efficient cooling than using ambient air. The environment of the power module and/or the ambient air surrounding the power module typically does not provide efficient cooling. The baseplate of the power module is sealed to the coolant manifold by an O-ring seal to prevent coolant from leaking from the manifold. Accordingly, a consistent force across each edge of the module is desired to ensure that the O-ring does not leak over its design life and environment. 
     Typically, the power module is mounted to the manifold by four bolts at the corners of the power module (through the aforementioned mounting  holes). The bolts pass through respective mounting holes in the baseplate and tightened within threaded holes in the manifold. The long space between mounting holes located at the corners allows the center portion of the edge of the baseplate to deflect. This deflection can cause a leak. The base plate has also been provided with a plurality of mounting holes intermediate the corner holes to prevent the deflection of the baseplate. While the additional mounting holes allow the power module to be securely mounted to the cooling manifold, this configuration increases the cost and labor to mount the power module. In addition, the intermediate mounting holes take up valuable space which could be used to mount devices or reduce the size of the power module. 
     SUMMARY OF THE INVENTION 
     It is therefore, a primary object of the present invention to provide a novel apparatus and method for mounting power modules. The power module is mounted over an opening of a fluid manifold so that liquid coolants flowing through the manifold comes into direct contact with the coolant for cooling the power module. As in the prior art, this arrangement has the advantage of a more efficient cooling than using ambient air. The environment of the power module and/or the ambient air surrounding the power module typically does not provide efficient cooling. The power module includes a thermally conductive baseplate to dissipate the excessive heat generated during operation. The baseplate of the power module is sealed to the coolant manifold by an O-ring seal to prevent coolant from leaking from the manifold. A consistent force across each edge of the module is maintained by a plurality of connecting elements to ensure that the O-ring does not leak over its design life and environment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         FIG. 1  is an exploded view of a power module mounted to a cooling manifold embodying the present invention; 
         FIG. 2  is a perspective view of the power module with a baseplate, a cover of the baseplate, and a manifold of  FIG. 1 ; and 
         FIG. 3  is a cross sectional view of power module of  FIG. 2  taken along line  3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1-3 , a hybrid power module assembly, generally designated  10  is mounted to a cooling manifold or heat sinking member  12  wherein liquid coolant flows. While a hybrid power module is illustrated, one skilled in the art will recognize that the present invention may apply to any electronic device that requires cooling. The hybrid power module includes electronic circuit/components thermally connected to a generally rectangular baseplate  14 . The baseplate  14  having an upper surface  16  and lower surface  18 . The power module  10  is supported at the upper surface  16  of the baseplate  14 . The manifold  12  has a top  20 , a bottom  22  and sides  24  and  26  which define a channel  28  in which liquid coolant flows. A rectangular opening  30  is defined through the top  20  into channel  28  of the manifold  12 . The baseplate  14  is fitted onto the rectangular opening  30  in the manifold  12  with a gasket (a sealing member)  31  disposed therebetween. It will be appreciated that the gasket could be of any type, including a stamped flat gasket. An O-ring gasket requires a groove for retention which can be cast into either the baseplate or the manifold. It is noted here that the rectangular shape is only exemplary and any suitable shape, preferably corresponding to the shape of the device requiring removal of heat, will suffice. Accordingly, the baseplate  14  and the opening  30  of the manifold may be of other shapes such as oval, round, or other suitable shapes. Indentations  32  are molded into sides  34  and  36  of a case  38  of power module assembly  10 . Case  38  is preferably plastic and encloses the electronic circuits of the power module assembly  10 .  
     A plurality of recesses  40  are formed in sides  24  and  26  of the manifold  12 . Recesses  40  are aligned with indentations  32  to position power module assembly  10  on manifold  12  over opening  30 . A plurality of connecting elements  44  retain power module assembly  10  on manifold  12 . In an exemplary embodiment, connecting elements  44  are generally C-shaped spring clips having an elongated portion  46 , an upper extension  48  and a lower extension  50 . Also, these clips are preferably comprised of metal and are resilient whereby they have a spring retention force. These spring clips are preferably made using a metal stamping process, as such is well known, and provides for a low cost method of manufacturing. Each of these spring clips is installed by mounting one of the extensions, e.g., lower extension  50  in a recess  40  and a force is applied to the elongated portion  46  which causes the upper extension  48  to be urged outwardly (and angled upwardly) as it pushes against the side of the case  38  of the power module assembly  10  until extension  48  enters indentations  32 , and snaps into place. These spring clips are uniformly distributed (located) along opposing sides of power module assembly  10 , to provide a consistent force across each edge of the module. 
     As is best seen in  FIGS. 2 and 3 , the lower surface  18  of the baseplate  14  is in direct contact with the coolant (not shown) flowing within channel  28  of the manifold  12 . It is this direct contact that sinks the heat away from the power module assembly  10  during operation thereof. 
     An advantage of the present invention is that this method of snap fitting the spring clip into the recesses does not require additional area on the baseplate. Further, the spring clips provide consistent pressure across each flange face for sealing. The clips are also low cost stampings similar to those used to clamp radiator housings together. Unlike screws or other threaded fasteners, the spring clips are self adjusting and will not loosen or back out over time. The spring clips also mitigate creep of joint materials. In addition, installation is simple since the spring clips can be accomplished by hand or with simple fixturing. This method can be used with spring clips alone or in  combination with the corner mounting screws. While the immediate application is for direct liquid cooling, this invention can be used to mount modules to a standard heatsink with a thermal grease interface or the like. 
     It will be understood that a person skilled in the art may make modifications to the preferred embodiment shown herein within the scope and intent of the claims. While the present invention has been described as carried out in a specific embodiment thereof, it is not intended to be limited thereby but is intended to cover the invention broadly within the scope and spirit of the claims.