Abstract:
The invention relates to an electronic device operating in difficult environments. The electronic device comprises at least one printed circuit board supporting heat-dissipating electronic components, a heat sink, a first side of which is in contact with electronic components on a first side of the printed circuit board, and a second side of which is designed to evacuate heat by convection, characterized in that it also comprises a cover delimiting a channel in which a coolant circulates to ensure convection, the cover being joined to the heat sink and the printed circuit board, and in that the channel prevents the coolant from coming into contact with the electronic components.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present Application is based on International Application No. PCT/EP2006/061780, filed on Apr. 24, 2006 which in turn corresponds to France Application No. 05 05210, filed on May 24, 2005, and priority is hereby claimed under 35 USC §119 based on these applications. Each of these applications are hereby incorporated by reference in their entirety into the present application. 
     FIELD OF THE INVENTION 
     The invention relates to an electronic device operating in difficult environments. 
     The invention is of particular use in aeronautics and particularly on board small and non-pressurized aircraft, in particular helicopters, that do not benefit from a protected climatic environment guaranteed by their structure or by their air conditioning function. Such a protected climatic environment is necessary to the operation of the electronic equipment, for example the printed circuit boards, mounted on board aircraft. In practice, a forced movement of coolant, such as air for example, in proximity to electronic equipment is used to evacuate the heat that the electronic equipment dissipates. The life span of such electronic equipment is degraded if the circulating coolant carries impurities, corrosive impurities for example. It is therefore necessary to ensure a circulation of coolant in proximity to the electronic equipment while avoiding any direct contact between the fluid and the electronic equipment. 
     DESCRIPTION OF THE PRIOR ART 
     One solution to this problem is to make an electronic gear module in which printed circuit boards are fitted seal-tight to the coolant. One drawback presented by this solution stems from the fact that the evacuation from the module of the heat dissipated by the electronic components carried by the printed circuit boards is then not always sufficient or can even be achieved only at the cost of a significant increase in the weight of the module caused by the use of heat drains to direct the heat dissipated by the printed circuit boards to the walls of the module. 
     One major aim of the invention is therefore to overcome this drawback. 
     SUMMARY OF THE INVENTION 
     To achieve this aim, the invention proposes an electronic device comprising an electronic gear module configured to house one or more plug-in electronic subassemblies, each electronic subassembly comprising
         a printed circuit board supporting heat-dissipating electronic components,   a heat sink, a first side of which is in contact with electronic components on a first side of the printed circuit board and a second side of which is designed to evacuate the heat by convection,       

     The subassembly also comprises:
         a cover joined to the heat sink and the printed circuit board, delimiting a channel between the second side of the heat sink and the cover, for a coolant to circulate to ensure convection, deformable seals ensuring the seal-tightness of the channel,       

     said channel preventing the coolant from coming into contact with the electronic components. 
     Compared to the state of the art described above, the invention offers a three-fold advantage:
         its heat dissipation effectiveness is reinforced;   its modularity helps to reduce the weight of the computers;   its compatibility with the known standards governing known aeronautical modules facilitates the design phases.       

     The cover of each electronic subassembly provides both a coolant channeling function for the electronic board that it comprises, and a function for isolating this flow from the components located on the second side of an electronic board of an adjacent electronic subassembly. 
     The heat exchange surface area with a coolant external to the module is directly linked to the integrated circuit board, as close as possible to the sources of heat that it is required to evacuate. The invention therefore makes it possible to avoid the use of a heat drain to evacuate the heat from the module, which is very favorable with regard to the thermal budget. This is all the more true when the number of integrated circuit boards fitted in the module is high, because the heat exchange surface area is proportional to the number of integrated circuit boards used. Also, the use of a heat drain covering all possible dissipation, since it can be heavy and/or bulky, is not always favorable in terms of the weight and volume budget. Such is the case, for example, when the module is equipped with a single integrated circuit board. 
     According to one characteristic of the invention, the electronic gear module is provided with openings enabling a coolant coming from outside the electronic gear module to circulate in the channel. 
     Advantageously, the device comprises means to ensure the seal-tightness of the channel relative to the useful interior space of the electronic gear module. 
     Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious aspects, all without departing from the invention. Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  represents an exploded view of an electronic subassembly of the inventive electronic device comprising a printed circuit board, a heat sink, a cover and deformable seals; 
         FIG. 2   a  represents, in a perspective view, an electronic gear module that can contain an electronic subassembly; 
         FIG. 2   b  represents, in a cut-away perspective view, the internal structure of the cavity formed by the electronic gear module represented in  FIG. 2   a;    
         FIG. 3  represents, in a cut-away perspective view, an inventive electronic device comprising an electronic subassembly as represented in  FIG. 1  and an electronic gear module as represented in  FIG. 2   b,  and explains the means by which the electronic subassembly is housed in the module; 
         FIG. 4  represents, in cross section, a detail of the internal structure of an inventive electronic device; 
         FIG. 5  represents, in cross section, an inventive electronic device comprising an electronic gear module and several electronic subassemblies. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     To facilitate the reading of the description, the same references denote the same elements in the different figures. 
       FIG. 1  represents, in an exploded view, an inventive electronic device comprising a printed circuit board  1 , a heat sink  5 , a cover  10  and deformable seals  16 . 
     The printed circuit board  1  supports electronic components that dissipate heat when they are powered and operating. Preferably, the electronic components that dissipate the most heat are assembled on a first side  111  of the printed circuit board  1 . 
     Advantageously, the heat sink  5  is roughly flat, parallel to the printed circuit board  1 . 
     A first side  51  of the heat sink  5  is designed to be placed in contact with electronic components on the first side  111  of the printed circuit board  1 , on a horizontal axis  100 . A second side  52  of the heat sink  5  is designed to evacuate the heat by convection. The second side  52  comprises, for example, fins whose dimension in a vertical axis  101  corresponds to the vertical dimension of the board  1 . 
     Advantageously, the cover  10  is roughly flat, parallel to the printed circuit board  1 . 
     The cover  10  is designed to be applied against the heat sink  5 , on the horizontal axis  100 . 
     The deformable seals  16  are of linear form, and are fixed to the heat sink  5 , or to the cover  10 . They maintain a free space between the second side  52  of the heat sink  5  and the cover  10 . 
     When the printed circuit board  1 , the heat sink  5 , the deformable seal  16 , and the cover  10  are joined together on the axis  100  to form a joined assembly, they form an electronic subassembly  1000 . In this case, the second side  52  of the heat sink  5  and the cover  10  delimit a seal-tight channel  4 , represented more explicitly in  FIG. 4 , in which a coolant  20  can circulate along the vertical axis  101 , to ensure convection of the heat dissipated by the heat sink  5 . 
     The coolant  20  is, for example, blown air, possibly carrying corrosive impurities. 
       FIG. 2   a  represents, in a perspective view, an inventive electronic gear module  15 . The horizontal axis  100  and the vertical axis  101  are common to  FIGS. 2   a  and  2   b.    
     The module  15  is metal, parallelepipedal in form and delimits an internal cavity. Horizontal sides  151 ,  152  of the module  15  comprise openings  2 , which are leading orifices connecting the interior and the exterior of the module. One side  153  of the module  15  is removable, and can be temporarily removed to introduce into the cavity formed by the module  15  at least one electronic subassembly  1000  similar to that of  FIG. 1 , on a horizontal axis  102 . One side  154  of the module  15  is equipped with at least one connector  150 , intended to be connected with a complementary connector. 
     The complementary connector is mounted on a backplane of a subrack, to provide the electrical connections for the electronic gear of the module  15 , with the external environment in which they are intended to operate. 
     A module equipped with such a connector  150  is “rackable” in that it can be placed with others in an electronic gear storage rack with standardized dimensions. 
     This type of module  15  is routinely used in aeronautics, for example to produce onboard computers. When the removable side  154  closes the module  15 , the module  15  is seal-tight to the coolant  20  in which it is submerged, apart from the openings  2 . 
     Advantageously, the electronic gear module  15  is pluggable and can be mounted, with others, removably on a subrack. 
       FIG. 2   b  represents a partial, cut-away perspective view of an inventive electronic gear module  15 . The module  15  comprises, on internal walls of the horizontal sides  151 ,  152 , a locking means and sliders  6 . The locking means, not represented, is used to join the subassembly  1000  to the module  15 . The sliders  6  are used to guide the electronic subassembly  1000  inside the module  15 . The sliders  6  include leading orifices  9 , connecting the interior space of the module  15  with fluid circulation filaments  71  and  72 . The filaments  71 ,  72  are, themselves, connected to the outside of the module  15 , through openings  2 , placed on the surface of the module  15 , and leading to the filaments  71 ,  72 . The openings can be seen in  FIG. 2   a  and are not represented in  FIG. 2   b.  Apart from the leading orifices  9 , and the openings  2 , the filaments  71 ,  72  are seal-tight. 
       FIG. 3  represents, in a perspective view, an inventive electronic device comprising a subassembly  1000  identical to that represented in  FIG. 1 , and an electronic gear module  15  identical to that represented in  FIG. 2   b.  The subassembly  1000  comprises a printed circuit board  1 , a heat sink  5 , deformable seals  16 , not visible in  FIG. 3 , and a cover  10 . 
     The cover  10  and the second side  52  of the heat sink  5  delimit a sealed channel  4 , visible in  FIG. 4 . The channel  4  has two ends  81 ,  82  located, in the representation of  FIG. 3 , respectively on the bottom and top parts of the subassembly  1000 . 
     The module  15  is partially represented to show how the subassembly  1000  is housed in the module  15 . The subassembly  1000 , guided by the sliders  6 , can, in the module  15 , take a position, called locked position, in which a locking means joins it to the module  15 . Once in the locked position, the electronic subassembly  1000  is fully inserted inside the module  15 , which makes it possible to enclose the subassembly in the module  15  by replacing the side  153  of the module  15 , to close it. 
     When the subassembly  1000 , housed in the module  15 , is in the locked position, the leading orifices  9 , and the ends  81 ,  82  of the channel  4 , are perfectly juxtaposed. Thus, a coolant  20 , in which the exterior of the module  15 , including all its sides, is submerged, can enter into the module  15 , exclusively through the openings  2 . Said coolant then follows the circulation filaments  71 ,  72 , to reach the leading orifices  9 , enter into the channel  4 , and lick the second side  52  of the heat sink  5 , avoiding any contact with the electronic components carried by the printed circuit board  1 . 
       FIG. 4  represents a detail of the contact between the electronic subassemblies  1001 ,  1002 , similar to those of  FIG. 1 , and a module  15 , similar to that of  FIG. 2   b,  in a partial view, in cross section on a plane orthogonal to that of the printed circuit boards of the subassemblies, or even along the plane formed by  100  and  101 . 
     These two electronic subassemblies  1001 ,  1002  are placed in the locked position, parallel to one another, in the module  15 . Each of the subassemblies  1001 ,  1002  is guided by a slider  61 ,  62  and joined to the module  15 , by a locking means which is not represented. Each subassembly  1001 ,  1002  comprises a printed circuit board  1051 ,  1052 , a heat sink  501 ,  502 , deformable seals which are not represented in this figure, identical to those represented in  FIG. 1 , and a cover  1011 ,  1012 . For each electronic subassembly  1001 ,  1002 , a seal-tight channel  41 ,  42  is formed between the heat sink  501 ,  502  and the cover  1011 ,  1012  that comprise it. 
     One end  811 ,  812  of the channel forms an inlet for a coolant  20 , coming from outside the module  15 , and another end,  821 ,  822 , not represented, forms an outlet for the coolant  20 . The ends  811  and  812  lead to orifices  9 , placed on a wall of a fluid circulation filament  71 , internal to the module  15 . The wall of the filament  71  also comprises openings  2 , which are leading orifices to the outside of the module  15 , and which are not represented in this figure. The number and the size of the leading orifices  9  are suited to each channel  41 ,  42  to correspond to the convection dissipation requirement of the corresponding heat sink  51 ,  52 . The number and the size of the openings  2  are adapted to correspond to the overall convection dissipation requirement of the heat sinks of the electronic subassemblies enclosed in the module  15 . 
     The connection between the channel  41 ,  42  and the fluid circulation filaments  71 ,  72  is seal-tight. The seal-tightness is provided on the one hand by the locking means, and on the other hand by seal-tight deformable seals  121  and  122  placed between the electronic subassembly and the internal structure of the module  15 . 
     A coolant  20 , external to the module  15 , penetrates into the module  15  through the openings  2 , placed on a common wall of the module  15  and the filament  71 . It is transported by the filament  71  to leading orifices  9 , which give access to the end  811 ,  812  of the seal-tight channel  41 ,  42 . The coolant  20  then passes through the seal-tight channel  41 ,  42  to reach the other end  821 ,  822 , not represented, of the channel  41 ,  42  through the leading orifices  921 ,  922 , also not represented, which give access to the filament  72 , again not represented. The coolant  20  finally passes through the filament  72  and leaves the module  15  through the openings  2 , placed on a common wall of the module  15  and the filament  72 . 
       FIG. 5  represents an inventive electronic device comprising an electronic gear module  15  and six electronic subassemblies  1001 ,  1002 ,  1003 ,  1004 ,  1005 ,  1006 , similar to those of  FIG. 1 , housed in the module  15 , in their locked position, in a cross-sectional view on a plane orthogonal to the printed circuit boards of the subassemblies, or even on the plane formed by  100  and  102 . 
     The module  15  comprises internal connectors  130 , into which are plugged electronic subassemblies  1000 . The internal connectors  130  are carried by an interconnection module  140  comprising electronic contacts, each contact comprising two ends. One end of the contacts is connected to the connector  150  of the module  15 . The other end of the contacts is connected to the contacts of the printed circuit board. 
     In other words, the printed circuit board  1  plugs into the electronic gear module  15 . 
     Advantageously, the electronic gear module  15  and the printed circuit board  1  housed in the electronic gear module  15  conform to a specification from the following list: ARINC 600, MIL 83 527, ARINC 404A. 
     It will be readily seen by one of ordinary skill in the art that the present invention fulfils all of the objects set forth above. After reading the foregoing specification, one of ordinary skill in the art will be able to affect various changes, substitutions of equivalents and various aspects of the invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalent thereof.