Abstract:
A device with increased heat dissipation abilities for supporting printed wiring boards includes a chassis for holding printed wiring boards, a plurality of fins attached to the chassis, and a heat pipe in each of the plurality of fins that is capable of transferring heat from the chassis to the surrounding ambient by absorbing heat from the chassis at a first end of the heat pipe and releasing the heat into the ambient at a second end of the heat pipe.

Description:
BACKGROUND 
       [0001]    The present invention relates to cooling apparatuses for printed wiring boards, and in particular, to a housing for printed wiring boards with improved heat dissipation abilities. 
         [0002]    Thermal management of aircraft mounted electronic components is becoming increasingly more challenging with the higher density of more powerful, but smaller electronic components. Electronic components are held on printed wiring boards that mechanically support and electrically connect the electronic components. Printed wiring boards absorb heat generated by the electronic components. High heat can damage printed wiring boards and limit the life of the printed wiring board. High heat can also damage the electronic components and cause them to become unreliable. For these reasons, cooling systems and device are needed to remove heat from printed wiring boards. 
         [0003]    Due to space limitations on aircrafts, printed wiring boards are typically stacked in a printed wiring board stack-up. A printed wiring board stack-up is typically held in a housing or chassis that supports the printed wiring board stack-up. The housing or chassis also acts as a cooling apparatus for the printed wiring boards. Heat can transfer through the printed wiring boards to the housing or chassis and can then be dispelled into an ambient. Housings and chassis can have fins running on an outside surface to provide more contact area with the ambient to increase the heat dissipation abilities of the housing or chassis. 
       SUMMARY 
       [0004]    A device with increased heat dissipation abilities for supporting printed wiring boards includes a chassis for holding printed wiring boards, a plurality of fins attached to the chassis, and a heat pipe in each of the plurality of fins that is capable of transferring heat from the chassis to the surrounding ambient by absorbing heat from the chassis at a first end of the heat pipe and releasing the heat into the ambient at a second end of the heat pipe. 
         [0005]    A device with increased heat dissipation abilities for supporting printed wiring boards includes a housing that supports a plurality of printed wiring boards on ledges that run along interior surfaces of the housing, a plurality of fins connected to a first side and a second side of the housing, a cavity in each of the plurality of fins, and a heat pipe in the cavity in each of the plurality of fins to transfer heat generated by the printed wiring boards in the housing to an ambient surrounding the housing. 
         [0006]    A method for cooling printed wiring boards includes transferring heat generated on a printed wiring board to a chassis in which the printed wiring board is held, absorbing heat into a heat pipe that is positioned in a hollow fin on the chassis, transferring the heat through the heat pipe, and releasing the heat from the heat pipe into an ambient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a chassis that is capable of holding printed wiring boards. 
           [0008]      FIG. 2  is a cross-sectional view of the chassis showing heat pipes running through fins on the chassis, taken along line  2 - 2  of  FIG. 1 . 
           [0009]      FIG. 3  is a cross-sectional view of the chassis with printed wiring boards, taken along line  2 - 2  of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    In general, the present invention relates to cooling devices for printed wiring boards. Printed wiring boards can be stacked on top of each other in locations where space is limited. Printed wiring board stack-ups are typically supported by a chassis with fins. The chassis acts as a cooling apparatus for the printed wiring board stack-up, as heat can transfer from the printed wiring boards through the chassis and fins into an ambient. Placing heat pipes in the fins can increase the amount of heat that can be transferred through the fins of the chassis, as heat pipes enable more efficient and effective use of the fin area. 
         [0011]      FIG. 1  is a perspective view of chassis  10  that is capable of holding printed wiring boards. Chassis  10  includes first side  20 , second side  22 , top side  24 , bottom side  26 , first end  28 , second end  30 , cavity  40 , ledges  42  (including ledge  42 A, ledge  42 B, ledge  42 C, ledge  42 D, ledge  42 E, ledge  42 F, ledge  42 G, ledge  42 H, ledge  42 I, ledge  42 J, ledge  42 K, and ledge  42 L), and fins  50  (including fin  50 A, fin  50 B, fin  50 C, fin  50 D, fin  50 E, fin  50 F, fin  50 G, fin  50 H, fin  50 I, fin  50 J, and fin  50 K). 
         [0012]    Chassis  10  is a housing that is capable of holding printed wiring boards. Chassis  10  has first side  20  that is opposite second side  22 , top side  24  that is opposite bottom side  26 , and first end  28  that is opposite second end  30 . In the embodiment shown, chassis  10  is made out of aluminum. In alternate embodiments, chassis  10  can be made out of any suitable material that is capable of supporting and cooling printed wiring boards. Chassis  10  can be manufactured with any suitable manufacturing process, including machining or casting. Chassis  10  can hold printed wiring boards in cavity  40 . In the embodiment shown in  FIG. 1 , cavity  40  runs through chassis  10  with a first opening at first end  28  and a second opening at second end  30 . In alternate embodiments, cavity  40  can run through chassis  10  in any direction and chassis  10  can have any number of openings. 
         [0013]    Positioned in cavity  40  are ledges  42 . Ledges  42  are rectangular shaped flanges that extend longitudinally from first end  28  to second end  30  along a first interior side of cavity  40  (shown in  FIG. 1  as ledges  42 A- 42 F) and a second interior side of cavity  40  (shown in  FIG. 1  as ledges  42 G- 42 L). Ledges  42  are positioned in cavity  40  to provide a support upon which printed wiring boards can be supported. Ledges  42  can be manufactured with chassis  10  or added to chassis  10  after it has been manufactured. 
         [0014]    Fins  50  are positioned on first side  20  and second side  22  of chassis  10 . In the embodiment shown in  FIG. 1 , fins  50  are rectangular shaped flanges that extend longitudinally from first end  28  to second end  30  along an exterior surface of first side  20  and second side  22 . In alternate embodiments, fins  50  can have any suitable shape and can be placed on any number of sides of chassis  10 . Fins  50  can be manufactured with chassis  10  or added to chassis  10  after it has been manufactured. Fins  50  are positioned on chassis  10  to dispel heat from chassis  10  into an ambient. Chassis  10  can be positioned in an aircraft so that cooling air flows around and between fins  50 . 
         [0015]    Chassis  10  is cooled with convective heat transfer. Convective heat transfer transfers heat through the movement of fluids, and more specifically from a hotter location to a cooler location by moving a cooler fluid over a warmer location. Chassis  10  is cooled when cooling air flows around chassis  10 , as the cooling air moves over the solid surface of chassis  10  to absorb heat from chassis  10 . 
         [0016]    Placing fins  50  on chassis  10  is advantageous, as fins  50  increase the amount of surface area that cooling air can touch when cooling air is flowing around chassis  10 . The location and quantity of fins  50  on chassis  10  can vary to maximize cooling efficiency for any given application. The efficiency of convective heat transfer improves as the surface area between the hotter location and the cooler fluid increases, as there are more areas where heat can transfer out of chassis  10  into the cooling fluid. Having more effective convective heat transfer is advantageous, as it will improve the overall cooling of chassis  10 . 
         [0017]      FIG. 2  is a cross-sectional view of chassis  10  showing heat pipes  52  running through fins  50  on chassis  10 , taken along line  2 - 2  of  FIG. 1 . Chassis  10  includes first side  20 , second side  22 , top side  24 , bottom side  26 , cavity  40 , ledges  42  (including ledge  42 A, ledge  42 B, ledge  42 C, ledge  42 D, ledge  42 E, ledge  42 F, ledge  42 G, ledge  42 H, ledge  42 I, ledge  42 J, ledge  42 K, and ledge  42 L), fins  50  (including fin  50 A, fin  50 B, fin  50 C, fin  50 D, fin  50 E, fin  50 F, fin  50 G, fin  50 H, fin  50 I, fin  50 J, fin  50 K, fin  50 L, fin  50 M, fin  50 N, fin  50 O, fin  50 P, fin  50 Q, fin  50 R, fin  50 S, fin  50 T, fin  50 U, and fin  50 V), and heat pipes  52  (including heat pipe  52 A, heat pipe  52 B, heat pipe  52 C, heat pipe  52 D, heat pipe  52 E, heat pipe  52 F, heat pipe  52 G, heat pipe  52 H, heat pipe  52 I, heat pipe  52 J, heat pipe  52 K, heat pipe  52 L, heat pipe  52 M, heat pipe  52 N, heat pipe  52 O, heat pipe  52 P, heat pipe  52 Q, heat pipe  52 R, heat pipe  52 S, heat pipe  52 T, heat pipe  52 U, and heat pipe  52 V). 
         [0018]    Chassis  10  is capable of holding printed wiring boards in cavity  40 . Cavity  40  runs longitudinally through chassis  10  from a first end to a second end. In the embodiment shown in  FIG. 2 , cavity  40  includes six ledges  42  on a first interior surface and six ledges  42  on a second interior surface. In alternate embodiments, the number of ledges in chassis  10  can vary. Ledges  42  are positioned in cavity  40  to support printed wiring boards. Ledges  40  are rectangular shaped flanges that extend inwards from chassis  10 . 
         [0019]    Cavity  40  has ledges  42 A- 42 F positioned on a first interior side and ledges  42 G- 42 L positioned on a second interior side. Ledge  42 A runs longitudinally through cavity  40  above bottom side  26  and below ledge  42 B; ledge  42 B runs longitudinally through cavity  40  between ledge  42 A and ledge  42 C; ledge  42 C runs longitudinally through cavity  40  between ledge  42 B and ledge  42 D; ledge  42 D runs longitudinally through cavity  40  between ledge  42 C and ledge  42 E; ledge  42 E runs longitudinally through cavity  40  between ledge  42 E and ledge  42 F; and ledge  42 F runs longitudinally through cavity  40  above ledge  42 E and below top side  24 ; ledge  42 G runs longitudinally through cavity  40  above bottom side  26  and below ledge  42 H; ledge  42 H runs longitudinally through cavity  40  between ledge  42 G and ledge  42 I; ledge  42 I runs longitudinally through cavity  40  between ledge  42 H and ledge  42 J; ledge  42 J runs longitudinally through cavity  40  between ledge  42 I and ledge  42 K; ledge  42 K runs longitudinally through cavity  40  between ledge  42 J and ledge  42 L; and ledge  42 L runs longitudinally through cavity  40  above ledge  42 K and below top side  24 . 
         [0020]    Fins  50  are positioned on first side  20  and second side  22  of chassis  10  in the embodiment shown in  FIG. 2 . In alternate embodiments, the number of fins on each side can vary and fins  50  can be positioned on any number of sides of chassis  10  with any arrangement. Fins  50 A- 50 K run longitudinally across first side  20  from a first end to a second end of chassis  10  and fins  50 L- 50 V run longitudinally across second side  22  from a first end to a second end of chassis  10 . Fin  50 A is positioned above bottom side  26  and below fin  50 B; fin  50 B is positioned between fin  50 A and fin  50 C; fin  50 C is positioned between fin  50 B and fin  50 D; fin  50 D is positioned between fin  50 C and fin  50 E; fin  50 E is positioned between fin  50 D and fin  50 F; fin  50 F is positioned between fin  50 E and fin  50 G; fin  50 G is positioned between fin  50 F and fin  50 H; fin  50 H is positioned between fin  50 G and fin  50 I; fin  50 I is positioned between fin  50 H and fin  50 J; fin  50 J is positioned between fin  50 I and fin  50 K; fin  50 K is positioned above fin  50 A and below top side  24 ; fin  50 L is positioned above bottom side  26  and below fin  50 M; fin  50 M is positioned between fin  50 L and fin  50 N; fin  50 N is positioned between fin  50 M and fin  50 O; fin  50 O is positioned between fin  50 N and fin  50 P; fin  50 P is positioned between fin  50 O and fin  50 Q; fin  50 Q is positioned between fin  50 P and fin  50 R; fin  50 R is positioned between fin  50 Q and fin  50 S; fin  50 S is positioned between fin  50 R and fin  50 T; fin  50 T is positioned between fin  50 S and fin  50 U; fin  50 U is positioned between fin  50 T and fin  50 V; fin  50 V is positioned above fin  50 U and below top side  24 . 
         [0021]    Fins  50  each have a cavity running through them in which heat pipes  52  can be placed. The cavities in fins  50  can either be formed in fins  50  during manufacturing of chassis  10 , or the cavities can be cut into fins  50  after chassis  10  is manufactured using any suitable manufacturing process, for instance drilling. In the embodiment shown, heat pipes  52  are placed longitudinally through fins  50  so that first ends of heat pipes  52  are positioned near a second end of chassis  10  and a second end of heat pipes  52  are positioned near a first end of chassis  10 . Heat pipe  52 A is placed in fin  50 A; heat pipe  52 B is placed in fin  50 B; heat pipe  52 C is placed in fin  50 C; heat pipe  52 D is placed in fin  50 D; heat pipe  52 E is placed in fin  50 E; heat pipe  52 F is placed in fin  50 F; heat pipe  52 G is placed in fin  50 G; heat pipe  52 H is placed in fin  50 H; heat pipe  52 I is placed in fin  50 I; heat pipe  52 J is placed in fin  50 J; heat pipe  52 K is placed in fin  50 K; heat pipe  52 L is placed in fin  50 L; heat pipe  52 M is placed in fin  50 M; heat pipe  52 N is placed in fin  50 N; heat pipe  52 O is placed in fin  50 O; heat pipe  52 P is placed in fin  50 P; heat pipe  52 Q is placed in fin  50 Q; heat pipe  52 R is placed in fin  50 R; heat pipe  52 S is placed in fin  50 S; heat pipe  52 T is placed in fin  50 T; heat pipe  52 U is placed in fin  50 U; and heat pipe  52 V is placed in fin  50 V. In alternate embodiments, heat pipes  52  can be placed longitudinally through fins  50  but only extend a predetermined distance through heat pipes  52  from a first location to a second location. This placement is advantageous when chassis  10  is being used for particular applications with hot electronic components positioned in particular locations in chassis  10 , as a first end of heat pipe  52  can be positioned near the hot electronic component and a second end of heat pipe  52  can be positioned in a cooler location. 
         [0022]    Heat pipes  52  are positioned in fins  50  to transfer heat through heat pipes  52  to a cooler location. Heat pipes  52  are sized and shaped to fit in the cavities in fins  50  and can be held in place in fins  50  with any suitable means. In the embodiment shown, heat pipes  52  each include a hollow housing. The housing can contain a working fluid that is capable of two-phase heat transfer and a wick material on interior surfaces of the housing to wick the working fluid from the second end of heat pipes  52  to the first end of heat pipes  52 . Heat from chassis  10  will enter heat pipes  52  at the first end of heat pipes  52 , causing the working fluid to vaporize. The vaporized working fluid can then be transferred through heat pipe  52 . The vaporized working fluid can then release the heat from the second end of heat pipe  52  into an ambient, causing the working fluid to condense. The wick material can then transfer the condensed working fluid back to the first end of heat pipes  52 . Heat pipes  52  can be constructed out of any suitable materials, including any suitable housing material, any suitable working fluid, and any suitable wick material. In alternate embodiments, fins  50  can act as the hollow housing for heat pipes  52  and heat pipes  52  can be formed in chassis  10  when chassis  10  is manufactured. 
         [0023]    Heat pipes  52  are placed in fins  50  to increase the cooling abilities of chassis  10 . As discussed with reference to  FIG. 1 , chassis  10  primarily dissipates heat through convection. When convective heat transfer is relied upon for cooling, chassis  10  is limited in where it can be positioned on an aircraft, as cooling airflow is required to cool chassis  10 . Thus, if chassis  10  is mounted in a location on aircraft  10  with low airflow, the cooling abilities of chassis  10  will become less effective. Relying solely on cooling airflow to cool chassis  10  limits where chassis  10  can be used in aircraft  10 . 
         [0024]    Placing heat pipes  52  in fins  50  of chassis  10  is advantageous, as heat pipes  52  increase the effectiveness of the cooling abilities of chassis  10 . Heat pipes  52  will transfer heat with phase-change heat transfer, thus chassis  10  no longer relies solely on convection cooling to cool chassis  10 . This increase the flexibility of where chassis  10  can be positioned in an aircraft, including areas where cooling airflow is more limited. Chassis  10  can also be placed in higher temperature environments, as the heat can be more effectively spread through chassis  10  and dissipated in an ambient with heat pipes  52 . Further, increasing the cooling abilities of chassis  10  means higher heat generating and more powerful electronic components can be placed on printed wiring boards in chassis  10 , as chassis  10  can more effectively cool these components compared to prior cooling arrangements. 
         [0025]      FIG. 3  is a cross-sectional view of chassis  10  with printed wiring boards  60 , taken along line  2 - 2  of  FIG. 1 . Chassis  10  includes first side  20 , second side  22 , top side  24 , bottom side  26 , cavity  40 , ledges  42  (including ledge  42 A, ledge  42 B, ledge  42 C, ledge  42 D, ledge  42 E, ledge  42 F, ledge  42 G, ledge  42 H, ledge  42 I, ledge  42 J, ledge  42 K, and ledge  42 L), fins  50  (including fin  50 A, fin  50 B, fin  50 C, fin  50 D, fin  50 E, fin  50 F, fin  50 G, fin  50 H, fin  50 I, fin  50 J, fin  50 K, fin  50 L, fin  50 M, fin  50 N, fin  50 O, fin  50 P, fin  50 Q, fin  50 R, fin  50 S, fin  50 T, fin  50 U, and fin  50 V), and heat pipes  52  (including heat pipe  52 A, heat pipe  52 B, heat pipe  52 C, heat pipe  52 D, heat pipe  52 E, heat pipe  52 F, heat pipe  52 G, heat pipe  52 H, heat pipe  52 I, heat pipe  52 J, heat pipe  52 K, heat pipe  52 L, heat pipe  52 M, heat pipe  52 N, heat pipe  52 O, heat pipe  52 P, heat pipe  52 Q, heat pipe  52 R, heat pipe  52 S, heat pipe  52 T, heat pipe  52 U, and heat pipe  52 V). Also included are printed wiring boards  60  (including printed wiring board  60 A, printed wiring board  60 B, and printed wiring board  60 C) and electronic components  62  (including electronic component  62 A, electronic component  62 B, electronic component  62 C, electronic component  62 D, electronic component  62 E, electronic component  62 F, electronic component  62 G, electronic component  62 H, electronic component  62 I, electronic component  62 J, electronic component  62 K, and electronic component  62 L). 
         [0026]    Chassis  10  has cavity  40  running from a first end of chassis  10  to a second end of chassis  10 . Printed wiring boards  60  can be placed in cavity  40  of chassis  10  and supported by ledges  42 . A first edge of printed wiring board  60  can be positioned on one ledge  42  on the first interior surface of cavity  40  and a second edge of printed wiring board  60  can be positioned on one ledge  42  on the second interior surface of cavity  40 . Printed wiring boards  60  are positioned in cavity  40  by press fitting printed wiring boards  60  between the first interior surface and the second interior surface of cavity  40 . This will suspend the printed wiring board in cavity  40  of chassis  10 . Ledge  42 A and ledge  42 G are positioned across from one another to support a printed wiring board between them; ledge  42 B and ledge  42 H are positioned across from one another to support a printed wiring board between them; ledge  42 C and ledge  42 I are positioned across from one another to support a printed wiring board between them; ledge  42 D and ledge  42 J are positioned across from one another to support a printed wiring board between them; ledge  42 E and ledge  42 K are positioned across from one another to support a printed wiring board between them; and ledge  42 F and ledge  42 L are positioned across from one another to support a printed wiring board between them. In the embodiment shown in  FIG. 3 , printed wiring board  60 A is suspended between ledge  42 B and ledge  42 H; printed wiring board  60 B is suspended between ledge  42 D and ledge  42 J; and printed wiring board  60 C is suspended between ledge  42 E and ledge  42 K. In alternate embodiments, the number of printed wiring boards  60  can vary and the arrangement of printed wiring boards  60  in cavity  40  can vary. 
         [0027]    Electronic components  62  are positioned on printed wiring boards  60  in cavity  40 . Electronic components  62  can be positioned on both a top side and a bottom side of printed wiring boards  60 . Electronic component  62 A, electronic component  62 B, and electronic component  62 C are positioned on a bottom side of printed wiring board  60 A; electronic component  62 D is positioned on a top side of printed wiring board  62 A; electronic component  62 E and electronic component  62 F are positioned on a bottom side of printed wiring board  60 B; electronic component  62 G and electronic component  62 H are positioned on a top side of printed wiring board  60 B; electronic component  62 I and electronic component  62 J are positioned on a bottom side of printed wiring board  60 C; and electronic component  62 K and electronic component  62 L are positioned on a top side of printed wiring board  60 C. 
         [0028]    Fins  50  are positioned on first side  20  of chassis  10  and second side  22  of chassis  10  in the embodiment shown in  FIG. 3 . In alternate embodiments, fins  50  can be positioned on any number of sides of chassis  10 . Fins  50  extend outwardly from chassis  10  and each fin  50  has one heat pipe  52  placed in it. Heat pipes  52  run longitudinally through fins  50  and are positioned to transfer heat from a first end of heat pipe  52  to a second end of heat pipe  52  to better dissipate heat through chassis  10 . 
         [0029]    In the embodiment shown in  FIG. 3 , hotter electronic components  62  will be placed near edges of printed wiring board  60 . With this arrangement, the heat from the hotter electronic components  62  can transfer more directly to chassis  10 . The heat from electronic components  62  will transfer into ledges  42  and the first interior surface and second interior surface of cavity  40  of chassis  10 . The heat will then flow through chassis  10  to fins  50 . The heat that transfers to fins  50  can then be absorbed by heat pipe  52  at a first end. Absorbing heat into heat pipe  52  will cause the working fluid to vaporize. The vaporized working fluid can then flow through heat pipe  52  to a second end of heat pipe  52  where it will be released from heat pipe  52  through fin  50  to an ambient, thus cooling chassis  10 . 
         [0030]    Chassis  10  is typically cooled solely by flowing cooling air over fins  50  to cool chassis  10  with convective heat transfer. This arrangement is limited in application, as placing chassis  10  in areas with low airflow limits the cooling abilities of chassis  10 . Placing heat pipes  52  in fins  50  of chassis  10  and transferring heat from hot electronic components  62  to cooler locations through heat pipes  52  is advantageous, as it provides more effective heat transfer through fins  50  of chassis  10 . Heat pipes  52  can absorb heat from hot electronic components  62  on printed wiring boards  60  and transfer the heat through fin  50  to a cooler location in chassis  10 . The heat that is transferred to the cooler location can then be released into an ambient through fin  50 . Chassis  10  is cooled by flowing cooling air over fins  50  to cool chassis  10  with convective heat transfer. The combination of convective heat transfer provided by fins  50  and phase-change heat transfer provided by heat pipes  52  increases the overall cooling effectiveness of chassis  10 . 
         [0031]    Having more effective cooling abilities allows higher heat generating and higher power electronic components  62  to be used on printed wiring boards  60  that are placed in chassis  10 . These electronic components  62  are typically smaller than previously used electronic components, which gives the added benefit of reducing the overall size and weight of chassis  10 . Reducing the weight of components in aircrafts is advantageous, as aircrafts function more efficiently at lower weights. Further, space in aircrafts is limited, so being able to use smaller electronic components will save valuable space. 
         [0032]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.