Abstract:
A set-top box is provided that comprises a housing having a first vertical outer wall with a first vent and a second vertical outer wall with a second vent; a circuit board having a first heat source element and a second heat source element; a contoured heatsink in thermal engagement with the first heat source element, wherein the contoured heatsink overlies at least one-third of the circuit board and extends along the first vertical side wall; and a second heatsink contacting the second heat source element, wherein the second heatsink is located in only one half of the device and is aligned with the second vent. The multiple heatsinks and associated vents work in concert to improve heat dissipation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit, under 35 U.S.C. §365 of International Application PCT/US2011/036171, filed May 12, 2011, which was published in accordance with PCT Article 21(2) on Nov. 24, 2011 in English and which claims the benefit of U.S. Provisional Patent Application No. 61/346,073, filed May 19, 2010 and U.S. Provisional Patent Application No. 61/400,767 filed Aug. 2, 2010. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to quiet set-top boxes having improved heat dissipating capabilities. 
     BACKGROUND OF THE INVENTION 
     Set-top boxes continue to be in high demand and an ever increasing need exists to reduce the size and improve aesthetic appeal, performance, functionality, and robustness of these devices and the like. As such, many set-top boxes now require smartcard readers, hard drives, and other heat generating elements. 
     Particular problems that such set-top boxes face are damage due to heat generation. However, a need exists for a means for dissipating heat without creating other complications such as noticeable noise or large spacial or footprint requirements. As such, heat dissipation fans, which tend to improve electrical robustness of the set-top boxes, are not preferable, because they do introduce noise and increase the size of set-top boxes. Also, other set-top box designs having vents on the top of the set-top boxes surprisingly require more internal free space (i.e., a larger outer casing) when there are no fans employed to appropriately dissipate heat. Additionally, these top vent systems place the set-top box in jeopardy of damage due to liquid spills. 
     In light of the requirement for set-top boxes to appropriately dissipate heat and yet also house more electronic components and meet customer preferences, a need exists for a new set-top box design that has improved heat dissipating capabilities. 
     SUMMARY OF THE INVENTION 
     An electronic device is provided that comprises a housing having a first vertical outer wall with a first vent and a second vertical outer wall with a second vent; a circuit board having a first heat source element and a second heat source element; a contoured heatsink in thermal engagement with the first heat source element, wherein the contoured heatsink overlies at least one-third of the circuit board and extends along the first vertical side wall; and a second heatsink contacting the second heat source element, wherein the second heatsink is located in only one half of the device and is aligned with the second vent. The contoured heatsink can have a planar peripheral portion and a central depression portion in which the planar peripheral portion completely or partially surrounds the central depression portion and the central depression portion contacts the first heat source element. The contoured heatsink can substantially overlie the circuit board and completely overlie the second heatsink. The second heatsink can be a finned heatsink or the second heatsink can be a contoured heatsink having a second planar peripheral portion and a second central depression in which the second planar peripheral portion surrounds at least a portion of the second central depression portion, and the second central depression portion contacts the second heat source element. If the second heatsink is a contoured heatsink, then the contoured heatsink can overlie less than half the circuit board and the second heatsink can overlie more than one-third of the circuit board. The device can comprise a frame that has a base and embosses, wherein the base is under the circuit board and the embosses contact and support the circuit board. The frame can have at least a first vertical side wall oriented along the first vertical outer wall and a second vertical side wall oriented along the second vertical outer wall in which the first vertical side wall has a first interior vent aligned with the first vent and the second vertical side wall has a second interior vent aligned with the second vent. The second heat source element can be a smart card reader and can be below the circuit board, wherein the circuit board can have heat passage via holes therethrough over the second heat source element and under the second heatsink where it contacts the circuit board or a thermal pad thereon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying figures of which: 
         FIG. 1  shows a cross sectional interior view of the assembled set-top box according to a first embodiment of the invention with a front portion of the set-top box removed; 
         FIG. 2  shows a perspective view of the underside of the main printed circuit board according to the invention; 
         FIG. 3  shows a perspective view of the upper side of the main printed circuit board according to the invention; 
         FIG. 4  shows a perspective view of the top broad heat sink on the main printed circuit board according to a first embodiment of the invention; and 
         FIG. 5  shows a cross sectional interior view of the assembled set-top box according to a second embodiment of the invention with a front portion of the set-top box removed. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The invention is directed to arrangements for cooling an electronic assembly that generates a thermal load, for example a smart card reader, when the electronic assembly is disposed in a hostile thermal environment. A hostile thermal environment is one in which there is insufficient ventilation for adequate cooling, for example, a densely populated electronic box such as a set-top box, wherein desired design criteria are directed to compact, sleek designs with small footprints. Providing for sufficient cooling to dissipate thermal loads in such a set-top box is challenging under any circumstances. 
     In the exemplary embodiments of the invention disclosed herein, the cooling problem is exacerbated by including in a set-top box a low profile smart card reader that generates its own thermal load and that is mounted on the bottom side of a multilayer printed circuit board (PCB) disposed inside the set-top box. Dissipating the thermal load of the smart card reader is even more difficult due to a mounting location at the bottom of the set-top box, beneath a multilayer PCB on which are mounted other electronic components generating other thermal loads, and far removed from the top of the set-top box. With respect to conventional wisdom, placing the smart card reader in such a location is quite counter-intuitive. However, placing the smart card reader in such a location does enable the implementation of a desirable sleek design without objectionable top vents or objectionable fans. It will be understood by those skilled in the art that, in many if not most cases, vents in a set-top box may not be altogether avoided. 
     An electronic assembly such as a smart card reader can be safely positioned in a hostile thermal environment as described above, in accordance with the inventive arrangements taught herein. The smart card reader contacts are located on the bottom of the smart card reader and push the smart card upward against the bottom printed circuit board surface. Since the card surface is in direct contact with the printed circuit board, a patch or area of many copper-plated thru-hole vias is advantageously added in the board at the location of the smart card contacts. Other highly thermally conductive metal can be used to plate the vias. A thermally conductive pad is advantageously placed on the patch of vias and a heat sink is advantageously placed on the pad. A top broad heat sink has proved to be an effective way to cool the main integrated circuit of the set-top box, but the smart card reader adds an additional thermal load that may not be dissipated by the conventional top broad heat sink. 
     There are two exemplary embodiments taught herein and shown in the drawings for advantageously dissipating the thermal load generated by the smart card reader. In a first embodiment, a finned convecting heat sink  58  advantageously radiates heat through convection to vents on the outer sides  34  of the outer cover  28  of a set-top box  1 . The first embodiment can be appreciated by particular reference to  FIGS. 1-4 . 
       FIG. 1  shows an internal view of the set-top box  1  in an assembled form with a front portion of the set-top box removed according to the first embodiment.  FIG. 1  shows a top broad heat sink  10 , which is an internal component. The top broad heat sink  10  can be a generally contoured plate that has a generally planar periphery  12  and a contoured central feature such as a pocket, central depression, notch, recess, multilevel depression, or mesa extending from and/or into a plane of the planar periphery. The central feature or central depression  11  can have side walls extending from the planar periphery and form an obtuse angle therewith. The contoured feature can have a flat bottom designed to contact the main integrated circuit and/or other heat generating component  17  on a main printed circuit board  13  which can be below it. 
       FIG. 1  further shows a main printed circuit board  13  or the like, which can be generally flat. The main printed circuit board  13  can have a main integrated circuit  17  or the like in a central region and holes for mounting and/or securing the main printed circuit board  13  to a frame pan  18 . The main integrated circuit and other heat generating or hot components  17  can contact the flat bottom or other portion of the central depression  11  of the top broad heat sink  10 , which can be in thermal contact with the other heat generating or hot components through a thermal joint  27  which could be a pad. The main printed circuit board  13  is shown being mounted and/or secured to embosses  20  of the frame pan  18  by use of screws, bolts or solder pad joints  43  through the holes or contact points in the circuit board  13 , wherein the main printed circuit board  13  is effectively contacting the frame pan  18 . This contact can be thermal contact. 
       FIG. 2  shows a perspective view of the underside of the main printed circuit board  13  or the like. The main printed circuit board  13  can have in a central region of holes and associated pins  16  for primary or additional mounting and/or securing the main printed circuit board  13  to a frame pan  18 . Other features of the main printed circuit board are shown in the figure which can include jack panel connectors  15  at one edge and a button cluster  14  at another edge. These edges can be opposing edges.  FIG. 2  shows how the smart card reader  61  can be positioned on the main printed circuit board  13 . 
       FIG. 3  shows another perspective view of the upper side of the main printed circuit board  13  or the like in contact with the frame  18 .  FIG. 3  shows the main printed circuit board  13  can have main integrated circuit or other heat generating component  17  in a central region and holes and associated pins  16  for mounting and/or securing the main printed circuit board  13  to a frame pan  18 . Additionally shown is the finned convecting heat sink  58 . 
     In a particular example shown in  FIG. 3 , the finned convecting heat sink  58  is constructed of 24 fins in which there are four rows of flat evenly spaced fins with the planar portion oriented along the x-axis (or the long axis which is parallel to the front of the set-top box) and in which there are six columns of evenly spaced fins oriented along the y-axis (or short axis which is parallel to the sides of the set-top box). The finned convecting heat sink  58  having a long dimension in the x-axis being 17.78 mm, a short dimension in the y-axis being 10.18 mm, and a height being 10.11 mm. Keeping these dimensions within 20% of the stated dimensions can be effective. The gaps between the fins are U-shaped or V-shaped in which the depths of the gaps are greater than half the height of the finned convecting heat sink  58 . 
       FIG. 4  shows a perspective view of the top broad heat sink  10  on the main printed circuit board  13 . Here, one can see that the top broad heat sink  10  substantially covers the main printed circuit board  13 . 
     Regarding the smart card reader  61 ,  FIG. 1  further shows how the smart card reader  61  can be in contact with the main printed circuit board  13  and immediately thereunder. The smart card reader  61  is shown having a smart card  64  inserted therein through a smart card entrance port  63  in one of the outer sides  34 . The smart card reader  61  is shown being in contact with at least one thermal pad joint  62  that conducts heat generated by the smart card reader  61  to the finned convecting heat sink  58  which is also in contact with the main printed circuit board  13  and positioned immediately thereon. Here, heat via holes  65  are shown being in the a main printed circuit board  13  to permit the heat from the smart card reader  61  to propagate to the finned convecting heat sink  58 . The heat via holes  65  can be copper plated and the population of the heat via holes can be located substantially along and over the perimeter of the smart card reader  61  and uniformly distributed over the smart card reader  61  to optimize heat transfer from the smart card reader  61 . It is advantageous to have the total plan view area of the via holes exceeding one-half area the plan view area of the via hole region, which is the region where the finned convecting heat sink  58  or the second heat sink contacts circuit board or the thermal pad joint. The vias can have vertical walls and can have an aspect ratio, which is a width or diameter of the via hole to height ratio, of 0.5 to 10. 
     Additionally, the set-top box  1  in  FIG. 1  can have an outer cover  28  that further includes an upper wall  31 , lower wall  32 , and multiple outer sides  34 . The exterior side of the lower wall  32  can include rubber feet  33  which can be at least 6 mm in height to ensure adequate air entry under the set-top box for improved thermal management. 
       FIG. 1  also shows at least one proximal vent  59  in one of the outer sides  34  which is positioned in the general proximity of the finned convecting heat sink  58 . It is preferable that the proximal vent  59  be positioned in one of the vertical outer sides  34  at a place that is closest to the finned convecting heat sink  58 . At least one general vent  60  is shown which can be at other locations on other outer sides  34 . The general vents  60  can further assist with the dissipation of heat. Additionally, the frame pan  18  can have side walls  23  that have complementary vents  66  which can be aligned with the vents of the outer sides  34 . Having the vents on the outer sides in the combination of top broad heat sink  10  and the finned convecting heat sink  58  eliminates or can eliminate the need for vents in the upper wall  31 . 
       FIG. 1  further shows outer gaps  41  between the side walls  23  of the frame pan  18  and the outer side  34  of the outer cover  28 ; inner gaps  40  between the edge of the planar periphery  12  of the top broad heat sink  12  and the side walls  23  of the frame pan  18 ; bottom gap  42  between the lower wall  32  of the outer cover  28  and the base  22  of the frame pan  18 ; and upper gap  44  between the upper wall  31  of the outer cover  28  and the planar periphery  12  of the top broad heat sink  10 . The bottom gap  42  and upper gap  44  prevent the outer cover  28  from overheating. 
     Since the card surface is in direct contact with the printed circuit board, a patch or area of many copper-plated through hole vias is advantageously added in the board at the location of the smart card contacts. A thermally conductive pad is advantageously placed on the patch of vias  62  and a heat sink is advantageously placed on the pad. A top broad heat sink has proved to be an effective way to cool the main integrated circuit of the set top box, but the smart card reader adds an additional thermal load that cannot be dissipated by the conventional top broad heat sink. However, the finned heat sink and proximal vents have enhanced the thermal management of the set-top box. 
     In a second embodiment, the top broad radiating heat sink, previously embodied as a unitary heat sink, is advantageously split or divided into two parts or two separate heat sinks. One of the two parts is in thermal contact with the main integrated circuit in the set-top box. The other of the two parts is in thermal contact with the smart card through the patch or area of vias. The second embodiment can be appreciated by reference to  FIG. 5 . 
       FIG. 5  shows an internal view of the set-top box  1  in an assembled form with a front portion of the set-top box removed according to the second embodiment.  FIG. 5  shows first top broad heat sink  10   a , which is an internal component. The top broad heat sink  10   a  can be a generally contoured plate that has a generally planar periphery  12   a  and a contoured central feature such as a pocket, central depression, notch, recess, multilevel depression, or mesa extending from and/or into a plane of the planar periphery, wherein the planar periphery  12   a  preferably only surrounds part of the or central depression  11   a . Here, the planar periphery  12   a  surrounds 3 sides of the central depression  11   a . The central feature or central depression  11   a  can have side walls extending from the planar periphery and form an obtuse angle therewith. The contoured feature can have a flat bottom designed to contact the main integrated circuit and/or other heat generating component  17  on a main printed circuit board  13  which can be below it. 
       FIG. 5  also shows the second top broad heat sink  10   b , which is an internal component. The top broad heat sink  10   b  can also be a generally contoured plate that has a generally planar periphery  12   b  and a contoured central feature such as a pocket, central depression, notch, recess, multilevel depression, mesa extending from and/or into a plane of the planar periphery, wherein the planar periphery  12   b  preferably only surrounds part of the central depression  11   b . In the one embodiment, the planar periphery  12   b  surrounds 3 sides of the central depression  11   b . The central feature or central depression  11   b  can have side walls extending from the planar periphery and form an obtuse angle therewith. The contoured feature can have a flat bottom designed to contact the main printed circuit board  13  in the region where the smart card reader  61  is located. The smart card reader  61  is shown being in contact with at least one thermal pad joint  62  that conducts heat generated by the smart card reader  61  to the second top broad heat sink  10   b  which is also in contact with the main printed circuit board  13  and thereon. Here, heat transmissive via holes  65  are positioned in the main printed circuit board  13  to permit the heat from the smart card reader  61  to propagate to the second top broad heat sink  10   b . The heat via holes  65  can be copper plated and the population of the heat via holes can be located substantially along the perimeter of the smart card reader  61  and uniformly distributed over the smart card reader  61  to optimize heat transfer from the smart card reader  61 . The vias can have the same characteristics and dimensional aspects in this embodiment as in the first embodiment. 
     In the second embodiment, the main printed circuit board  13 , frame pan  18  and the outer cover  28  are generally the same as in the first embodiment of the invention. The frame pan  18  also can have complementary vents  66  which can be aligned with the vents  60  of the outer sides  34 , wherein the edges of planar peripheries  12   a ,  12   b  run along the outer sides  34 . 
     It should be understood that although examples of the claimed inventions specifically mention set-top boxes and circuit boards, the invention is not limited to these features. For example, the invention is applicable to computers and other electronic devices having heat generating components. Furthermore, the invention is also applicable to electronic parts other than circuit boards which can generate heat. 
     The invention is not limited to the precise arrangements and instrumentalities shown. As such, the invention is intended to apply, for example, to heat source elements such as hard drives, smart card readers, integrated circuits, and light sources that could be used to light buttons. Further, when a heatsink is said to be contacting a heat source element, this can imply through direct contact or contact through an intermediary component such as via holes and/or thermal pads or thermal joints. Additionally, the expression “vent” can imply a single vent opening or multiple localized vent openings; the expression “substantially overlying” is intended to mean completely overlying or overlying at 90% of a surface of a structure; the expression “planar peripheral portion” can mean that the portion is completely planar or can include portions which are generally planar, but may have some raised portions or groves which may be needed to add structural integrity or may be needed to accommodate components in the set-top box.