Abstract:
A hold down for an electronic device is provided that includes a bottom frame, a circuit board mounted above the bottom frame, a thermal pad mounted on the circuit board, and a heat sink associated with the thermal pad. The hold down includes a frame that defines a perimeter having a plurality of retainers that are configured to engage with a plurality of mating locations defined on at least a bottom frame to provide a biasing force that retains the heat sink against a circuit board that is positioned between the bottom frame and the hold down.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/572,314, filed Jul. 14, 2011, the contents of which are hereby incorporated by reference herein. This application relates to PCT Application PCT/US12/028,000 filed on Mar. 7, 2012. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a set top box, and more particularly, a set top box having a hold down for retaining a heat sink. 
       BACKGROUND 
       [0003]    Thermal management remains a significant challenge in set top boxes. With the introduction of more components such as smart card readers and increased functionalities, which tend to produce more heat, the need for an improved thermal management system exists. 
         [0004]    An additional complication in set top boxes is the need to reduce the size of set top boxes due to consumer preference. This trend for compactness also makes thermal management a challenge, because this greater compactness with an increase in the number of internal components generally results in a concentration of heat. 
         [0005]    Proper thermal contact between a thermal pad on a circuit board and a heat sink improves heat dissipation from the circuit board. Existing means for securing the heat sink against the thermal pad result in undesirable rattling of the heat sink against the thermal pad and set top box. Additionally, existing securing means do not provide sufficient contact of the thermal pad with the heat sink. 
         [0006]    Therefore, a need exists for a retainer to secure a heat sink in proper contact with the thermal pad and stabilize the heat sink to reducing rattling. 
       SUMMARY 
       [0007]    A hold down for an electronic device is provided that urges a heat sink against a circuit board. The heat sink snaps into a bottom frame. The hold down includes a frame having retainers that match and engage slots in the bottom frame and the heat sink. The hold down provides a biasing force that urges the heat sink against the circuit board. 
         [0008]    Embodiments of the invention provide a hold down for a set top box or the like that includes a bottom frame, a circuit board mounted above the bottom frame, a thermal pad mounted on the circuit board, and a heat sink associated with the thermal pad. The hold down can include a frame that defines a perimeter having a plurality of retainers that are configured to engage with a plurality of mating locations defined on at least a bottom frame to provide a biasing force that retains the heat sink against a circuit board that is positioned between the bottom frame and the hold down. The heat sink can include a planar portion surrounding a central depression portion and/or another depression portion. The hold down secures the thermal pad of the circuit board between the central depression portion and/or other portion of the heat sink and the circuit board. The hold down can include a plurality of wires that cross each other, which can be over or in the central depression. The plurality of wires can be dimensioned such that the biasing force is applied across a top surface of the heat sink. The plurality of wires can include central portions that extend downwards along an inner surface of the central depression portion of the heat sink. The heat sink can include grooves in the planar portion for receiving the wires. The heat sink can include a second central depression portion that contacts a second heat generating component on the circuit board. The bottom frame can include vertically extending portions on opposing sides having slots and the heat sink can include vertical extensions having clips that snap into the slots of the bottom frame, thereby securing the heat sink to the bottom frame. The retainers can include U-shaped or V-shaped contours that are received in the mating locations of the bottom frame and the heat sink. The retainers can include a first vertical portion, a lower horizontal portion, and second vertical portion that is received in the mating locations of the bottom frame and the heat sink. 
         [0009]    Embodiments of the invention are directed to an electronic device comprising: a bottom frame, a circuit board mounted above the bottom frame, a thermal pad mounted on the circuit board, a heat sink associated with the thermal pad, and a hold down for providing a biasing force that retains the heat sink against the thermal pad. The hold down can comprise a frame that defines a perimeter having a plurality of retainers that are configured to engage with a plurality of mating locations defined on at least the bottom frame. The heat sink can include a planar portion surrounding a central depression portion and the hold down secures the thermal pad of the circuit board between the central depression portion of the heat sink and the circuit board. The hold down includes a plurality of wires that cross each other. The plurality of wires can be dimensioned such that the biasing force is applied across a top surface of the heat sink. The plurality of wires can include central portions that extend downwards along an inner surface of the central depression portion of the heat sink. The heat sink includes grooves in the planar portion for receiving the wires. The grooves can have a V or U profile to provide space for the hold down such that the hold down has no portion that is higher than the planar portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A more detailed understanding of the invention may be had from the following description, in conjunction with the accompanying drawings, wherein: 
           [0011]      FIG. 1  is an exploded view of a set top box according to the prior art; 
           [0012]      FIG. 2  is an enlarged view showing the heat sink of  FIG. 1  prior to attachment with the bottom frame; 
           [0013]      FIG. 3  illustrates the interior components of the set top box of  FIGS. 1-2  with the heat sink attached to the bottom frame; 
           [0014]      FIG. 4  is an exploded view of the set top box with the hold down; 
           [0015]      FIG. 5  illustrates grooves in the heat sink for engaging the hold down; 
           [0016]      FIG. 6  illustrates how the hold down engages the top surface of the heat sink and the mating locations of the bottom frame; 
           [0017]      FIG. 7  illustrates the slots of the bottom cover; 
           [0018]      FIG. 8  illustrates alternative retainers of the hold down; and 
           [0019]      FIG. 9  illustrates the hold down including a bow in the downward direction. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    As illustrated in  FIG. 1 , a circuit board  5  is housed within a top cover  7  of a set top box  1 . A thermal barrier  4  is positioned between the circuit board  5  and a bottom frame  2 . A smart card reader  3  is connected to the circuit board  5  through an aperture  8  in the thermal barrier  4 . The set top box  1  has internal components including the smart card reader  3 , the thermal barrier  4 , the circuit board  5 , and a heat sink  6  that contacts the circuit board  5  and is positioned between the bottom frame  2  and the top cover  7 . The thermal barrier  4  includes a thermal insulating material that preferably has substantially the same profile as the circuit board  5  or a profile that is at least 80% of the area profile of the circuit board  5 . The thermal barrier  4  keeps the smart card reader  3  and other components under the circuit board  5  from overheating, in part, by preventing heat from transferring from the circuit board  5  and the components thereon. 
         [0021]    The heat sink  6  is a heat dissipating feature that removes heat from the circuit board  5 . The heat sink  6  has a top plan profile that completely covers the circuit board  5  or substantially covers the circuit board  5  such that at least 80% of the circuit board  5  is covered. The heat sink  6  may include a thermal pad  9 . The heat sink  6  is a contoured plate that has a generally planar periphery  52  and a recessed feature such as a central depression  53  into a plane of the planar periphery  52 , wherein the planar periphery  52  preferably surrounds the central depression  53 . The central depression  53  has side walls extending from the planar periphery  52  and forming an obtuse angle therewith. The central depression  53  has a flat bottom that is designed to contact the circuit board  5 , the heat generating components on the circuit board  5 , and/or the thermal pad  9 . 
         [0022]    The heat sink  6  has vertical extensions  64  at the outer edges of the planar periphery  52  that are perpendicular to the planar periphery  52  and that extend over the circuit board  5  and contact the bottom frame  2  or vertically extending portions  62  of the bottom frame  2 . The heat sink  6  attaches to the bottom frame  2  through slots and clips formed on these elements. The vertically extending portions  62  extend from the bottom frame  2  and have receiving slots  61  that are designed to receive clips  71  formed on the vertical extensions  64  of the heat sink  6 . The vertically extending portions  62  may be plastic components, and as such, allow the heat sink clips  71  to elastically snap into the slots  61 , thereby securing the heat sink  6  to the bottom frame  2 . As illustrated in  FIG. 2 , the arrow indicates how the heat sink clips  71  are pressed downward onto the bottom frame slots  61 . 
         [0023]      FIG. 3  is a perspective view of interior components of the set top box  1 . The set top box  1  may include a second central depression  90  that contacts a secondary thermal pad  99  associated with the smart card reader  3 . The bottom frame  2  may include a smart card access slot  91  below the circuit board  5  and one of the vertical extensions  64  of the heat sink  6 . The slot  91  may also be between the vertically extending portions  62  of the bottom frame  2 . The second central depression  90  thermally communicates with the smart card reader  3  through an aperture  8  in the circuit board  5  or the secondary thermal pad  99  through the circuit board  5 . 
         [0024]    The set top box  1  described in  FIGS. 1-3  further includes a hold down  130  to secure the heat sink  6  against the circuit board  5 .  FIG. 4  shows an exploded view of the set top box  1  with the hold down  130 . The hold down  130  includes a frame that defines a perimeter. The hold down  130  may be a rectangular frame that generally matches the shape of the heat sink  6 . The perimeter of the hold down  130  includes retainers  103  arranged at the ends of the hold down  130 . The retainers  103  are shaped to match and engage mating locations provided on at least the bottom frame  2 . The heat sink  6  may also include mating locations for the retainers  103 . The hold down  130  is preferably constructed from a rigid flexible material, such as a wire or multiple wires, preferably  304  stainless steel, that may extend diagonally to bias the heat sink  6  downwards against the thermal pad  9  and to provide contact between the circuit board  5 , the thermal pad  9 , and the central depression  53  of the heat sink  6  for proper thermal dissipation. The wires may cross each other such that one wire includes a bent portion that extends below the other wire. The region where the hold down components or wires cross can be centralized to be over the central depression and can inside the central depression. The hold down or wires can be applied to the prior art assemblies to enhance heat transfer to the heatsink. 
         [0025]    The bottom surface of the central depression  53  and the circuit board  5  contact the thermal pad  9  on opposite sides and sandwich the thermal pad  9  between them. The hold down  130  improves the surface contact among these components. 
         [0026]    The hold down  130  may be formed from a resilient material. The hold down  130  is preferably dimensioned such that the hold down  130  is tensioned when installed and exerts a biasing force across the top of the heat sink  6  or at a specific location on the heat sink  6  after the retainers  103  of the hold down  130  engage the mating locations of the bottom frame  2  and the heat sink  6 . 
         [0027]    The top surface of the heat sink  6  may define a longitudinal plane and the frame of the hold down  130  may extend in this plane or in a parallel plane. As shown in  FIG. 9 , when the hold down  130  engages the mating locations of the bottom frame  2  and the heat sink  6  and the hold down  130  engages the top surface of the heat sink  6 , the heat sink  6  and the hold down  130  bows in the downward direction away from the initial plane or planes. The hold down  130  may also include end portions that rise vertically above the longitudinal plane of the heat sink  6 . The extent of the hold down  130  between the end portions may bow downwardly to apply force to the heat sink  6 . The hold down  130  may include a central portion that extends downward into the central depression  53  of the heat sink  6  and along the inner contours of the central depression  53  such that the hold down  130  is in further contact with the heat sink  6  and movement is further reduced. As compared to existing set top boxes, the hold down  130  allows for a thinner thermal pad  9  to be used because of the biasing force from the hold down  130  on the heat sink  6 . 
         [0028]      FIGS. 5-8  show various features of the set top box  1  and the hold down  130 . The retainers  103  of the hold down  130  engage slots  92  formed on the vertically extending portions  62  of the bottom frame  2  and slots  120  formed on the vertical extensions  64  of the heat sink  6 .  FIG. 5  shows an assembled cutaway view of the set top box  1  with the hold down  130  pressing the central depression  53  of the heat sink  6  downward onto the thermal pad  9  on the circuit board  5 . The heat sink  6  may include grooves  67  that are sufficiently deep to receive the hold down  130  and prevent the hold down  130  from protruding above the heat sink  6 . The grooves  67  allow the vertical height of the set top box  1  to remain the same as compared to set top boxes without a hold down. The vertical extensions  64  of the heat sink  6  may also include cut out portions  140  that are shaped to receive portions of the hold down  130 . 
         [0029]      FIG. 6  is sectional side view of the set top box  1  and illustrates the improved contact of the bottom surface of the central depression  53  with the thermal pad  9  as compared to existing set top boxes.  FIG. 7  illustrates the slots  61  on the bottom frame  2  for receiving the clips  71  of the heat sink  6 , and the slots  92  for receiving the retainers  103  at the ends of the hold down  130 .  FIG. 8  shows alternative embodiments of the retainers  103  of the hold down  130  and illustrates the retainers  103  may include any suitable end which secures the hold down  130  with the mating locations of the bottom frame  2  and the heat sink  6 . The retainers  103  may include ends  132  with U-shaped or V-shaped inward contours that engage the slots  92  of the bottom frame  2  and the slots  120  of the heat sink  6 . The retainers  103  may alternatively include ends  134  with a first vertical portion, a lower horizontal portion, and second vertical portion which engage the slots  92 ,  120  of the bottom frame  2  and heat sink  6 . As noted above, the ends  132 ,  134  may engage the slots  92 ,  120  in such a way to tension the hold down  130 . 
         [0030]    The foregoing illustrates only some of the possibilities for practicing the invention. Many other embodiments are possible within the scope and spirit of the invention. It is, therefore, intended that the foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their full range of equivalents.