Abstract:
A backing plate for joining a heat removal device to a heat source. The backing plate can include a planar plate region having a first face and a second face opposite the first face. The backing plate can also include at least one boss projecting from the first face and having an opening therein for receiving a fastener.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 61/601,585 filed Feb. 22, 2012, the content of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Electronic devices can generate a large amount of unwanted heat, which if not properly dissipated can adversely impact such devices. One way to dissipate the heat is by circulating air with a fan. Where air cannot be readily circulated and/or in cases where the air in not sufficiently clean, however, the heat from an electronic device can be dissipated by securing the electronic device to a heat removal device such as a heat pipe or thermosyphon. These heat removal devices typically include an evaporator, a condenser, and a heat dissipating feature such as a fin or other exterior surface of the heat removal device. For efficient heat dissipation, it is desirable to have the electronic device in contact with the evaporator, and the condenser in contact with the heat dissipating feature. However, the force required to secure the heat removal device to the electronic device sufficiently to achieve a desired level of thermal conductivity can sometimes deform or damage the heat removal device. 
     SUMMARY 
     Some embodiments of the present invention provide a backing plate for joining a heat removal device to a heat source. The backing plate includes a planar plate region having a first face and a second face opposite the first face, and at least one boss projecting from the first face, the boss having an opening therein for receiving a fastener. 
     In some embodiments, a backing plate for joining a heat removal device to a heat source with a fastener is provided, wherein the heat removal device has a first side and a second side. The backing plate includes a base having a first surface facing the first side of the heat removal device when secured thereto, and a second surface facing away from the heat removal device when secured thereto, and a boss extending along a longitudinal axis away from the base and toward the heat removal device when secured thereto, the boss shaped to releasably engage with the fastener from the second side of the heat removal device to clamp the heat removal device between the base of the backing plate and the fastener, and wherein the base has a footprint larger than a cross-sectional area of the boss taken in a plane orthogonal to the axis to distribute axial force from the boss across the first side of the heat removal device when secured thereto. 
     Some embodiments of the present invention provide a method of assembling a heat removal device onto a heat source. The method includes steps of providing a heat removal device having an evaporator side and a condenser side and at least one aperture defined therethrough, the aperture extending between the evaporator side and the condenser side of the heat removal device; disposing a backing plate against the condenser side of the heat removal device, the backing plate including at least one boss sized to fit within the at least one aperture, the boss adapted to mate with a fastener; disposing the evaporator side of the heat removal device against the heat source; inserting the at least one boss into the at least one aperture; passing the fastener through the heat source; and attaching the fastener to the boss to secure the backing plate and the heat removal device to the heat source. 
     In some embodiments, an electronic device is provided. The electronic device includes an electrical heat source; a heat removal device having a first side, a second side opposite the first side, and a vapor chamber; a backing plate on the first side of the heat removal device and having a boss extending at least partially through the vapor chamber; and a fastener extending at least partially through the vapor chamber from the second side of the heat removal device and secured to the boss, wherein the heat removal device is clamped between the fastener and the backing plate, which cooperate to exert a compressive load upon the heat removal device. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exploded view of an embodiment of a vapor chamber backing plate adjacent to a circuit board. 
         FIG. 2  shows a heat source having several heat removal devices attached thereto. 
         FIG. 3  shows the condenser side of a heat removal device with space for multiple backing plates, where a single backing plate without windows is installed. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     Aspects of the present invention relate to a backing plate that can secure a heat removal device to a heat source (e.g., a circuit board, one or more microprocessors, and the like) with a high level of force without damaging or unacceptably deforming the heat removal device. In some embodiments, the backing plate includes a generally planar body to distribute the force required to couple the heat removal device to the heat source over an area larger than the cross-sectional area of the fastening locations of the heat source and heat removal device, thereby preventing unacceptable deformation of the heat removal device. 
     The heat source can include, for example, an insulated-gate bipolar transistor (IGBT) or other type of circuit boards. In this regard, the heat sources can include diffuse sources of heat as well as point sources of heat (e.g., CPUs on a circuit board). 
     Heat removal devices such as a heat pipe (whether in the form of a plate-type heat spreader, an elongated closed pipe, or any other shape or form), a thermosyphon, or any other heat removal device having a vapor chamber, an evaporator adjacent the heat source, and a condenser typically opposite the evaporator, can be used in conjunction with the backing plate of the present invention. In many cases, the heat removal devices are sealed under vacuum and contain a small amount of working fluid such as water, ethanol, methanol, or ammonia, which evaporates at the evaporator surface and condenses at the condenser surface, transferring heat away from the heat source. 
     In some embodiments, a heat-dissipating device can be secured to the condenser of the heat removal device for dissipating heat to a body of cooling fluid (e.g., to the environment, a flowing or convective body of fluid, and the like), to another heat exchange device, and the like. By way of example only, the heat-dissipating device can be a set of fins of any type, such as those shown in  FIG. 1 . 
     According to various embodiments, the disclosed backing plate structure, which can also be referred to as a bolster plate, can include bosses that extend into through holes in the heat removal device to receive fasteners from the evaporator side of the heat removal device. The bosses permit the heat removal device to be tightly secured to the heat source by bearing a relatively high level of force while preventing damage to the heat removal device. 
       FIG. 1  is an exploded view of an embodiment of a heat removal device  10  according to the present invention. The heat removal device  10  includes an evaporator  12  and a condenser  14 , either or both of which can be defined by structure of the heat removal device  10  at which working fluid within the heat removal device  10  evaporates and condenses, respectively, in operation of the device  10 . In various embodiments, the heat removal device  10  can also have a heat-dissipating device  16  such as a fin attached thereto.  FIG. 2  also shows a heat source  30  (e.g., a circuit board in the illustrated embodiment) having three separate heat removal devices  10  attached thereto, where one of the heat removal devices ( FIG. 2 , left) has two separate backing plates  18  attached to the condenser  14  side. In the embodiment of  FIG. 2 , a fastener  24  (e.g., a screw as shown, by way of example only) can be attached through an aperture in the heat source  30  to attach the backing plate  18  and the heat removal device  10  to the heat source  30 , such that the heat source  30  is clamped between the backing plate and the fastener  24 . In this manner, the fastener  24  and backing plate  18  can exert a compressive force upon each heat removal device  10 , and in some embodiments can also exert a compressive force upon the heat source  30  and the heat removal device  10  to improve heat conduction across the interface therebetween. 
     In some embodiments, any or all of the backing plates  18  can be coupled to shared or respective (dedicated) heat dissipation devices  16  such as sets of fins (omitted from  FIG. 2  for clarity).  FIG. 3  shows a heat removal device  10  having space for multiple backing plates  18 , where a backing plate  18  is installed (left) in one location while another location is unoccupied (right). By securing a heat dissipating device  16  to the backing plate  18  rather than directly to the condenser side of the heat removal device  10 , it is possible to remove the heat dissipating device  16  by removing the fasteners  24  thereof, and then removing the backing plate  18  with the heat dissipating device  16  attached thereto. This capability can also provide the ability to access, maintain, repair, remove, and replace one heat source (e.g., one circuit board sharing the same heat removal device  10  with one or more other circuit boards) or portion of a heat source (e.g., a microprocessor or electronic element on a heat source  30  having several) without disturbing others. 
     In certain embodiments, the heat removal device  10  can be formed of annealed copper. However, while annealed copper is well-suited to many applications due to its heat-conducting properties, annealed copper (and a number of other otherwise desirable materials) is relatively soft. As a result, the heat removal device  10  can bend or compress under high levels of force that are sometimes required to couple the heat removal device  10  to a heat source  30 , particularly in those cases where compressive force is desired to increase thermal conductivity between the heat source  30  and the heat removal device  10 . Thus, a backing plate  18  can be disposed adjacent the condenser  14  of the heat removal device  10  to spread the force required to couple the heat removal device  10  to the heat source  30  in a thermally-conductive manner (see  FIGS. 1, 2, and 3 ). As described further below, the backing plate  18  can have a variety of sizes and shapes, and can cover any amount of the surface of the condenser  14 . Nevertheless, in certain embodiments where particularly high levels of force are applied, the components can be stressed and deformed even with the use of a backing plate  18 . 
     Therefore, in certain embodiments the backing plate  18  can further include one or more bosses  20  extending from one face of the backing plate (e.g., extending from a base of the backing plate  20 ) and which extend into respective apertures through the heat removal device  10  (i.e., through-holes  22  of the heat removal device) to receive fasteners  24  for fastening to the heat source  30  ( FIG. 1 ). In some embodiments, the bosses  20  have a length that is comparable to the depth of the through holes  22 , or a length that is less than the depth of the through holes  22 . The number of through holes  22  and bosses  20  that are used depends on factors such as the sizes and shapes of the heat source  30 , the backing plate  18 , and the heat removal device  10 , as well as the distribution of individual point sources of heat on the heat source  30 . 
     In some embodiments, the backing plate  18  includes one or more openings or windows  28  which, among other advantages, reduce the weight of the backing plate  18  ( FIGS. 1 and 2 ). 
     Also, in some embodiments, the backing plate  18  can be at least partially received within a recess  26  on the condenser side of the heat removal device  10 . For example, in those embodiments in which the backing plate  18  has a base that is substantially plate-shaped from which the bosses  20  extend as described herein, the base can be at least partially received within the recess. In some embodiments, the base of the backing plate is recessed within the condenser side of the heat removal device so that the surface of the backing plate  18  opposite the bosses  20  and adjacent exterior surfaces of the condenser side of the heat removal device  10  are co-planar or substantially co-planar. In this manner, a heat dissipating device  16  can be more readily attached to adjacent co-planar surfaces of the backing plate  18  and the heat removal device  10 , or can otherwise simultaneously be in contact with such surfaces. 
     In those embodiments of the present invention having a backing plate  18  with a window  28  (whether the backing plate  18  is recessed within the condenser  14  as described above or not), any part of the condenser  14  can extend into the window  28 . In such embodiments, a heat dissipating device  16  (e.g., a fin, as described above) can be in contact with the condenser  14  which extends upward through the window  28  ( FIG. 1 ). Alternatively, the window can be unoccupied by any portion of the condenser  14 , in which case a heat dissipating device  16  can be shaped to extend into the window  28  in those embodiments where direct contact between the heat dissipating device  16  and the condenser  14  is desired. 
     When the heat removal device  10  is fully assembled, the fasteners  24  run through the heat source  30  and attach to the bosses  20 , tightly joining together the heat source  30 , the heat removal device  10 , the backing plate  18 , and the heat dissipating mechanism  16  (e.g., fin) if used, in a thermally-conductive manner. 
     The backing plate  18  (i.e., the base of the backing plate  18 ) can have various shapes, such as rectangular, square, circular, triangular, any other regular or irregular polygons, or irregular shapes. Similarly, the window  28  can be various shapes, such as rectangular, square, circular, triangular, any other regular or irregular polygons, or irregular shapes. Further, the backing plate  18  can have more than one window  28 , and each window  28  can have the same or different shapes. 
       FIG. 1  shows a plurality of bosses  20  on a single backing plate  18 , although the backing plate  18  can have as few as one boss  20 . In some embodiments, a backing plate  18  with one boss  20  can be preferred because it is simple in construction and can reduce the cost of manufacturing. However, a backing plate  18  with two or more bosses  20  can alternatively be preferred because load can be distributed more evenly across a larger face of the backing plate  18 , and/or because the backing plate  18  can be held more firmly in place and can be less prone to twisting or rotating when there is more than one boss  20 . Each boss  20  can be cylindrically shaped, but can also have any number of other cross-sectional shapes including, but not limited to, circular, rectilinear (square or otherwise), elliptical, or any other regular or irregular polygonal shapes such as star shapes or other shapes having three or more sides where the faces of the shapes include convex and/or concave portions. As used herein and in the appended claims, the cross-sectional shapes are defined in a plane extending through the boss  20  and that is orthogonal to the longitudinal axis of the boss  20 . 
     A given backing plate  18  can include a combination of bosses  20  having various sizes and shapes. Also, in some embodiments, one or more of the through holes  22  in the heat removal device  10  can be sized to receive the fasteners  24  alone, without a boss  20 . 
     In some embodiments, each boss  20  can be tapered along at least a portion of its length such that it is wider at the point where it connects to the backing plate  18 . Also, each boss  20  can be adapted to receive a particular type of fastener  24 . For example, the bosses  20  can be internally threaded to receive fasteners  24  such as screws. In other embodiments, each boss  20  is adapted to mate with or otherwise be secured to a respective fastener in any other suitable manner, such as an externally-threaded boss received within a threaded aperture (e.g., blind hole) of a fastener  24 , bosses  20  that are brazed or soldered to fasteners  24  under compression during joining operations (e.g., by a temporary frame, brace, or other structure), and the like. 
     In embodiments with a plurality of bosses  20 , each boss  20  can have a similar size and shape, but in some embodiments one or more bosses  20  can have a different size or shape than the other bosses  20  to facilitate accurate alignment of the backing plate  18  onto the heat removal device  10 . In some embodiments, a plurality of bosses  20  (and their associated through holes  22 ) are arranged in a rectangular grid or a non-rectangular pattern to suit the layout of the heat source  30  (e.g., circuit board) and/or the heat removal device  10 . Bosses  20  can also be evenly spaced across the heat source  30 , or can be more unevenly spaced as desired (i.e., to be more closely spaced in desired areas). In the case where the heat source  30  is a circuit board, the bosses  20  and their associated fasteners  24  can be located so as to accommodate the placement of devices such as chips, while ensuring that regions of the circuit board which have higher heat production, such as where a CPU is located, are near one or more bosses  20  to ensure improved a thermally conductive connection with the heat removal device  10 . 
     In some embodiments, the backing plate  18  is formed of a material that is stronger than that of the heat removal device. By way of example only, the backing plate  18  can be formed of stainless steel. The bosses  20  can be formed of metals with good thermal conductivity, such as copper or aluminum, and can be made of the same or different material than the base of the backing plate  18 . For improved thermal conductivity, gold- or silver-plated metals can be used for the backing plate  18  and/or the bosses  20 . In some embodiments, the backing plate  18  measures 2-50 cm in a length dimension, and 2-50 cm in a width dimension. Also in some embodiments, the thickness of the base of the backing plate  18  can be from about 1 mm to about 10 mm. In various embodiments, the backing plate  18  is dimensioned so as to cover at least a portion of an insulated-gate bipolar transistor (IGBT) on a circuit board. While  FIG. 1  shows a heat removal device  10  which includes one backing plate  18 , in some embodiments ( FIG. 2 ) the heat removal device  10  can include a plurality of backing plates  18  which are distributed across the condenser  14  side of the heat removal device  10 , where each of the backing plates  18  can be the same or a different shape, each may or may not have one or more windows  28 , and each may or may not be partially or fully received within a respective matching recess  26  of the heat removal device  10 . 
     As mentioned above, among other considerations, having multiple backing plates  18  on a single heat removal device  10  can permit individual backing plates  18  to be removed and replaced separately. This can be beneficial where one or more fins or other heat-dissipating mechanisms  16  are coupled to the backing plates  18  and can need to be replaced if they are damaged. In yet another embodiment ( FIG. 2 ), there can be multiple heat removal devices  10 , each with a separate backing plate  18 , on a given heat source  30 , in some cases enabling removal and replacement of a heat removal device  10  from the heat source  30  without disturbing other heat removal devices  10  secured to the heat source. Each of the heat removal devices  10  and associated backing plates  18  can have different sizes and shapes, and can have varying numbers of bosses  20  and windows  28  depending on factors such as the size, shape, and distribution of point sources of heat on the heat source  30 . 
     In various embodiments, the length of each boss  20  is set so as to be flush with the evaporator surface of the heat removal device  10  in the assembled state. In general, the length of a boss  20  can be comparable to the depth of the through hole  22  in which the boss  20  is intended to be received. The depth of the through hole  22 , in turn, can be generally the same as the thickness of the heat removal device  10 , minus the depth of the recess  26 , if present. In some embodiments, the bosses  20  are initially produced slightly longer than required. The backing plate  18  with such bosses  20  is then assembled into the heat removal device  10 , and the protruding ends of the bosses  20  are trimmed (e.g. by a flycut) so as to be flush with the evaporator surface of the heat removal device  10 . Each boss can have a cross sectional area which is large enough to distribute the compressive load exerted by the fasteners  24 . Accordingly, each boss  20  can measure 2 mm to 25 mm in length, and 1 mm to 25 mm in diameter. In some embodiments in which the heat removal device  10  can withstand limited compressive forces, each boss  20  can be dimensioned so as to be slightly recessed relative to the evaporator  12  or the condenser  14 . 
     By virtue of the relative size of the boss  20  and the backing plate base from which the boss extends, axial force from the boss  20  (experienced when the fastener  24  is tightened to clamp the heat removal device  10  between the backing plate  18  and the fastener  24 , and in some embodiments between the backing plate  18  and the heat source  30 ) is distributed across the backing plate base and therefore across a condenser surface of the heat removal device  10 . The backing plate base can have a footprint that is larger than the cross-sectional area of the boss  20  to enable this distribution. This force distribution reduces the likelihood of heat removal device deformation and damage, and can improve heat exchange between the heat source  30  and the heat removal device. 
     In some embodiments, the bosses  20  are formed separately from the backing plate  18  and are attached to the backing plate  18  in any suitable manner, such as by brazing, soldering, or welding. In some embodiments, the bosses  20  can be attached to the backing plate  18  by fasteners such as screws or rivets, which can facilitate later removal of the bosses  20  from the backing plate  18 , if desired. 
     In still other embodiments, the bosses  20  can be separate from and not be attached to the base of the backing plate  18 . In such embodiments, the bosses  20  can be inserted into the through holes  22  during assembly and, like the attached bosses  20 , would also serve the purpose of resisting compressive forces applied by the fasteners  24 . In the embodiments in which the bosses  20  are not attached to the base of the backing plate  18 , it is desirable to use fasteners  24  which attach at both ends, e.g. rivets, screws with nuts, or other similar types of fasteners  24 . Alternatively, the backing plate itself could be threaded to accept fasteners  24  such as screws while the bosses  20  could be threaded or unthreaded. 
     Alternatively, in certain embodiments, the bosses  20  can be integral with the base of the backing plate  18 . The combined backing plate base and bosses  20  can be formed by casting in some embodiments. In other embodiments, however, the combined backing plate base and bosses  20  can be formed by shaping a block of a metal, for example using one or more of milling, grinding, laser cutting, stamping, plasma cutting, and high pressure water jets cutting, to provide a single element having dimensional precision and stability. In still other embodiments, the combined backing plate base and bosses  20  can be molded using a thermally-conductive polymer. 
     Various types of fasteners  24  can be used, where the fasteners  24  generally have an elongated shaft with a head portion at one or both ends, and where at least a portion of the head extends laterally away from the shaft. The fasteners  24  can be secured in place in various ways, where the method of securing affects how readily the fasteners  24  can be removed. For example, the fasteners  24  can be screws, rivets, or pins with barbed shafts. One or both ends of the fastener (depending on the type of the fastener used) can also include a washer or other element under the head of the fastener for distributing force of the head of the fastener  24  over a broader area of the backing plate  18  or the heat source  30 , as applicable, in order to prevent stressing and possible damage to the respective structure. One or both of the respective surfaces of the backing plate  18  and the heat source  30  can be recessed or countersunk so that the head(s) of the fasteners  24  are flush or recessed relative to the nearby surface. 
     Varying levels of force can be applied to the fasteners  24 . In some embodiments, the fasteners  24  are tightened so as to bring together the heat source  30 , the heat removal device  10 , and the backing plate  18  (often having one or more heat-dissipating devices  16  attached thereto as described above) in thermally-conductive contact with one another. The use of bosses  20  permits an even higher level of force to be applied to the fasteners  24  without damaging (e.g. cracking, deforming, or compressing) the heat source  30 , the backing plate  18 , or the heat removal device  10 . In some embodiments, the fastener  24  can be tightened under 40 inch-pounds (in-lbs) of torque such that the total force exerted by the fastener  24  is 1052 pounds. In various embodiments, a single fastener  24  can be tightened under at least 50 in-lbs of torque, although other torque values are possible. In those embodiments with backing plates  18  having bosses, the amount of force applied to a single fastener  24  can be increased without causing damage to the heat source  30 , the heat removal device  10 , or the backing plate  18 . 
     As described above, in some embodiments, each backing plate  18  has one or more heat dissipation devices  16  such as a set of fins coupled thereto. In some embodiments, each heat-dissipating device  16  can be secured to the backing plate  18 , such as by brazing, soldering, or welding. In other embodiments, the heat-dissipating device  16  can be attached to the backing plate  18  by fasteners  24  such as screws, rivets, or barbed pins. In still other embodiments, the heat-dissipating device  16  can be attached (also by means such as brazing, soldering, or welding) to the heat removal device  10  instead of, or in addition to, the backing plate  18 . With various manners of attachment, however, the heat-dissipating device  16  can be permanently secured or can be removed from the backing plate  18  or heat removal device  10 . 
     In some embodiments, the backing plate  18  can be more permanently attached to the heat removal device  10 , for example by welding, soldering, or brazing together the parts described above. While this could make disassembly more difficult, it would have the advantage of making a connection with very high thermal conductivity. 
     As disclosed herein, various embodiments of the present invention also include methods of replacement of one or more backing plates  18  from a heat source  30  and heat removal device  10 . In various embodiments, the heat removal device  10  and the backing plate  18 , with optional bosses  18  and fins  16  (or other heat-dissipating elements) attached thereto, are attached to the heat source  30  in a manner that facilitates rapid assembly, disassembly, removal, and replacement, for example using screws as fasteners  24 . Replacement can also be facilitated by having several individual backing plates  18 , heat removal devices  10 , and/or heat dissipating mechanisms  16  in a system (e.g., see  FIGS. 2 and 3 ), which can be individually removed and replaced as needed without having to completely remove a single large component. 
     In some embodiments, the present invention provides a method of assembling a heat removal device  10  onto a heat source  30 . The method can include steps of: providing a heat removal device  10  having an evaporator  12  side and a condenser  14  side and at least one through hole  22  therein, the through hole  22  extending between the evaporator  12  side and the condenser  14  side of the heat removal device  10 ; disposing a backing plate  18  against the condenser  14  side of the heat removal device  10 , the backing plate  18  including at least one boss  20  sized to fit within the at least one through hole  22 , the boss  20  being adapted to receive a fastener  24 ; disposing the evaporator  12  side of the heat removal device  10  against the heat source  30 ; inserting the at least one boss  20  into the at least one through hole  22 ; and passing the fastener  24  through the heat source  30  and into the boss  20  to secure the backing plate  18  and the heat removal device  10  to the heat source  30 . In some embodiments, the backing plate  18  can also include a heat-dissipating mechanism  16  such as a fin attached thereto.