Patent Publication Number: US-2006011324-A1

Title: Wound, louvered fin heat sink device

Description:
FIELD OF THE INVENTION  
      This device relates to heat sinks, and in more particular applications to improved fins for heat sink devices that include a fan for cooling an electronic component such as an integrated circuit chip, a CPU chip, a large scale chip package, or a very large scale chip package, especially an impingement airflow fan.  
     BACKGROUND OF THE INVENTION  
      Heat sink devices that include a base plate having one surface adapted for receiving heat from an electronic device and another surface for mounting a heat conductive, serpentine fin, and an impingement airflow fan for directing an air flow perpendicular to the surface of the plate on which the fin is mounted are well known. Examples of such heat sink devices are disclosed in U.S. Pat. Nos. 4,753,290, 5,251,101, 5,299,632, 5,494,098, 5,597,034, 6,109,341, and 6,135,200. Additionally, U.S. Pat. Nos. 6,336,497 and 6,360,816 show examples of similar devices wherein a cylindrical post extends upward from the surface of the plate, with fins wrapped around the post to receive the air flow from the impingement airflow fan. U.S. Pat. No. 6,223,813 discloses a similar heat sink wherein pin fins are wrapped around a cylindrical post.  
     SUMMARY OF THE INVENTION  
      It is the primary object of the invention to provide a new and improved heat sink device.  
      In accordance with one aspect of the invention, an improvement is provided in a heat sink device for cooling an electronic component having a surface that rejects heat. The heat sink device includes a fan overlying the surface to direct an airflow towards the surface. The fan has a rotational axis. The improvement includes a fin wound about a central axis, the central axis extending parallel to the rotational axis, and the fin including louvered surfaces that extend parallel to the central axis.  
      In one aspect, the improvement further includes a plate having first and second surfaces, the first surface configured to receive heat rejected from the surface of the electronic component, and the second surface underlying the fan; and a spiral wound fin on the second surface of the plate and underlying the fan, the fin including a strip of metal coiled about the central axis. The strip has the louvers formed therein extending parallel to the central axis between spaced side margins of the strip. In a further aspect, each of the louvers has a louver angle that opens radially outward in a direction of rotation of the fan.  
      According to one aspect, the improvement further includes an elongate conductive post and at least one serpentine fin. The post includes first and second end surfaces and a circumferential surface extending between the end surfaces parallel to the central axis, the first end surface being configured to receive heat rejected from the surface of the electronic component. The at least one serpentine fin is wrapped around the circumferential surface and has alternating peaks and valleys joined by louvered side walls, each of the peaks and valleys extending generally parallel to the central axis.  
      In accordance with one aspect of the invention, a heat sink device is provided for cooling an electronic component having a surface that rejects heat. The device includes a plate and a spiral wound fin. The plate has first and second surfaces, with the first surface configured to receive heat rejected from the surface of the electronic component. The spiral wound fin is on the second surface of the plate and includes a strip of metal coiled about an axis extending generally perpendicular to the second surface. The strip has louvers formed therein extending parallel to the axis between spaced side margins of the strip.  
      In one aspect, each of the louvers of the spiral wound fin has a louver angle, and the louver angles vary as a function of a radial distance from the axis.  
      According to one aspect, at least one of the side margins includes a plurality of spaced tabs, each of the tabs extending from the strip to engage an adjacent portion of the at least one of the side margins to maintain a desired spacing between adjacent coils of the spiral wound strip. In a further aspect, each of the tabs extends in a radially outward direction from the strip.  
      In one aspect, the device further includes a wire coiled about the axis and sandwiched between adjacent coils of the strip to maintain a desired spacing between the adjacent coils. In one further aspect, the wire is sandwiched between adjacent portions of one of the side margins. In another aspect, the wire is sandwiched between louvers of adjacent coils of the strip.  
      In accordance with one aspect, the strip has a width extending parallel to the louvers and the louvers extending over 80% to 95% of the width. In a preferred aspect, the louvers extend over 88% to 93% of the width.  
      In accordance with one aspect of the invention, a heat sink device is provided for transferring heat from an electronic component to a cooling airflow provided by a fan, with the electronic component having a surface that rejects heat. The heat sink device includes an elongate conductive post and at least one serpentine fin. The elongate conductive post includes first and second end surfaces and a circumferential surface extending between the end surfaces in a direction of elongation of the conductive post. The first end surface is configured to receive heat rejected from the surface of the electronic component. The at least one serpentine fin is wrapped around the circumferential surface and has alternating peaks and valleys joined by louvered side walls, each of the peaks and valleys extending parallel to the direction of elongation.  
      In one aspect, each of the louvers extends perpendicular to the direction of elongation.  
      According to one aspect, the at least one serpentine fin has a width extending parallel to the direction of elongation; and the device further includes a shroud covering a radially outermost portion of the at least one serpentine fin and extending over 30% to 60% of the width farthest from the first end surface. In a further aspect the shroud includes a band.  
      In accordance with one aspect, the device further includes a second serpentine fin wrapped around the circumferential surface between the circumferential surface and the at least one serpentine fin, and having alternating peaks and valleys extending parallel to the direction of elongation and joined by louvered side walls. A separating band is sandwiched between second serpentine fin and the at least one serpentine fin. In a further aspect, the separating band is perforated.  
      In one aspect, the circumferential surface is cylindrical in shape.  
      Other objectives, aspects, and advantages will become apparent from a review of the entire specification, including the drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an elevation view of a heat sink device embodying the present invention;  
       FIG. 2  is a plan view of the heat sink device of  FIG. 1 ;  
       FIG. 3  is a perspective view of the heat sink device of  FIG. 1 ;  
       FIG. 4  is an enlarged view of the encircled area marked  4 - 4  in  FIG. 3 ;  
       FIGS. 5A and 5B  are enlarged, partial views of the encircled area marked  5 - 5  in  FIG. 2  showing alternate embodiments for a fin structure used therein;  
       FIG. 6  is a side elevation of another heat sink device embodying the invention;  
       FIG. 7  is a plan view of the device shown in  FIG. 6 ;  
       FIG. 8  is a perspective view of the device shown in  FIG. 6 ; and  
       FIG. 9  is an enlarged section view taken from line  9 - 9  in  FIG. 7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      As seen in  FIGS. 1-3 , an impingement airflow heat sink device  10  is provided for cooling an electronic component  12 , such as for example an integrated circuit, a CPU chip, a large scale chip package, or a very large scale chip package, having a surface  14  that rejects heat. The heat sink device  10  includes a plate  16  having first and second surfaces  18  and  20  with the surface  18  configured to receive heat rejected from the surface  14  electronic component  12 ; a fan, shown schematically at  22  in  FIG. 1  only, overlying the second surface  20  to direct an impingement airflow, shown generally by the arrows  24 , toward the second surface  20  substantially perpendicular to the second surface  20 ; and a louvered fin  26  underlying the fan and bonded to the second surface so as to transfer heat from the plate  16  to the airflow  24  and the environment surrounding the heat sink device  10 .  
      The plate  16  is preferably a solid, one piece construction with the surfaces  18  and  20  being substantially planar and parallel to each other, particularly if the surface  14  of the electronic component  12  is planar. However, it may be advantageous in some applications for at least the surface  18  to have a non-planar configuration if required to conform to a non-planar surface  14  on the electronic component  12 . In this regard, the surface  18  will typically be seated against the surface  14  or have a bonding layer or a layer of thermal grease or gel therebetween. However, in some application it may be desirable to space the surface  18  and  14  apart. Further, the plate  16  may serve as a cap or lid for the electronic component  12 . Additionally, as an alternative to a solid, one piece construction, the plate  16  could include heat pipes embedded therein, or could be a multi piece, hollow construction forming a planar type heat pipe on the interior of the construction. It should be understood that while the surfaces  20  and  18  are shown as having a square or rectangular shape in  FIGS. 2 and 3 , this is for purposes of illustration and in some applications other shapes for the surfaces  20  and  18  may be desirable, such as for example, a circular shape that would conform essentially to the outer extent of the fin  26 , or other shapes that would conform essentially to the perimeter of the electronic component  12  for the particular application. Preferably, the plate  16  is made from a suitable heat conducting material, such as aluminum, copper or their alloys.  
      The fan  22  is preferably a so called “impingement” or “pancake” type fan, many suitable types of which are well-known in the industry. Typically, the fan  22  will include a housing (not shown) that rotatably mounts a fan impeller, shown schematically at  28 , driven by an electric motor (not shown) about an axis  29  substantially perpendicular to the surface  20 . Preferably, the fan  22  is configured to distribute the airflow  24  over as large a portion of the fin  26  as is possible given the packaging restraints for the heat sink device  10 . The fan  22  will typically be attached to the remainder of the heat sink device  10  either by a suitable attachment structure that extends past the fin  26  to engage the plate  16  or by bonding the housing of the fan to the fin  26  using a suitable bonding technique, such as epoxy bonding. However, in some applications it may be desirable to mount the fan  22  to other structures associated with the electronic component  12 , such as a housing that carries the electronic component  12  and the heat sink device  10 . In any event, because the mounting of the fan  22  relative to the remainder of the heat sink device  10  is not critical to the understanding or the function of the heat sink device  10  with respect to the slit fin  26 , further description of the various means for mounting the fan  22  will not be provided herein.  
      As best seen in  FIGS. 2 and 3 , the fin  26  is a spiral wound fin that is wound about a central axis  40  extending parallel to the rotational axis  29  and preferably aligned therewith so that the fin  26  is centered on the axis  29 . The fin  26  is made from a strip  42  of metal coiled about the axis  40  to define a plurality of coils  43  of the strip  42 . The strip  42  has louvers  44 , best seen in  FIG. 4 , formed therein extending parallel (within reasonable manufacturing tolerances) to the axes  29 , 40  between spaced side margins  46 , 48  of the strip  42 . For purposes of illustration, not all of the louvers  44  are shown in  FIGS. 2 and 3 , but it should be understood that the louvers  44  preferably extend throughout the entire coiled length of the strip  42 . As best seen in  FIG. 1 , the side margins preferably extend parallel (within reasonable manufacturing tolerances) to the surface  20 . As best seen in  FIG. 5A , each of the louvers  44  has a louver angle α, which in  FIG. 5A  is 45°. It should be appreciated that the louver angle α can vary from 90° down to near 0°, depending upon the particular requirements of each application. Furthermore, it should be appreciated that in some applications it will be desirable for all of the louvers  44  to have the same louver angle α, while in other applications it will be desirable to have the louver angle α vary as a function of radial distance from the axis  40 , depending upon the particular parameters of each application, such as the particular parameters of the fan  22  and the heat sink device  12 . Preferably, as shown in  FIG. 5A , the louver angles a open radially outward in the direction of rotation of the fan, shown schematically by arrows A in  FIGS. 5A and 5B . However, it should be understood, that in some applications it may be desirable for the louver angles α to open radially outward in the opposite direction of the rotation of the fan.  
      As best seen in  FIG. 1 , the strip  42  has a width W extending parallel to the louvers  44 . Preferably, the louvers have a width W L  that extend over 80% to 95% of the width W, and in highly preferred embodiments, the width W L  extends over 88% to 93% of the width W. It is also preferred for the side margins  46  and  48  to have essentially identical widths W S  divided from the remainder of the width W not taken up by the louvers  44 . However, in some applications, it may be desirable for the side margins  46 , 48  not to have equal widths W S .  
      As seen in  FIG. 5A , in some embodiments a plurality of spaced tabs  50  can be provided in one or both the side margins  46  and  48 , with each of the tabs  50  extending from the strip  42  to engage an adjacent portion of the corresponding side margin  46 , 48  in an adjacent coil  43  to maintain a desired spacing S between adjacent coils  43  of the spiral wound strip  42 . While it is possible for the tabs  50  to extend either radially inward or outward from the strip,  FIG. 5A  illustrates all of the tabs  50  extending in a radially outward direction from the strip  42 .  
      As seen in  FIG. 5B , in some embodiments it may be desirable to maintain the desired spacing S between adjacent coils  43  of the strip  42  by coiling a wire  54  about the axis  40  such that the wire is sandwiched between adjacent coils  43  of the strip  42  to maintain the desired spacing S. The spacing S will be a function of the diameter D of the wire. As seen in  FIG. 5B , it is preferable that the wire be sandwiched between the louvers  44  of the adjacent coils  43  of the strip  42 . Alternatively, in some embodiments it may be desirable for the wire to be sandwiched between adjacent portions of the side margin  46  adjacent the surface  20  so as not to block the air flow  24  from the fan  22 .  
      The louvers  44  direct the air flow  24  from the fan  22  through the coiled strip  42  to exit the outermost coil  43  after having removed heat from the fin  26  and the plate  16 . In this regard, it should be appreciated that the louver angle α will influence the pressure drop through the fin  26  and thus the optimum louver angle(s) α will depend upon fan design and other factors such as louver size, including louver pitch and louver width W L , fin spacing S, fin thickness t, etc.  
      It should be appreciated that the spiral wound fin  26  can provide a relatively dense configuration of fin surfaces similar to what could be provided by a pin-fin type construction. However, in some applications, such high density may not be desirable.  
       FIGS. 6-9  illustrate another embodiment of a heat sink device  60 , with like numbers representing like features. The heat sink device  60  of  FIGS. 6-9  differs from the device  10  of  FIGS. 1-5B  in that the plate  16  has been replaced with a conductive center post  62 , and the spiral fin  26  has been replaced by at least one serpentine fin (two serpentine fins  64  and  66  shown in  FIGS. 6-9 ), with each of the fins  64 , 66  having alternating peaks  68  and valleys  70  joined by louvered side walls  72 . For purposes of illustration, louvers are shown only in  FIG. 9  and on one of the side walls  72  of  FIG. 8 . As best seen in  FIGS. 6 and 8 , the peaks  68  and valleys  70  preferably extend parallel (within reasonable manufacturing tolerances) to the axes  29  and  40 . The device  60  of  FIGS. 6-9  is similar to the device  10  of  FIGS. 1-5B  in that the fins  64  and  66  are both wound about the central axis  40  that extends parallel to the rotational axis  29 , with the fins  64 , 66  including louvered surfaces (defined by the side wall  72 ) that extend parallel (within reasonable manufacturing tolerances) to the central axis  40 .  
      The center post  62  includes a pair of spaced, end surfaces  74  and  76 , and a circumferential surface  78  extending between the end surfaces  74 , 76  in a direction of elongation of the conductive post  62 . While it is preferred for the circumferential surface to be cylindrical in shape, in some applications it may be desirable for the circumferential surface to have other shapes. As with the end surface  18 , the end surface  74  is configured to receive heat rejected from the surface  14  of the electronic component  12  and is preferably planar. However, again as with the surface  18 , it may be advantageous in some applications for the surface  74  to have a nonplanar configuration if required to conform to a nonplanar surface  14  on the electronic component  12 . It may be desirable in some applications for the center post  62  to be a solid, one piece construction made of a suitable heat conductive material, such as copper or aluminum. Alternatively, in other applications, it may be desirable for the center post  62  to have heat pipes embedded therein or to be a multi piece, hollow construction that defines a heat pipe in the interior of the construction.  
      As best seen in  FIG. 9 , the louvered side walls  72  include a plurality of louvers  80  formed therein, preferably extending between the associated peak  68  and valley  70  perpendicular (within reasonable manufacturing tolerances) to the axes  29  and  40 . It should be appreciated that the configuration of the louvers, including the louver pitch, louver angle α, and louver pattern, will be highly dependent upon the parameters of each particular application.  FIG. 9  illustrates one possible louver pattern wherein the direction of the air flow  24  tends to be redirected through the side walls  72  by the pattern of the louvers  80 , which are angled outwardly in one direction in an upper half of the side wall  72  and then in the opposite direction in the lower half of the side wall  72 .  
      As best seen in  FIGS. 7 and 8 , if more than one serpentine fin is utilized, it is preferred to provide a separator sheet  84  sandwiched between the fins  64 , 66 , and specifically between the peaks  68  of the fin  64  and the valleys  70  of the fin  66 . In some applications, it may be desirable for the sheet  84  to be perforated to allow the air flow  24  to pass through the sheet  84 . Similarly, it may be desirable for the sheet to extend over only the upper 30% to 60% of the width W farthest from the surface  74 .  
      As best seen in  FIGS. 6-8 , in some applications it may be desirable for the device  60  to include a shroud, shown in  FIGS. 6-8 , in the form of a band  86 , covering the radially outermost portion of the outermost fin  66  and extending over 30% to 60% of the width W farthest from the first end  74 . In the illustrated embodiment, the shroud  86  extends over 50% of the uppermost portion of the width W. The shroud  86  acts to direct the impingement air flow  24  downward through the fins  64 , 66  and their louvers  80  to the lowermost portion of the fins  64 , 66  before the air flow  24  can exit radially and/or axially from the fins  64 , 66 .  
      The fins  26 , 64 , 66  can be made from any suitable heat conductive material, such as for example, copper or aluminum. Preferably, the fin  26  is bonded, such as by brazing or soldering, to the surface  20  of the base plate  16 . Preferably, the peaks  68  and valleys  70  of the fins  64  and  66  are bonded, such as by brazing or soldering, to the associated surfaces of the conductive post  62 , separator sheet  84 , and shroud  86 .  
      While the axes  29  and  40  have been shown as parallel and aligned, it should be appreciated that in some applications it may be desirable for the axes  29  and  40  not be parallel and/or not to be aligned. Further, while the devices  10  and  60  have been described in connection with a pancake-type fan, other types of fans may prove more desirable in some applications.