Abstract:
An actively cooled daughterboard system. One more daughterboards are mounted in parallel rows on a motherboard. Each daughterboard is oriented substantially perpendicular to the motherboard, but may optionally be mounted at an oblique angle relative to the motherboard. Each daughterboard has a low-profile thermally-efficient heatsink mounted thereon. A fan shroud partially covers the daughterboards, but has openings in its sides for directing air flow through plural fins on the heatsinks and through a fan mounted to the top of the fan shroud. The inventive daughterboard system enables multiple high heat dissipating daughterboards to be placed closer together than the daughterboard systems of the prior art while still keeping the daughterboards adequately cooled. Moreover, because only a single fan is used to cool all of the daughterboards under the shroud, noise and expense are reduced relative to prior art systems that employed one or more fans per daughterboard.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to cooling techniques for electronic circuitry. More particularly, the invention relates to techniques for cooling electronic components that are mounted on a daughterboard. 
     BACKGROUND 
     Computer-related electronic systems are commonly constructed using multiple interconnected circuit boards. The largest of these circuit boards is typically called the motherboard. Ancillary circuit boards such as CPU cards, memory cards and input/output cards are typically called daughterboards. Sockets are provided on the motherboard for receiving one or more daughterboards and making appropriate electrical connections between components mounted on the daughterboards and those mounted on the motherboard. Such sockets are usually designed so that the daughterboards may be easily removed and replaced. 
     Special thermal management problems are presented by motherboard/daughterboard systems wherein high heat dissipation components are mounted on the daughterboards. Specifically, it has been found that fan-driven heat sinks are necessary to prevent the high heat dissipation components such as CPU chips on the daughterboards from overheating. 
     One example of such a motherboard/daughterboard system is described in the single edge contact cartridge (“SECC”) packaging specifications promulgated by Intel Corporation. Referring now to FIG. 1, the packaging specification for boxed SECC 2  processors describes a daughterboard  100  on which a CPU is mounted. Daughterboard  100  is adapted to engage a socket  102  on a motherboard  104  so that daughterboard  100  is oriented substantially perpendicular to motherboard  104 . A heatsink  106  is disposed on one side of daughterboard  100  between the CPU and a fan  108 . On the opposite side of daughterboard  100 , an SECC 2  cover plate  110  is provided to help anchor heatsink  106  to daughterboard  100 . Heatsink  106  is generally rectangular and includes plural elongate fins  112 . Each of fins  112  lies on a plane that is substantially parallel to motherboard  104 . The axis of rotation of fan  108  is also substantially parallel to motherboard  104 . A fan shroud  114  is provided to direct air flow through heatsink  106  from the ends of fins  110  to the middle of fins  110  under fan  108  as shown in FIG.  2 . 
     Heatsink  106  also includes tabs  116  on either end. (Tabs  116  are best illustrated in FIG. 3.) Each of tabs  116  defines a notch  118  for engaging a retaining member of socket  102 . An example of such a retaining member is universal retention mechanism  400  (“URM”) shown in FIG.  4 . URM  400  includes a frame with top surfaces  406  and a resilient arm  402 . Resilient arm  402  includes retaining ledges  404 . Typically, one URM  400  is disposed on each end of socket  102  with its retaining ledges  404  facing inward toward the socket. When daughterboard  100  is pushed into socket  102 , notches  118  on either side of heatsink  106  engage the underside of ledges  404 , thereby helping to retain daughterboard  100  in socket  102 . 
     A number of disadvantages are associated with prior art motherboard/daughterboard systems such as those illustrated in FIGS. 1-3. For example, it is frequently necessary to place multiple daughterboards in parallel rows on the same motherboard. Because each prior art daughterboard has a heatsink  106 , a shroud  114  and a fan  108  stacked in a direction perpendicular to the plane of the daughterboard, multiple prior art daughterboards require a large amount of motherboard area. Moreover, systems that require multiple prior art daughterboards are expensive and noisy because each daughterboard in the system includes a noiseproducing and relatively expensive fan  108 . 
     It is therefore an object of the invention to provide a daughterboard system that conserves motherboard area when it is necessary to mount more than one daughterboard on the motherboard. 
     It is a further object to provide such a daughterboard system so that high heat dissipation components such as CPU chips can be mounted on the daughterboard. 
     It is a still further object to make the daughterboard system less expensive and less noisy than the daughterboard systems of the prior art. 
     SUMMARY OF THE INVENTION 
     These and other objects are realized by an actively cooled daughterboard system according to a preferred embodiment of the invention. 
     In one aspect, one more daughterboards are mounted in parallel rows on a motherboard. Each daughterboard is oriented substantially perpendicular to the motherboard, but may optionally be mounted at an oblique angle relative to the motherboard. Each daughterboard has a low-profile thermally-efficient heatsink mounted thereon. Each heatsink is thermally coupled to one or more heat dissipating electronic components mounted to the respective daughterboard. A fan shroud partially covers the daughterboards, but has openings in its sides for directing air flow through plural fins on the heatsinks and through a fan mounted to the top of the fan shroud. Preferably, the fan is oriented with its axis of rotation substantially parallel to the plural fins of the heatsinks. The inventive daughterboard system enables multiple high heat dissipating daughterboards to be placed closer together than the daughterboard systems of the prior art while still keeping the daughterboards adequately cooled. Moreover, because only a single fan is used to cool all of the daughterboards under the shroud, noise and expense are reduced relative to prior art systems that employed one or more fans per daughterboard. 
     In another aspect, the fan shroud may include one or more protrusions on each end for engaging retaining ledges housed in retaining members on opposite ends of the daughterboard sockets. In such an embodiment, the fan shroud may also include shoulder surfaces for engaging the tops of the retaining members. The shoulder portions act as insertion stops when the shroud is placed over the daughterboards. Insertion is stopped after the protrusions of the shroud have engaged the retaining ledges on the retaining members. This aspect enables easy removal and replacement of the shroud. 
     In another aspect, the fan shroud may include one or more guide slots on each end for engaging tabs on the heatsinks as the shroud is placed over the daughterboards. This aspect facilitates proper alignment of the shroud during installation. 
     In still another aspect, the daughterboard system may be housed in a host computer chassis so that the fan of the daughterboard system has its effluent air path proximate to the intake air path of a chassis ventilation fan. In this manner, heat removal from the daughterboards is further enhanced by the action of the ventilation fan for the host system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of an actively-cooled daughterboard system according to the prior art. 
     FIG. 2 is an oblique view of the daughterboard system of FIG.  1 . 
     FIG. 3 is a top plan view of the daughterboard system of FIG.  1 . 
     FIG. 4 is an oblique view of a daughterboard retaining mechanism according to the prior art. 
     FIG. 5 is an oblique view of an actively cooled daughterboard system according to a preferred embodiment of the invention. 
     FIGS. 6,  7  and  8  are oblique, side and top plan views, respectively, of the fan shroud of FIG.  5 . 
     FIGS. 9 and 10 are exploded and assembled side views, respectively, of the daughterboard system of FIG.  5 . 
     FIG. 11 is an oblique view of the daughterboard system of FIG. 5 housed in a host computer chassis according to a preferred embodiment of the invention. 
     FIGS. 12,  13  and  14  are oblique, side and top plan views, respectively, of a first heatsink for optional use with the daughterboard system of FIG.  5 . 
     FIG. 15 is an oblique view of a heatsink mounting pin. 
     FIGS. 16,  17  and  18  are oblique, side and top plan views, respectively, of a second heatsink for optional use with the daughterboard system of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Actively cooled daughterboard system. FIG. 5 illustrates an actively cooled daughterboard system  500  according to a preferred embodiment of the invention. In daughterboard system  500 , one or more daughterboards are housed inside a fan shroud  600 . (In the embodiment shown, two daughterboards are so housed.) Each daughterboard housed within shroud  600  has a heat generating component such as a CPU mounted on it, and each daughterboard assembly includes a heatsink that is thermally coupled to the heat generating component. Preferably, each heatsink includes a plurality of transverse fins (to be further described below) oriented so that air may pass between the fins in a direction generally parallel to the plane of the associated daughterboard. Active cooling is provided by a single fan  700  mounted on the top of shroud  600  as shown. Using a single fan in this manner eliminates the need for multiple fans located on the individual daughterboard assemblies. 
     Fan shroud  600  is illustrated in more detail in FIGS. 6-8. Fan shroud  600  has openings  602  in both sides  604  and openings  606  in both ends  608 . In addition, there is an opening  610  in top surface  612  underneath the footprint of fan  700 . The purpose of openings  602 ,  604  and  610  is to direct air flow through the plural transverse fins of the heatsinks and through fan  700 . Preferably, fan  700  is mounted on shroud  600  as shown in FIGS. 7 and 8 so that the axis of rotation of fan  700  is substantially parallel with planes of the daughterboards (and thus also parallel with the outer ends of the transverse fins of the heatsinks). When fan  700  is so oriented, air flow will occur generally in the direction indicated by arrows  702  (side intake, top effluent) and  802  (end intake, top effluent). In alternative embodiments, the direction of the airflow may be reversed by changing the blow direction of fan  700 . 
     In the embodiment shown, fan shroud  600  was constructed from a single sheet of aluminum alloy which was cut and then folded into the configuration shown. Alternative materials and construction methods may, of course, be employed. Fan  700  was mounted to the top of shroud  600  by inserting plastic rivets in mounting holes  614 . Alternative mounting methods may be used. 
     It is a feature of the invention that shroud  600  includes protrusions  616  on each end  608  for engaging retaining ledges  404  of retaining members  400 . In addition, shroud  600  also includes shoulder portions  618  which act as insertion stops when shroud  600  is placed over the tops of the daughterboards. (Shoulder portions  618  engage the top surface of retaining members  400  to stop the movement of shroud  600  toward motherboard  502  as shroud  600  is being placed over the daughterboards.) Preferably, protrusions  616  should be disposed below shoulder portions  618  by a distance that will allow them to engage the undersides of retaining ledges  404  just before shoulders  618  contact the top surfaces of retaining members  404 . In an embodiment, ends  608  were separated by a distance that was slightly smaller than the distance between retaining members  400 . Such a spacing was adequate to enable protrusions  616  to engage retaining ledges  404  when shroud  600  was placed over the daughterboards. 
     It is an additional feature of the invention that shroud  600  includes guide slots  620  on each end  608 . Each of the heatsinks on the daughterboards includes end tabs  116 . After the daughterboards have been installed into their sockets on motherboard  502  as shown in FIG. 9, notches  118  in end tabs  116  engage retaining ledges  404  on one end of ledges  404 , leaving the other end of retaining ledges  404  free. Guide slots  620  are used to properly align shroud  600  over tabs  116  for installation as indicated by dashed lines  902 . When slots  620  are disposed over tabs  116 , protrusions  616  align themselves with the free end of retaining ledges  404 . Shroud  600  is lowered into position until protrusions  616  engage the free end of retaining ledges  404  as shown in FIG.  10 . It can be seen in FIG. 10 that shoulder portions  618  on shroud ends  608  act as insertion stops when they engage the top surfaces of retaining members  400 . 
     Additional heat removal efficiency may be achieved by mounting daughterboard system  500  in a host computer chassis  1100  as shown in FIG.  11 . In the configuration of FIG. 11, the effluent path  1104  of fan  700  is proximate to the intake path  1106  of a chassis ventilation fan  1102 . This enables chassis fan  1102  to direct heat-containing effluent from daughterboard system  500  to the exterior of chassis  1100 . 
     First preferred heatsink. A first preferred heatsink for optional use with daughterboard system  500  will now be described with reference to FIGS. 12-14. Heatsink  1200  was extruded using an aluminum 6063-T5 material. Other materials and fabrication techniques may be used. Heatsink  1200  includes a rectangular base portion  1202  having a longitudinal dimension  1204  longer than its transverse dimension  1206 . Tabs  116  were cut on either end of the base portion, for engaging retaining members  400  disposed proximate to a socket of a motherboard  502 . Four holes were drilled into the bottom of base portion  1202  for receiving mounting pins  1208  for anchoring heatsink  1200  to a daughterboard. Numerous transverse fins  1210  were integrally formed with base portion  1202  during extrusion. Fins  1210  were radially displaced from one another, as shown. 
     Base portion  1202  has end parts  1214  and a central part  1212 . Central part  1212  is preferably disposed directly over the heat generating component(s) of the daughterboard, and is thicker than end parts  1214  to enhance heat removal effectiveness over the components. In the illustrated embodiment, the thickness of central part  1212  of base portion  1202  varies according to an inner radius  1300  of fins  1210 . In one embodiment, inner radius  1300  was approximately 119.2 mm. The profile  1302  formed by the outer ends of fins  1210  varies according to an outer radius  1304 . In one embodiment, outer radius  1304  was approximately 136.8 mm and was constant for each of fins  1210 . The inner radius, however, was not constant for each of fins  1210 . Specifically, inner radius  1306  (associated with the fins coupled to end parts  1214  of base portion  1202 ) was slightly longer than inner radius  1300  (associated with the fins coupled to central part  1212  of base portion  1202 ). Variation of the inner fin radius in this manner enables additional fins to be placed on heatsink  1200  while maintaining a constant outer radius  1302 . 
     Preferably, central part  1212  of base portion  1202  is adapted to be coupled to the a heat generating component of the daughterboard. In one embodiment, this was accomplished by attaching a thermally conductive aluminum foil to the central area  1216  of the bottom of base  1202 . One material that was found to be useful for this purpose is sold under the trademark THERMSTRATE, and is available from Foxcon, Inc. under the part number 081-0001-558. 
     Mounting pins  1208  are illustrated in more detail in FIG.  15 . Each pin  1208  has a stem  1502  with a knurled cylindrical portion  1500  on one end and a clip retaining lip  1504  on the other end. During assembly, knurled portion  1500  is pressed into the previously-drilled receiving holes on the bottom of base  1202  of heatsink  1200  forming a friction fit. Clip retaining lips  1504  are used to secure heatsink  1200  to the daughterboard by means of a retaining clip. Retaining clips useful for this purpose are available from Foxcon, Inc. under the part number 025-0002-960. Other means may optionally be used to secure heatsink  1200  to the daughterboard. 
     Second preferred heatsink. A second preferred heatsink  1600  for optional use with daughterboard system  500  will now be described with reference to FIGS. 16-18. Heatsink  1600  was extruded using the same material as heatsink  1200 . Other materials and fabrication techniques may be used. Heatsink  1600  includes a rectangular base portion  1602  having a longitudinal dimension  1604  longer than its transverse dimension  1606 . Tabs  116  were cut on either end of the base portion, for engaging retaining members  400  disposed proximate to a socket of a motherboard  502 . Four holes were drilled into the bottom of base portion  1602  for receiving mounting pins  1208  for anchoring heatsink  1600  to a daughterboard. Numerous transverse fins  1610  were integrally formed with base portion  1602  during extrusion. Fins  1610  are all parallel to each other and orthogonal to the bottom of base portion  1602 . 
     Base portion  1602  has end parts  1614  and a central part  1612 . The central part  1612  is thicker than the end parts  1614  to enhance heat removal over the heat generating components of the daughterboard. The thickness of central part  1612  of base portion  1602  varies according to a radius  1700 . Radius  1700  may be approximated by step differences in the depths of fins  1610 . For example, in the embodiment shown, five central fins  1702  are the shallowest depth  1704 . Two groups of five endmost fins  1706  have the deepest depth  1708 . And fin pairs  1710 ,  1712  have intermediate depths  1714 ,  1716 , respectively. The profile formed by the outer ends of fins  1710  is constant relative to the bottom of the base portion  1602 . 
     Like heatsink  1200 , heatsink  1600  is preferably adapted to be coupled to a heat generating component of the daughterboard by attaching thermally conductive aluminum foil to the bottom of base  1602  in central area  1616 . Also like heatsink  1200 , pins  1208  may be used to secure heatsink  1600  to the daughterboard. 
     While the invention has been described in detail in relation to a preferred embodiment thereof, the described embodiment has been presented by way of example and not by way of limitation. It will be understood by those skilled in the art that various changes may be made in the form and details of the described embodiment without deviating from the spirit and scope of the invention as defined by the appended claims.