Patent Document

FIELD OF THE INVENTION  
       [0001]     This invention relates to the field of devices for cooling electrical and electronic circuitry, and more particularly to devices, systems and methods for cooling such circuits using waterblocks and associated tubing.  
       BACKGROUND  
       [0002]     To ensure proper functionality and reliability, manufacturers typically test flash memory chips before shipping them to customers. One system commonly employed to test flash memory chips is the Agilent V5400 Apache Tester.  
         [0003]     As illustrated in  FIG. 1 , one version of the V5400 Apache Tester  100  comprises test head  110 , support rack  120  for supplying test head  110  with electrical power, cooling water and compressed air (not shown in the Figures) and computer workstation  130 , which serves as the user interface to Tester  100 . Manipulator  140  supports and positions test head  110 . Support rack  120  is attached to manipulator  140  and serves as the interface between test head  110  and AC power, cooling water and compressed air. Tester  100  may also comprise additional support racks. Agilent&#39;s V5400 tester  100  shown in  FIG. 1  has the ability to test Flash, DRAM, SRAM and stacked memory devices.  
         [0004]     Test head  110  is an important component in the system and comprises tester electronics. In one configuration, tester  100  shown in  FIG. 1  offers up to 4,608 channels and  144  independent test sites and is capable of asynchronously testing up to  144  independent devices. Test head electronic components supply power to various devices under test (DUTs) and perform measurements thereon.  
         [0005]     As test electronics are forced to ever-greater speeds and densities, a major problem becomes removal of the internal heat generated by test head  110  and the circuitry being tested thereon. In prior generations of tester  100 , air cooling was sufficient. As clock speeds have increased, however, signal path length has become a critical issue. Minimizing path length has led to miniaturization by a factor of over thousand in the last five years, to such an extent that it is no longer practical to air-cool current-generation automated test equipment. Greater speed compounds the problem, as heat generation increases with clock speed. Higher pin count testers are becoming the norm as well, further increasing the total thermal power dissipation required in a tester.  
         [0006]     The foregoing factors result in liquid cooling being one of the few if not only practical methods for removing heat generated by modern test electronics. The magnitude of the problem becomes fully apparent by noting that high pin count testers having volumes less than 20 ft. 3  are now capable of generating between about 40 kW and about 80 kW of heat.  
         [0007]     In general the most reliable methods of liquid cooling seek to isolate the cooling fluid from the electronics of tester  100  and test head  110 , as opposed to immersion cooling. This is accomplished using waterblocks (sometimes referred to as ‘cold plates’). The active circuitry is mounted to a PC board, which in turn is mounted to a waterblock. In some cases certain components may be directly mounted to the waterblock for enhanced cooling. Various methods of mounting may be used, so the top or the bottom of a PC board may be contacting the waterblock. In many machines, circuits are mounted to both sides of a waterblock, to either minimize space or more fully utilize an expensive component (i.e., a waterblock). The working fluid may be water or some other liquid. Water has the highest cooling performance of the common chosen working fluids, but a variety of considerations may preclude its use in some applications.  
         [0008]     Waterblocks are generally constructed of an easily machined metal having high thermal conductivity such as aluminum or copper. Water or another fluid is routed through passages formed in the metal, and thereby removes heat. While this may seem to be a relatively straightforward process, many considerations come into play. For instance, some waterblocks have large internal passages, while others have small cross section passages. Heat transfer considerations generally favor small passages with very high liquid velocities to most effectively remove heat. This aids heat removal, at the expense of greater power required to pump the liquid. It should be noted that the ability to tailor the location of the water passage also can be used to aid the cooling of certain regions or devices that may have higher power dissipation requirements or more stringent temperature requirements.  
         [0009]     Most waterblocks are of a style where the working fluid contacts the metal block directly. In one such waterblock, an aluminum plate has long holes drilled through its midplane. Inlet and outlet tubes are glued into two such holes, with the inlet and outlet tubes forming a u-shaped return tube. Other styles of this type of waterblock may also be fabricated by milling corresponding serpentine passages into two plates, gluing the two halves together and adding inlet and outlet tubes in a manner similar to a clamshell.  
         [0010]     It has been discovered that waterblocks having inlet and outlet tubes formed therein can spring leaks at any of the glued joints. An alternative might be to braze the inlet and outlet joints, but doing so would introduce the potential for corrosion due to the presence of the brazing alloy.  
         [0011]     Another means of providing liquid cooling to a waterblock is to employ a style of waterblock referred to as “tube-in-slab.” To preclude the possibility of leaks occurring at joints, the fluid passage is one continuous piece of tubing. In such a style of waterblock, a serpentine passage is routed into the waterblock. A tube is formed to follow the contour routed in the plate. The whole length of tube is then forced into the plate, resulting in a waterblock with no joints in the fluid path. The cross section of the passage and that of the tube is such that a tight fit exists when the tube is forced into the groove. In some styles, the tube is deformed after insertion to further enhance contact between the tube and block. In addition to the physical contact, a material to aid heat transfer is often placed between the tube and the block. Thermal filled epoxy is often employed in such an application, although the tube may also be brazed in place or even surrounded by a thermal grease. The purpose of the epoxy, glue, brazing material or grease is to enhance heat conduction between the block and the outer surface of the tube, since without their presence a microscopic air gap would otherwise exist.  
         [0012]     Although the tube-in-a-slab design has many advantages, barriers to implementing such a construction exist owing to high manufacturing costs. The blocks must be machined to size and shape and then have a suitable groove routed in them. Tubing must be bent to precisely the same shape as the groove. Filler material must be dispensed into the groove, the tubing laboriously forced in, and finally the surface re-cut to remove the filler material that has been squeezed out. For next-generation testers to be economically built, cooling cost on a per unit area basis must decrease considerably.  
         [0013]     Some typical prior art waterblocks are illustrated in cross-section in  FIGS. 2 and 3 .  FIG. 2  illustrates a cross section of one type of tube-in-slab waterblock  200 , where cross-sectional groove  300  is routed in the relatively thick plate from which waterblock  200  is formed. Groove  300  is sized to accept cooling tube  230  therewithin easily, cooling tube  230  having inner lumen  240 , inner surface  2650  and outer surface  250 . Thermally conductive epoxy or other suitable material  290  is dispensed in groove  300 , cooling tube  230  is inserted in groove  300  and cooling tube  230  is swaged downwardly (and thus outwardly) into groove  300 , thereby serving to push outer surface  250  of cooling tube  230  tightly against inner surface  310  of groove  300 . Such a tight fit ensures a thin glue line and facilitates heat transfer. Top surface  210  of waterblock  200  is then fly cut for planarity.  
         [0014]      FIG. 3  shows another style of waterblock  200  having no bonding material  290  for cooling tube  230 , which is swaged into groove  300  (which has a different shape from groove  300  shown in  FIG. 2 ). In  FIG. 3 , sharp corners in groove  300  and inner surface  310  thereof firmly engage outer surface  250  of cooling tube  230 . Such a design permits sufficient deformation of cooling tube  230  tube against inner surface  310  to provide excellent heat transfer. Note that in the design of waterblock  200  shown in  FIG. 3 , the upper portion of outer surface  250  of cooling tube  230  is positioned below substantially planar first surface  210  of waterblock  200 .  
         [0015]     Note that the two constructions of waterblock  200  shown in  FIGS. 2 and 3  share the disadvantage of being relatively thick, which is necessary to resist the spreading forces applied thereto when cooling tube  230  is placed or forced therein. Waterblock  200  must, of course, be thicker than groove  300  to be milled. Thickness in addition to the groove  310  must therefore be added to waterblock  200  to maintain planarity of waterblock  200  during and after the swaging process.  
         [0016]     As will be seen by referring to  FIGS. 2 and 3 , waterblock  200 , groove  300  and cooling tube  230  have rather elaborate and complicated forms and shapes, which those skilled in the art will understand increase considerably the cost of manufacturing and assembling waterblock  200 . The elaborate shapes and forms of such waterblocks, grooves and cooling tubes are necessary owing to the significant thermal and mechanical stresses to which waterblock  200  and cooling tube  230  are subjected during use. Moreover, most of the cost of a tube-in-slab waterblock may be ascribed to machining operations for placing the cooling tube in the waterblock and to the subsequent cleanup of adhesive.  
         [0017]     It will now be seen that forming the complicated shapes and forms of, and employing the expensive methods and materials used to manufacture, waterblocks  200 , grooves  300  and cooling tubes  230  shown in  FIGS. 2 and 3  increase manufacturing costs. What is needed is a simpler means of attaching cooling tubes to a waterblock that eliminates the need to machine expensive grooves in the waterblock.  
       SUMMARY OF THE INVENTION  
       [0018]     In accordance with one aspect of the present invention, a device for cooling at least one heat-generating electrical or electronic circuit in a circuit board is provided. In such an embodiment, the device comprises at least a first waterblock comprising a first surface configured for engagement with or positioning adjacent the circuit board, the waterblock comprising at least a second surface, at least a first cooling tube comprising at least a first lumen and an outer surface, the at least first lumen being configured to carry a liquid therethrough such that the liquid does not leak from or through the tube to the outer surface thereof. The at least first cooling tube operably engages and is attached to the second surface of the waterblock, the second surface of the waterblock containing no voids, recesses or grooves for accepting the at least first cooling tube therein, the first cooling tube being configured to carry away at least a portion of the heat generated by the electrical or electronic circuit when the liquid flows therethrough.  
         [0019]     In another embodiment of the present invention, a method of making a device for cooling at least one heat-generating electrical or electronic circuit in a circuit board, the device comprising at least a first waterblock comprising a first surface configured for engagement with or positioning adjacent the circuit board, the waterblock further comprising at least a second surface, at least a first cooling tube comprising at least a first lumen and an outer surface, the at least first lumen being configured to carry a liquid therethrough such that the liquid does not leak from or through the tube to the outer surface thereof, the at least first cooling tube operably engaging and being attached to the second surface of the waterblock, the second surface of the waterblock containing no voids, recesses or grooves for accepting the at least first cooling tube therein, the first cooling tube being configured to carry away at least a portion of the heat generated by the electrical or electronic circuit when the liquid flows therethrough, the method comprising providing the waterblock; providing the cooling tube; and attaching the cooling tube to the waterblock.  
         [0020]     The present invention further includes within its scope various methods making and using the foregoing components, devices and systems.  
         [0021]     The various embodiments of the cooling tube and waterblock of the present invention reduce manufacturing and materials costs, and therefore reduce costs associated with prior art means and methods of cooling electrical or electronic circuitry employing liquid-cooling techniques. For example, many of the various embodiments of the present invention eliminate machining of waterblocks and attendant costs, eliminate time otherwise spent inserting and swaging tubes into grooves, eliminate cleanup after swaging, and use low cost “featureless” cooling tubes attached to one or more sides of one or more waterblocks. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The foregoing and other aspects of the invention will become apparent after having read the detailed description of a preferred embodiment of the invention set forth below and after having referred to the following drawings, in which like reference numerals refer to like parts:  
         [0023]      FIG. 1  shows a prior art Agilent V5400 Apache memory chip tester;  
         [0024]      FIG. 2  shows a schematic cross-sectional representation of a first embodiment of a prior art waterblock and accompanying groove and cooling tube;  
         [0025]      FIG. 3  shows a schematic cross-sectional representation of a second embodiment of a prior art waterblock and accompanying groove and cooling tube;  
         [0026]      FIG. 4  shows a first embodiment of a waterblock and accompanying cooling tube of the present invention;  
         [0027]      FIG. 5  shows a second embodiment of a waterblock and accompanying cooling tube of the present invention;  
         [0028]      FIG. 6  shows a third embodiment of a waterblock and accompanying cooling tube of the present invention, and  
         [0029]      FIG. 7  shows a fourth embodiment of a waterblock and accompanying cooling tube of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     As employed in the specification and claims hereof, the term “waterblock” means a plate-shaped member formed of a material having thermal characteristics which favor the transfer of thermal energy therethrough; the term “cooling tube” means a member capable of carrying a fluid in at least one lumen thereof, the fluid transporting thermal energy away through the tube from an external source of thermal energy; the term “substantially planar first surface” means a surface of a waterblock to which a cooling tube is attached, the first surface forming a substantially flat surface that may be interrupted by ridges or cooling fins disposed thereon or machined or stamped therein.  
         [0031]     Many of the various embodiments of the present invention relate to components, devices, systems and methods of providing waterblocks that reduce manufacturing costs by eliminating machining operations. In such embodiments, a relatively featureless plate or waterblock  200  formed of sheet metal or another suitable thermally conductive material replaces highly machined prior art plates or tube-in-slab waterblocks described above. Although many embodiments of waterblock  200  of the present invention have features such as tapped holes or threaded inserts for mounting a PCB to waterblock  200 , such features are very low cost features in comparison to the prior art practice of precision-milling grooves.  
         [0032]     Many of the various embodiments of the present invention may further reduce machining costs by permitting waterblock  200  to comprise sheet metal that may be sheared to size at relatively low cost. As shown in  FIG. 4 , in one embodiment of the present invention, instead of placing cooling tube  230  in routed groove  300 , cooling tube  230  one portion of outer surface  250  may be flattened slightly and affixed to sheet metal waterblock  200 . In some embodiments of the present invention, cooling tube  230  is flattened to a D- or O-shaped cross section after serpentine bends are formed in cooling tube  230 , although other cross-sectional shapes are also contemplated such as circular, elliptical, rectangular and square cross-sections.  
         [0033]     Referring now to  FIGS. 4 and 5 , flattening at least one side of cooling tube  230  increases the surface area over which outer surface  250  of cooling tube  230  engage substantially planar first surface  210  of waterblock  200 , thereby promoting adhesion and heat transfer. If the bonding material employed to secure cooling tube  230  to first surface  210  has relatively low thermal conductivity (as is the case with some thermally conductive epoxies), the relatively large surface area of outer surface  250  over which a bond may develop between cooling tube  230  and first surface  210  reduces thermal resistance arising from water flowing through lumen  240  of cooling tube  230 . Thermal flux is also promoted by cooling tube  230  having a wide contact area with first surface  210 , which reduces the fin effect (the resistance of heat flowing around the tube periphery).  
         [0034]     In some embodiments of the present invention, waterblock  200  is formed of sheet metal comprising an aluminum alloy, which has low weight and high thermal conductivity. It is not necessary that cooling tubes  230  be formed of the same alloy or material as waterblock  200 . In most applications where use of the present invention is practical and economic, under typical operating conditions no significant thermally-induced stresses will arise from differential expansion of cooling tube  230  and waterblock  200 . In some cases it is desired that the sheet metal employed to form waterblock  200  be copper owing to its high thermal conductivity. Note, however, that materials other than aluminum and copper may be used to form waterblock  200 , including, but not limited to a ceramic-containing materials, stainless steel, zinc, nickel, thermally-conductive plastic, aluminum-silicon carbide composites, and alloys, combinations or mixtures of all the foregoing, as well as thermally conductive plastics and composites.  
         [0035]     Continuing to refer to  FIGS. 5 and 6 , in many embodiments of the present method thermally conductive epoxy provides the best choice for bonding material  290 , although a wide variety of other materials and methods may be used to attach cooling tube  230  to waterblock  200 . Among such materials and methods are adhesive-containing materials, suitable thermally conductive materials, foam, caulk, tape, glue, epoxy, soldering and brazing.  
         [0036]     Cooling tube  230  may further be secured to waterblock  200  by means of brackets or clips (not shown in the Figures) for holding cooling tube  230  against upper surface  210 , either as a means of primary attachment or to provide strain relief. The brackets or clips may have legs or portions that are secured to waterblock  200  by means of bolts, screws or adhesive. In such cases, thermally-filled grease or thermal interface pads may be disposed between outer surface  250  and first surface  210  to facilitate thermal conduction. An electrically nonconductive or electrically insulative, but thermally conductive, material may also be disposed between outer surface  250  and first surface  210  to electrically isolate cooling tube  230  from waterblock  200 .  
         [0037]     The liquid employed in cooling tube  230  is preferably water, but may also be one or more of COOLANOL (a speciality coiling fluid manufactured by EXXON), polyalpha olefin (PAO) dielectric coolant fluid, synthetic hydrocarbon oil, ethylene glycol, an ethylene glycol/water mixture, or any other suitable cooling fluid.  
         [0038]     In preferred embodiments of the present invention, few or no post-attachment steps are required to clean up waterblock  200  after cooling tube  230  has been secured thereto. For example, in preferred embodiments of the present invention no material squeeze-out into critical areas results from attachment of cooling tube  230  to waterblock  200 , and thus no cleanup is generally required.  
         [0039]     Also in preferred embodiments of the present invention, and unlike in the prior art where high-precision bending of cooling tube  230  was required for tube  230  to fit machined groove  300  in tube-in-slab waterblock  200 , relatively featureless and substantially planar first surface  210  of waterblock  200  permits minor imperfections in cooling tube  230  bending or cross section or surface  210  planarity, typically have no impact on proper operation of cooling tube  230  or waterblock  200 . The present invention&#39;s tube-on-plate construction may also be employed in applications where a single seamless piece of cooling tube  230  eliminates or reduces the possibility of leaks.  
         [0040]     In one embodiment of the tube-on-plate method and device of the present invention, a suitable sheet metal plate is sheared from a larger plate to form waterblock  200 . Cooling tube  230  is bent into an appropriate serpentine shape, the shape being configured to meet predetermined heat transfer goals. Accordingly, uniform loops may or may not be formed in cooling tube  230 , depending on anticipated heat flux and temperature conditions. Cooling tube  230  may further be configured to be routed adjacent critical heat-emitting components. In some applications, cooling tube  230  may also be configured such that tube  230  crosses over itself out-of-plane. Such out-of-plane “jumps” are preferably not left dangling but instead are secured to waterblock  200  by some appropriate means such as brackets, clamps or clips.  
         [0041]     In some methods and devices of the present invention, cooling tube  230  is first bent into a preferred serpentine configuration, followed by flattening a portion of outer surface  250  to yield an oval or D-shaped cross-sectional shape by any one of a variety of suitable means. It is preferred that flattening of cooling tube  230  occur after tube  230  has been bent into an appropriate contour so as to minimize the possibility of undesirable out-of-plane flattening of cooling tube  230 . Thermal epoxy is then dispensed along flattened portions of cooling tube  230 , preferably by a dispensing robot that mixes and accurately dispenses epoxy on such flattened portions. Finally, cooling tube  230  is pressed and held against first surface  210  of waterblock  200  with moderate and uniform force until the epoxy has cured and hardened. Waterblock  200  is then inspected and appropriate holes are drilled to mount one or more PCBs thereon. All of the foregoing steps are carried out with little to no machining or hand work, thereby reducing costs.  
         [0042]     In the event cooling tube  230  is attached to first surface  210  of waterblock  200  by means of brazing, a brazing alloy is applied as a paste or plated on flattened portions of tube  230 . If cooling tube  230  is secured to waterblock  200  by means of clamps, brackets or clips, a dispensing or screening process may be employed to accurately dispense and spread thermal grease onto appropriate portions of tube  230  or first surface  210 . Note that although a sheet metal plate may be employed to form waterblock  200 , thicker plates may be employed to form waterblock  200  and indeed may be preferred in some applications.  
         [0043]     In addition to lower manufacturing costs, the present invention possesses mechanical advantages. In currently-practiced methods of tube-in-slab construction, some distortion of waterblock  200  results which may range between minor and severe and that that varies with the techniques and materials used. Such distortion presents difficulties with flatness and feature placement, since all major machining has been finished before cooling tube  230  is pressed into routed groove  300 . The present invention presents no such difficulties since cooling tube  230  is not pressed or swaged into a groove.  
         [0044]     Various embodiments of the present invention are characterized in having relatively slim or low profiles. In such embodiments, waterblock  200  has a relatively small thickness  270 ,  270   a  or  270   b , which in turn permits the total thickness  280  of waterblock/PCB assembly  295  to be relatively small. See  FIGS. 5, 6  and  7 .  
         [0045]     As illustrated in  FIGS. 6 and 7 , circuit board  320  may require cooling but does not afford sufficient space and volume to permit the use of a large waterblock. Accordingly, in alternative embodiments of the present invention, typically although not necessarily where circuit board  320  is characterized in having relatively low heat dissipation, cooling tube  230  is routed around the periphery of board  320 . See  FIGS. 6 and 7 . In another alternative embodiment of the present invention, a sheet metal plate or other suitable material having a recess disposed in a portion thereof for accepting circuit board  320  therein and forming a periphery thereabout is employed to form waterblock  200 , more about which we say below.  
         [0046]     The material from which waterblock  200  of  FIG. 6  is preferably formed is copper owing to its low thermal resistance, but other suitable metals, alloys and materials may be used. Cooling tube  230  is mounted along the periphery of circuit board  320  and preferably on the same side of the PCB as electrical/electronic circuitry mounted thereon to permit double use of space above the plane of the board bottom (see  FIG. 6 ). Note that some areas of sheet metal in waterblock  200  of  FIG. 6  could be punched out relatively easily to permit back side components to be mounted thereon.  
         [0047]     Yet another means of providing a space- and volume-saving construction in the present invention is illustrated in  FIG. 6 , where circuit board  320  has electrical/electronic circuitry and components  330  mounted on both sides thereof. In such an embodiment of the present invention, surfaces  220   a  and  220   b  may be configured to engage the surfaces of components  330  mounted on circuit board  320 , such components being optimized for top-side cooling (as is usually the case for components designed for air cooling). Cooling tube  230  is preferably although not necessarily located at the periphery of circuit board  320  and is bonded to waterblocks  200   a  and  200   b  by means of adhesives  290   a  and  290   b . Waterblocks  200   a  and  200   b  dissipate heat generated by components  330  on both sides of circuit board  320 .  
         [0048]     Small gaps between components  330  and waterblocks  200   a  and  200   b  arising from non-planarity of components or waterblocks may be filled by a thermal interface material disposed in such gaps to enhance thermal conductivity. In another embodiment of the present invention, mechanical pressure generated by appropriately positioned bolts, screws, glue or other means of fastening cause surfaces  220   a  and  220   b  to engage the bottom and top surfaces, respectively, of components  330  to enhance thermal conductivity. Cooling tube  230  may encircle circuit board  320  or be positioned on one, two or three sides thereof, depending on heat flux and size requirements.  
         [0049]     The present invention includes within its scope various methods of making and using waterblock  200  and cooling tube  230  of the present invention.  
         [0050]     As will now become apparent, while specific embodiments of waterblock  200  and cooling tube  230  of are described and disclosed herein, many variations and alternative embodiments of the present invention may be constructed or implemented without departing from the spirit and scope of the present invention. It is to be understood, therefore, that the scope of the present invention is not to be limited to the specific embodiments disclosed herein, but is to be determined by looking to the appended claims and their equivalents. Consequently, changes and modifications may be made to the particular embodiments of the present invention disclosed herein without departing from the spirit and scope of the present invention as defined in the appended claims.

Technology Category: g