Waterblock for cooling electrical and electronic circuitry
A waterblock and accompanying cooling tube for carrying away heat generated by electrical or electronic components mounted on a circuit board or other substrate are disclosed. The cooling tube is attached to the waterblock by means of an adhesive or other suitable material, and is not positioned in a groove machined into the surface of the waterblock as has been done in past. The unique design of the waterblock and cooling tube eliminates the need to machine expensive grooves in the waterblock, thereby reducing manufacturing costs.
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.
BACKGROUNDTo 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.
As illustrated in
Test head 110 is an important component in the system and comprises tester electronics. In one configuration, tester 100 shown in
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.
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.
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.
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.
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.
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.
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.
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.
Some typical prior art waterblocks are illustrated in cross-section in
Note that the two constructions of waterblock 200 shown in
As will be seen by referring to
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
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.
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.
The present invention further includes within its scope various methods making and using the foregoing components, devices and systems.
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 DRAWINGSThe 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:
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.
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.
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
Referring now to
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.
Continuing to refer to
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.
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.
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.
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'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.
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.
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.
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.
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.
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, 270a or 270b, which in turn permits the total thickness 280 of waterblock/PCB assembly 295 to be relatively small. See
As illustrated in
The material from which waterblock 200 of
Yet another means of providing a space- and volume-saving construction in the present invention is illustrated in
Small gaps between components 330 and waterblocks 200a and 200b 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 220a and 220b 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.
The present invention includes within its scope various methods of making and using waterblock 200 and cooling tube 230 of the present invention.
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.
Claims
1. A device for cooling at least one heat-generating electrical or electronic circuit in a circuit board, comprising:
- (a) 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;
- (b) 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;
- wherein 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.
2. The device of claim 1, wherein the second surface is substantially flat.
3. The device of claim 1, wherein the first surface is configured for attachment to at least a portion of the circuit board.
4. The device of claim 1, wherein a portion of the outer surface of the cooling tube is configured for attachment to the second surface of the waterblock.
5. The device of claim 4, wherein the portion of the outer surface of the cooling tube is substantially flat and configured for engagement or positioning on the second surface of the waterblock.
6. The device of claim 1, wherein the at least first tube is one of circular, elliptical, rectangular, square, D-shaped and flattened in cross-section.
7. The device of claim 1, wherein at least a portion of the cooling tube is serpentine in shape.
8. The device of claim 1, wherein an adhesive-containing material is disposed between the second surface and the cooling tube.
9. The device of claim 8, wherein the adhesive-containing material is at least one of a thermally conductive material, foam, tape, glue, epoxy and thermally conductive epoxy.
10. The device of claim 1, wherein a solder or brazing material is disposed between the second surface and the cooling tube.
11. The device of claim 1, wherein a thermally conductive material is disposed between the second surface and the cooling tube.
12. The device of claim 1, wherein the waterblock is grooveless.
13. The device of claim 1, wherein the waterblock has no groove for accepting the cooling tube therein.
14. The device of claim 1, wherein the first surface is substantially planar.
15. The device of claim 1, wherein the waterblock comprises cooling fins or cooling grooves.
16. The device of claim 1, wherein the waterblock comprises a material selected from the group consisting of aluminum, a ceramic-containing material, stainless steel, copper, zinc, aluminum-silicon carbide, and alloys, combinations or mixtures of all the foregoing.
17. The device of claim 1, wherein the waterblock comprises a material selected from the group consisting of aluminum, stainless steel, copper, zinc, aluminum-silicon carbide and alloys, combinations or mixtures of all the foregoing.
18. The device of claim 1, wherein the first cooling tube comprises a material selected from the group consisting of aluminum, stainless steel, copper, zinc and alloys, combinations or mixtures of all the foregoing.
19. The device of claim 1, wherein the first cooling tube is attached to the waterblock by at least one of glue, epoxy, a thermally conductive adhesive, a fixture for attachment of the tube to the waterblock, at least one bolt, at least one screw, brazing, soldering, welding, crimping and combinations or mixtures of any of the foregoing.
20. The device of claim 9, further comprising a plurality of waterblocks.
21. The device of claim 9, further comprising a plurality of cooling tubes.
22. The device of claim 1, wherein the liquid is selected from the group consisting of water, COOLANOL, Polyalpha Olefin (PAO) dielectric coolant fluid, synthetic hydrocarbon oils ethylene glycol and ethylene glycol/water mixture.
23. A means for cooling at least one heat-generating electrical or electronic circuit in a circuit board, comprising:
- (a) at least a first means for conducting thermal energy comprising a first surface configured for engagement with or positioning adjacent the circuit board, the thermal energy conducting means further comprising at least a second surface;
- (b) at least a first means for carrying a fluid within a lumen comprising an outer surface, the lumen being configured to carry the fluid therethrough such that the fluid does not leak from or through the fluid carrying means to the outer surface thereof;
- wherein the fluid carrying means operably engages and is attached to the second surface of the thermal energy conducting means, the second surface of the thermal energy conducting means containing no voids, recesses or grooves for accepting the fluid carrying means therein, the fluid carrying means being configured to carry away at least a portion of the heat generated by the electrical or electronic circuit when the fluid flows therethrough.
24. The device of claim 22, wherein the second surface is substantially flat.
25. The device of claim 22, wherein the first surface is configured for attachment to at least a portion of the circuit board.
26. The device of claim 1, wherein a portion of the outer surface of the fluid carrying means is configured for attachment to the second surface of the thermal energy conducting means.
27. 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:
- (a) providing the waterblock;
- (b) providing the cooling tube; and
- (c) attaching the cooling tube to the waterblock.
Type: Application
Filed: Oct 25, 2005
Publication Date: Apr 26, 2007
Inventors: John Andberg (Santa Cruz, CA), Noriyuki Sugihara (Campbell, CA)
Application Number: 11/257,669
International Classification: F28F 7/00 (20060101);