Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
  • F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
  • F28D15/0266—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with separate evaporating and condensing chambers connected by at least one conduit; Loop-type heat pipes; with multiple or common evaporating or condensing chambers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L23/00—Details of semiconductor or other solid state devices
  • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
  • H01L23/46—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements involving the transfer of heat by flowing fluids
  • H01L23/473—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements involving the transfer of heat by flowing fluids by flowing liquids
  • H01L23/4735—Jet impingement
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

• the present invention relates generally to spray cooling thermal management systems and more specifically it relates to a spray cooling system that provides high heat flux evaporative cooling of electronic component hotspots.
• Liquid cooling is well known in the art of cooling electronics. As air cooling heat sinks continue to be pushed to new performance levels, so has their cost, complexity, and weight. For some time, liquid cooling solutions have been developed and tested, but other than specialty applications they have yet to gain widespread commercial adoption. As computer power consumptions continue to increase, liquid cooling will provide significant advantages to computer manufacturers which will force its use. The present invention provides significant advantages over both air cooling and prior art liquid cooling solutions.
• Liquid cooling technologies use a cooling fluid for removing heat from an electronic component. Liquids can hold and transfer heat at a rate many times that of air.
• Single-phase liquid cooling systems place a pure liquid in thermal contact with the component to be cooled. With these systems, the cooling fluid absorbs heat as sensible energy.
• Other liquid cooling systems such as spray cooling, are two-phase processes. In these systems, heat is absorbed by the cooling fluid as latent energy gains.
• Two-phase cooling or commonly referred to as evaporative cooling, provides the ability to deliver more efficient, more compact and higher performing liquid cooling systems than single- phase systems.
• An exemplary two-phase cooling method is spray cooling.
• Spray cooling uses a pump for supplying fluid to one or more nozzles that transform the coolant supply into droplets. These droplets impinge the surface of the component to be cooled and can create a thin coolant film. Energy is transferred from the surface of the component to the thin-film. Because the fluid is dispensed at or near its saturation point, the absorbed heat causes the thin-film to turn to vapor. This vapor is then condensed, often by means of a heat exchanger, or condenser, and returned to the pump.
• U.S. Patent No. 5,220,804 provides a method of increasing a spray cooling system's ability to remove heat.
• the '804 patent describes a method of managing system vapor that further thins the coolant film which increases evaporation, improves convective heat transfer, and liquid and vapor reclaim.
• Electronic components create varying amounts of heat across their surfaces and a varying amount of heat as a function of time.
• Today's microprocessors may be constructed on a silicon die roughly 1 cm by 1 cm.
• the die may have multiple zones for different functions. Such zones may be for inputs and outputs (l/Os), level 1 cache, level 2 cache, and the core.
• the core may be roughly 0.5 cm by 0.5 cm and is where the main computer processing takes place. Although the core may only be 25% of the total area of the die, it creates almost the entire heat generation by the chip and may be considered a chip "hotspot".
• a chip might be rated for an average heat load of 110 watts, with an average heat flux of 110 watts per centimeter squared, the core may generate 100 watts of that heat and have a heat flux of 400 watts per centimeter squared.
• This non-uniform heat flux distribution poses a significant challenge to the cooling system as it is desirable to keep the entire chip at nearly the same operating temperature. Cooling systems that rely on heat spreading may not provide this ability as they rely on conduction spreading, resulting in significant temperature gradients across the chip.
• One method of cooling the core of a computer chip is to divide the chip into thermal zones and to cool each of the chip's zones at a different rate.
• U.S. Pat. No. 6,443,323 describes a method of variably cooling a computer component through the use of incremental sprayers. The incremental sprayers deposit fluid onto each zone at a mass flow rate necessary for complete phase change. Drops are ejected from an orifice in serial. Although this method improves the efficiency of the system, that is in attaining complete phase change of all dispensed fluid, the incremental dispensing method does not provide dispensing characteristics necessary to create high heat flux thin-film evaporative cooling and high performance cooling of hotspots.
• Yet another method of cooling the core is two-phase microchannels, such as described by U.S. Pat. No. 4,450,472. Although this method does not use spray cooling, the design does provide the ability to remove heat in the range of 400 -1000 watts per square centimeter using water.
• the system discloses a method of placing a very small microchannel array on an electronic component. Although microchannel cooling methods may effectively lower the temperature of the core, due to large pressure drops and resulting size limitations they do not efficiently address the needs of the non-hotspot areas of the die.
• the present invention is a spray cooling thermal management device that cools an electronic component creating a varying amount of heat across its surfaces.
• Liquid coolant is dispensed upon the surface of the component.
• the liquid coolant is dispensed as a continuous atomized droplet pattern.
• the atomized pattern creates a high heat flux evaporative cooling thin- film over the one or more core areas.
• the present invention optimizes the atomized pattern for maximum heat removal rates. Any excess, non-vaporized, fluid flowing outward from the hotspot is used to cool the lower heat flux (non-core) areas of the component through the creation of a thick coolant film thereon.
• FIG. 1 A block diagram illustrating an exemplary computing environment in accordance with the present invention.
• FIG. 1 A block diagram illustrating an exemplary computing environment in accordance with the present invention.
• FIG. 1 A block diagram illustrating an exemplary computing environment in accordance with the present invention.
• FIG. 1 A block diagram illustrating an exemplary computing environment in accordance with the present invention.
• FIG. 1 A block diagram illustrating an exemplary computing environment in accordance with the present invention.
• Another embodiment of the present invention uses a liquid-vapor separator for separating liquid and vapor from the exit stream of a spray module prior to condensing the vapor.
• the result is a near pure vapor at the inlet of the condenser which is potentially more efficient and has a more repeatable performance than a condenser with substantial two-phase flow at its inlet.
• Yet another embodiment of the present invention enhances the surface of the chip to be spray cooled through the use of etched open microchannels. These microchannels are formed either directly into the top surface of the chip or through the use of a secondary etched microchannel plate bonded to the top surface of the chip.
• Figure 1 is a perspective view of a computer chip mounted onto a substrate
• Figure 2 is a top view of computer chip with multiple zones
• Figure 3 is a perspective view of a spray module mounted onto the substrate and encompassing the chip from Figure 1;
• Figure 4 is a section view, along line A-A of Figure 3, showing the inside the a spray module according to the present invention
• Figure 5 is a partial view of Figure 4 showing a spray plate located over the chip to be cooled according to the present invention
• Figure 6 is a side view of a spray plate with hotspot vapor management protrusions
• Figure 7 is an alternative embodiment of the present invention showing a secondary nozzle spraying onto the thick-film
• Figure 8 is another alternative embodiment of the present invention showing an angled atomizer
• Figure 9 is a bottom perspective view of a spray plate with a hotspot vapor management protrusion
• Figure 10 is a block diagram of a simple spray cool system
• Figure 11 is a block diagram of a spray cool system using a liquid and vapor separator
• Figure 12 is a side section view of a separator of Figure 11 ;
• Figure 13 is a side partial view of a spray cooled secondary etched microchannel plate, with the microchannels enlarged for clarity.
• Applicant hereby incorporates by reference the following U.S. patents: U.S. Patent No. 5,220,804 for a high heat flux evaporative cooling system; and U.S. Patent No. 5,860,602 and U.S. Patent No. 6,016,969, each for a laminated array of pressure swirl atomizers, and U.S. Patent No. 6,108,201 for a fluid control apparatus and method for spray cooling and U.S. Pat. Application No. 10/281,391 for an actuated atomizer.
• Computer chip 2 may be a microprocessor, Field Programmable Gate Array (FPGA), Application Specific Integrated Circuit (ASIC), or any other commonly used electronic component.
• Chip 2 is attached to substrate 4 using any one of a wide range of commonly known packaging technologies (not shown), including: ball grid array, pin grid array, land grid array, and wirebond.
• the present invention is not limited to any one' particular interconnect or packaging method.
• Figure 2 shows a typical microprocessor version of chip 2.
• the top surface of chip 2 has several zones, each with a unique function, unique power consumption, and thus, a unique heat generation rate. Although multiple zones are identified by Figure 2, they can be lumped into high and low heat flux zones. Low heat generation zones may be, but are not limited to, memory (L1 and L2 cache), l/Os and controllers.
• a chip may have multiple hotspots as areas of execution and floating point calculations may be done in separate locations on the die, each hotspot located over a core.
• FIG. 3 shows a spray module 10 attached to substrate 4 and encompassing chip 2.
• Spray module 10 may be attached to substrate 4 through the use of adhesives, soldering, or mechanical fastening such as but not limited to the methods described by U.S. Pat. No. 6,108,201 incorporated herein by this reference.
• Spray module 10 is used for dispensing a supply of liquid coolant onto the surface of chip 2. Fluid enters module 10 through an inlet 14 and exits through an outlet 16. Although only one outlet 16 is shown, multiple are possible. In fact, wherein computer desktops are most often orientated in one of two orientations, desktop or tower, it may be preferable to have a plurality of outlet 16 at ninety degree angles to each other.
• Spray module 10 is part of a well known and understood two-phase cooling cycle (shown in Figure 10).
• a pump 5 is used for supplying a cooling fluid at an optimal spray cooling flow rate and pressure level.
• the cooling fluid can be any one of the well known spray cooling fluids, including but not limited to FC-72, Fluorinert (a Trademark of 3M), water and water mixtures.
• FC-72 Fluorinert
• a condenser 8 cools the fluid and returns liquid to pump 5.
• the system and components of the spray cool system are well known and understood in the field, and thus, they will not be discussed in further detail.
• Spray module 10 has an outer housing 12 that provides the structural rigidity to the overall module.
• Housing 12 can be constructed from many materials, including aluminum and plastic.
• housing 12 is designed to provide the ability to be molded or die-casted (as shown in Figure 4), thus providing low manufacturing costs.
• a fluid supply enters inlet 14 located at the top of housing 12, by means of a supply tube (not shown).
• the connection between inlet 14 and the supply tube is preferably removable through the use of a common quick disconnect fitting.
• the coolant flowing through inlet 14 then enters a manifold area created between housing 12 and a spray plate 30.
• Spray plate 30 provides the means for dispensing the cooling fluid onto chip 2.
• Plate 30 is shown inserted into a pocket within housing 12, where it can be glued, fastened or swaged into place. Due to the one piece design of housing 12, it is not necessary to provide a fluid tight seal between spray plate 30 and housing 12, but it is desirable to provide a tight fit and thus minimize pressure losses.
• Spray plate 30 contains one or more nozzles that provide the means of transforming the supply of coolant into one or more continuous droplet streams.
• an atomizer 32 is shown located over core 3. Although one atomizer 32 is shown, depending upon the type of fluid used, the size of core 3, and the spray cone angle of atomizer 32, there may be one or more atomizers placed above core 3.
• a method of creating spray plate 30 is described by U.S. Pat. No. 5,860,602 and U.S. Pat. No. 6,016,969 for a laminated pressure swirl atomizer. Another method is to insert button-style atomizers into plate 30.
• chip 2 produces highly variable heat fluxes as a function of time, that is it cycles from peak performance to "sleep" mode, it may be advantageous to make atomizer 32 variable and controllable as described by U.S. Pat. Application No. 10/281,391.
• the variable atomizer in conjunction with an electronic control system makes it possible to achieve direct component temperature feedback and overall thermal performance control.
• Atomizer 32 provides the means for removing significant amounts of heat directly from core 3. Through the use of atomizer 32, droplet size, distribution and momentum can all be controlled and optimized in a fashion that provides a thin-film 40 over core 3 , as shown in Figure 5. As described by the dissertation by Tilton, the thickness of thin-film 40 can significantly affect the ability of the coolant to remove heat. Generally, the thinner thin-film 40 becomes the more heat it can remove.
• optimization of coolant dispensing characteristics may also yield a unique event that occurs when droplets impinge a flat surface, called hydraulic jump.
• This jump process occurs when a thin-film fluid flows radially and then jumps in height based upon its Froude number going from supercritical (thin-film) to subcritical (thick-film).
• a supercritical thin-film may be, but is not limited to, the range of 100 micrometer to 400 micrometers thick, and the jumped thick-film may be in the range, but is not limited to, 3000 micrometers to 4000 micrometers using water.
• a hydraulic jump provides the means of creating thin-film 40 and thick-film 42 and the ability to cool core 3 of chip 2 at a rate greater than the non-core areas of chip 2.
• a hydraulic jump may also provide a thermal buffer in the event that spray becomes momentarily interrupted.
• thin-film 40 may be capable of absorbing heat fluxes up to a thousand or more watts per square centimeter over the small area of core 3
• thick-film 42 may be capable of efficiently and reliably providing heat removal rates generally less than 100 watts per square centimeter over the large area low-heat-flux zones of chip 2.
• the process of etching microchannels is described by U.S. Pat. No. 4,450,472 and U.S. Pat. Application No. 10/052,859, both are herein incorporated by reference.
• open etched microchannels may significantly increase the effectiveness of the present spray cooling invention.
• Open channel spray cooled microchannels are not limited by pressure drops created by the need for small hydraulic diameters, as is the case with closed microchannel systems.
• Open microchannel spray cooling is also limited by the need to use fluid manifolding. Therefore, open microchannel spray cooling may provide the ability to have smaller hydraulic diameters, and higher resulting heat transfer coefficients, than closed microchannel cooling systems.
• a secondary etched microchannel plate 44 may be thermally attached to chip 2 providing the benefits of surface enhancements and the potential use of a non- dielectric fluid.
• Both open channel spray cooling microchannel methods provide increased nucleation sites, improved vaporization conditions and increased surface areas; all of which are known to benefit spray cooling.
• a hotspot vapor management protrusion 34 extends from spray plate 30 in the direction of and in a spaced apart relationship to chip 2.
• vapor management protrusion 34 forces the vapor within the system, and more particularly vapor in close proximity to the atomization zone, to flow downward and outward along thin-film 40. The result is a further thinning of thin-film 40 and increased heat removal rates.
• the gap between chip 2 and vapor management protrusion 34 is a variable of design, often optimized through experimentation, but ISR typically uses gaps between 1/2 mm and 3/4 mm.
• atomizer 32 In the event that multiple hotspots are present on a given chip, it may be desirable to have multiples of atomizer 32 and multiples of vapor management protrusion 34. Also located in protrusion 34, and shown in Figure 9, is a plurality of vapor return orifices 37 which allow for the recirculation of vapor within spray module 10.
• Figure 7 shows a secondary nozzle 36 used to assist in the creation and performance of thick-film 42.
• nozzle 36 may simply add fluid to thick-film 42 in the event that atomizer 32 does not produce enough excess fluid to maintain thick-film 42 over the low heat flux areas of chip 2.
• nozzle 36 is not required to produce a thin evaporative film capable of very large heat fluxes.
• nozzle 36 may be, but is not limited to, an incremental sprayer, a drop on demand orifice, a jet orifice, a piezoelectric actuated jet impingement orifice, or an actuated atomizer. All methods provide the means of supplementing the cooling fluid to thick-film 42.
• Figure 8 shows another alternative embodiment of the present invention.
• atomizer 32 dispenses fluid at a generally non- perpendicular angle to core 3.
• thick-film 42 is further encouraged to flow over and cover the non-hotspot areas of chip 2.
• This embodiment may also achieve benefits through they the addition of secondary nozzle 36 or vapor management protrusion 34.
• Angled spray cooling may also benefit from the addition of etched microchannels parallel to the direction of spray.
• Cooling fluid that exits spray module 10 is not likely to be a pure vapor, as ideal in terms of cycle efficiency.
• prior art systems try to optimize the spray system for complete fluid vaporization within module 10, the present invention is optimized for cooling the performance enhancing core of a chip.
• Figure 12 shows an addition to the system that simplifies its design and use.
• a separator 7 may be placed between condenser 8 and spray module 10. Separator 7 separates liquid from vapor and transfers the higher energy vapor to condenser 8 and the lower energy liquid to pump 5 ( Figure 13).
• vapor and liquid may be separated through the use of a spiral separator as described by U.S. Pat. No.

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• 2004
  • 2004-02-24 US US10/786,452 patent/US20050183844A1/en not_active Abandoned
• 2005
  • 2005-02-14 WO PCT/US2005/004444 patent/WO2005081812A2/en active Application Filing
  • 2005-02-14 CA CA002556666A patent/CA2556666A1/en not_active Abandoned
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