BACKGROUND
The invention relates generally to an apparatus for cooling a heated surface and, more particularly, to a heat sink with microchannel cooling for semiconductor power devices.
The development of higher-density power electronics has made it increasingly more difficult to cool power semiconductor devices. With modern silicon-based power devices capable of dissipating up to 500 W/cm2, there is a need for improved thermal anagement solutions. When device temperatures are limited to 50K increases, natural and forced-air cooling schemes can only handle heat fluxes up to about one (1) W/cm2. Conventional liquid cooling plates can achieve heat fluxes on the order of a twenty (20) W/cm2. Heat pipes, impingement sprays, and liquid boiling are capable of larger heat fluxes, but these techniques can lead to manufacturing difficulties and high cost.
An additional problem encountered in conventional cooling of high heat flux power devices is non-uniform temperature distribution across the heated surface. This is due to the non-uniform cooling channel structure, as well as the temperature rise of the cooling fluid as it flows through long channels parallel to the heated surface.
One promising technology for high performance thermal management is microchannel cooling. In the 1980's, it was demonstrated as an effective means of cooling silicon integrated circuits, with designs demonstrating heat fluxes of up to 1000 W/cm2 and surface temperature rise below 100° C.
U.S. patent application Ser. No. 10/998,707, Stevanovic et al. discusses drawbacks associated with a number of known heat sink designs. As discussed in Stevanovic et al., desired heat sink properties include improved thermal performance, relatively simple assembly to reduce manufacturing cost, and scalability for accommodating small and large power devices as well as different numbers of power devices. In addition, it would be desirable for the apparatus to provide electrical isolation between high power devices and the coolant. Moreover, volume and weight are important limitations in many power electronics applications, so compact heat exchangers are desired.
BRIEF DECSRIPTION
One aspect of the present invention resides in an apparatus for cooling at least two heated surfaces. The apparatus includes a base plate defining a number of upper and lower supply manifolds and a number of upper and lower exhaust manifolds. The upper and lower supply manifolds are configured to receive a coolant, and the upper and lower exhaust manifolds are configured to exhaust the coolant. The upper (lower) supply and exhaust manifolds are interleaved. The apparatus further includes an upper substrate having an inner surface and an outer surface. The inner surface is coupled to the base plate and defines a number of microchannels configured to receive the coolant from the upper supply manifolds and to deliver the coolant to the upper exhaust manifolds. The microchannels are oriented substantially perpendicular to the upper supply and exhaust manifolds. The outer surface is in thermal contact with one of the heated surfaces. The apparatus further includes a lower substrate having an inner surface and an outer surface. The inner surface is coupled to the base plate and defines a number of microchannels configured to receive the coolant from the lower supply manifolds and to deliver the coolant to the lower exhaust manifolds. The microchannels are oriented substantially perpendicular to the lower supply and exhaust manifolds. The outer surface is in thermal contact with another of the heated surfaces. The apparatus further includes a supply plenum configured to supply the coolant to the upper and lower supply manifolds and an exhaust plenum configured to exhaust the coolant from the upper and lower exhaust manifolds. The supply plenum and exhaust plenum are oriented in a plane of base plate.
Another aspect of the present invention resides in an apparatus for cooling at least two heated surfaces. The apparatus includes a base plate, as described above. The apparatus further includes an upper substrate comprising a top layer, an insulating layer and an inner layer. The inner layer defines a number of microchannels, described above. The insulating layer is disposed between the top and inner layers, the inner layer is coupled to the base plate, and the top layer is in thermal contact with one of the heated surfaces. The apparatus further includes a lower substrate comprising a bottom layer, a second insulating layer and a second inner layer. The second inner layer defines a number of microchannels, described above. The second insulating layer is disposed between the bottom and second inner layers, the second inner layer is coupled to the base plate, and the bottom layer is in thermal contact with another of the heated surfaces. The apparatus further includes a supply plenum and an exhaust plenum, as described above.
Yet another aspect of the present invention resides in an apparatus for cooling at least two heated surfaces. The apparatus includes a base plate, as described above. The apparatus further includes an upper substrate that includes a top layer and an insulating microchannel layer. The insulating microchannel layer defines a number of microchannels, described above. The insulating microchannel layer is disposed between the top layer and the base plate, and the top layer is thermally coupled to one of the heated surfaces. The apparatus further includes a lower substrate that includes a bottom layer and an insulating microchannel layer. The insulating microchannel layer defines a number of microchannels, described above. The insulating microchannel layer is disposed between the bottom layer and the base plate, and the bottom layer is thermally coupled to another of the heated surfaces. The apparatus further includes a supply plenum and an exhaust plenum, as described above.
DRAWINGS
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
FIG. 1 is a perspective view of an apparatus for cooling at least two heated surfaces;
FIG. 2 shows interleaved upper and lower supply and exhaust manifolds within a base plate of the apparatus of FIG. 1;
FIG. 3 depicts, in cross-sectional view, an exemplary heat-sink with microchannels formed in the inner surfaces of the upper and lower substrates;
FIG. 4 depicts, in cross-sectional view, an exemplary heat-sink with microchannels formed in insulating microchannel layers;
FIG. 5 depicts, in cross-sectional view, an exemplary heat-sink for use with low-voltage devices;
FIG. 6 illustrates in side view a double-sided heat sink apparatus for cooling multiple power devices;
FIG. 7 is a top view of the manifolds for the double-sided heat sink module of FIGS. 2 and 3; and
FIG. 8 is a side view of the manifolds for the double-sided heat sink module of FIG. 7.
DETAILED DESCRIPTION
An apparatus 10 (for example a heat sink) for cooling at least two heated surfaces 42, 44 is described first with reference to FIGS. 1, 2 and 6. As shown, for example in FIGS. 1 and. 6, the apparatus 10 includes a base plate 8, which is shown in greater detail in FIG. 2. As shown, for example, in FIG. 2, the base plate 8 defines a number of upper supply manifolds 12, a number of upper exhaust manifolds 14, a number of lower supply manifolds 16 and a number of lower exhaust manifolds 18. The upper and lower supply manifolds 12, 16 are configured to receive a coolant, and the upper and lower exhaust manifolds 14, 18 are configured to exhaust the coolant. As indicated, the upper supply and exhaust manifolds 12, 14 are interleaved, and the lower supply and exhaust manifolds 16, 18 are interleaved. For the illustrated embodiments, the supply manifolds 12, 14, 16 and 18 are oriented in a plane of the base plate 8.
As shown for example in FIG. 6, the apparatus 10 further includes an upper substrate 20 having an inner surface 22 and an outer surface 24. The inner surface 22 is coupled to the base plate 8. As indicated, for example in FIG. 3, the inner surface 22 defines a number of microchannels 26 configured to receive the coolant from the upper supply manifolds 12 and to deliver the coolant to the upper exhaust manifolds 14. The microchannels 26 are oriented substantially perpendicular to the upper supply and exhaust manifolds 12, 14, as indicated in FIG. 1, for example. The outer surface 24 is thermally coupled to one of the heated surfaces 40, as indicated in FIG. 6, for example.
As shown for example in FIG. 6, the apparatus 10 further includes a lower substrate 50 having an inner surface 52 and an outer surface 54. The inner surface 52 is coupled to the base plate 8. As indicated, for example, in FIG. 3, the inner surface 52 defines a number of microchannels 56 configured to receive the coolant from the lower supply manifolds 16 and to deliver the coolant to the lower exhaust manifolds 18. The microchannels 56 are oriented substantially perpendicular to the lower supply and exhaust manifolds 16, 18. The outer surface 24 is thermally coupled to another of the heated surfaces 44, as indicated in FIG. 6, for example.
For the illustrated embodiment, the apparatus 10 further includes a supply plenum 30 configured to supply the coolant to the upper and lower supply manifolds 12, 16 and an exhaust plenum 32 configured to exhaust the coolant from the upper and lower exhaust manifolds 14, 18. As indicated, for example, in FIG. 2, the supply plenum 30 and the exhaust plenum 32 are oriented in a plane of the base plate 8.
In operation, the microchannels 26, 56 provide the link between the supply and exhaust manifolds. This provides the beneficial heat transfer performance of microchannels with a controlled pressure loss between the manifolds. Moreover, the use of two independent sets of supply and exhaust manifolds, one for cooling an upper power device(s) 80 and the other for cooling a lower power device(s) 82, which are interdigitated, permits coolant to uniformly pass to the top and bottom of the module 10. By attaching the microchannel substrates 20, 50 to the top and bottom of the module, the heat exchanger is closed, permitting cooling on two surfaces using a heat exchanger volume previously used to cool only one surface.
In non-limiting examples, the heated surfaces correspond to power devices, non-limiting examples of which include Insulated Gate Bipolar Transistors (IGBT), Metal Oxide Semiconductor Field Effect Transistors (MOSFET), Diodes, Metal Semiconductor Field Effect Transistors (MESFET), and High Electron Mobility Transistors (HEMT). Those skilled in the art will recognize that these are examples of power devices and that the invention is by no means limited to these examples. Rather, apparatus 10 may be used to cool these or other power devices.
As used herein the phrase “oriented substantially perpendicular” should be understood to mean that the microchannels 26 (56) are oriented at angles of about ninety degrees plus/minus about thirty degrees (90+/−30 degrees) relative to the inlet and outlet manifolds 12, 14 (16, 18). According to a more particular embodiment, the microchannels 26 (56) are oriented at angles of about ninety degrees plus/minus about fifteen degrees (90+/−15 degrees) relative to the inlet and outlet manifolds 12, 14 (16, 18).
Many coolants can be employed for apparatus 10, and the invention is not limited to a particular coolant. Exemplary coolants include water, ethylene-glycol, oil, aircraft fuel and combinations thereof. According to a particular embodiment, the coolant is a single phase liquid. In operation, the coolant enters the manifolds 12, 16 in base plate 8 and flows through microchannels 26, 56 before returning through exhaust manifolds 14, 18. More particularly, coolant enters supply plenum 30, whose fluid diameter exceeds that of the other channels in apparatus 10, according to a particular embodiment, so that there is no significant pressure-drop in the plenum. For example, the fluid diameter of supply plenum 30 exceeds that of the other channels by a ratio of about three-to-one (3:1) relative to the manifold hydraulic diameter. For this example, the difference in the pressure drop for a single plenum channel (of equal length) would be of the order of 1/(3ˆ5)=1/243 of the loss of the loss in the manifold. The coolant exits apparatus 10 through exhaust plenum 32. It should be noted that this simple example assumes that all of the flow passes from one plenum to one manifold, so that the pressure scales at the ratio given above. In the illustrated embodiments of the present invention, however, there are multiple manifolds branching off of a single plenum. Accordingly, the increased number of channels partly tempers the increased pressure loss due to reduced flows in each channel.
According to a particular embodiment, base plate 8 comprises a thermally conductive material. Exemplary materials include copper, Kovar, Molybdenum, titanium, ceramics and combinations thereof. The invention is not limited to specific base plate materials.
Exemplary microchannel 26, 56 configurations are discussed and illustrated in U.S. patent application Ser. No. 10/998,707, referenced above.
The inlet and outlet configuration for the base plate 8 affects the heat transfer effectiveness of the apparatus 10. For the exemplary arrangement shown in FIG. 8, each of the upper and lower supply manifolds 12, 16 is tapered such that a cross-section of the respective upper or lower supply manifold is larger at the supply plenum than at the exhaust plenum. In addition, for the exemplary arrangement shown in FIGS. 2 and 8, each of the upper and lower supply manifolds 12, 16 extends from the supply plenum 30 and is oriented substantially perpendicular to the supply plenum 30. As discussed in U.S. patent application Ser. No. 10/998,707, referenced above, dimensional factors may be tailored to enhance thermal performance. For example, in particular embodiments, the upper and lower supply manifolds 12, 16 are characterized by a width in a range of about 0.5 mm to about 1 mm. According to a particular embodiment, the upper and lower supply manifolds 12, 16 are about 0.5 mm wide.
For the exemplary arrangement shown in FIG. 8, each of the upper and lower exhaust manifolds 14, 18 is tapered such that a cross-section of the respective upper or lower exhaust manifold is larger at the exhaust plenum than at the supply plenum. In addition, for the exemplary arrangement shown in FIGS. 2 and 8, each of the upper and lower exhaust manifolds 14, 18 extends from the exhaust plenum 32 and is oriented substantially perpendicular to the exhaust plenum 32. In particular embodiments, the upper and lower exhaust manifolds are characterized by a width in a range of about 0.5 mm to about 1 mm. According to a particular embodiment, the upper and lower exhaust manifolds are about 0.5 mm wide.
FIG. 7 is a top view of the manifolds of FIG. 2. For the exemplary embodiment illustrated in FIG. 7, the number of the upper supply and exhaust manifolds 12, 14 differ by one. However, the example shown in FIG. 7, in which there are four upper supply manifolds 12 and five upper exhaust manifolds 14, is merely illustrative. Similarly, for certain embodiments, the number of the lower supply and exhaust manifolds 16, 18 differ by one. For the illustrated embodiments, the supply plenum 30 and the exhaust plenum 32 are substantially uniform in cross-section. In other embodiments, the supply plenum 30 and the exhaust plenum 32 are tapered. In non-limiting examples, the coolant is selected from the group consisting of water, ethylene-glycol, oil, aircraft fuel and combinations thereof. The apparatus 10 accommodates cooling with single phase flow, such as impingement or cross-flow cooling. The apparatus 10 also accommodates cooling with two-phase flow, such as boiling or spray cooling. Dielectric fluids, such as FC-72, HFE7100 and conductive fluids such as water can be used as the coolant, depending upon the design of the jet and the packaging.
Depending on the thickness of the heat sink module 10, the top and bottom side manifolds may need to be offset and staggered. In which case, the lengths of the individual microchannel links would be longer relative to the single-sided module described in U.S. patent application Ser. No. 10/998,707, referenced above, but would permit double-sided cooling. For the illustrated embodiment of FIGS. 1, 2 and 7, the upper and lower supply manifolds 12, 16 are offset, and the upper and lower exhaust manifolds 14, 18 are offset. For certain other embodiments, the upper supply manifolds 12 are aligned with one of the lower exhaust and supply manifolds 18, 16, and the upper exhaust manifolds 14 are aligned with the other of the lower exhaust and supply manifolds 18, 16.
For the exemplary embodiments of FIGS. 3 and 4, the upper and lower substrates 20, 50 comprise at least one thermally conductive material and at least one electrically isolating material. According to particular embodiments, substrates 20, 50 are formed of either a direct bonded copper (DBC) or an active metal braze (AMB) structure. DBC and AMB refer to processes by which copper layers are directly bonded to a ceramic substrate. Exemplary ceramic bases include aluminum-oxide (AL2O3), aluminum nitride (AIN), berilium oxide (BeO) and silicon nitride (Si3N4). Both DBC and AMB are convenient structures for substrates 20, 50 and the use of the same conductive material (in this case, copper) on both sides of the ceramic base provides thermal and mechanical stability. Of course, substrates 20, 50 can be constructed from other materials, such as gold or silver. Beneficially, the substrates 20, 50 can be attached to base plate 8 using any one of a number of techniques, including brazing, bonding, diffusion bonding, soldering, or pressure contact such as clamping. This provides a simple assembly process, which reduces the overall cost of the apparatus 10. Moreover, by attaching the substrates 20, 50 to base plate 8, fluid passages are formed under the upper and lower heated surfaces 40, 42, enabling practical and cost-effective implementation of the microchannel cooling technology.
For the exemplary embodiment illustrated in FIG. 3, the upper substrate 20 comprises a top layer 62, an insulating layer 64 and an inner layer 66. For this embodiment, the microchannels 26 are formed in the inner layer 66, and the insulating layer 64 is disposed between the top layer 62 and the inner layer. The inner layer 66 is attached to the base plate 8, and the top layer is coupled to one of the heated surfaces 42. For example, the inner layer 66 is attached to the base plate 8 by brazing, bonding, diffusion bonding, soldering, pressure contact such as clamping or other attachment means. For the exemplary embodiment of FIG. 3, the heated surface 40 is coupled to the top layer 62 by solder 68, as shown. For the exemplary embodiment depicted in FIG. 3, microchannels 26 extend through the inner layer 66. In other words, the microchannel depth is equal to the thickness of the inner layer 66. CFD modeling results demonstrated improved performance for tall, high-aspect ratio microchannels, such as those shown in FIG. 3. For a typical thickness of the inner layer of a substrate, the microchannels in FIG. 3 would be about 0.3 mm tall. Of course other implementations are possible, and for an alternative embodiment (not shown) the microchannels 26 do not extend through the thickness of the inner layer 66, thereby isolating the insulating layer 64 from the coolant, which flows through microchannels 26. Beneficially, the ceramic layer 64 provides electrical isolation between the coolant and the power devices 80 mounted atop substrate 20. According to a particular embodiment, top layer 62 and inner layer 66 are formed of copper (Cu), and insulating layer 64 is a ceramic selected from the group consisting of AIN, Al2O3, Si3N , BeO or combinations thereof. According to a more particular embodiment, the microchannels 26 are formed in the copper layer 66 on the underside of a substrate 20.
For the lower portion of the arrangement shown in FIG. 3, the lower substrate 50 comprises a bottom layer 72, a second insulating layer 74 and a second inner layer 76. For this embodiment, the microchannels 56 are formed in the second inner layer 76, and the second insulating layer 74 is disposed between the bottom layer 72 and the second inner layer 76. The second inner layer is attached to the base plate 8, and the bottom layer is coupled to another of the heated surfaces 44. For the illustrated embodiment, the lower substrate 50 is similar in construction, dimensions and materials to the upper substrate 50. Reference number 82 indicates power devices mounted on substrate 50, and reference number 58 indicates a solder layer for coupling the heated surface 44 of the power device 82 to the bottom layer 72.
Another exemplary embodiment is shown in FIG. 4. For this embodiment, the upper substrate 20 includes a top layer 162 and an insulating microchannel layer 164, and the microchannels 26 are formed in the insulating microchannel layer 162. The insulating microchannel layer 164 is disposed between the top layer 162 and the base plate 8, and the top layer 162 is coupled to one of the heated surfaces 42 of the power device(s) 80. As shown in FIG. 4, the microchannels 26 do not extend through insulating microchannel layer 164, in order to isolate the coolant from the heated surface 42 of the power device(s) 80. More particularly, the remaining ceramic layer acts as a dielectric barrier between power devices 80 atop substrate 20 and the coolant. Beneficially, while maintaining electrical isolation, this embodiment also eliminates the thickness of material between the power devices 80, 82 and the coolant, resulting in improved thermal performance.
For the lower portion of the arrangement shown in FIG. 4, the lower substrate 50 includes a bottom layer 172 and an insulating microchannel layer 174, and the microchannels 56 are formed in the insulating microchannel layer 174. As shown, the insulating microchannel layer 174 is disposed between the bottom layer 172 and the base plate 8, and the bottom layer 172 is coupled to another of the heated surfaces 44 of the power device(s) 82. For the illustrated embodiment, the construction and materials of the lower substrate 50 are similar to that of the upper substrate 20. According to a more particular embodiment, upper substrate 20 further includes a lower layer 166 disposed between and attached to the insulating microchannel layer 164 and the base plate 8, as shown for example in FIG. 4. For this particular embodiment, lower substrate 50 further includes an upper layer 176 disposed between and attached to the insulating microchannel layer 174 and the base plate 8, as shown for example in FIG. 4. Exemplary materials for the lower layer 76 and upper layer 176 include copper.
Another embodiment is shown in FIG. 5. For this embodiment, the upper substrate 20 includes an inner layer 28, and microchannels 26 are formed in and extend partially through the inner layer 28. As shown in FIG. 5, the lower substrate 50 includes a second inner layer 38, and microchannels 56 are formed in and extend partially through the second inner layer 38. Exemplary materials for the inner layers 28, 38 include but are not limited to copper, molybdenum, aluminum, composite materials such as aluminum silicon carbide (AlSiC) and aluminum graphite composites, for example the material sold under the tradename Metgraf™, as well as alloys, such as cobalt-nickel ferrous alloys, for example the material sold under the tradename Kovar™. In other applications, ceramics or silicon may be used to form inner layers 28, 38. For particular embodiments, the microchannels 26, 56 extend through the respective ones of the inner layers 28, 38, and the microchannels are less than about 200 μm wide and are separated by a number of gaps of less than about 200 μm. This embodiment is adapted for use with low voltage devices such as laser diodes, RF power devices and computer chips. For this embodiment, the upper substrate 20 may further include a top layer 88 and a lower layer 90, and the lower substrate 50 may further include a bottom layer 92 and an upper layer 94, as shown. In one non-limiting example, the top layer 88 of the upper substrate and the bottom layer 92 of the lower substrate are formed of copper. Exemplary materials for the lower layer 90 of the upper substrate and for the upper layer 94 of the lower substrate include but are not limited to copper, molybdenum, aluminum, composite materials such as aluminum silicon carbide (AlSiC) and aluminum graphite composites, for example the material sold under the tradename Metgraf™, as well as alloys, such as cobalt-nickel ferrous alloys, for example the material sold under the tradename Kovar™. In other applications, ceramics or silicon may be used to form lower and upper layers 90, 94.
Benefits of the double sided heat-sink module include reduction of weight, volume and number of heat sinks required. Other benefits of the invention include improved heat transfer due to increased surface areas and heat transfer coefficients for small, densely packed channels. In addition, the invention provides controlled pressure losses, due to the manifolding structure, for which the effective microchannel length is reduced to the distance between adjacent manifolds. Further, relatively uniform microchannel velocities are achieved by using a tapered manifold structure. Further, the invention enables simpler heat sink manufacturing processes, by reducing the number of bonds to the bond between the substrates and the base plate.
Although only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Patent Application
20070215325
