GB2480458A

GB2480458A - Cooling apparatus for cooling an electronic device

Info

Publication number: GB2480458A
Application number: GB1008304A
Authority: GB
Inventors: Richard John Moulding
Original assignee: JOHN G PECK Ltd
Current assignee: JOHN G PECK Ltd
Priority date: 2010-05-19
Filing date: 2010-05-19
Publication date: 2011-11-23
Anticipated expiration: 2030-05-19
Also published as: GB2480458B; GB201008304D0

Abstract

A heat sink 14 for cooling electronic device 10 comprising a second tier 24 of series connected cooling channels 20 located between a heat transfer surface 16 for contacting electronic device 10 and a first tier 22 of series connected cooling channels 20 wherein second tier 24 receives coolant from first tier 22. Heat sink 14 may include further heat transfer surface 40 for contacting power modules 42 and a third tier 44 of series connected cooling channels 20 located between first tier 22 and further heat transfer surface 40 wherein third tier 44 receives coolant fluid from first tier 22. A first subset of series connected cooling channels 20 in second and third tiers 24, 44 may receive coolant from a first subset of series connected cooling channels in first tier 22 (fig. 6). Cooling channels 20 in each tier 22, 24, 44 may be aligned with semiconductor chips (12, fig. 1) of power module 10. Manifolds (26, 38, fig. 1) connect cooling channels 20 in each of tiers 22, 24, 44 in series and also provide a connection between first tier 22 and second and third tiers 24, 44 using recesses (30, 30a, fig. 10).

Description

TITLE

Cooling apparatus for cooling an electronic device

FIELD OF THE iNVENTION

The present invention relates generally to cooling apparatus for cooling one or more electronic devices. The cooling apparatus is particularly, but not exclusively, suitable for cooling one or more electronic devices in the form of one or more power modules each comprising a plurality of semiconductor chips connected in parallel. The semiconductor chips are typically insulated gate bipolar transistors (IGBTs) or diodes.

BACKGROUND TO THE INVENTION

Semiconductor chips used in the manufacture of certain electronic devices generate significant amounts of heat which can lead to high operating temperatures. High operating temperatures are undesirable because they can compromise the performance of electronic devices.

Cooling apparatus can be used to control the temperature of electronic devices and typically comprises a heat sink, in contact with the electronic device, which has one or more cooling passages for carrying coolant fluid.

In large electronic devices such as power modules in which IGBTs or other semiconductor chips are connected in parallel, there is a need to maintain the semiconductor chips at substantially the same temperature, typically within a tolerance of ± 1°C. There is, therefore, a need for cooling apparatus which provides for uniform cooling of such electronic devices and which is also easy to manufacture and operate.

Cooling apparatus for cooling a small electronic device, such as a computer processor module, is described in US 6,337,794 Bi (International Business Machines). In one particular embodiment, described with reference to Figures 5, 5A and 5B, the cooling apparatus comprises a heat sink including first and second serpentine channels mounted in a tiered arrangement for carrying coolant fluid. The coolant fluid inlets and outlets for the first and second serpentine channels are provided at opposite locations, so that the coldest fluid in the upper tier is coupled with the warmest fluid in the lower tier, and vice-versa. The need for independent coolant fluid flows through the first and second serpentine channels in the upper and lower tiers results in a complicated cooling apparatus in which the average temperature of the coolant, and hence the temperature of the electronic device, can be difficult to control.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided cooling apparatus for cooling an electronic device, the cooling apparatus comprising a heat sink member including: a heat transfer surface for contacting an electronic device; a first tier of cooling channels connected in series and having a coolant fluid inlet; a second tier of cooling channels connected in series and having a coolant fluid outlet, the second tier of series-connected cooling channels being located adjacent to the heat transfer surface, between the first tier of series-connected cooling channels and the heat transfer surface; wherein the second tier of series-connected cooling channels receives coolant fluid from the first tier of series-connected cooling channels.

Coolant fluid flows from the coolant fluid inlet to the coolant fluid outlet, initially through the series-connected cooling channels in the first tier and thereafter through the series-connected cooling channels in the second tier, adjacent to the heat transfer surface.

The coolant fluid flowing through the first tier of series-connected cooling channels is thermally coupled to the coolant fluid flowing through the second tier of series-connected cooling channels and this thermal coupling leads to temperature averaging between the coolant fluid flowing through the series-connected cooling channels in the first and second tiers. Due to this temperature averaging, a uniform surface temperature is provided across the heat transfer surface, and in particular in the regions of the heat transfer surface with which the series-connected cooling channels in the second tier are aligned. This provides for uniform cooling of the electronic device, and in particular semiconductor chips of the electronic device with which the cooling channels are normally aligned.

Although coupling between the coolant fluid in upper and lower tiers is mentioned briefly in US 6,337,794 (discussed above), the present invention offers the advantage that because the first tier of cooling channels is connected to the second tier of cooling channels to provide a single continuous cooling passage, an independent fluid flow for each of the first and second tiers is not needed. The cooling apparatus according to the invention is, therefore, simpler to implement and provides more predictable temperature averaging between the coolant fluid flowing through the cooling channels in the first and second tiers.

A plurality of electronic devices may be cooled by the cooling apparatus. The electronic devices may be arranged on the heat transfer surface so that the heat transfer surface contacts the plurality of electronic devices.

The first and second tiers may each comprise first and second subsets of series-connected cooling channels. A first subset of series-connected cooling channels in the second tier may receive coolant fluid from a first subset of series-connected cooling channels in the first tier. A second subset of series-connected cooling channels in the second tier may receive coolant fluid from a second subset of series-connected cooling channels in the first tier.

The coolant fluid inlet is typically arranged to supply coolant fluid in parallel to both the first and second subsets of series-connected cooling channels in the first tier.

Additionally, the coolant fluid outlet is typically arranged to remove coolant fluid in parallel from both the first and second subsets of series-connected cooling channels in the second tier.

This arrangement using first and second subsets of cooling channels supplied by a single coolant fluid inlet enables a greater flow rate of coolant fluid to be employed.

Because there are two parallel cooling paths for the coolant fluid, the flow speed in each cooling path is halved thereby reducing back pressure. Also, because each of the parallel cooling paths is half of the length of an equivalent series cooling path, there is a further reduction in back pressure for a given flow rate of coolant fluid.

The cooling channels in the first tier normally have the same cross-sectional area as the cooling channels in the second tier. This ensures that the flow speed of the coolant fluid remains constant in each tier, which is important for uniform heat transfer. The cross-sectional shapes of the cooling channels in the first and second tiers can be different, provided that the cross-sectional area is constant.

The cooling apparatus could include a plurality of said heat sink members which could be fastened or joined together, for example by welding or other suitable means.

Such a cooling apparatus would include multiple heat transfer surfaces and the heat sink members could, thus, be arranged to provide a multi-sided cooling apparatus.

In some embodiments the heat sink member may include a further heat transfer surface. The heat sink member may thus include a third tier of cooling channels connected in series and having a further coolant fluid outlet. The third tier of series-connected cooling channels may be located adjacent to the further heat transfer surface, between the first tier of series-connected cooling channels and the further heat transfer surface. Typically, the third tier of series-connected cooling channels receives coolant fluid from the first tier of series-connected cooling channels. The further heat transfer surface may contact one or more further electronic devices and particular embodiments of the cooling apparatus may thus be used to cool one or more electronic devices located on opposite sides of the heat sink member, in which case it will be appreciated that the heat sink member is positioned between the electronic devices.

A first subset of series-connected cooling channels in the third tier may receive coolant fluid from the first subset of series-connected cooling channels in the first tier.

A second subset of series-connected cooling channels in the third tier may receive coolant fluid from the second subset of series-connected cooling channels in the first tier. The further coolant fluid outlet may be arranged to remove coolant fluid in parallel from both the first and second subsets of series-connected cooling channels in the third tier. As explained above, the use of multiple parallel cooling paths enables higher flow rates of cooling fluid to be employed without a significant increase in back pressure.

The cooling channels in the second tier may have the same cross-sectional area as the cooling channels in the third tier. The cross-sectional area of the cooling channels in the first tier may be twice the cross-sectional area of the cooling channels in each of the second and third tiers. Again, this ensures that the flow speed of coolant fluid through the inner first tier and outer second and third tiers remains constant.

The heat sink member typically comprises a main body in which the cooling channels are formed. The main body may be extruded to form the cooling channels therein.

This is typically the most cost effective method for manufacturing the main body of the heat sink member but it will be understood that other manufacturing methods can be used. For example, the cooling channels could be formed in the main body by machining a solid block of material.

The apparatus typically comprises first and second manifolds at opposite ends of the main body. The first and second manifolds provide the series-connections between the cooling channels in each tier and also provide the connection(s) between the tiers. The first and second manifolds are manufactured separately from the main body and are attached to the opposite ends of the main body, for example by welding or any other suitable means of attachment. The first and second manifolds may be selectively attachable to the opposite ends of the main body.

Each of the first and second manifolds may include a series of recesses at selected locations in the surface contacting the respective end of the main body to provide the series connections between desired cooling channels in the main body and to provide the connection(s) between the tiers in the main body. Pairs of first and second manifolds having different forms provided by different patterns of recesses may, therefore, be attached to the opposite ends of a standard main body to provide different patterns of series connections between the cooling channels in each tier and different connections between adjacent tiers. For example, one form of pair of first and second manifolds may series-connect all of the cooling channels in the first and second tiers and connect the first and second tiers of cooling channels so that the second tier of series-connected cooling channels receives coolant fluid from the first tier of series-connected cooling channels, thus providing a single cooling flow path for the coolant fluid. A different form of first and second manifolds may, however, series-connect first and second subsets of cooling channels in each of the first and second tiers and connect the first and second subsets in the first tier with the respective first and second subsets in the second tier, thus providing two parallel cooling flow paths for the coolant fluid as described above.

Embodiments of the invention thus provide the significant benefit that a standard main body may be manufactured and configured to provide cooling flow paths and a coolant flow rate/speed that suit a particular application simply by selecting suitable first and second manifolds and attaching them to the opposite ends of the main body.

In alternative embodiments, each of the first and second manifolds may comprise a plate member having a planar surface in contact with the respective end of the main body. The connections between the cooling channels in each tier and between the tiers may be provided by openings between selected cooling channels. The openings may be provided by the absence of material forming the main body between selected cooling channels.

The first manifold may contain the coolant fluid inlet to direct coolant fluid into the cooling channels in the first tier. The first manifold may contain the coolant fluid outlet to remove coolant fluid from the cooling channels in the second tier. The first manifold may contain the further coolant fluid outlet to remove coolant fluid from the cooling channels in the third tier in embodiments of the cooling apparatus in which first, second and third tiers of series-connected cooling channels are provided.

The cooling channels in each tier are typically aligned with the cooling channels in the or each adjacent tier. This provides for optimal temperature averaging between the coolant fluid flowing through corresponding cooling channels in adjacent tiers. The coolant fluid inlet may also be aligned with the coolant fluid outlet(s) of the or each adjacent tier. The coolant fluid inlet and the coolant fluid outlet(s) may be provided at a central region of the first manifold.

The cooling apparatus is typically used to cool an electronic device in the form of a power module comprising a plurality of parallel-connected semiconductor chips. The cooling channels are preferably aligned with the semiconductor chips in the power module to maximise the cooling effect.

Embodiments of the present invention also provide a fluid cooled electronic apparatus comprising a cooling apparatus according to the aforesaid embodiments of the present invention and an electronic device in thermal contact with the heat transfer surface of the heat sink member of the cooling apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an exploded diagrammatic plan view of cooling apparatus according to a first embodiment of the present invention; Figures 2 to 4 are diagrammatic cross-sectional views respectively along the lines A-A, B-B and C-C shown in Figure 1; Figure 5 is an exploded diagrammatic plan view of cooling apparatus according to a second embodiment of the present invention; Figures 6 to 8 are diagrammatic cross-sectional views respectively along the lines D-D, E-E and F-F shown in Figure 5; Figure 9 is a diagrammatic cross-sectional view of a heat sink member of a cooling apparatus according to a third embodiment of the present invention; and Figures 10 and 11 are diagrammatic cross-sectional views of first and second manifolds of the cooling apparatus shown in Figure 9.

DETAILED DESCRiPTION OF EMBODIMENTS OF THE iNVENTION Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings.

Figures 1 and 2 show diagrammatically an electronic device in the form of a power module 10. The power module 10 comprises a plurality of semiconductor chips 12, such as IGBTs and diodes, which are connected in parallel. As discussed above, there is a need to maintain the temperature of the parallel-connected semiconductor chips 12 of a typical power module 10 within a predetermined range, for example ±1°C, for effective operation of the power module 10.

A first embodiment of a cooling apparatus which can be used to cool the power module 10, and therefore maintain the temperature of the parallel-connected semiconductor chips 12 within the predetermined range, is illustrated in Figures 1 to 4. The cooling apparatus comprises a heat sink member 14 having a generally planar heat transfer surface 16 which contacts a generally planar surface of the power module 10. The heat sink member 14 comprises a main body 18 and a plurality of cooling channels 20 are formed in the heat sink member 14, for example by extruding the main body 18. Although only one power module 10 is illustrated, it should be understood that several power modules 10 could be arranged in thermal contact with the heat transfer surface 16 so that they are simultaneously cooled by the cooling apparatus.

As best seen in Figure 2, the heat sink member 14 comprises first and second tiers 22, 24 of cooling channels 20 which are arranged adjacent to each other. The cooling channels 20 in each tier 22, 24 are aligned so that that the cooling channels 20 in the second tier 24 overlie the cooling channels 20 in the first tier 22. The power module and the heat sink member 14 are arranged so that the cooling channels 20 are also aligned with the semiconductor chips 12 in the power module 10 to provide optimum cooling. This is best illustrated in Figure 1.

The second tier 24 of cooling channels 20 is located adjacent to the heat transfer surface 16, between the first tier 22 of cooling channels 20 and the heat transfer surface 16. In the illustrated embodiment, the cooling channels 20 in the first and second tiers 22, 24 have a slightly different cross-sectional shape, as best seen in Figure 2, but their cross-sectional area is the same to maintain a constant flow speed of coolant fluid.

The cooling apparatus includes first and second manifolds 26, 28 at opposite ends of the main body 18. For illustration purposes, the first and second manifolds 26, 28 are shown slightly spaced from the main body 18 in Figure 1, but in use they are located in abutment with the respective ends of the main body 18. The first and second manifolds 26, 28 are normally welded to the main body 18, but any suitable means of attachment can be used. For example, the first and second manifolds 26, 28 could be secured to the respective end of the main body 18 using mechanical fasteners with a sealing means, such as a gasket, located between the first and second manifolds 26, 28 and the respective end of the main body. The first and second manifolds 26, 28 connect the cooling channels 20 in each of the first and second tiers 22, 24 in series and also provide a connection between the series-connected cooling channels 20 in the first tier 22 and the series-connected cooling channels 20 in the second tier 24.

Each of the first and second manifolds 26, 28 includes a series of recesses 30 in the surface which contacts the end of the main body 18 and those recesses 30 direct coolant fluid, for example a water/glycol mixture, flowing through the cooling channels 20 from one cooling channel 20 to another selected cooling channel 20. In the embodiment of Figures 1 to 4, the pattern of recesses 30 in the first and second manifolds 26, 28 series connects the cooling channels 20 in each of the first and second tiers 22, 24 so that when coolant fluid exits the end of a cooling channel 20 it -10 -is directed by one of the recesses 30 into an adjacent cooling channel 20 and flows in the opposite direction through that adjacent cooling channel 20.

The first manifold 26 includes a coolant fluid inlet 32 which directs coolant fluid into the first tier 22 of series-connected cooling channels 20 and a coolant fluid outlet 34 which removes coolant fluid from the second tier 24 of series-connected cooling channels 20. The coolant fluid inlet 32 and the coolant fluid outlet 34 are generally aligned with each other. One of the recesses 30a in the first manifold 26 provides a connection between the first tier 22 of series-connected cooling channels 20 and the second tier 24 of series-connected cooling channels 20, so that the cooling channels in the second tier 24 receive coolant fluid from the cooling channels 20 in the first tier 22.

The cooling apparatus of Figures 1 to 4 thus comprises a single cooling flow path in which coolant fluid enters the first tier 22 of series-connected cooling channels 20 via the coolant fluid inlet 32, flows through the cooling channels 20 in the first tier 22 and then into the cooling channels 20 in the second tier 24 via the recess 30a, and flows through the cooling channels 20 in the second tier 24 before finally exiting the second tier 24 of series-connected cooling channels 20 through the coolant fluid outlet 34.

The single cooling flow path thus consists of one continuous cooling passage.

As the coolant fluid flows through the cooling channels 20 in the first tier 22, from left to right in Figure 2, its temperature increases gradually as heat is transferred into the coolant fluid. In the second tier 24, the temperature of the coolant fluid continues to increase as it flows through the cooling channels 20 in the direction from right to left. The coolant fluid flowing through the cooling channels 20 in the first and second tiers 22, 24 is thermally coupled and as a result there is temperature averaging between the coolant fluid flowing through the cooling channels 20 in the first and second tiers 22, 24. Although there is an increase in coolant temperature between the coolant fluid inlet 32 and the coolant fluid outlet 34 (possibly up to 10°C in some embodiments), colder fluid flowing through the cooling channels 20 in the first tier 22 tends to cool the warmer fluid flowing through the cooling channels 20 in the second tier 24. The temperature in the regions of the heat transfer surface 16 with which the cooling channels 20 are aligned is thus substantially constant thereby maintaining the semiconductor chips 12 of the power module 10 at substantially the same temperature. There may in practice be a temperature variation of about 1°C across the heat transfer surface 16, but a temperature variation of this magnitude is perfectly acceptable as it does not normally compromise the operation of the power module 10.

Referring now to Figures 5 to 8, there is shown a cooling apparatus according to a second embodiment of the present invention. The cooling apparatus is similar to the first embodiment of the cooling apparatus illustrated in Figures 1 to 4 and corresponding components are, therefore, identified using corresponding reference numerals.

The second embodiment of the cooling apparatus includes a heat sink member 14 which is identical to the heat sink member 14 described with reference to Figures 1 to 4. The cooling apparatus also includes first and second manifolds 36, 38, but they differ from the first and second manifolds 26, 28 described with reference to Figures 1 to 4.

The pattern of recesses 30 in the first and second manifolds 36, 38 connects first and second subsets of cooling channels 20 in series in each of the first and second tiers 22, 24. The first tier 22 contains first and second subsets 22a, 22b of cooling channels 20 which are connected in series and the second tier 24 also contains corresponding first and second subsets 24a, 24b of cooling channels 20 which are connected in series.

The first manifold 36 contains the coolant fluid inlet 32 and this is located at a generally central region of the first tier 22 of cooling channels 20. The coolant fluid inlet 32 simultaneously supplies coolant fluid into an inlet cooling channel of each of the first and second subsets 22a, 22b of series-connected cooling channels 20 forming the first tier 22. This establishes two parallel cooling paths for the coolant fluid which flows through first and second subsets 22a, 22b of series-connected cooling channels in the first tier 22. The coolant fluid flows through the cooling channels 20 in the -12 -first tier 22 from the central region of the main body 18 towards the edges of the main body 18. The second manifold 38 includes a recess 30b which provides a connection between the first subset 22a of series-connected cooling channels 20 in the first tier 22 and the first subset 24a of series-connected cooling channels 20 in the second tier 24.

The second manifold also includes a recess 30c which provides a connection between the second subset 22b of series-connected cooling channels 20 in the first tier 22 and the second subset 24b of series-connected cooling channels 20 in the second tier 24.

Coolant fluid thus flows along separate, parallel, cooling flow paths from the first and second subsets 22a, 22b of series-connected cooling channels 20 in the first tier 22 to the respective first and second subsets 24a, 24b of series-connected cooling channels in the second tier 24. The coolant fluid flows through the first and second subsets 24a, 24b of cooling channels 20 in the second tier 24 to the coolant fluid outlet 34 which simultaneously removes coolant fluid from both of the parallel cooling flow paths provided by the respective first and second subsets of series-connected cooling channels 20.

The second embodiment of the cooling apparatus provides a substantially uniform temperature across the heat transfer surface 16 as a result of temperature averaging between the coolant fluid flowing through the cooling channels 20 in the first and second tiers 22, 24. However, in this second embodiment with parallel cooling flow paths, there is temperature averaging between the coolant fluid flowing through the first subsets 22a, 24a of series-connected cooling channels 20 in the first and second tiers 22, 24 and between the coolant fluid flowing through the second subsets 22b, 24b of series-connected cooling channels 20 in the first and second tiers 22, 24. As mentioned above, the use of parallel coolant flow paths is advantageous as it allows a higher flow rate of coolant fluid to be employed without an increase in back pressure.

It will be appreciated that the main body 18 forming the heat sink member 14 of the first and second embodiments of the cooling apparatus is the same and that different cooling path configurations can be provided simply by selecting suitable pairs of first and second manifolds, with an appropriate pattern of recesses 30, so that appropriate connections are made between the cooling channels 20 in the main body 18.

-13 -Referring now to Figures 9 to 11, there is shown a cooling apparatus according to a third embodiment of the present invention. The cooling apparatus is similar to the first and second embodiments of the cooling apparatus illustrated in Figures 1 to 8 and corresponding components are, therefore, identified using corresponding reference numerals.

In addition to the generally planar heat transfer surface 16, the heat sink member 14 includes a generally planar further heat transfer surface 40 which contacts a generally planar surface of one or more further power modules 42, similar to the power module(s) 10, or one or more other electronic devices. A single cooling apparatus according to the third embodiment of the present invention can thus be used to simultaneously cool multiple power modules 10 located on both sides of the heat sink member 14.

As best seen in Figure 9, the heat sink member 14 comprises a third tier 44 of cooling channels 20 which is located between the first tier 22 of cooling channels 20 and the further heat transfer surface 40. The cooling channels 20 in the third tier 44 are aligned with the cooling channels 20 in the first and second tiers 22, 24.

The connection pattern between the cooling channels 20 in the third tier 44 and the first tier 22 is the same as the connection pattern between the cooling channels 20 in the first tier 22 and the second tier 24 (already described with reference to Figures 1 to 4), so that the third tier 44 of series-connected cooling channels 20 receives coolant fluid from the first tier 22 of series-connected cooling channels 20. More particularly, the recess 30a in the first manifold 26 provides a connection between the first and second tiers 22, 24 of series-connected cooling channels 20 and between the first and third tiers 22, 44 of series-connected cooling channels 20. The first manifold 26 also includes a further coolant fluid outlet 46 which removes coolant fluid from the series-connected cooling channels 20 in the third tier 44.

-14 -The third embodiment of the cooling apparatus provides a substantially uniform temperature across the heat transfer surface 16 and the further heat transfer surface 40 as a result of temperature averaging between the coolant fluid flowing through the series-connected cooling channels 20 in the first and second tiers 22, 24 and between the coolant fluid flowing through the series-connected cooling channels 20 in the first and third tiers 22, 44.

In order to maintain a constant flow speed of coolant fluid through the cooling channels 20, which is necessary for effective cooling of the power modules 10, 42, the cross-sectional area of the cooling channels 20 in the first tier 22 is double the cross-sectional area of the cooling channels 20 in the second and third tiers 24, 44. The cross-sectional shape of the cooling channels 20 in each tier 22, 24, 44 could, of course, be different as discussed above.

It should be appreciated that the second embodiment of the cooling apparatus described above with reference to Figures 5 to 8 could be modified so that the heat sink member 14 also includes first, second and third tiers 22, 24, 44 of series-connected cooling channels 20. In such a modified arrangement, the connection pattern between the cooling channels 20 in the first tier 22 and the third tier 44 would be the same as the connection pattern between the cooling channels 20 in the first tier 22 and the second tier 24. More particularly, a first subset of series-connected cooling channels 20 in the third tier would be connected to, and receive coolant fluid from, the first subset 22a of series-connected cooling channels 20 in the first tier 22 and a second subset of series-connected cooling channels 20 in the third tier 44 would be connected to, and receive coolant fluid from, the second subset 22b of series-connected cooling channels 20 in the first tier 22. This connection pattern could be provided by first and second manifolds similar to the first and second manifolds 36, 38 described with reference to Figures 5 to 8. Accordingly, the further coolant fluid outlet 46 would be provided at a central region of the first manifold, in a position generally adjacent to the coolant fluid inlet 32 and the coolant fluid outlet 34 of the first manifold 36, such that the further coolant fluid outlet 46 would simultaneously -15-remove coolant fluid from the first and second subsets of series-connected cooling channels 20 in the third tier 44.

Although embodiments of the invention have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the present invention, as claimed.

Claims

-16 -CLAIMS1. Cooling apparatus for cooling an electronic device, the cooling apparatus comprising a heat sink member including: a heat transfer surface for contacting an electronic device; a first tier of cooling channels connected in series and having a coolant fluid inlet; a second tier of cooling channels connected in series and having a coolant fluid outlet, the second tier of series-connected cooling channels being located adjacent to the heat transfer surface, between the first tier of series-connected cooling channels and the heat transfer surface; wherein the second tier of series-connected cooling channels receives coolant fluid from the first tier of series-connected cooling channels.
2. Cooling apparatus according to claim I, wherein a first subset of series-connected cooling channels in the second tier receives coolant fluid from a first subset of series-connected cooling channels in the first tier and a second subset of series-connected cooling channels in the second tier receives coolant fluid from a second subset of series-connected cooling channels in the first tier.
3. Cooling apparatus according to claim 2, wherein the coolant fluid inlet is arranged to supply coolant fluid in parallel to both the first and second subsets of series-connected cooling channels in the first tier.
4. Cooling apparatus according to claim 2 or claim 3, wherein the coolant fluid outlet is arranged to remove coolant fluid in parallel from both the first and second subsets of series-connected cooling channels in the second tier.
5. Cooling apparatus according to any preceding claim, wherein the cooling channels in the first tier have the same cross-sectional area as the cooling channels in the second tier. -17-
6. Cooling apparatus according to any of claims I to 4, wherein the heat sink member includes: a further heat transfer surface; and a third tier of cooling channels connected in series and having a further coolant fluid outlet, the third tier of series-connected cooling channels being located adjacent to the further heat transfer surface, between the first tier of series-connected cooling channels and the further heat transfer surface; the third tier of series-connected cooling channels receiving coolant fluid from the first tier of series-connected cooling channels.
7. Cooling apparatus according to claim 6 when dependent on any of claims 2 to 4, wherein a first subset of series-connected cooling channels in the third tier receives coolant fluid from the first subset of series-connected cooling channels in the first tier and a second subset of series-connected cooling channels in the third tier receives coolant fluid from the second subset of series-connected cooling channels in the first tier.
8. Cooling apparatus according to claim 7, wherein the further coolant fluid outlet is arranged to remove coolant fluid in parallel from both the first and second subsets of series-connected cooling channels in the third tier.
9. Cooling apparatus according to any of claims 6 to 8, wherein the cooling channels in the second tier have the same cross-sectional area as the cooling channels in the third tier.
10. Cooling apparatus according to claim 9, wherein the cross-sectional area of the cooling channels in the first tier is double the cross-sectional area of the cooling channels in each of the second and third tiers.
11. Cooling apparatus according to any preceding claim, wherein the heat sink member comprises a main body in which the cooling channels are formed. -18-
12. Cooling apparatus according to claim 11, wherein the apparatus comprises first and second manifolds at opposite ends of the main body which series-connect the cooling channels in each tier and which connect the tiers.
13. Cooling apparatus according to claim 12, wherein the first manifold contains the coolant fluid inlet to direct coolant fluid into the cooling channels in the first tier.
14. Cooling apparatus according to claim 12 or claim 13, wherein the first manifold contains the coolant fluid outlet to receive coolant fluid from the cooling channels in the second tier.
15. Cooling apparatus according to any of claims 12 to 14 when ultimately dependent on claim 6, wherein the first manifold contains the further coolant fluid outlet to receive coolant fluid from the cooling channels in the third tier.
16. Cooling apparatus according to any preceding claim, wherein the cooling channels in each tier are aligned with the cooling channels in the or each adjacent tier.
17. Cooling apparatus for cooling an electronic device substantially as hereinbefore described with reference to the accompanying drawings.AMENDMENTS TO CLAIMS HAVE BEEN FILED AS FOLLOWS1. Cooling apparatus for cooling an electronic device, the cooling apparatus comprising a heat sink member including: a heat transfer surface for contacting the electronic device; a first tier of cooling channels connected in series and having a coolant fluid inlet; a second tier of cooling channels connected in series and having a coolant fluid outlet, the second tier of series-connected cooling channels being located adjacent to the heat transfer surface, between the first tier of series-connected cooling channels and the heat transfer surface; wherein the second tier of series-connected cooling channels receives coolant fluid from the first tier of series-connected cooling channels.2. Cooling apparatus according to claim I, wherein a first subset of the series-connected cooling channels in the second tier receives coolant fluid from a first subset of the series-connected cooling channels in the first tier and a second subset of the series-connected cooling channels in the second tier receives coolant fluid from a second subset of the series-connected cooling channels in the first tier.3. Cooling apparatus according to claim 2, wherein the coolant fluid inlet is arranged to supply coolant fluid in parallel to both the first and second subsets of the series-connected cooling channels in the first tier.4. Cooling apparatus according to claim 2 or claim 3, wherein the coolant fluid outlet is arranged to remove coolant fluid in parallel from both the first and second 0****S subsets of the series-connected cooling channels in the second tier. *0*5. Cooling apparatus according to any preceding claim, wherein the cooling : channels in the first tier have the same cross-sectional area as the cooling channels in the second tier.6. Cooling apparatus according to any of claims I to 4, wherein the heat sink member includes: a fitrther heat transfer surface on an opposite side of the heat sink member to 12. Cooling apparatus according to claim 11, wherein the apparatus comprises first and second manifolds at oppositc ends of the main body which series-connect the cooling channels in each tier and which connect the tiers.13. Cooling apparatus according to claim 12, wherein the first manifold contains the coolant fluid inlet to direct coolant fluid into the cooling channels in the first tier.14, Cooling apparatus according to claim 12 or claim 13, wherein the first manifold contains the coolant fluid outlet to receive coolant fluid from the cooling channels in the second tier.15. Cooling apparatus according to any of claims 12 to 14 when dependent on claim 6, wherein the first manifold contains the fUrther coolant fluid outlet to receive coolant fluid from the cooling channels in the third tier.16. Cooling apparatus according to any preceding claim, wherein the cooling channels in each tier are aligned with the cooling channels in the or each adjacent tier.17, Cooling apparatus for cooling an electronic device substantially as hereinbefore described with reference to the accompanying drawings.S...,. * SS ***n* * S * *0 * S S * a. * S * 000*