GB2388473A

GB2388473A - Compliant thermal interface for connecting electronic components to a heat sink

Info

Publication number: GB2388473A
Application number: GB0210524A
Authority: GB
Inventors: Martin P Mayhead; Sean Conor Wrycraft
Original assignee: Sun Microsystems Inc
Current assignee: Sun Microsystems Inc
Priority date: 2002-05-08
Filing date: 2002-05-08
Publication date: 2003-11-12
Anticipated expiration: 2022-05-08
Also published as: GB2388473B; GB0210524D0

Abstract

The interface 4, particularly for use where a number of different components of differing height are mounted on a common circuit board, comprises a casing with first and second external contact faces and which defines an internal volume within which a heat transfer liquid 44 is located that provides a heat transfer path from the first contact face to the second contact face, wherein the relative positions of the contact faces are variable by deforming a portion of the casing. The casing preferably comprises a pair of spaced apart plates 41,42 that are joined at their peripheries by a flexible or deformable sidewall 43 and at least one of the plates may be formed with a peripheral lip that is directed towards the other plate. One of the plates may be non-planar and comprise a number of contact regions situated in substantially parallel planes spaced from one another. Alternatively, the casing may comprise a sachet or pouch of a flexible material, formed from two sheets of a flexible material sealed together at their respective peripheral regions to enclose an internal volume. The sheets may also be sealed at locations away from their peripheries so as to form two or more internal volumes that are in fluid communication with each other. The heat transfer fluid is preferably a liquid such as water, glycerin, ethanol, ethylene glycol or ammonia or a mixture thereof. Alternatively, the heat transfer fluid may be a mixture of a liquid phase and vapour phase and may comprise one or deionised water and inert fluorocarbons.

Description

( Compliant Heat Sink Interface BACKGROUND OF THE INVENTION

5 The present invention relates to electronic components and circuitry, and is primarily concerned with the cooling of electronic components by the attachment of heat sinks thereto. Specifically, the invention is concerned with the provision of an interface between an 10 electronic component and a heat sink.

Electronic components such as processors generate heat when in operation, and must be protected from excessive temperatures to ensure their correct functioning. Heat 15 sinks are frequently used to remove heat from electronic components and thus regulate the temperature of the components. To provide for efficient thermal transfer between a heat-generating component and a heat sink, intimate contact must be maintained between the component 20 and the heat sink at the contact plane.

When a plurality of components are mounted to a common circuit board, differences in height of the components and misalignment between the components and the board 25 results in the upper surfaces of the components being

( non-coplanar, and thus a single planar heat sink cannot effectively contact all of the components. This difficulty has been addressed by placing an interface material between the components and the heat sink, or by 5 providing individual heat sinks for each of the components, leading to increased numbers of parts and increased assembly time and cost. The interface materials used hitherto have included a compressible heat-conductive sheet, and a thermally conductive paste.

10 The heat-conductive sheet is formed from resilient plastics material, but this suffers from the disdvantage that its heat conductivity is relatively low, and its limited resilience results in poor contact with the surfaces of the components and heat sink. The conductive 15 paste is time-consuming to apply to the components.

A need exists for an interface component which can provide effective thermal connection between a heat sink and a plurality of electronic components mounted on a 20 circuit board with production tolerances in the alignment of the components.

SUMMARY OF THE INVENTION

25 A first aspect of the present invention provides a

( generally planar interface element for thermally connecting an electronic component to a heat sink, the element comprising a heatconductive flexible or deformable enclosure containing a heat transfer fluid, 5 and wherein heat is transferable from one face of the interface element to the other through the fluid medium.

The heat transfer mechanism by which heat is transferred is by conduction in some embodiments of the invention, 10 while in other embodiments the heat transfer is effected by evaporation, vapour migration, and condensation of the fluid. In one embodiment of the invention, the enclosure is 15 formed from two plates or sheets, disposed in a substantially parallel spaced relation and sealed together at their periphery by a flexible sealing element or a deformable bead of sealing material.

20 A further embodiment of the invention provides an interface adapted to engage a plurality of differently sized components arranged on a circuit board by providing one face of the interface with a topology corresponding to the arrangement of the heat output surfaces of the 25 components when mounted.

In a further embodiment, the enclosure is formed from sheets of flexible metal or plastics foil, bonded or crimped together at their periphery to contain the heat transfer fluid in a sachet-like structure. The two 5 sheets may also be bonded together at points or in regions spaced from the periphery, to produce a quilted effect or to subdivide the sachet into two or more discrete volumes.

10 A second aspect of the invention provides a heat sink having a heat absorption surface with an integral compliant interface formed on the heat absorption surface. 15 third aspect of the invention provides an elecronic component having a heat output surface with an integral compliant interface formed on the heat output surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: 25 Figure 1 is a sectional side view of an electronic

component connected to a heat sink via a first interface according to the invention; Figure 2 is a sectional view of a second interface 5 according to the invention; Figure 3 is a schematic sectional view showing a plurality of components connected to a single heat sink; 10 Figure 4 is a sectional view of a third interface according to the invention; Figure 5 is a sectional view showing the interface of Figure 4 in use; Figure 6 is a sectional view showing a heat sink incorporating an interface according to the invention; Figure 7 is a sectional view showing the heat sink of 20 figure 6 in use; Figure 8 is a perspective view of an electronic component incorporating the interface of the present intention: 25 Figure 9 is a sectional view showing two components of

figure 8 connected to a single heat sink; Figure 10 is a sectional view showing a fourth interface of the present invention in use; Figure 11 is a perspective view of a fifth interface according to the invention; Figure 12 is a sectional view in the plane XII-XII of 10 Figure 11; and Figure 13 is an exploded view of a circuit assembly including a sixth interface according to the invention.

15 DESCRIPTION OF PARTICULAR EMBODIMENTS

Referring now to the drawings, in which like reference numerals are used to designate corresponding elements, Figure l shows in sectional side view a circuit board 1 20 to which an electronic component 2 is mounted. A heat sink 3 comprising a planar base part 3a and a plurality of upstanding cooling fins 3b is positioned above the electronic component 2, and thermal contact between the heat sink 3 and the component 2 is assured by an 25 interface element 4 positioned between them. Resilient

clamps 5 attached to anchor points 6 on the circuit board 1 urge the heat sink 3 and interface element 4 into close contact with each other and with the component 2.

5 The interface element 4 comprises an upper plate 41 and a lower plate 42, joined at their periphery by a bead of sealant 43 to enclose a volume of fluid 44. The plates 41 and 42 are formed from thermally conductive material such as copper, beryllium copper, aliminium, nickel, 10 brass or graphite and are from 2mm to 8mm in thickness.

Metal foils of from 0.05mm to 0.2mm in thickness may be used for the plates 41, 42 if flexibility is required.

Other materials such as plastics sheet or foil, metallised plastics sheet or foil, or fibre-reinforced 15 sheets of for example carbon fibre may be used for the plates 41 and 42, providing that they are thermally conductive and are not attacked by the fluid 44. For example, in an interface element using ethanol as the heat transfer fluid, the plates 41 and 42 should be made 20 of aluminium and not plastics foil.

The plates 41 and 42 need not be of the same thickness or material. One or both of the plates 41 and 42 may be formed with a peripheral lip 41a, 42a (seen in Figure 2) 25 to support the sealing bead 43 against outward

( hydrostatic forces. The minimum amount of materials is used if the sizes of the plates are made to correspond to the sizes of the component and the heatsink, respectively. These may be the same size and shape, or 5 may differ in area and outline.

The sealing bead 43 is a non-hardening material such as a silicone rubber or other synthetic rubber material.

The sealant 43 must sealingly contact or adhere to the 10 plates 41 and 42, and remain deformable to accommodate some relative movement of the plates. As an alternative to a sealing bead 43, a resilient or flexible sealing gasket or ring of polyurethane or the like may be used, or the plates 41, 42 may be joined by a bellows-like 15 structure of flexible sheet material such as thin metal foil of, for example, beryllium copper.

The interface element 4 shown in Figure 1 is shaped to correspond with the length and width dimensions of the 20 component 2 and the heat sink 3. The lower plate 42 of the interface element 4 is placed on top of the component, after optionally cleaning the contact surfaces of the component and the lower plate 42 to maximise contact efficacy, and the heat sink 3 is then placed with 25 the undersurface of its base 3a in contact with the upper

plate 41 of the interace element 4. Resilient clamps 5, comprising a hook 5a and a tension spring 5b, attach to anchor points 6 fixed to the circuit board. The hook 5a is engaged with the heat sink 3, to provide a clamping 5 force acting (downwardly as seen in Figure 1) to urge the heat sink 3 and interface 4 together, and to urge the interface 4 into close contact with the component 2.

Although only one clamp 5 is shown in Figure 1, it will be understood that more than one clamp may be provided 10 for each heat sink 3, and that by modifying the clamp a single clamp may engage and exert force on more than one heat sink 3. The clamp 5 may have any suitable configuration, provided that it acts to urge the interface, heat sink, and component into close contact.

The downward force exerted on the heat sink 3 by the clamp 5 is transmitted to the fluid 44 within the interface element 4, and the hydrostatic pressure of the fluid urges the upper and lower plates 41 and 42 into 20 close contact with their respective opposing surfaces of the heat sink 3 and the component 2. The plates 41 and 42 are sufficiently thin so as to be flexible under the hydrostatic pressures exerted, and are urged into intimate contact with their respective contact surfaces 25 by the pressure within the fluid 44.

As the component 2 heats up in use, heat is conducted through the lower plate 42 of the interface element 4 to the fluid 44. The heat is then transferred through the fluid 44 to the upper plate 41 of the interface 4, and 5 is conducted through the plate 41 to the base 3a of the heat sink 3. The heat then flows by conduction up the fins 3b and is dissipated to atmosphere by conduction and natural or forced convection.

10 The heat transfer through the fluid may be effected by conduction, when the interface 4 is filled with a liquid.

The thinner the interface is made then the less is the resistance to heat transfer by conduction through the fluid 44. Water is a suitable liquid, either alone or 15 with additives such as ethylene glycol to reduce its freezing point and raise its boiling point. The thickness of the liquid layer is made as small as possible, to present least resistance to heat flow. The liquid layer may be less than 2mm, or less than 0.5mm 20 thick. Alternatively, the interface 4 may be filled with a fluid 44 which is a mixture of a liquid phase and a vapour phase. Heat transfer is effected between the plates 42 25 and 41 by the liquid phase in contact with plate 42 being

heated and evaporating while vapour in contact with plate 41 condenses and drips down on to plate 42.

Suitable liquids for this "two phase" interface are de 5 ionised or an inert fluorocarbon such as i.Fluorinert.' HFE 7100 manufactured by 3M.

Figure 3 shows an application of the interface element 4. In the arrangement shown in Figure 3, a circuit board 10 1 has three electronic components 2a, 2b, 2c mounted thereon. The three components are similar in size, and while the outer components 2a and 2c are mounted in parallel with the circuit board 1, the central component 2b is inclined in relation to the circuit board, due to 15 mounting tolerances.

A single heat sink 3 is to be used to draw heat from all three of the electronic components 2a, 2b and 2c. In order to ensure adequate thermal contact, interface 20 elements 4a, 4b and 4c are interposed between the respective components 2a, 2b and 2c and the heat sink 3.

A downward force is applied to the heat sink 3, for example by resilient clamps similar to those shown in Figure 1, in order to urge the heat sink, interfaces and 25 components into intimate contact.

( As can be seen from Figure 3, the upper plates 41a, 41b and 41c of the interfaces 4a, 4b and 4c are pressed into intimate contact with the underside of the heat sink 3, and are thus in substantially co-planar alignment with 5 each other.

The lower plates 42a and 42c of the outer interfaces 4a and 4c are likewise in substantially co-planar arrangement with each other, since they are pressed 10 against the upper surfaces of the components 2a and 2c.

The lower plate 42b of the central interface 4b, however, is pressed into intimate contact with the upper face of the central component 2b, which is slightly inclined in 15 relation to the remaining components due to its inaccurate mounting on the circuit board 1. The flexibility of the sealing beads 43b of the central interface element 4b enables the lower plate 42b of the interface element 4b to be inclined relative to the upper 20 plate 41b, ensuring that contact is made with the component 2b over substantially the entire area of its upper surface.

Heat transfer between the components 2a, 2b, 2c and the 25 heat sink 3 is made by conduction of heat through the

lower plates 42a, 42b, 42c of the interfaces, by heat transfer through the fluid medium 44 to the upper plates 43a, 43b and 43c and thence by conduction through the upper plates 43a, 43b and 43c to the base 3a of the heat 5 sink 3. Heat is lost from the heat sink 3 to the atmosphere by means of the cooling fins 3b.

In the embodiment shown, the internal spaces of the interface elements 4a, 4b, 4c are completely filled with 10 liquid, and heat transfer from the lower plates 42a, 42b, 42c to the upper plates 43a, 43b, 43c is by means of conduction of heat through the fluid. The vertical thickness (as seen in Figure 3) of the interfaces 4a, 4b, 4c is kept to a minimum by reducing the height of the 15 sealing beads 43a, 43b, 43c so as to improve the rates of heat conduction through the fluid 44a, 44b, 44c and to suppress the formation of convection currents.

Figure 4 illustrates in sectional side view an interface 20 4 specifically tailored to fit a particular array of electronic components arranged on a circuit board.

Figure 5 shows the interface of Figure 4 in position on the array of components, with some misalignment of the 25 components.

In Figure 4, the interface 4 has an upper plate 41 shaped to correspond with the plan view of an array of components. Extending round the periphery of the upper plate is a sealing bead 43, which joins the upper plate 5 to a lower plate 42 of similar outline. The lower plate 42 has stepped regions which are spaced at different distances from the upper plate 41, the dimensions of these stepped regions and their distances from the upper plate 41 being arranged to correspond to the size, lo thickness and position of the components 2.

Figure 5 shows the interface 4 in position on an array of components 2d to 2g mounted on a circuit board 1.

Circuit components 2d and 2e have the same nominal 15 height, circuit component 2f has a nominal height substantially less than those of components 2d and 2e, and component 2g has a nominal height intermediate the heights of components 2f and 2e. Furthermore, in the embodiment shown, components 2d and 2f are mounted 20 slightly obliquely to the circuit board 1 while components 2e and 2g are correctly mounted in parallel to the circuit board 1. The oblique mounting of components 2d and 2f is shown to illustrate the possibility of incorrect mounting.

Once the interface 4 has been placed over the array of components, with the stepped regions in registry with their respective components, either a single heat sink or a plurality of heat sinks 3', 3" and 3"' is placed on 5 the upper plate 41 of the interface element 4. The heat sink or sinks 3 are held down, for example by resilient clamping devices to exert downward forces on the interface element 4.

10 The downward force exerted on the interface 4 by the heat sinks 3 causes the lower plate 42 of the interface element 4 to be pressed into close contact with the upper surfaces of the components 2 by the hydrostatic pressure of the fluid 44 in the interface element 4.

While the stepped arrangement of the lower plate 42 initially positions the various stepped regions of the lower plate in proximity to the upper surfaces of their respective components, the downward fluid pressure on the 20 lower plate 42 pushes the plate into close contact with the components, causing flexing of the plate 42 as necessary to align each stepped region with its respective component. This flexing is illustrated in Figure 5 in the region between components 2d and 2e, and 25 between components 2e and 2f.

In the interface element shown in Figures 4 and 5, the upper plate 41 may be constructed of substantially rigid material such as thin aluminium or other relatively stiff sheet, while the lower plate 42 is manufactured from a 5 thinner metal foil of higher flexibility, or from a pre formable plastics foil. The foil must be sufficiently strong to withstand the hyrdostatic pressure generated by the clamping forces applied to the heat sink 3.

10 Figure 6 is a schematic sectional side view of a heat sink incorporating an interface element, and Figure 7 shows the heat sink in position on two misaligned components mounted to a circuit board.

15 In Figure 6, the heat sink comprises a base 3a and a plurality of cooling fins 3b upstanding from the base 3a.

Extending around the periphery of the underside of the base 3a is a sealing bead 43 of flexible sealing 20 material. A flexible lower plate 42 is attached to the sealing beads 43, and the volume defined between the lower plate 42 and the undersurface of base 3a of the heat sink 3 is filled with a heat transfer fluid 44. The heat sink 3 of Figure 6 is particularly suited to operate 25 as a heat sink for a number of components 2 of similar

thickness mounted to a circuit board l, where at least one of the components is slightly misaligned relative to the circuit board 1. This situation is shown in Figure 6, where components 2h and 2i are mounted to circuit 5 board 1, with component 2i being slightly misaligned.

The heat sink 3 is placed over the two components 2h and 2i, as shown in Figure 7. A downward clamping force is applied to the heat sink 3, and this exerts a hydrostatic 10 pressure on the fluid 44 which urges the lower plate 42 to bend at its central region so that the left and right hand side regions (as seen in Figure 7) of the plate 42 are urged into close contact with the upper faces of the components 2h and 2i respectively, The deformable 15 sealing bead 43 is shown slightly crushed on the right hand side of Figure 7, to show the deformation of the bead which allows the lower plate 42 to bend into contact with the component 2i. By integrating the compliant interface with the heat sink 3, a thermal boundary 20 between the interface and heat sink is eliminated and heat transfer is facilitated.

Figures 8 and 9 show an electronic component 20 with an integral interface according to the invention.

Figure 8 is a perspective view of the component 20, which comprises a generally parallelepipedal housing 21 with electrical contacts 22 extending outwardly then downwardly from two opposing faces of the housing 21.

5 When mounted on a circuit board 1, the contacts 22 are fixed to conductive tracks on the circuit board or may be received in contact recesses of a socket to provide a removable mounting of the component to the circuit board. The upper face of the housing 21 has a peripheral sealing element or sealing bead 43, to which is attached to an upper plate 41. The volume defined between the upper plate 41, the housing 21 and the sealing bead 43 is 15 filled with heat transfer fluid 44. In Figure 8, the upper plate 41 is cut away to illustrate the structure more clearly.

Figure 9 shows two components 2Oa and 2Ob mounted to a 20 circuit board 1, the component 20a being correctly mounted on the circuit board 1 and the component 20b being incorrectly mounted, with a slight inclination away from the circuit board 1. A single heat sink 3 is placed on top of the components 20a and 20b, and is pressed 25 downwards into contact with the upper plates 41 of the

components 20a and 20b, for example by means of resilient clamping elements or threaded fasteners engaging the heat sink 3 and the circuit board 1. The sealing beads 43 of the components 20a and 20b deform due to this downward 5 pressure, and a hydrostatic pressure is developed in the fluid medium 44 which pushes the upper plates 41 into close contact with the underside of the base 3a of the heat sink 3.

10 It will be noted that in Figure 9 the heat sink 3 does not take up a position parallel to the plane of the circuit board 1. The final position of the heat sink 3 relative to the circuit board 1 will depend on the distribution of clamping forces, and the number of 15 components 20 which are engaged by the heat sink 3.

While Figure 9 shows only two components 20, it is envisaged that an array of a number of rows and columns of components 20 may be engaged by the same planar heat sink 3.

Figures 10 to 12 show an alternative embodiment of the interface wherein the upper and lower plates 41 and 42 of the interface are formed from a flexible sheet or foil material, the sheets being bonded or crimped together at 25 their peripheries to form a "sachet" enclosing a heat

conducting fluid.

Figure 10 shows a sectional side view of this embodiment of the interface, interposed between a heat sink 3 and 5 an electronic component 2 mounted on a circuit board 1.

The interface 40 shown in Figure 10 comprises upper and lower foil sheets 410, 420 attached together at their edges by crimps 420. The crimps 420 may be made by 10 placing edge regions of the foils 410 and 420 in contact, optionally applying a bonding agent therebetween, folding the edge region and applying pressure to form a joint between the upper and lower foils. The volume between the foils is filled with a heat transfer medium 440. The 15 heat transfer medium may be a liquid, or may be a gel or paste. The foils 410 and 420 are made of thin flexible material such as metal (e.g copper or aluminium) foil from 0.05 20 to 0.2mm thick or polymner foil of from 0.05 to O.Smm thick, and the heat transfer medium 440 may be water, optionally with additives to depress its freezing point and/or raise its boiling point so as to extend the temperature range over which the interface may be used.

25 Conventional anti-freeze additives such as ethylene

f glycol may be used, either in addition to water or instead of water. Glycerin, Ammonia and ethanol may also be used as heat transfer liquids.

5 In use, the interface 40 is placed on top of a component 2 mounted to a circuit board l, and a heat sink 3 is placed on top of the interface 40. A light downward pressure is applied to the heat sink 3, to produce a hydrostatic pressure within the fluid 440 which urges the 10 foils 410 and 420 into intimate contact with the undersurface of the heat sink 3 and with the component 2, respectively. Due to the increased flexibility of the foils 410, 420 as compared to the upper and lower plates 41 and 42 of earlier embodiments, effective contact IS between the components is ensured with only a small clamping force. Furthermore, with this embodiment the hydrostatic pressure of the heat transfer fluid 440 must not be raised beyond the capacity of the foil membranes 410 and 420 to contain it.

Figures 11 and 12 show an alternative embodiment of the interface, in perspective and sectional views, respectively. In this embodiment, the interface is formed from two bonded foil sheets 410 and 420, bonded 25 together at their edge regions and at an intermediate

bonding region 450 extending across the interface to divide the interface into two distinct 't cachets" S. each of which is filled with a heat transfer fluid 440. The dimensions of the interface 40 and the position and width 5 of the bonding region 450 are arranged so that the "sachets.' correspond in size and relative orientation to two components to be mounted on a circuit board, so that when the interface 40 is placed over the components each sachet" rests on top of one of the components. A heat 10 sink 3 may then be placed on top of the interface 40, and downward pressure applied to generate a hydrostatic pressure in the heat transfer fluid 440 which urges the foils 410 and 420 into close contact with their respective contact surfaces.

Figure 13 is an exploded view showing an interface 40 similar to that of Figure 11, but in this case the interface is sub-divided by two bonding regions 450a and 450b which extend widthwise and lengthwise of the 20 interface 40, respectively.

The interface is intended for use on an array of four components 2 which are mounted on a circuit board 1. The components 2 may be of disparate height and irregular 25 placing on the circuit board. The bonding regions 450a

and 450b of the interface 40 are positioned and dimensioned so that the interface 40 comprises a number of "sachets" S1 to S4, corresponding in number, position and size to the respective components 2. By providing 5 un-bonded areas extending across the bonding regions 450a and 450b, sachets S1 and S3 may for example be placed in fluid communication with each other so that when a downward force is applied on the interface by a heat sink 3, fluid can flow from sachet S1 to sachet S3 to 10 compensate for any disparity in height between their respective components 2.

In the embodiments described, the heat transfer medium is a liquid. It is to be understood that the volume 15 within the interface may be filled either entirely with a liquid, or with a mixture of liquid and vapour. In this latter case, heat transfer between the faces of the interface may be effected by evaporation of liquid at the lower face of the interface and condensation of the 20 vapour at the upper face of the interface. Condensed liquid may then return (drip or flow down) to the lower region of the interface for recycling. Suitable materials for the heat transfer medium in this vapour/liquid phase embodiment are de-ionised water, 25 inert fluorocarbons such as "Fluorinert" HFE 7100 (TM).

( Suitable inert liquids will have high latent heat of vapourisation, and a boiling point in the range 10-150 c.

The scope of the present disclosure includes any novel

5 feature or combination of features disclosed therein either explicitly or implicitly or any generalization thereof irrespective of whether or not it relates to the claimed invention or mitigates any or all of the problems addressed by the present invention. The applicant hereby 10 gives notice that new claims may be formulated to such features during the prosecution of this application or of any such further application derived therefrom. In particular, with reference to the appended claims, features from dependent claims can be combined with those 15 of the independent claims and features from respective independent claims can be combined in any appropriate manner and not merely in the specific combinations enumerated in the claims.

Claims

( Claims

1. A compliant thermal interface comprising: a casing having first and second external contact 5 faces and defining an internal volume; a heat transfer fluid in said volume providing a heat transfer path from said first contact face to said second contact face; and wherein the relative positions of the contact faces 10 are variable by deforming a portion of the casing.

2. A compliant interface according to claim 1, wherein the casing comprises a pair of spaced apart plates joined at their peripheries by a deformable sidewall.

3. A compliant interface according to claim 2, wherein at least one of the plates is formed with a peripheral lip directed toward the other plate.

20 4. A compliant interface according to claim 1, wherein the casing comprises a pair of spaced apart plates joined at their peripheries by a flexible sidewall.

5. A compliant interface according to any of claims 2 25 to 4, wherein the first contact face comprises an

exterior surface of one of the plates, and the second contact face comprises an exterior surface of the other of the plates.

5 6. A compliant interface according to claim 5, wherein one of the contact faces is non-planar.

7. A compliant interface according to claim 6, wherein said one contact face comprises a plurality of contact 10 regions situated in substantially parallel planes spaced one from another.

8. A compliant interface according to claim 1, wherein the casing comprises a sachet or pouch of a flexible 15 material. 9. A compliant interface according to claim 9, wherein the casing comprises two sheets of a flexible material sealed together at their respective peripheral regions 20 to enclose an internal volume.

10. A compliant interface according to claim 10, wherein the sheets of flexible material are sealed together at one or more regions spaced from the periphery 25 of the sheets.

i f 11. A compliant interface according to claim 10, wherein the sheets of flexible material are bonded together at one or more regions extending across the sheets to form at least two internal volumes.

12. A compliant interface according to claim 11, wherein at least two of said internal volumes are in fluid communication with each other.

10 13. A compliant interface according to any preceding claim wherein said heat transfer fluid in said volume is a liquid.

14. A compliant interface according to claim 13, 15 wherein said heat transfer fluid in said volume is at least one of water, glycerin, ethanol, ethylene glycol and ammonia.

15. A compliant interface according to claim 14, 20 wherein said heat transfer fluid in said volume is a mixture of water and one or more additives.

16. A compliant interface according to claim 15, wherein said additive is ethylene glycol.

( 17. A compliant interface according to any of claims 1 to 12, wherein said heat transfer fluid in said volume is a mixture of liquid phase and a vapour phase.

5 18. A compliant interface according to claim 17, wherein said heat transfer fluid in said volume is a mixture of liquid phase and a vapour phase of one of deionized water, and inert fluorocarbons.

10 19. A heat sink, comprising: a base having a surface for absorbing heat; a casing having a contact face and defining with said surface of said base an internal volume; a heat transfer fluid in said volume providing a 15 heat transfer path from said contact face to said surface; and wherein the relative positions of the contact face and said surface are variable by deforming a portion of the casing.

20. A heat sink according to claim 19, wherein the casing comprises a plate joined to the base at the periphery of the surface by a deformable sidewall.

25 21. A heat sink according to claim 19, wherein the

casing comprises a plate joined to the base at the periphery of the surface by a flexible sidewall.

22. A heat sink according to any of claims 19 to 21, 5 wherein said heat transfer fluid in said volume is a liquid. 23. A heat sink according to claim 22, wherein said heat transfer fluid in said volume is water.

24. A heat sink according to claim 22, wherein said heat transfer fluid in said volume is a mixture of water and one or more additives.

15 25. A heat sink according to claim 24, wherein said additive is ethylene glycol.

26. A heat sink according to any of claims 19 to 21, wherein said heat transfer fluid in said volume is a 20 mixture of liquid phase and a vapour phase.

27. A heat sink according to claim 26 wherein said heat transfer fluid in said volume is a mixture of liquid phase and a vapour phase of one of deionized water, and 25 inert fluorocarbons.

( 28. An electronic component, comprising: a housing having a surface for emitting heat; a casing having a contact face and defining with said surface of said base an internal volume; 5 a heat transfer fluid in said volume providing a heat transfer path from said contact face to said surface; and wherein the relative positions of the contact face and said surface are variable by deforming a portion of 10 the casing.

29. An electronic component according to claim 28, wherein the casing comprises a plate joined to the base at the periphery of the surface by a deformable sidewall.

30. An electronic component according to claim 28, wherein the casing comprises a plate joined to the base at the periphery of the surface by a flexible sidewall.

20 31. An electronic component according to any of claims 28 to 30, wherein said heat transfer fluid in said volume is a liquid.

32. An electronic component according to claim 31, 25 wherein said heat transfer fluid in said volume comprises

! one of water, glycerin, ethylene glycol, ammonia and ethanol. 33. An electronic component according to claim 31, 5 wherein said heat transfer fluid in said volume is a mixture of water and one or more additives.

34. An electronic component according to claim 33, wherein said additive is ethylene glycol.

35. An electronic component according to any of claims 28 to 30 wherein said heat transfer fluid in said volume is a mixture of liquid phase and a vapour phase.

15 36. An electronic component according to claim 35, wherein said heat transfer fluid in said volume is a mixture of liquid phase and a vapour phase of one of deionised water, and inert fluorocarbons.

20 37. An electronic circuit comprising: an electronic component; a compliant interface comprising: a casing having first and second external contact faces and defining an internal volume; 25 a heat transfer fluid in said volume providing a

( heat transfer path from said first contact face to said second contact face; and wherein the relative positions of the contact faces are variable by deforming a portion of the casing; 5 a heat sink; wherein the interface is positioned between said electronic component and said heat sink with one contact face of the interface in thermal contact with the component and the other contact face of the interface in 10 thermal contact with the heat sink; and a clamping element urging the component, the interface and the heat sink together.

38. An electronic circuit comprising: 15 an electronic component; a heat sink, comprising: a base having a surface for absorbing heat; a casing having a contact face and defining with said surface of said base an internal volume; 20 a heat transfer fluid in said volume providing a heat transfer path from said contact face to said surface; and wherein the relative positions of the contact face and said surface are variable by deforming a portion of 25 the casing; and

( a clamping element urging the component and the heat sink together.

39. An electronic circuit comprising: 5 an electronic component, comprising: a housing having a surface for emitting heat; a casing having a contact face and defining with said surface of said base an internal volume; a heat transfer fluid in said volume providing a 10 heat transfer path from said contact face to said surface; and wherein the relative positions of the contact face and said surface are variable by deforming a portion of the casing; and 15 a clamping element urging the component and the heat sink together.

40. A compliant thermal interface substantially as hereinbefore described with reference to Figure l, Figure 20 2, Figure 3, Figures 4 and 5, Figure 10, Figures 11 and 12 or Figure 13 of the accompanying drawings.

41. A heat sink substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying 25 drawings.

( 42. An electronic component substantially as hereinbefore described with reference to Figures 8 and 9 of the accompanying drawings.