INTERFACIAL THERMAL TRANSFER STRUCTURE

Abstract

An apparatus that interfaces thermal transfer components is described. The apparatus includes a soft, thermally conductive metal that enables a capillary flow path with a contact surface of a thermal transfer component and an imbibing thermal interface material. The thermal transfer component is a heat sink. The thermally conductive metal includes large pores that intertwine with smaller pores of the contact surface.

Description

TECHNICAL FIELD

The present techniques relate generally to the thermal management of a computing system. More specifically, the present techniques relate to the thermal management of a computing system using an interfacial thermal transfer structure.

BACKGROUND ART

Modern computer components generate large amounts of thermal energy during operation. Such thermal energy negatively impacts the performance of the components and results in heat related damage to the component components. Therefore, heat sinks are typically implemented to remove thermal energy from components. Such heat sinks generally function, at least in part, by thermal conduction through physical contact with a portion of the component.

Resistance to thermal conduction at an interface between a component and a heat sink can undermine the efficiency and effectiveness of the heat sink. Therefore, numerous thermal interface materials (TIMs) have been developed to more efficiently conduct heat from the component to the heat sink. However, conventional TIMs, such as particle laden polymers, phase change materials, thermal pastes, and the like, are not very reliable. A number of commercially-available TIMs have high initial performance, but fail to meet end of life (EOL) requirements. TIM degradation is exacerbated by several factors, including large integrated heat spreader (IHS) area, low compression pressure for TIMs, and flatness variation (or non-coplanarity).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram showing an interfacial thermal transfer structure integrated to a heat sink;

FIG. 1B is a block diagram showing an interfacial thermal transfer structure integrated to a heat sink;

FIG. 2A is a block diagram showing an interfacial thermal transfer structure integrated to a heat sink;

FIG. 2B is a block diagram showing an interfacial thermal transfer structure integrated to a heat sink;

FIG. 3A is a block diagram showing an interfacial thermal transfer structure integrated to a heat sink;

FIG. 3B is a block diagram showing an interfacial thermal transfer structure integrated to a heat sink;

FIG. 4 is a block diagram showing an interfacial thermal transfer structure integrated to a heat sink;

FIG. 5 is a block diagram showing an embodiment of the interfacial thermal transfer structure;

FIG. 6A is a block diagram showing an example material of the interfacial thermal transfer structure;

FIG. 6B is a block diagram showing the example material of the interfacial thermal transfer structure; and

FIG. 7 is a computing device including an interfacial thermal transfer structure.

The same numbers are used throughout the disclosure and the figures to reference like components and features. Numbers in the 100 series refer to features originally found in FIG. 1; numbers in the 200 series refer to features originally found in FIG. 2; and so on.

DESCRIPTION OF THE EMBODIMENTS

Thermal solution designs often employ thermal pastes, phase change materials, and the like to enable temperature control of lidded packages to meet EOL reliability requirements. Often, these TIMs are composed of a low thermal conductivity organic phase, such as silicone grease, interspersed with high conductivity metal or ceramic particles to enable a higher effective thermal conductivity composite. However, such materials have several limitations, including large thermal resistances, susceptibility to voiding, and dry out (or pump out).

Increasing the volume fraction of particles increases thermal conductivity and effective viscosity of the material system. This increased effective viscosity prevents the formation of thin bond lines, and reduces the contact resistance between the metal substrate (e.g., the heat sink base or IHS) and the TIM. However, thermal pastes dispersed with high concentrations of particles suffer from thermal property variation because of flocculation of particles, particle-fluid phase separation during squeeze out, and high pressure generation at the substrate-particle contact points.

Reliability requirements dictate sustenance of minimum bond line thicknesses (BLTs) for TIMs throughout the life of the product. However, a known failure mechanism of wetting certain TIMs, such as thermal pastes, is void formation via paste pumping during repeated thermal and pressure cycles.

Accordingly, embodiments described herein provide an interfacial thermal transfer structure to be used in association with conventional TIMs. The structure, in one embodiment, is a capillary-wick-enabled TIM that creates liquid wicking paths for conventional TIMs, and provides an improved thermal conductivity. An apparatus with the capillary-wick-enabled TIM has improved thermal conductivity, in comparison to conventional TIMs, used without the interfacial thermal transfer structure. Additionally, the capillary-wick-enabled TIM slows the degradation of conventional TIMs from pump-out.

In the following description and claims, the terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” may mean that two or more elements are in direct physical or electrical contact. However, “coupled” may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other.

Some embodiments may be implemented in one or a combination of hardware, firmware, and software. Some embodiments may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by a computing platform to perform the operations described herein. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine, e.g., a computer. For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; or electrical, optical, acoustical or other form of propagated signals, e.g., carrier waves, infrared signals, digital signals, or the interfaces that transmit and/or receive signals, among others.

An embodiment is an implementation or example. Reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” “various embodiments,” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the present techniques. The various appearances of “an embodiment,” “one embodiment,” or “some embodiments” are not necessarily all referring to the same embodiments. Elements or aspects from an embodiment can be combined with elements or aspects of another embodiment.

Not all components, features, structures, characteristics, etc. described and illustrated herein need be included in a particular embodiment or embodiments. If the specification states a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, for example, that particular component, feature, structure, or characteristic is not required to be included. If the specification or claim refers to “a” or “an” element, that does not mean there is only one of the element. If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element.

It is to be noted that, although some embodiments have been described in reference to particular implementations, other implementations are possible according to some embodiments. Additionally, the arrangement and/or order of circuit elements or other features illustrated in the drawings and/or described herein need not be arranged in the particular way illustrated and described. Many other arrangements are possible according to some embodiments.

In each system shown in a figure, the elements in some cases may each have a same reference number or a different reference number to suggest that the elements represented could be different and/or similar. However, an element may be flexible enough to have different implementations and work with some or all of the systems shown or described herein. The various elements shown in the figures may be the same or different. Which one is referred to as a first element and which is called a second element is arbitrary.

FIG. 1A is a block diagram showing an interfacial thermal transfer structure 102 integrated to a heat sink 104. The structure 102 is also referred to herein as, the TIM carrier, and the continuous phase of the TIM. The continuous phase of the TIM may be created using a soft, thermally conductive material, e.g., polymers, metals, that enables a capillary flow path (smaller pores 106˜20-100 μm) intertwined with large pores 108 (˜1-2 mm). The TIM carrier may be constructed of expanded metal grids that facilitate the creation of a dual-porosity wick, such as a woven wire mesh. These wicking materials can be directly bonded to the base of the heat sink 104 using conventional manufacturing processes such as soldering, brazing, diffusing bonding, and the like. Alternatively, the wicking patterns can be machined on the base of the heat sink itself. The thickness of the TIM carrier may range from 25-500 μm. The TIM carrier not only enables liquid wicking paths but also enables contact between top and bottom substrates, e.g., the heat sink 104 and a the source (not shown), such as a circuit, controller, heat spreader, and the like. In the interstitial space 106 within the TIM carrier, conventional TIMs, such as thermal pastes and greases can be placed to improve the effective thermal conductivity of the interfacial thermal transfer structure 102.

Also, the interfacial thermal transfer structure 102 can manage multiple phases. Liquid imbibes in to smaller pores 106 between the TIM carrier and heatsink base 104 more rapidly, and to a higher level than, liquid imbibes into larger pores due to capillarity, which is surface tension driven. In this way, the interfacial thermal transfer structure 102 enables the flow of excess, e.g., paste, away from areas of nearest contact to areas that benefit from additional paste or grease. The effect is analogous to dipping a bundle of capillary tubes of differing diameter in a fluid, i.e., capillary action. Due to capillary action, the smallest diameter tubes have the highest capillary driving force and thus, fill first and to a higher level than the larger diameter tubes. The presence of capillary pores may enable the interfacial thermal transfer structure 102 to maintain a minimum BLT throughout the life of the interfacial thermal transfer structure 102, and the heat sink 104. The interfacial thermal transfer structure 102 also enables a method to manage non-coplanarity or warpage (static and dynamic) issues for large IHS packages. Non-coplanarity issues involve transferring heat between contacting bodies that are curved or out of flatness. Depending on the type interface material, non-coplanarity might induce large air gaps or large bondline thickness. Static and dynamic warp issues refer to having out-of-flatness at room temperature (or a steady-state), and transient variation in flatness due to temperature cycling, respectively. Static warp may be related to the manufacturing process inducing a concave, convex, wave, or non-flat profile on a surface. Dynamic warp may be a concave, convex, wave, or non-flat profile on a surface due to thermal contraction and expansion of the material, or a change in the surface profile when subjected to a force or load.

A potential mechanism for voiding is via paste pumping during repeated thermal and pressure cycles by trapping air cells. While the physics of voiding is not completely understood, it is known that pressure gradients, viscosity and surface tension play a role. The interfacial thermal transfer structure 102 creates a pathway to reduce the pump out of pastes or greases during the repeated thermal cycling by reducing the pressure gradients in comparison to conventional TIMs alone. The pressure reduction is achieved by provision of smaller capillary flow channels in the imperfections of the in-contact surfaces of the structure 102, the heatsink 104, and the source (not shown), that enables liquid flow along the mesh wires of the interfacial thermal transfer structure 102 and the larger pore 108 networks that enable long-range evacuation or volume-filling of paste.

In contrast, an interface with conventional TIMs, but not the interfacial thermal transfer structure 102, does not enable the thermal interface materials to flow between induced pressure gradients during thermal cycling. Instead, voids form and grow over time. Accordingly, providing an interface that also includes the interfacial thermal transfer structure 102 allows for a reduction in flow resistance between regions of higher and lower pressure. This slows the formation and growth of voids over time.

In one application using IHS specifications, commercial thermal grease (kpaste=3.5 W/mK) as TIM2, and off-the-shelf copper (kCopper=390 W/mK) wire screen mesh as wick, estimated effective thermal conductivity was 11.9 W/mK for 90% porosity wick. Effective thermal conductivity was determined using the relationship keff=kpaste(kCopper/kpaste)(1−ε)̂0.59 where c is the porosity of the screen wick. This increase in thermal conductivity translates (after accounting for contact resistance and warpage contribution) approximately to 200-300 percent reduction in TIM2 thermal resistance (for End of Life requirements).

FIG. 1B is a block diagram showing the interfacial thermal transfer structure 102 integrated to the heat sink 104. FIG. 1B shows measurements of the various components of the structure 102 and heat sink 104.

FIG. 2A is a block diagram showing interfacial thermal transfer structures 202-1, 202-2 integrated to a heat sink 204. In an embodiment, screen meshes can be stacked on top of one other, either aligned or offset, to increase effective thermal conductivity and the thickness of the thermal interface material. In FIGS. 2A, 2B, interfacial thermal transfer structure 202-2 is shown stacked on top of interfacial thermal transfer structure 202-1, in an offset position. FIG. 2B is a block diagram showing a side view of interfacial thermal transfer structures 202-1, 202-2 integrated to heat sink 204.

In an alternative embodiment, wicking patterns or capillary flow paths can be directly printed on the base of the heat sink itself (or any contacting body) by conventional processes, such as machining, embossing and so on. FIG. 3A is a block diagram showing capillary trenches 302-A printed on a heat sink 304-A. FIG. 3B is a block diagram showing capillary trenches 302-B printed on a heat sink 304-B.

In another embodiment, interfacial thermal transfer structures can be strategically placed for an improvement in thermal transfer in specific areas. For example, FIG. 4 is a block diagram showing an interfacial thermal transfer structure 402 integrated to a heat sink 404.

FIG. 5 is a block diagram showing an embodiment of an interfacial thermal transfer structure 500. The interfacial thermal transfer structure 102 can be used in other ways to enable a pathway for controlled dispersal of high thermal conductivity particles. Using solution synthesis or dip coating methods, conductive particles 502 can be placed on a structure 504, a priori to integration with the heat sink 104. These conductive particles 502 may be attached to surfaces of the structure 504 by Van der Waals forces. During squeeze flow (of polymers), the particles “fall” off the structure 504 to enable localized dispersion of conductive particles 502. After squeeze flow of thermal paste (with lower volume fraction particles, and hence lower viscosity) particles 502 are locally dispersed.

FIGS. 6A-3B are block diagrams showing an example material 600 of an interfacial thermal transfer structure. In one approach for designing porous materials for the interfacial thermal transfer structure 102, the pores of the material 600 of the structure 102 can be geometrically configured to enable negative Poisson's ratio behavior. As understood by one of ordinary skill in the art, Negative Poisson ratio materials swell when stretched and get thinner when compressed. In FIG. 6A, an example negative Poisson ratio material 600 is shown swollen. In FIG. 6B, the material 600 is in a deformed state of negative Poisson ratio material due to tensile forces. This design of pores is anticipated to mitigate coefficient of thermal expansion (CTE) mismatch related thermal stresses. It is noted that the negative Poisson ratio material is expanding laterally when pulled by tensile forces as against contraction (in the lateral dimensions) in a conventional positive Poisson ratio material.

FIG. 7 is a block diagram of a computing device 700 including an interfacial thermal transfer structure. The computing device 700 may be, for example, a laptop computer, desktop computer, tablet computer, mobile device, or server, among others. The computing device 700 may include a central processing unit (CPU) 702 that is configured to execute stored instructions, as well as a memory device 704 that stores instructions that are executable by the CPU 702. The CPU may be coupled to the memory device 704 by a bus 706. Additionally, the CPU 702 can be a single core processor, a multi-core processor, a computing cluster, or any number of other configurations. Furthermore, the computing device 700 may include more than one CPU 702. The instructions that are executed by the CPU 702 may be used to implement shared virtual memory. The memory device 704 can include random access memory (RAM), read only memory (ROM), flash memory, or any other suitable memory systems. For example, the memory device 704 may include dynamic random access memory (DRAM).

The CPU 702 may also be linked through the bus 706 to a display interface 708 configured to connect the computing device 700 to a display device 710. The display device 710 may include a display screen that is a built-in component of the computing device 700. The display device 710 may also include a computer monitor, television, or projector, among others, that is externally connected to the computing device 700.

The computing device also includes a storage device 712. The storage device 712 is a physical memory such as a hard drive, an optical drive, a thumbdrive, an array of drives, or any combinations thereof. The storage device 712 may also include remote storage drives. The storage device 712 includes any number of applications 714 that are configured to run on the computing device 700.

The computing device 700 may also include a network interface controller (NIC) 716 may be configured to connect the computing device 700 through the bus 706 to a network 718. The network 718 may be a wide area network (WAN), local area network (LAN), or the Internet, among others.

According to embodiments described herein, the computing device 700 also includes an interfacial thermal transfer structure 720 and a heat sink 722. The interfacial thermal transfer structure 720

The block diagram of FIG. 7 is not intended to indicate that the computing device 700 is to include all of the components shown in FIG. 7. Further, the computing device 700 may include any number of additional components not shown in FIG. 7, depending on the details of the specific implementation.

All optional features of the computing device described above may also be implemented with respect to either of the methods described herein or a computer-readable medium. Furthermore, although flow diagrams and state diagrams may have been used to describe embodiments, the present techniques are not limited to those diagrams or to the corresponding descriptions herein. For example, flow need not move through each illustrated box or state or in exactly the same order as illustrated and described.

The present techniques are not restricted to the particular details listed herein. Indeed, those skilled in the art having the benefit of this disclosure will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the present techniques. Accordingly, it is the following claims including any amendments thereto that define the scope of the present techniques.

Claims

1. An apparatus that interfaces thermal transfer components, the apparatus comprising a soft, thermally conductive metal that enables a capillary flow path with a contact surface of a thermal transfer component comprising a heat sink, and an imbibing thermal interface material, the thermally conductive metal comprising large pores that intertwine with smaller pores of the contact surface.

2. The apparatus of claim 1, comprising expanded metal grids that facilitate the creation of a dual-porosity wick.

3. The apparatus of claim 2, wherein the dual-porosity wick comprises a woven wire mesh.

4. The apparatus of claim 1, being integrated with a base of the heat sink.

5. The apparatus of claim 1, comprising a thickness ranging between 75 μm and 150 μm.

6. The apparatus of claim 1, the large pores comprising interstitial spaces comprising the imbibing thermal interface material.

7. The apparatus of claim 1, the larger pores ranging in diameter from 1 mm-2 mm.

8. The apparatus of claim 1, the smaller pores ranging in diameter from 20 μm-100 μm.

9. The apparatus of claim 1, the capillary flow enabling a flow of excess imbibing thermal interface material from areas of nearest contact between the apparatus and the heat sink, to areas that benefit from additional imbibing thermal interface material.

10. An apparatus that interfaces thermal transfer components, the apparatus integrated with a base of a heat sink, the apparatus comprising a soft, thermally conductive metal that enables a capillary flow path with a contact surface of a thermal transfer component comprising a heat spreader and an imbibing thermal interface material, the metal thermally conductive metal comprising large pores that intertwine with smaller pores of the contact surface.

11. The apparatus of claim 10, comprising a printed capillary flow path on the contact surface.

12. The apparatus of claim 11, the printed capillary flow path generating expanded metal grids that facilitate the creation of a dual-porosity wick.

13. The apparatus of claim 10, comprising a plurality of thermally conductive mesh.

14. The apparatus of claim 11, comprising a plurality of thermally conductive mesh.

15. The apparatus of claim 11, the plurality of thermally conductive mesh comprising large pores overlaying with respect to large pores of other mesh.

16. The apparatus of claim 11, comprising a plurality of thermally conductive mesh with large pores interspaced with respect to large pores of other mesh.

17. The apparatus of claim 10, large pores comprising interstitial spaces comprising the imbibing thermal interface material.

18. An apparatus that interfaces a heat sink and a heat spreader, the apparatus comprising a soft, thermally conductive metal that enables a capillary flow path with a contact surface of the heat sink, a contact surface of the heat spreader and an imbibing thermal interface material, when the apparatus is in contact with a portion of a surface of both the heat sink and the heat spreader, the thermally conductive metal comprising large pores that intertwine with smaller pores of the contact surface, the large pores comprising interstitial spaces comprising the imbibing thermal interface material.

19. The apparatus of claim 18, comprising a printed capillary flow path on the contact surface.

20. The apparatus of claim 19, the printed capillary flow path generating expanded metal grids that facilitate the creation of a dual-porosity wick.

21. The apparatus of claim 20, comprising a plurality of thermally conductive mesh.

22. The apparatus of claim 21, the plurality of thermally conductive mesh comprising large pores interspaced with respect to large pores of other mesh.