Compliant heat sink

A compliant heat sink for transporting heat away from at least one electronic component, the heat sink includes a body, where the body includes a flexible element thermally contacting at least one electronic component. The heat sink further includes a cavity located in the body, where the cavity is at least partially covered by the flexible element. The heat sink further includes a raised member of the body coupled to the flexible element, where a portion of the raised member partially extends into the cavity. The heat sink further includes a guiding structure of the body coupled in the cavity of the body, wherein the guiding structure is adapted for guiding the movement of the raised member in a moving direction.

FIELD OF THE INVENTION

The present invention relates to cooling of electronic components, and more specifically to cooling of microchips.

BACKGROUND

Electronic devices generate heat during operation. High performance integrated circuits such as computer processors containing nanometer scaled structures are among the electronic devices that are most sensitive to heat. Subject to the available cooling power, these components and devices are operated within certain boundaries of operational parameters such as voltage, clocking frequency, and idle time, which are known as the thermal envelope of the electronic device.

Integrated circuits are commonly manufactured on thin, flat, semiconductor dice mounted in a package. Heat generated in the die is transported through the package into, for example, ambient air or a liquid coolant. In practice, a semiconductor die is not perfectly flat, but has a slightly curved or warped (e.g., convex) surface.

Semiconductor dice are often manufactured with standardized sizes, for example, 20×20 mm. It is expected that dice for future high-end applications such as servers in a data center will be made with larger dimensions than are usual today. Another recent development is the use of packages comprising vertically stacked chips. Both developments increase the vertical amplitude of a non-uniform cooling surface of an electronic device.

SUMMARY

One aspect of an embodiment of the present invention discloses a compliant heat sink for transporting heat away from at least one electronic component, the heat sink comprising, a body, wherein the body includes a flexible element thermally contacting at least one electronic component, a cavity located in the body, wherein the cavity is at least partially covered by the flexible element, a raised member of the body coupled to the flexible element, wherein a portion of the raised member partially extends into the cavity, and a guiding structure of the body coupled in the cavity of the body, wherein the guiding structure is adapted for guiding the movement of the raised member in a moving direction.

DETAILED DESCRIPTION

It is an objective of the present invention to provide for an improved heat sink for transporting heat away from at least one electronic component and a cool-able electronics system as specified in the independent claims. Embodiments of the invention are given in the dependent claims. Embodiments of the present invention can be freely combined with each other if they are not mutually exclusive.

In one aspect, the invention relates to a compliant heat sink for transporting heat away from at least one electronic component. The heat sink comprises a body, a flexible element for thermally contacting the at least one electronic component, and a raised member. The body comprises a cavity, which is covered by the flexible element. The raised member is fixed to the flexible element and extends into the cavity. The body further comprises a guiding structure located in the cavity and adapted for guiding the movement of the raised member in a moving direction.

In a further aspect, the invention relates to a cool-able electronics system, which comprises at least one electronic component and the heat sink according to an embodiment of the invention. The heat sink is mounted on the at least one electronic component, which is thermally coupled to the heat sink by a full-area contact of the at least one electronic component to the flexible element.

The compliant heat sink100according to embodiments of the present invention may provide a strong and stable thermal coupling to sensitive electronic components with uneven, curved, warped or other non-uniform cooling surfaces. Sensitive electronic components require a cooling apparatus or heat sink to prevent overheating. Thermal coupling to a heat sink is often provided for an electronic component with a flat surface by means of a lidded package with a flat, rigid lid and one or more layers of a thermal interface material (TIM) to compensate unevenness on small scales. However, electronic components with a large area cannot be treated as approximately flat devices as they might exhibit unevenness on the scale of the cooling area. A rigid lid might provide thermal coupling to merely part of the cooling area of the component, resulting in inefficient cooling due to long cooling paths for part of the cooling area and unacceptable TIM thicknesses such that the thermal insulation of the TIM compared to the heat sink material outweighs the capability to increase heat conductivity by filling microscopic gaps.

FIG. 1depicts a schematic cut through a compliant heat sink, in accordance with an embodiment of the present invention.

The largest part of heat sink100is formed by heat sink body102, which is shown here with a basically rectangular contour. Cavity112is formed on the side of body102, which is intended to face the electronic component to be cooled. Cavity112is closed with flexible element108, which is fixed to body102along the rim of cavity112. Cavity112is also shown with a basically rectangular structure. Body102in the center of cavity112on a cavity wall, which is facing flexible element108, forms guiding structure106. Raised member110, also with a rectangular cross-section, is fixed to flexible element108in the center of cavity112. Height and width of raised member110are chosen such that it extends sufficiently far into cavity112that guiding structure106receives raised member110and part of the lateral surfaces of raised member110are contacting guiding structure106.

Raised member110and guiding structure106form a heat path from the center of flexible element108to body102. Without raised member110and guiding structure106, heat generated by an electronic component in thermal contact with flexible element108would be transported to body102through the thin flexible element108and possibly also by heat-conducting gas or vapor filled into cavity112. Preferably, flexible element108, raised member110, and guiding structure106are made of materials with a high heat conductivity. Therefore, the additional heat path formed by raised member110and flexible element108in the center of cavity112may strongly increase heat transport away from the center of the electronic component.

All solid parts of compliant heat sink100according to embodiments of the invention are preferably made of materials with a high thermal conductivity. Although materials exist with a higher thermal conductivity, a cost-effective choice for the solid components of heat sink100are metals like aluminum or copper or metal alloys with a high thermal conductivity. More specific material choices for the single path will be discussed in the following.

As used herein, body102of compliant heat sink100according to embodiments of the invention is a piece of a rigid, heat conducting material which is large enough to host cavity112which is capable of covering a cooling area of a single electronic component or a footprint area of an arrangement of more than one electronic components to be cooled. Body102forms the mechanical framework of heat sink100. In the depictions ofFIGS. 1-7, the body consists of a thick plate for spreading and transporting the heat collected from the electronic components to a heat exchanger, and sidewalls of cavity112providing mechanical connectivity to a structure hosting the electronic component (e.g., a substrate or a circuit board).

Being the largest part of heat sink100, it is preferably made of a material which offers a sufficient amount of heat conduction. Body102can be formed from a metal plate, the metal being one of aluminum and copper. Body102may be implemented with any shape which is suitable for the available space for mounting and for connecting it to further cooling equipment downstream of the heat transfer path, including, but not limited to, the basically rectangular cross-section shown inFIGS. 1-7.

In an embodiment, body102is thermally coupled to an air-cooling component for exchanging the heat with ambient air of heat sink100. In another embodiment, body102is thermally coupled to a liquid cooling component for exchanging the heat with a heat transport liquid. Both cooling components may establish a continuous heat flow away from the one or more electronic components to be cooled, enabling it to operate in an allowable temperature range or thermal envelope.

On a side designed for facing the at least one electronic component, body102comprises cavity112. InFIGS. 1-7, cavity112is located at the bottom of body102, which corresponds to an application where the compliant heat sink100is installed above an electronic component that is mounted on a substrate or circuit board with a horizontal orientation. However, it is clear to those of ordinary skill in the art that the electronic component to be cooled may be likewise oriented in a vertical plane or in any other tilted or slanted direction as required by the particular installation. For the purpose of this disclosure, terms like ‘horizontal’, ‘vertical’, ‘above’, ‘below’, ‘next to’, ‘left’, ‘right’ etc. which describe absolute or relative spatial orientations or arrangements refer, unless otherwise noted, to the embodiments depicted inFIGS. 1-7, where heat sink100is oriented to face the at least one electronic component in a horizontal plane.

A main purpose of cavity112is to provide space perpendicular to a cooling surface of the electronic component, i.e., in the vertical direction ofFIG. 1. The horizontal dimensions are chosen to slightly exceed the horizontal dimensions or footprint area of a particular model, class, series, or arrangement of electronic components. Vertically, cavity112dimensions should slightly exceed the largest expectable unevenness of the electronic component such that it provides enough vertical space for establishing a full area contact with the cooling surface of the electronic component without wasting thermal path length.

Cavity112may, for instance, be removed, e.g., by milling or cutting, from the bulk material of body102from bottom upward, such that guiding structure106can be formed as one piece with the rest of body102and cavity112is closed or sealed afterwards with flexible element108, as shown e.g., inFIG. 1. Many other manufacturing processes can be apparently used to create body102with cavity112. In particular, body102can be formed with cavity112in a single manufacturing step. If, for instance, body102is formed in a casting or molding process, designing the model accordingly can provide cavity112.

Alternatively, cavity112and most of the solid parts of heat sink100may be formed by removing material from a precursor of body102upside-down, such that flexible element108and raised member110are formed as one part with body102and guiding structure106is connected with body102to close cavity112as a separate piece afterwards, as shown inFIG. 3. For the purpose of description, cavity boundaries opposing flexible element108will herein be referred to as the ‘ceiling’ of cavity112, whereas the lateral boundaries, as depicted inFIGS. 1-7, will be referred to as the ‘sidewalls’. Cavity112may be open or closed with respect to ambient pressure.

Cavity112may be filled with a gas or vapor to provide additional thermal contact between body102and flexible element108besides the thermal path formed by the fixture of flexible element108to body102and raised member110contacting guiding structure106. According to an embodiment, cavity112is filled with air, nitrogen, methanol vapor, ethanol vapor, or an arbitrary combination thereof. These materials may provide a means to achieve mentioned additional thermal coupling with sufficient heat transport performance. The cavity may be filled with any other gas typically used in vapor chambers.

Moreover, a gas or vapor filling of cavity112may provide a means for reacting to sudden temperature changes of the electronic component to be cooled. This may yield a quicker thermal response of the thermal expansion coefficient mismatched heat path formed by flexible element108and guiding structure106, or alternatively, of an expansion layer500surrounding guiding structure106, as will be explained in further detail below.

According to an embodiment of the invention, the pressure within cavity112exceeds an ambient air pressure of heat sink100. The ambient air pressure may be atmospheric pressure or a pressure level of a pressurizing system, e.g., a cooling system, which is typically used to provide positive air pressure for a computing center. A pressurized cavity112may enable compliant heat sink100to form a full area of thermal contact with electronic components having a concave cooling surface.

Flexible element108, as used herein, is a thin piece of a material with a high thermal conductivity. The dimensions are similar to those of the cavity opening, such that it can be fixed to body102to cover or seal cavity112. Alternatively, flexible element108is a thin, flat section of body102, which has been spared from forming cavity112in an upside-down process. In this case, the horizontal dimensions of flexible element108are identical to those of cavity112. If implemented as a separate piece, flexible element108may be formed from a different material than body102.

Flexible element108acts as a membrane, which is spanned under cavity112. The main purposes are to provide a full area contact with a curved or other non-uniform cooling area of a heat-generating electronic component and to spread this heat across thickness into raised member110and cavity112and to transport the heat along the area towards the bulk of body102. It provides the mechanical compliance, which is needed to collect the heat from all regions of the non-uniform surface with a high coupling efficiency.

According to an embodiment, flexible element108is made of a metal or metal alloy with a high thermal conductivity, such as an alloy based on Mg, Zn, or Al, copper, or alloys based on Si, SiC, or W. The thickness is optimized for responding elastically to the contact with the cooling surface of the electronic component. It should be thick enough that it will not get ruptured when force is applied to install heat sink100on the at least one electronic component, but it should be as thin as possible in order to minimize the force which is needed for installing in order to prevent damage from the electronic component.

In addition to these requirements, flexible element108should also bear the shear stress occurring in the region between the perimeter of the electronic component and the sidewalls of cavity112. In typical and projected application scenarios, large electronic components like microchip dice have curvature amplitudes between 100 μm and 1 mm. Accordingly, suitable membrane thicknesses are expected to be in the range between 300 μm and 1.5 mm.

In order to maximize the thermal coupling efficiency between flexible element108and body102, a firm metal-to-metal fixture should be used to fix flexible element108, if implemented as a separate part, to body102. A soldered, brazed or welded connection appears appropriate for this purpose.

FIG. 2depicts a schematic cut through a compliant heat sink, the flexible element being actuated, in accordance with an embodiment of the present invention.

In this embodiment, compliant heat sink100ofFIG. 1includes flexible element108in an actuated state, i.e., during application of heat sink100to an electronic component (not shown) with a convexly curved cooling surface. The slightly pre-tensioned flexible element108adapts to the curved geometry of the cooling surface and gets bent into the cavity volume. Raised member110fixed to flexible element108at the center of cavity112is pushed upward and further into guiding structure106. The contact surface between raised member110and guiding structure106thus becomes larger, yielding increased heat conductivity of the heat path formed by these two parts.

According to an embodiment, the coefficient of thermal expansion of flexible element108exceeds the coefficient of thermal expansion of body102. During heat up of the at least one electronic component, heat is stored in the large heat capacity of body102. The heat stored in body102causes body102to expand thermally, the thermal expansion being greatest in the largest dimension.

In the embodiments depicted inFIGS. 1-7, thermal expansion of body102is greatest in horizontal directions. As a result, the horizontal dimensions of cavity112increase slightly and the fixture of flexible element108moves away from the center. Hence, heating up heat sink100increases strain of flexible element108, which may eventually lead to destruction. This effect may be compensated if flexible element108has a higher coefficient of thermal expansion than body102. However, care should be taken that the difference in thermal expansion coefficients is not too large as this may cause flexible element108to release from the cooling surface of the electronic component.

As used herein, raised member110is a small piece of metal, which is fixed to the center of flexible element108. The fixture is preferably of the same kind as that used for connecting flexible element108to body102. Alternatively, raised member110and flexible element108are machined from the same part such that no connecting technology is needed. Flexible element108may be selected from the list of materials given for flexible element108. Flexible element108may be formed from a different material than body102, if not implemented as a single part. Preferably, raised member110is made of the same material as flexible element108to prevent thermal expansion of flexible element108relative to raised member110.

Raised member110should match guiding structure106by width and should be tall enough to be received by guiding structure106when the flexible element108is in the maximum deflection from the ceiling of cavity112. Upon actuation or relaxation of flexible element108, raised member110is pushed into or pulled out of guiding structure106in moving direction120perpendicular to the substrate or circuit board to which the at least one electronic component is mounted. InFIGS. 1-7, moving direction120of raised member110is vertical. Raised member110is depicted with a rectangular cross-section inFIGS. 1-7, but it can be implemented with numerous different shapes as will be understood by those of ordinary skill in the art.

According to an embodiment raised member110is any one of a cone, a cylinder, a pin, a fin, a dome, a prism, and combinations thereof. The shape of raised member110may be suitably selected to provide the best possible thermal coupling for the available space and the targeted cooling performance. For instance, a pin or a cylinder may be selected if cavity112has a regular horizontal cross-section (e.g., circular or square), whereas a fin may be more suitable for cavity112with a rectangular horizontal cross-section to gain a larger contact area between raised member110and guiding structure106.

The mentioned shapes may also be advantageously combined with each other. Examples include a cylinder with a dome-shaped tip, which may facilitate insertion or reinsertion of raised member110into guiding structure106during assembly or for changing usage scenarios, or a slightly conical prism, which may provide a robust mechanical and thermal contact to guiding structure106as the pressure applied on heat sink100for mounting is converted to horizontal component forces which press the flat prism surfaces of raised member110and guiding structure106firmly against each other.

According to an embodiment, the coefficient of thermal expansion of raised member110exceeds the coefficient of thermal expansion of guiding wall104. Heat sink100is usually installed on the at least one electronic component in a cold state. When the electronic component heats up, the heat will spread through flexible element108into raised member110, causing raised member110to grow vertically and horizontally. The vertical growth of raised member110may increase the contacting surface with guiding structure106, while horizontal growth may cause raised member110to exert a vertical force on guiding structure106, thus closing microscopic gaps and providing a firmer mechanical and thermal contact to body102.

According to an embodiment, the material of any one of raised member110and flexible element108comprises any one of: Cu and an alloy based on Mg, Zn, Al, Si, SiC, or W. The mentioned materials may ensure a high cooling performance of heat sink100by providing a heat path with a high thermal conductivity.

Guiding structure106, as used herein, is a part located at the ceiling of cavity112, opposing flexible element108and facing raised member110. Guiding structure106provides an opening towards flexible element108, as well as guiding wall104for receiving and contacting raised member110as it moves in moving direction120. One guiding structure106always forms a pair with one raised member110. If only one pair of guiding structure106and raised member110is present, it is preferably horizontally centered with cavity112. Preferably, guiding structure106is permanently receiving raised member110to provide an initial contact length between raised member110and guiding structure106when flexible element108is unstrained or in a deflection away from ceiling of the cavity112.

Guiding wall104may be subdivided into more than one segment. The top of guiding structure106may not necessarily be aligned with the ceiling, but it should offer sufficient vertical space such that raised member110does not touch the top for the largest expectable unevenness of the cooling surface of the at least one electronic component. The horizontal structure of guiding wall104should fit the contour of raised member110. Guiding structure106may be formed as one part with body102, or alternatively, it may be part of a separate piece which is connected to body102after cavity112, raised member110and flexible element108have been formed as one semi-finished product.

Guiding structure106furthermore serves the purpose to spread the heat transported from the at least one electronic component through flexible element108and raised member110into the heat spreading section or plate of body102. The inner surfaces of guiding wall104are preferably smooth as to provide a good thermal coupling on a microscopic scale.

According to an embodiment, guiding wall104of guiding structure106is protruding into cavity112. This may allow for designing body102with a thinner heat spreading section as no additional heat path length is created, as would be the case if guiding structure106were extending beyond the cavity ceiling into body102. InFIGS. 1-3, guiding wall104is shown with two protruding rectangular segments whose width is comparable to the width of raised member110. Providing guiding wall104with a width of at least half the width of raised member110may prevent a bottleneck due to insufficient heat conduction in the central heat path. Preferably, guiding wall104is dimensioned between 100 and 2000 μm. Selecting too small of a width for guiding wall104may diminish the thermal transport capability of guiding structure106.

According to an embodiment, guiding wall104is bendable in bending direction122perpendicular to moving direction120of raised member110. This may allow for guiding wall104to adapt to the thermal expansion of raised member110. Furthermore, bendable guiding wall104can be pressed against raised member110to ensure a robust thermal contact. As described below, the external force necessary to bend guiding wall104against raised member110may be generated by thermal expansion of a secondary material present in cavity112.

Another advantage of bendable guiding wall104may be that sticking of guiding structure106and raised member110may be avoided when heat sink100is removed from the electronic component. The bendability of guiding wall104is preferably of an elastic nature. This may allow for repeated usage of compliant heat sink100with different electronic components, where heat sink100may undergo more than one cycle of installing and uninstalling. Bendability of guiding wall104is dependent on a selection of a width within a specified range. A maximum width of 2000 μm is deemed feasible to prevent usage limitations due to unnecessary rigidity of guiding wall104.

FIGS. 1-3show different scenarios of creating a strong thermal link between raised member110and guiding structure106by means of producing them from materials with mismatched thermal expansion coefficients. InFIGS. 1 and 2, raised member110is made of a material with a higher thermal expansion coefficient than body102. During usage, heat will spread into raised member110, causing it to expand thermally and exert a horizontal force on guiding structure106, thus strengthening the thermal coupling in the central heat path.

FIG. 3depicts a schematic cut through a compliant heat sink, the guiding structure being part of an insert, in accordance with an embodiment of the present invention.

InFIG. 3, however, body102, flexible element108, and raised member110are made, as one piece from the same material and guiding structure106is part of insert300, which is connected to the sidewalls of cavity112. For example, insert300may be soldered or welded with body102, but other connections like a threaded joint are also possible. InFIG. 3, insert300comprising guiding structure106is made of a material with a higher thermal expansion coefficient than body102. As heat spreads through heat sink100during usage, the dimensions of insert300will grow relative to the framework of body102and also raised member110. This may likewise improve the thermal coupling between raised member110and guiding structure106, but care should be taken that the thermal expansion of insert300does not adversely affect structure of the body102. This may, for instance, be achieved by designing body102with horizontal interconnections out of the image plane, which provide a sufficient rigidity against thermal expansion of insert300, or by using a threaded joint with sufficient tolerance for connecting insert300to body102.

In general, raised member110should be manufactured with a width between 10% and 40% of the cavity width. As mentioned before for guiding structure106, a too narrow raised member110might yield insufficient heat transport capability to provide a necessary cooling power, which is expected to range up to 1 kW, while too large a raised member110may deteriorate the elasticity of flexible element108.

FIG. 4depicts a schematic cut through a compliant heat sink with a tapered guiding wall, in accordance with an embodiment of the present invention.

According to an embodiment, the guiding wall104comprises a tapering towards the flexible element108.FIG. 4shows a schematic cut through an exemplary heat sink100, where raised member110is made of a material with a different coefficient of thermal expansion than guiding structure106and guiding wall104comprises a tapering towards flexible element108. The tapering direction towards flexible element108means that the thickness of guiding wall104is smallest at the tip, which is facing flexible element108.

As a consequence, sections of guiding wall104which are in contact with raised member110may be more flexible in bending direction122perpendicular to moving direction120of raised member110, while the rigidity and the thermal coupling of guiding structure106with the bulk of body102increases towards the ceiling of cavity112due to the larger thickness in this region. Tapered guiding wall104may therefore provide an improved adaptability to thermal expansion of raised member110and high heat conductivity towards body102at the same time. If heat sink100is implemented with expansion layer500as described further below, the thin part of guiding wall104may analogously respond more flexibly to thermal expansion of expansion layer500.

According to an embodiment, heat sink100further comprises expansion layer500, where expansion layer500adjoins at least part of guiding wall104and a surface of body102opposite to guiding wall104, and where expansion layer500further has a larger coefficient of thermal expansion than body102.

FIG. 5depicts a schematic cut through a compliant heat sink with an expansion layer being present in the cavity, in accordance with an embodiment of the present invention.

FIG. 5shows the schematic cut ofFIG. 4with the difference that raised member110and flexible element108are made of the same material and that expansion layer500is deposited at the ceiling of cavity112in a manner that it fills the space between tapered guiding wall104and sidewalls of cavity112, while guiding structure106encompassed by guiding wall104is free from the expansion layer material to provide vertical space for guiding movement of raised member110in moving direction120. Due to a larger coefficient of thermal expansion compared to body102, expansion layer500may exert a horizontal force on guiding wall104, pressing it tighter onto raised member110. Expansion layer500receives the heat causing the expansion primarily from body102. A gas or vapor atmosphere in the chamber assist this process, which provides a shorter thermal path between flexible element108and expansion layer500.

Generating external pressure on guiding wall104may reduce the size of microscopic gaps between raised member110and guiding wall104caused by surface unevenness. Hence, expansion layer500may improve a poor initial thermal contact caused by surface roughness of the parts in the central heat path in a cold state of heat sink100. As can be seen inFIGS. 5-7, expansion layer500preferably covers the cavity ceiling with a thickness, which is comparable to the length or height of guiding wall104or the different sections. It is formed from a suitable solid material with a larger coefficient of thermal expansion than body102, including metals and metal alloys, but also non-metallic materials such as epoxy compounds.

According to an embodiment, at least part of guiding wall104is elongated by a groove600, which immediately adjoins guiding wall104and extends into body102. Groove600is understood here as a pit extending along guiding wall104or at least one of the segments.

FIG. 6depicts a schematic cut through a compliant heat sink with a groove adjoining the guiding wall, in accordance with an embodiment of the present invention.

FIGS. 6 and 7show a cut through an exemplary heat sink100,where guiding wall104comprises one section with a tapering towards flexible element108and another thin section with a rectangular cross-section, body102, guiding structure106, flexible element108and raised member110are formed from the same material, expansion layer500is present at the ceiling of cavity112, and the thin section of guiding wall104is prolonged outside of the gap receiving raised member110by groove600immediately adjoining the thin section of guiding wall104and extending into the ceiling. Such gap may increase the bendability of the thin guiding wall section by reducing surface strain when exerted to vertical force generated by expansion layer500.

Dividing guiding wall104into a thin and a tapered part as shown inFIGS. 6 and 7may enable the formation of a tighter thermal-mechanical contact between raised member110and guiding structure106and thus further increase the heat transport performance of heat sink100through the central heat path.

FIG. 7depicts a schematic cut through a compliant heat sink, the expansion layer extending into a slot in the body, in accordance with an embodiment of the present invention.

According to an embodiment, expansion layer500extends into slot700in body102opposite to guiding wall104.FIG. 7shows a cut through a similar heat sink100as that shown inFIG. 6, the difference being that slot700is formed along the ceiling into one of the sidewalls of cavity112and expansion layer500extends into slot700such that it is completely filled by the expansion layer material. Expansion layer500enlarged this way may provide for a sufficiently large thermal expansion of expansion layer500to form a tight thermal-mechanical connection between guiding structure106and raised member110even when the temperature difference between the at least one electronic component to be cooled and a coolant outside of heat sink100(e.g., ambient air or a heat transfer liquid) is small.

As an example, the highest operating temperature is 80° C. for many electronic components and a cooling air temperature is typically 30° C. In this example, an operating state with a low temperature difference would feature an electronic component temperature of, e.g., 50° C. Heat sink100providing a high cooling power also in this state could enable a high-performance operation of the electronic component over a longer time until it reaches temperature maximum. Moreover, a prolonged expansion layer500may provide support for rapid temperature changes of the electronic component because the heat causing thermal expansion of expansion layer500reaches the expansion layer material over a shorter path and through an increased surface area, and therefore high cooling performance may be provided also for electronic components which are frequently subject to strong variations in workload or performance.

According to an embodiment, guiding structure106further comprises a friction lowering coating interfacing guiding structure106and raised member110. According to an embodiment, guiding structure106further comprising a heat conducting coating interfacing guiding structure106and raised member110.

A friction lowering coating may be any liquid, viscous or solid material (e.g., a grease, oil or powder), which is capable of compensating the surface roughness of raised member110and guiding structure106. A heat conducting coating may be any liquid, viscous, or solid material, which is capable of increasing thermal conduction between guiding structure106and raised member110by providing an interface with a high thermal conductivity, compared to dry metal-metal contact.

A friction lowering coating and a heat conducting coating may be different materials used at the same time. For instance, the two coatings may be two immiscible gels or a suspension like thermal grease, which comprises the friction lowering coating and the heat conducting coating. However, a single coating material800may provide the functions of both coatings as well. Such dual-purpose coating material800is preferably selected from the group of carbon or carbon fiber-based materials, two non-exhaustive examples being graphite or carbon nanotubes (CNTs).

Another advantage of using a friction lowering coating may be the capability to facilitate vertical relaxation of flexible element108and raised member110upon relief of heat sink100from the electronic component. For this purpose, a friction lowering coating with a high thermal stability is preferably used.

FIG. 8Adepicts a coating interfacing the guiding structure and the raised member in cold state, in accordance with an embodiment of the present invention.

FIGS. 8A and 8Bshows a detail fromFIGS. 6 and 7, where the surface roughness of guiding structure106and raised member110is visible. The microscopic gap between raised member110and guiding structure106is partially filled with coating material800depicted as a black area. Coating material800extends into the irregularities of the two adjoining surfaces. InFIG. 8A, heat sink100is in a cold state, e.g., after installation of heat sink100on the electronic component, but before the electronic component is switched on.FIG. 8Bdepicts a coating interfacing the guiding structure and the raised member in heated-up state, in accordance with an embodiment of the present invention.

InFIG. 8B, heat sink100is heated up and expansion layer500is extended thermally, pressing guiding wall104against raised member110. It is seen fromFIGS. 8Aand8B that merely parts of the adjoining surfaces form a metal-to-metal contact with a high thermal conductivity. By spreading into the microscopic surface structure of the two interfacing parts, coating800provides a thermal coupling between surface regions, which are not contactable by purely mechanical means. Coating800may therefore increase thermal conductivity of the central heat path by increasing the active heat transfer surface of the mechanical contact between raised member110and guiding structure106. InFIGS. 8A and 8B, coating800is shown as an elastic material which does not significantly spread along the two adjacent surfaces upon actuation of guiding wall104. It is understood however that the coating800may be inelastic and move vertically if the gap between raised member110and guiding structure106is deformed horizontally.

The compliant heat sink100may advantageously be used to cool more than one electronic component in parallel. The two embodiments described in the following are envisioned to provide this capability. According to an embodiment, cavity112, flexible element108, raised member110and guiding structure106form a heat transfer unit which comprises a single one of body102and multiple ones of the heat transfer unit. According to an embodiment, raised member110and guiding structure106form a heat transfer unit which comprises a single one of body102, a single one of cavity112, a single one of the flexible element108, and multiple ones of the heat transfer unit.

Cooling more than one electronic component in parallel may be accomplished by using multiple heat transfer units. In the first case, body102comprises multiple cavities, wherein each cavity112is equipped with a flexible element108, a raised member110, and a guiding structure106and is adapted for providing high performance heat transfer for one of the multiple electronic components. In the other case, only one cavity112covered by a flexible element108is present in body102, but it comprises multiple heat transfer paths, each comprising a raised member110and guiding structure106.

Embodiments under the first case may be more advantageous if the plurality of electronic components spreads over a large footprint area, while embodiments under the second case may be more advantageous if the plurality of electronic components has merely small differences in form factor. Embodiments under both cases may be advantageous if the amount of available space is insufficient to use multiple heat sinks100comprising merely one heat transfer unit in parallel.

The compliant heat sink100may form a cool-able electronic system together with at least one electronic component to be cooled. According to an embodiment of the cool-able electronics system, the at least one electronic component comprises a semiconductor die with a curved surface and the thermal coupling is a thermal coupling of the die to heat sink100.

Advantages of this system shall be demonstrated with the following example. A large-area semiconductor die has a thermal envelope which allows for a maximum operational temperature of 85° C. and exhibits a convex curvature to the heat sink100. Using a package with a flat lid, a sufficiently strong thermal coupling can only be achieved in a central area of the bulge. Heat generated at the boundaries of the semiconductor die spreads towards the heat sink100through a second bond line of thermal interface material and through the semiconductor itself into a central region, where higher cooling power is available. In order to maintain all regions of the die below maximum operational temperature, the ambient air of the system must be maintained at 30° C. to keep the die's essential region at80° C., allowing for a temperature gradient within the die of 5° C.

If the semiconductor die, however, is part of the mentioned cool-able electronic components, the flexible element108may adapt to the convex surface structure of the die, providing a more uniform heat transport for all regions of the die. An ambient air temperature of 35° C. may be used to keep the die temperature at 80° C. throughout, which may beneficially reduce the power requirement for air conditioning. Furthermore, a larger heat tolerance may be created for operating the semiconductor die, which may substantially reduce the risk of overheating.