Thermal interface material structures including protruding surface features to reduce thermal interface material migration

A process of forming a thermal interface material structure includes forming an assembly that includes a thermal interface material disposed between a first mating surface and a second mating surface. The first mating surface is associated with a module lid, and the second mating surface is associated with a heat sink. Protruding surface features are incorporated onto the first mating surface or the second mating surface. The process also includes compressing the assembly to form a thermal interface material structure. The thermal interface material structure includes the thermal interface material disposed within an interface defined by the first mating surface and the second mating surface. The protruding surface features protrude from the first mating surface or the second mating surface into selected areas of the interface to limit relative movement of the mating surfaces into the selected areas during thermal cycling to reduce thermal interface material migration out of the interface.

BACKGROUND

In an electronic device, a thermal interface material (also referred to as a “TIM”) is a material (e.g., a grease or a putty) that is disposed between a heat generating component of an electronic device (e.g., a die, a memory component, an inductor, etc.) and a heat dissipating component (e.g., a heat spreader or a heat sink) in order to facilitate efficient heat transfer between the heat generating component and the heat dissipating component. The powering up or powering down of the electronic device may cause temperature changes which may cause a relative motion between the heat generating component and the heat dissipating component, including in-plane motion and out-of-plane motion due to coefficient of thermal expansion (CTE) mismatch. This relative motion may cause the thermal interface material to squeeze out of the interface gap. This phenomenon is commonly referred to as “pump-out” of the thermal interface material and results in increased thermal resistance due to loss of material from the interface.

SUMMARY

According to an embodiment, a process of forming a thermal interface material structure is disclosed. The process includes forming an assembly that includes a thermal interface material disposed between a first mating surface and a second mating surface. The first mating surface is associated with a module lid, and the second mating surface is associated with a heat sink. Protruding surface features are incorporated onto the first mating surface or the second mating surface. The process also includes compressing the assembly to form a thermal interface material structure. The thermal interface material structure includes the thermal interface material disposed within an interface defined by the first mating surface and the second mating surface. The protruding surface features protrude away from the first mating surface or the second mating surface into selected areas of the interface to limit relative movement of the first mating surface and the second mating surface into the selected areas during thermal cycling to reduce thermal interface material migration out of the interface.

According to another embodiment, an electronic component cooling assembly is disclosed that includes an electronic component, a module lid, a heat sink, and a thermal interface material. The module lid forms a heat spreader surrounding the electronic component, and the module lid has surface features protruding away from a module lid mating surface. The heat sink has a heat sink mating surface, and the thermal interface material is disposed within an interface between the module lid mating surface and the heat sink mating surface. The surface features protrude away from the module lid mating surface into selected areas of the interface to limit relative movement of the mating surfaces into the selected areas during thermal cycling in order to reduce migration of the thermal interface material out of the interface.

According to another embodiment, an electronic component cooling assembly is disclosed that includes an electronic component, a module lid, a heat sink, and a thermal interface material. The module lid forms a heat spreader surrounding the electronic component, and the module lid has a module lid mating surface. The heat sink has surface features that protrude away from a heat sink mating surface, and the thermal interface material is disposed within an interface between the module lid mating surface and the heat sink mating surface. The surface features protrude away from the heat sink mating surface into selected areas of the interface to limit relative movement of the mating surfaces into the selected areas during thermal cycling of the electronic component in order to reduce migration of the thermal interface material out of the interface.

DETAILED DESCRIPTION

The present disclosure describes thermal interface material (TIM) structures that include protruding surface features to reduce TIM migration (also referred to as “TIM pumping” or “TIM pump-out”). The thermal interface material structures of the present disclosure incorporate surface features onto a particular mating surface, such that the features protrude into selected areas of an interface (including a thermal interface material, such as a thermal grease or putty) separating the particular mating surface from another mating surface. In some cases, the protruding features may be incorporated onto a mating surface of a heat spreader (also referred to herein as a module lid) that surrounds an electronic component (also referred to herein as a lidded module) and distributes heat away from the electronic component. In other cases, the protruding features may be incorporated onto a mating surface of a heat sink that overlies the module lid and is separated from the module lid by the interface (that includes the thermal interface material).

During thermal cycling, a CTE mismatch between the module lid and the heat sink may cause relative motion (in-plane and out-of-plane) between the module lid and the heat sink. By incorporating surface features that protrude from a mating surface into selected areas of the interface, the potential relative movement of the mating surfaces in the selected areas may be limited. Limiting the relative movement may reduce strain on the thermal interface material in areas of the interface proximate to the protruding features. Reducing the strain on the thermal interface material may reduce the potential for TIM pump-out and the associated increase in thermal resistance due to loss of material from the interface.

Referring toFIG. 1, a prior art diagram100illustrates a heat source102(e.g., an integrated circuit or other heat-generating component of an electronic device) that dissipates heat using a heat sink104that is joined to the heat source102by a thermal interface material106, such as a thermal grease or a thermal putty. The top portion ofFIG. 1illustrates that compressing the thermal interface material106between the heat source102and the heat sink104may fill an interface gap between a mating surface of the heat source102and a mating surface of the heat sink104in order to form an interface for efficient removal of heat from the heat source102via the heat sink104.

The heat source102and the heat sink104may correspond to different materials that have different CTE values. The bottom portion ofFIG. 1illustrates that, due to the CTE mismatch between the heat source102and the heat sink104, thermal changes associated with thermal cycling (e.g., powering up or powering down of an electronic device) cause relative movement (in-plane and out-of-plane) of the heat source102and the heat sink104. To illustrate, during thermal cycling, the heat source102may bow upward into a central area of the interface, and the heat sink104may bow downward into the central area of the interface, resulting in a significant reduction of interface thickness between the heat source102and the heat sink104in the central area of the interface. The resulting strain may cause the thermal interface material106to migrate away from the central area of the interface over time, identified as TIM pump-out by the dashed lines ofFIG. 1. Pump-out of the thermal interface material106results in increased thermal resistance due to loss of material from the interface.

By contrast, the thermal interface material structures of the present disclosure incorporate surface features onto a mating surface of a particular heat transfer component of an electronic component cooling assembly that includes two heat transfer components (e.g., a heat spreader and a heat sink) separated by an interface that includes a thermal interface material (e.g., a thermal grease or putty). The heat spreader surrounds an electronic component and distributes heat away from the electronic component. The heat spreader is also referred to herein as a module lid, and the electronic component within the heat spreader is also referred to herein as a lidded module. In some cases, the surface features may be incorporated onto a mating surface of the heat spreader, as further described with respect to the example depictedFIG. 2. In other cases, the surface features may be incorporated onto a mating surface of the heat sink, as further described with respect to the example depictedFIG. 3.

The surface features protrude from the mating surface of the particular heat transfer component into selected areas of the interface. As described further herein, the protruding features may limit the relative movement of the mating surfaces in the selected areas of the interface during thermal cycling due to CTE mismatch. Limiting the relative movement may reduce strain on the thermal interface material in areas of the interface proximate to the protruding features. Reducing the strain on the thermal interface material may reduce the potential for TIM pump-out and the associated increase in thermal resistance due to loss of material from the interface.

Referring toFIG. 2, a diagram200illustrates an electronic component cooling assembly202that includes an example of a first TIM structure210of the present disclosure (identified as “TIM Structure(1)” inFIG. 2), according to one embodiment. The electronic component cooling assembly202is illustrated in a perspective view on the left side ofFIG. 2, and a selected portion of the electronic component cooling assembly202that includes the first TIM structure210is illustrated in a cross-sectional view on the right side ofFIG. 2. The cross-sectional view illustrates that the first TIM structure210includes a thermal interface material212(e.g., a thermal grease or putty) that forms an interface between a heat sink214and a module lid216. The perspective view illustrates that the module lid216corresponds to a heat spreader surrounding an electronic component218that distributes heat generated by the electronic component218during operation. To illustrate, the electronic component218may include a die, a central processing unit (CPU), a graphics processing unit (GPU), or a field programmable gate array (FPGA), among other alternatives. The first TIM structure210ofFIG. 2represents an example in which protruding features220(also referred to herein as “bumps”) are incorporated onto a module lid mating surface222(identified as “Mating Surface(1)” inFIG. 2) in order to reduce or eliminate pump-out of the thermal interface material212by preventing excessive relative movement of the module lid216and the heat sink214during thermal cycling, such as the excessive relative movement depicted in the prior art diagram100ofFIG. 1. Alternatively or additionally, protruding features may be incorporated onto a heat sink mating surface224(identified as “Mating Surface(2)” inFIG. 2), as illustrated and further described herein with respect toFIG. 3.

In the particular embodiment depicted inFIG. 2, the protruding features220are incorporated onto the module lid216and protrude out from the module lid mating surface222into selected areas of the interface between the module lid mating surface222and the heat sink mating surface224. In a particular embodiment, the protruding features220may be incorporated onto the module lid216through a forming process during manufacturing of the module lid216. In another embodiment, channels may be machined, as indicated by residual lines250, or otherwise incorporated into the module lid216, and the channels may be filled with a material that is appropriate for the module lid216in order to form the protruding features220. In some cases, the module lid216may be formed from a module lid material, such as a nickel-based material, a copper-based material, an aluminum-based material, or any combination thereof, among other alternative materials. As an illustrative, non-limiting example, when the module lid216is formed from a nickel-based material, the channels may be filled with a nickel-based material that is the same as the nickel-based material of the module lid216or that is substantially similar to the nickel-based material of the module lid216. Alternatively, with respect to the example in which the module lid216is formed from a nickel-based material, the channels may be filled with other material(s) compatible with the nickel-based material for efficient transfer of heat away from the module lid216into the thermal interface material212.

The bottom portion ofFIG. 2illustrates that the protruding features220may prevent excessive relative movement of the module lid216and the heat sink214during thermal cycling. In the particular embodiment illustrated inFIG. 2, the protruding features220are positioned in a central area of the interface separating the module lid216and the heat sink214. During thermal cycling, the module lid216may bow upward into the central area of the interface, and the heat sink214may bow downward into the central area of the interface. As previously described herein with respect to the prior art diagram100ofFIG. 1, this may result in a significant reduction of interface thickness in the central area. By positioning the protruding features220in the central area of the interface, the potential reduction of interface thickness in the central area is limited by a distance that the protruding features220extend into the interface from the module lid mating surface222.

FIG. 2depicts an illustrative, non-limiting example in which the protruding features220include three protruding features that are distributed substantially uniformly along the module lid mating surface222in the central area of the interface. Further,FIG. 2illustrates an example in which each of the protruding features220has a substantially similar shape (e.g., a bump shape). It will be appreciated that the number of protruding features220, the position/distribution of protruding features220on the module lid mating surface222, the size/shape of each of the protruding features220, or a combination thereof, may vary. As an example, in some cases, the protruding features220may be “strategically” patterned based on characteristics of the individual components of the electronic component cooling assembly202, such as characteristics of the heat sink214and/or characteristics of the module lid216, among other possible factors. As another example, when the module lid216is from a first manufacturer, the module lid216may tend to bow more to one side than a module lid from a second manufacturer. In this case, the protruding features220may be incorporated onto the module lid mating surface222in a particular “strategic” pattern when the module lid216is from the first manufacturer, and the protruding features220may be incorporated onto the module lid mating surface222in a different “strategic” pattern when the module lid216is from the second manufacturer.

Thus,FIG. 2illustrates a first example of a thermal interface material structure of the present disclosure in which protruding features are incorporated onto a module lid mating surface. In the example ofFIG. 2, the features protrude from the module lid mating surface into selected areas of an interface separating the module lid mating surface from a heat sink mating surface (e.g., into a central area of the interface). The protruding features may limit the relative movement of the mating surfaces in the selected areas during thermal cycling due to CTE mismatch. Limiting the relative movement may reduce strain on the thermal interface material in areas of the interface proximate to the protruding features. Reducing the strain on the thermal interface material may reduce the potential for TIM pump-out and the associated increase in thermal resistance due to loss of material from the interface.

Referring toFIG. 3, a diagram300illustrates an electronic component cooling assembly302that includes an example of a second TIM structure310of the present disclosure (identified as “TIM Structure(2)” inFIG. 3), according to one embodiment. The electronic component cooling assembly302is illustrated in a perspective view on the left side ofFIG. 3, and a selected portion of the electronic component cooling assembly302that includes the second TIM structure310is illustrated in a cross-sectional view on the right side ofFIG. 3. The cross-sectional view illustrates that the second TIM structure310includes a thermal interface material312(e.g., a thermal grease or putty) that forms an interface between a heat sink314and a module lid316. The perspective view illustrates that the module lid316corresponds to a heat spreader surrounding an electronic component318that distributes heat generated by the electronic component318during operation. To illustrate, the electronic component318may include a die, a CPU, a GPU, or an FPGA, among other alternatives. The second TIM structure310ofFIG. 3represents an example in which protruding features320(also referred to herein as “bumps”) are incorporated onto a heat sink mating surface324(identified as “Mating Surface(2)” inFIG. 3) in order to reduce or eliminate pump-out of the thermal interface material312by preventing excessive relative movement of the module lid316and the heat sink314during thermal cycling, such as the excessive relative movement depicted in the prior art diagram100ofFIG. 1. Alternatively or additionally, protruding features may be incorporated onto a module lid mating surface322(identified as “Mating Surface(1)” inFIG. 3), as previously described herein with respect to the first TIM structure210ofFIG. 2.

In the particular embodiment depicted inFIG. 3, the protruding features320are incorporated onto the heat sink314and protrude out from the heat sink mating surface324into selected areas of the interface between the heat sink mating surface324and the module lid mating surface322. In a particular embodiment, the protruding features320may be incorporated onto the heat sink314through a forming process during manufacturing of the heat sink314. In another embodiment, channels may be machined or otherwise incorporated into the heat sink314, and the channels may be filled with a material that is appropriate for the heat sink314in order to form the protruding features320. In some cases, the heat sink314may be formed from a heat sink material, such as an aluminum-based material or a copper-based material, among other alternative materials. As an illustrative, non-limiting example, when the heat sink314is formed from an aluminum-based material, the channels may be filled with an aluminum-based material that is the same as the aluminum-based material of the heat sink314or that is substantially similar to the aluminum-based material of the heat sink314. Alternatively, with respect to the example in which the heat sink314is formed from an aluminum-based material, the channels may be filled with other material(s) compatible with the aluminum-based material for efficient transfer of heat to the heat sink314.

The bottom portion ofFIG. 3illustrates that the protruding features320may prevent excessive relative movement of the module lid316and the heat sink314during power or thermal cycling. In the particular embodiment illustrated inFIG. 3, the protruding features320are positioned in a central area of the interface separating the module lid316and the heat sink314. During thermal cycling, the module lid316may bow upward into the central area of the interface, and the heat sink314may bow downward into the central area of the interface. As previously described herein with respect to the prior art diagram100ofFIG. 1, this may result in a significant reduction of interface thickness in the central area. By positioning the protruding features320in the central area of the interface, the potential reduction of interface thickness in the central area is limited by a distance that the protruding features320extend into the interface from the heat sink mating surface324.

FIG. 3depicts an illustrative, non-limiting example in which the protruding features320include three protruding features that are distributed substantially uniformly along the heat sink mating surface324in the central area of the interface. Further,FIG. 3illustrates an example in which each of the protruding features320has a substantially similar shape (e.g., a bump shape). It will be appreciated that the number of protruding features320, the position/distribution of protruding features320on the heat sink mating surface314, the size/shape of each of the protruding features320, or a combination thereof, may vary. As an example, in some cases, the protruding features320may be “strategically” patterned based on characteristics of the individual components of the electronic component cooling assembly302, such as characteristics of the heat sink314and/or characteristics of the module lid316, among other possible factors.

Thus,FIG. 3illustrates a second example of a thermal interface material structure of the present disclosure in which protruding features are incorporated onto a heat sink mating surface. In the example ofFIG. 3, the features protrude from the heat sink mating surface into selected areas of an interface separating the heat sink mating surface from the module lid mating surface from a (e.g., into a central area of the interface). The protruding features may limit the relative movement of the mating surfaces in the selected areas during thermal cycling due to CTE mismatch. Limiting the relative movement may reduce strain on the thermal interface material in areas of the interface proximate to the protruding features. Reducing the strain on the thermal interface material may reduce the potential for TIM pump-out and the associated increase in thermal resistance due to loss of material from the interface.

Referring toFIG. 4, a flow diagram illustrates a particular embodiment of a process400of forming a thermal interface material structure having protruding surface features incorporated onto selected areas of a module lid mating surface to prevent excessive relative movement of mating surfaces during thermal cycling in order to reduce pump-out of thermal interface material. In the particular embodiment depicted inFIG. 4, the process400further includes forming an electronic component cooling assembly that includes the thermal interface material structure. It will be appreciated that the operations shown inFIG. 4are for illustrative purposes only and that the operations may be performed in alternative orders, at alternative times, by a single entity or by multiple entities, or a combination thereof. For example, one entity may incorporate surface features onto selected areas of a module lid, while the same entity or a different entity may utilize the module lid (having the protruding surface features) to form a heat spreader surrounding an electronic component. In some cases, another entity may form an assembly by disposing the thermal interface material (e.g., a thermal grease or putty) on the module lid mating surface (including the protruding surface features) and disposing the heat sink mating surface on the thermal interface material, while the same entity or a different entity may compress the assembly to form the electronic component cooling assembly that includes the thermal interface material structure.

The process400includes incorporating surface features onto selected areas of a first mating surface associated with a module lid, at402. The surface features protrude from the first mating surface. For example, referring to the first TIM structure210depicted inFIG. 2, the module lid216may have the protruding features220incorporated onto the module lid mating surface222. In some cases, the protruding features220may be formed during formation of the module lid216. In other cases, while not shown in the example ofFIG. 2, after formation of the module lid216(having the module lid mating surface222), channels may be machined into the module lid mating surface222, and the channels may be filled with a material that is appropriate for the particular module lid material (e.g., a nickel-based material, in some cases).

In the particular embodiment depicted inFIG. 4, the process400includes utilizing the module lid having the protruding surface features incorporated onto the first mating surface to form a heat spreader surrounding an electronic component, at404. Referring toFIG. 2, after incorporating the protruding features220onto the module lid mating surface222, the module lid216(including the protruding features220) may be used to form a heat spreader surrounding the electronic component218. In other cases, the protruding features220may be formed on the module lid mating surface222after the module lid216has been utilized to form a heat spreader to surround the electronic component218.

The process400also includes forming an assembly that includes a thermal interface material disposed between the module lid mating surface (having the protruding surface features) and a heat sink mating surface, at406. The process further includes compressing the assembly to form an electronic component cooling assembly having a thermal interface material structure that includes the thermal interface material disposed within an interface defined by the module lid mating surface and the heat sink mating surface, at408.

For example, referring toFIG. 2, the electronic component cooling assembly202may be formed by compressing an assembly that includes the thermal interface material212disposed between the module lid mating surface222(having the protruding features220) and the heat sink mating surface224. The right side ofFIG. 2illustrates that, after compression, the electronic component cooling assembly202includes the first TIM structure210in which the thermal interface material212is disposed within an interface defined by the module lid mating surface222and the heat sink mating surface222.

The bottom portion ofFIG. 2illustrates that the protruding features220may prevent excessive relative movement of the module lid216and the heat sink214during thermal cycling. In the particular embodiment illustrated inFIG. 2, the protruding features220are positioned in a central area of the interface separating the module lid216and the heat sink214. During thermal cycling, the module lid216may bow upward into the central area of the interface, and the heat sink214may bow downward into the central area of the interface. As previously described herein with respect to the prior art diagram100ofFIG. 1, this may result in a significant reduction of interface thickness in the central area. By positioning the protruding features220in the central area of the interface, the potential reduction of interface thickness in the central area is limited by a distance that the protruding features220extend into the interface from the module lid mating surface222.

Thus,FIG. 4illustrates an example of a process of forming a thermal interface material structure having protruding surface features incorporated onto selected areas of a module lid mating surface to prevent excessive relative movement of mating surfaces during thermal cycling in order to reduce pump-out of thermal interface material.

Referring toFIG. 5, a flow diagram illustrates a particular embodiment of a process500of forming a thermal interface material structure having protruding surface features incorporated onto selected areas of a heat sink mating surface to prevent excessive relative movement of mating surfaces during thermal cycling in order to reduce pump-out of thermal interface material. In the particular embodiment depicted inFIG. 5, the process500further includes forming an electronic component cooling assembly that includes the thermal interface material structure. It will be appreciated that the operations shown inFIG. 5are for illustrative purposes only and that the operations may be performed in alternative orders, at alternative times, by a single entity or by multiple entities, or a combination thereof. For example, one entity may utilize a module lid to form a heat spreader surrounding an electronic component, while another entity may incorporate surface features onto selected areas of the heat sink mating surface. In some cases, another entity may form an assembly by disposing the thermal interface material (e.g., a thermal grease or putty) on the module lid mating surface and disposing the heat sink mating surface (including the protruding surface features) on the thermal interface material, while the same entity of a different entity may compress the assembly to form the electronic component cooling assembly that includes the thermal interface material structure.

The process500includes disposing a thermal interface material on a mating surface of a module lid, at502. The module lid forms a heat spreader surrounding an electronic component. For example, referring toFIG. 3, the module lid316may form a heat spreader surrounding the electronic component318, and the thermal interface material312may be disposed on the module lid mating surface322.

The process500includes incorporating surface features onto selected areas of a heat sink mating surface, at504. The surface features protrude from the heat sink mating surface. For example, referring to the second TIM structure310depicted inFIG. 2, the heat sink314may have the protruding features320incorporated onto the heat sink mating surface324. In some cases, the protruding features320may be formed during formation of the heat sink314. In other cases, while not shown in the example ofFIG. 3, after formation of the heat sink (having the heat sink mating surface324), channels may be machined into the heat sink mating surface324, and the channels may be filled with a material that is appropriate for the particular heat sink material (e.g., an aluminum-based material, in some cases).

The process500also includes forming an assembly that includes the thermal interface material disposed between the module lid mating surface and the heat sink mating surface (having the protruding surface features), at506. The process further includes compressing the assembly to form an electronic component cooling assembly having a thermal interface material structure that includes the thermal interface material disposed within an interface defined by the module lid mating surface and the heat sink mating surface, at508.

For example, referring toFIG. 3, the electronic component cooling assembly302may be formed by compressing an assembly that includes the thermal interface material312disposed between the module lid mating surface322the heat sink mating surface324(having the protruding features320). The right side ofFIG. 3illustrates that, after compression, the electronic component cooling assembly302includes the second TIM structure310in which the thermal interface material312is disposed within an interface defined by the module lid mating surface322and the heat sink mating surface324.

The bottom portion ofFIG. 3illustrates that the protruding features320may prevent excessive relative movement of the module lid316and the heat sink314during thermal cycling. In the particular embodiment illustrated inFIG. 3, the protruding features320are positioned in a central area of the interface separating the module lid316and the heat sink314. During thermal cycling, the module lid316may bow upward into the central area of the interface, and the heat sink314may bow downward into the central area of the interface. As previously described herein with respect to the prior art diagram100ofFIG. 1, this may result in a significant reduction of interface thickness in the central area. By positioning the protruding features320in the central area of the interface, the potential reduction of interface thickness in the central area is limited by a distance that the protruding features320extend into the interface from the heat sink mating surface324.

Thus,FIG. 5illustrates an example of a process of forming a thermal interface material structure having protruding surface features incorporated onto selected areas of a heat sink mating surface to prevent excessive relative movement of mating surfaces during thermal cycling in order to reduce pump-out of thermal interface material.