Thermal interface materials and methods for processing the same   

Abstract: A thermal interface material is provided for use to fill a gap between surfaces in a thermal transfer system to transfer heat between the surfaces. The thermal interface material includes a base material and thermally conductive particles dispersed within the base material. The thermal interface material is conditioned under reduced pressure (e.g., prior to being placed in the gap between the surfaces, while being placed in the gap, after being placed in the gap, etc.) and, within about forty-eight hours or less of conditioning, the conditioned thermal interface material is either positioned in a container that inhibits ambient gas from contacting it (either alone or applied to the surfaces), or used to transfer heat between the surfaces. As such, the thermal interface material is substantially free of cracks following exposure to thermal cycling comprising a temperature change of at least about 100 degrees Celsius for at least about 10 cycles.

The present disclosure generally relates to thermal interface materials conditioned under reduced pressure, for example, reduced atmospheric pressure, etc., and methods for conditioning the thermal interface materials. Such conditioning of the thermal interface materials can be done prior to packaging the thermal interface materials; prior to, while, or after installing the thermal interface materials in thermal transfer systems; prior to or while using the thermal interface materials to transfer heat between thermal transfer surfaces in thermal transfer systems; etc.

This section provides background information related to the present disclosure which is not necessarily prior art.

Electrical components, such as semiconductors, integrated circuit packages, transistors, etc., typically have pre-designed temperatures at which the electrical components optimally operate. Ideally, the pre-designed temperatures approximate the temperature of the surrounding air. But the operation of electrical components generates heat. If the heat is not removed, the electrical components may then operate at temperatures significantly higher than their normal or desirable operating temperatures. Such excessive temperatures may adversely affect the operating characteristics of the electrical components and the operation of the associated devices.

To avoid or at least reduce the adverse operating characteristics from the heat generation, the heat should be removed, for example, by conducting the heat from the operating electrical components to heat sinks. The heat sinks may then be cooled by conventional convection and/or radiation techniques. During conduction, the heat may pass from the operating electrical components to the heat sinks either by direct surface contact between the electrical components and heat sinks and/or by contact of the electrical components and heat sink surfaces through intermediate mediums or thermal interface materials. The thermal interface materials may be used to fill gaps between thermal transfer surfaces, in order to increase thermal transfer efficiency, as compared to having the gaps filled with air, which is a relatively poor thermal conductor.

SUMMARY

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

Disclosed herein are example embodiments of systems and methods relating to processing thermal interface materials for improving reliability, operability, etc. of the thermal interface materials when used with thermal transfer systems (e.g., to transfer heat between thermal transfer surfaces of the systems, etc.) to thereby improve reliability, operability, etc. of the thermal transfer systems during such use, particularly when the thermal transfer systems undergo cyclic changes in temperature during such use. Also disclosed are example embodiments of thermal interface materials that have been processed in accord with the present disclosure, including thermal interface materials that have been conditioned under reduced pressure. In such embodiments, conditioning of the thermal interface materials can be done prior to, while, or after installing the thermal interface materials between thermal transfer surfaces in thermal transfer systems, or even prior to or while using the thermal interface materials to transfer heat between the thermal transfer surfaces in the thermal transfer systems. In some example embodiments, the conditioned thermal interface materials (e.g., separate from thermal transfer systems, installed in the thermal transfer systems, etc.) may be further packaged and/or stored (e.g., alone, in combination with the thermal transfer systems in which they are installed, etc.) under conditions so as to inhibit contact of the conditioned thermal interface materials with ambient gases.

Example embodiments of the present disclosure are generally directed toward thermal interface materials suitable for use to fill gaps between surfaces and/or transfer heat between the surfaces (e.g., in thermal transfer systems, etc.). In one example embodiment, a thermal interface material generally includes a base material and thermally conductive particles dispersed within the base material. At a first time period, the thermal interface material is substantially free of cracks following exposure of the thermal interface material to thermal cycling between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius for at least about 10 cycles during use of the thermal interface material to fill a gap between at least two surfaces. At a second time period, after exposure of the thermal interface material to ambient air for at least about eight hours, the thermal interface material exhibits crack formation following exposure of the thermal interface material to thermal cycling between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius for at least about 10 cycles during use of the thermal interface material to fill a gap between at least two surfaces.

In another example embodiment, a thermal interface material generally includes a base material and thermally conductive particles dispersed within the base material. Here, the thermal interface material is conditioned under reduced pressure and, within about forty-eight hours or less of conditioning the thermal interface material, the conditioned thermal interface material is either positioned in a container that inhibits ambient gas from contacting the conditioned thermal interface material, or the thermal interface material is used to transfer heat between thermal transfer surfaces of a thermal transfer system. In this example embodiment, the thermal interface material can be conditioned prior to, while, or after installing the thermal interface material in the thermal transfer system. Or, the thermal interface material could be conditioned at anytime prior to or while using the thermal interface material to transfer heat between the thermal transfer surfaces of the thermal transfer system.

Example embodiments of the present disclosure also generally relate to methods for processing thermal interface materials to improve operational reliability of the thermal interface materials when used to transfer heat between at least two thermal transfer surfaces. In one example embodiment, a method generally includes conditioning the thermal interface material under reduced pressure such that the thermal interface material is substantially free of cracks following exposure to thermal cycling comprising a temperature change of at least about 100 degrees Celsius for at least about 10 cycles.

Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a flowchart illustrating operations of an example method for processing a thermal interface material in accordance with the present disclosure;

FIG. 2 is a perspective view of an example system operable to help process a thermal interface material in accordance with the present disclosure;

FIG. 3 is a photograph of a sample of a thermally conductive putty initially exposed to ambient laboratory conditions for about 24 hours and then submerged in degassed liquid silicone under reduced pressure in a vacuum chamber, and shown in the vacuum chamber in the degassed liquid silicone at about a time a reduced pressure of about 127 Torr (about 5 inches of mercury absolute (inHg abs)) was achieved in the vacuum chamber;

FIG. 4 is a photograph of a sample of the same thermally conductive putty of FIG. 3 conditioned at a reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes in accordance with the present disclosure and then submerged in degassed liquid silicone under reduced pressure in a vacuum chamber, and shown in the vacuum chamber in the degassed liquid silicone at about a time a reduced pressure of about 127 Torr (about 5 inHg abs) was achieved in the vacuum chamber;

FIG. 5 is a photograph of a sample of the same thermally conductive putty of FIG. 3 conditioned at a reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes in accordance with the present disclosure, then exposed to ambient laboratory conditions for about 12 hours, and then submerged in degassed liquid silicone under reduced pressure in a vacuum chamber, and shown in the vacuum chamber in the degassed liquid silicone at about a time a reduced pressure of about 127 Torr (about 5 inHg abs) was achieved in the vacuum chamber;

FIG. 6 is a photograph of a sample of the same thermally conductive putty of FIG. 3 conditioned at a reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes in accordance with the present disclosure, then stored in a sealed bag under vacuum for about 1 month, and then submerged in degassed liquid silicone under reduced pressure in a vacuum chamber, and shown in the vacuum chamber in the degassed liquid silicone at about a time a reduced pressure of about 127 Torr (about 5 inHg abs) was achieved in the vacuum chamber;

FIG. 7 is a photograph of a sample of a thermally conductive putty conditioned at a reduced pressure of about 381 Torr (about 15 inHg abs) for about 5 minutes in accordance with the present disclosure and then subjected to thermal cycling analysis;

FIG. 8 is a photograph of a sample of the same thermally conductive putty of FIG. 7 not conditioned at a reduced pressure and subjected to the same thermal cycling analysis as the sample shown in FIG. 7;

FIG. 9 is a photograph of a sample of a thermally conductive putty conditioned at a reduced pressure of about 381 Torr (about 15 inHg abs) for about 5 minutes in accordance with the present disclosure and then subjected to thermal cycling analysis;

FIG. 10 is a photograph of a sample of the same thermally conductive putty of FIG. 9 not conditioned at a reduced pressure and subjected to the same thermal cycling analysis as the sample shown in FIG. 9;

FIG. 11 is a photograph of a sample of a thermally conductive putty conditioned at a reduced pressure of about 381 Torr (about 15 inHg abs) for about 5 minutes in accordance with the present disclosure and then subjected to thermal cycling analysis;

FIG. 12 is a photograph of a sample of the same thermally conductive putty of FIG. 11 not conditioned at a reduced pressure and subjected to the same thermal cycling analysis as the sample shown in FIG. 11;

FIG. 13 is a photograph of a sample of a thermally conductive grease conditioned at a reduced pressure of about 381 Torr (about 15 inHg abs) for about 5 minutes in accordance with the present disclosure and then subjected to thermal cycling analysis;

FIG. 14 is a photograph of a sample of the same thermally conductive grease of FIG. 13 not conditioned at a reduced pressure and subjected to the same thermal cycling analysis as the sample shown in FIG. 13;

FIG. 15 is a photograph of a sample of a thermally conductive putty exposed to ambient laboratory conditions for about 24 hours and then subjected to thermal cycling analysis;

FIG. 16 is a photograph of a sample of the same thermally conductive putty of FIG. 15 conditioned at a reduced pressure of about 5 inHg abs for about 15 minutes in accordance with the present disclosure and then subjected to thermal cycling analysis;

FIG. 17 is a photograph of a sample of the same thermally conductive putty of FIG. 15 conditioned at a reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes in accordance with the present disclosure, then exposed to ambient laboratory conditions for about 24 hours, and then subjected to thermal cycling analysis; and

FIG. 18 is a photograph of a sample of the same thermally conductive putty of FIG. 15 conditioned at a reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes in accordance with the present disclosure, then packaged in a sealed container under vacuum for about 1 month, and then subjected to thermal cycling analysis.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

The following description is merely example in nature and is in no way intended to limit the present disclosure, application, or uses.

Thermal interface materials may be used to fill gaps between thermal transfer surfaces in thermal transfer systems (e.g., between surfaces of heat generating components (e.g., electronic devices, hot water devices, etc.) and surfaces of heat removing components (e.g., heat sinks, etc.), etc.) in order to increase thermal transfer efficiency between the surfaces, as compared to having the gaps filled with air which is a relatively poor thermal conductor. The thermal interface materials generally include base materials (e.g., silicone-based base materials, etc.) and thermally conductive particles (e.g., ceramic particles, etc.) dispersed (e.g., provided, located, etc.) within the base materials. Thermally conductive putties, thermally conductive greases, and thermal gap pads are example types of thermal interface materials that can be used to fill such gaps between thermal transfer surfaces.

As recognized by the inventors hereof some thermal interface materials may suffer from reliability issues when subjected to thermal cycling at temperatures above, for example, about 65 degrees Celsius (e.g., when the thermal interface materials are used in connection with heat generating components that are cyclically turned on and off and that cyclically heat to temperatures above about 65 degrees Celsius and then cool, etc.). For example, during use between surfaces cracks may form in the thermal interface materials, and/or the thermal interface materials may pump out of the gaps between the thermal transfer surfaces (leaving voids in the thermal interface materials). This in turn can decrease thermal transfer between the thermal transfer surfaces because the air filling the cracks and/or voids will have a lower thermal conductivity than the thermal interface materials.

As an example, the inventors hereof have recognized that cracks sometimes form in thermal interface materials when used in applications that undergo such cyclic changes in temperature (e.g., when used to fill gaps between thermal transfer surfaces, etc.). Without being bound by theory, the inventors hereof hypothesize that such cracks are caused by movement of gas (e.g., air, etc.) entrained within the thermal interface materials. Temperature changes in the thermal interface materials cause the entrained gas (along with the actual matrices of the thermal interface materials) to expand and contract and thus move within the thermal interface materials. Over time, the gas migrates and collects, and forms weak points within the thermal interface materials at which the cracks (or fissures) form (e.g., due to internal stresses, etc.).

The inventors hereof have unexpectedly discovered that subjecting thermal interface materials to reduced pressure conditioning (e.g., removing entrained gas from the thermal interface materials, reducing an amount of entrained gas in the thermal interface materials, etc.) within a specific time frame before storing, shipping, using, etc. the thermal interface materials can help improve operational reliability (e.g., consistency of thermal transfer between thermal transfer surfaces, etc.) of the thermal interface materials (as compared to the same thermal interface materials not similarly conditioned). Such conditioning can be done, for example, prior to, while, or after installing the thermal interface materials in thermal transfer systems (e.g., prior to, while, or after positioning the thermal interface material in gaps between the thermal transfer surfaces in the thermal transfer systems, etc.), or even prior to or while using the thermal interface materials to transfer heat between thermal transfer surfaces of the thermal transfer systems.

For example, the inventors hereof have found that subjecting thermal interface materials to reduced pressure conditioning (e.g., bulk supplies of the thermal interface materials, etc.) substantially reduces formation of cracks in the thermal interface materials when used to transfer heat between thermal transfer surfaces in applications that undergo cyclic changes in temperature (thus improving operational reliability of the thermal interface materials as previously described). In particular, the inventors hereof have found that using the thermal interface materials (e.g., to transfer heat between the thermal transfer surfaces, etc.) within about 48 hours or less (e.g., within about 24 hours or less, within about 12 hours or less, within about 8 hours or less, etc.) after subjecting the thermal interface materials to reduced pressure conditioning substantially reduces formation of cracks in the thermal interface materials during such use of the thermal interface materials. The inventors hereof have also found that further storing the conditioned thermal interface materials (e.g., alone, already applied to thermal transfer surfaces, etc.) under conditions that inhibit the thermal interface materials from coming into contact with ambient gas (e.g., in sealed containers, under reduced pressure, etc.) after subjecting the thermal interface materials to reduced pressure conditioning, and then later using the stored thermal interface materials (e.g., to transfer heat between thermal transfer surfaces, etc.), also substantially reduces formation of cracks in the thermal interface materials when exposed to cyclic changes in temperature during such use.

In addition, the inventors hereof have found that such benefits associated with subjecting thermal interface materials to reduced pressure conditioning (e.g., reduction in crack formation, improved operational reliability, etc.) are reversible over time, and in fact disappear if the conditioned thermal interface materials are subsequently exposed to ambient gas for a period of time (e.g., for about 8 hours or more, etc.) before being used (e.g., to transfer heat between thermal transfer surfaces, etc.) or being stored as described herein. But the inventors hereof have found that such benefits can be re-achieved by subsequently subjecting the thermal interface materials to reduced pressure conditioning within a specific time frame before the thermal interface materials are used. As such, the inventors hereof have found that operations for reduced pressure conditioning the thermal interface materials can be applied repeatedly to the thermal interface materials to indefinitely maintain such benefits. Such reconditioning can be done, for example, prior to, while, or after installing the thermal interface material in thermal transfer systems, or even while using the thermal interface materials to transfer heat between thermal transfer surfaces of the thermal transfer systems.

Example embodiments of the present disclosure thus relate to thermal interface materials (e.g., bulk supplies of the thermal interface materials, etc.) subjected to reduced pressure conditioning within a specific time frame of being used (e.g., used to transfer heat between thermal transfer surfaces, etc.), as well as to methods for subjecting the thermal interface materials to reduced pressure conditioning and systems for subjecting the thermal interface materials to reduced pressure conditioning (e.g., in preparation for use, etc.). For example, some example embodiments include conditioning thermal interface materials by subjecting the thermal interface materials (e.g., alone, already applied to thermal transfer surfaces, etc.) to reduced pressure and then using the thermal interface materials, for example, to transfer heat between thermal transfer surfaces in thermal transfer systems, etc. Such conditioning can be done, for example, prior to, while, or after installing the thermal interface material in thermal transfer systems (e.g., prior to, while, or after positioning the thermal interface material in gaps between the thermal transfer surfaces, etc.), or even prior to or while using the thermal interface materials to transfer heat between thermal transfer surfaces of the thermal transfer systems. Some example embodiments further include packaging the conditioned thermal interface materials (e.g., alone, already applied to thermal transfer surfaces, etc.) in containers (e.g., sealed containers, etc.) under conditions that inhibit contact of the thermal interface materials with ambient gases, and maintaining the thermal interface materials in the containers under such conditions as desired (e.g., until the thermal interface materials are to be used, during storage of the thermal interface materials, during transport of the thermal interface materials, etc.) to thereby improve operational reliability of the thermal interface materials when unsealed and used by end users.

Example embodiments will now be described more fully with reference to the accompanying drawings.

FIG. 1 illustrates a flowchart of an example method 100 for use in processing a thermal interface material (e.g., a bulk supply of the thermal interface material, etc.) in accordance with the present disclosure. Such processing can help inhibit formation of cracks and/or help improve operational reliability of the thermal interface material, for example, when used to transfer heat between thermal transfer surfaces of components in thermal transfer devices that undergo cyclic changes in temperature. The example method 100 is described in connection with processing a thermal interface material prior to installing the thermal interface material in a thermal transfer system. However, it should be appreciated that the example method 100 is also applicable to processing a thermal interface material while installing it into a thermal transfer system as well as to processing a thermal interface material after it is already installed to a thermal transfer system.

The illustrated method 100 generally includes an operation 102 of conditioning the thermal interface material by subjecting the thermal interface material to reduced pressure, and an operation 104 of inhibiting ambient gas from contacting the conditioned thermal interface material, for example, prior to using the thermal interface material in the thermal transfer system. The method 100 may be applied to any size and/or quantity of thermal interface materials (e.g., bulk quantities of thermal interface materials, etc.).

In the example method 100, the operation 102 of conditioning the thermal interface material generally includes positioning the thermal interface material in a conditioning system (e.g., within a container portion of the conditioning system, etc.) and reducing the pressure around the thermal interface material, for example, to thereby remove entrained gas from the thermal interface material, etc. The conditioning system is configured to hold the thermal interface material in a generally sealed condition. This allows for a desired reduced pressure to be achieved within the conditioning system around the thermal interface material (and then subsequently maintained as desired). The conditioning system can include a vacuum chamber, a hermetically sealable bucket (e.g., a five-gallon bucket, etc.), a sealable bag (e.g., a plastic heat-seal bag, etc.), at least one or more dispensing cartridge, at least one or more sealable tubes, any suitable sealable packaging or container, conditioning system 220 illustrated in FIG. 2, forty-gallon mixers, etc. within the scope of the present disclosure. In other example embodiments, the operation 102 of conditioning the thermal interface material may include at least one or more other suitable operations, for example, for removing entrained gas from the thermal interface material, etc.

As just described, reducing the pressure around the thermal interface material can include removing gas (e.g., air, etc.) from inside the conditioning system around the thermal interface material using suitable operations (e.g., suction operations, vacuum operations, other sealing operations, etc.). This creates a low-pressure environment (e.g., a moderate vacuum, etc.) around the thermal interface material in the conditioning system where a pressure around the thermal interface material is less than ambient pressure outside the conditioning system (e.g., ambient air pressure, etc.). For example, a resulting pressure around the thermal interface material may be between about 1.0% of a perfect vacuum (about 29.5 inches of mercury absolute (inHg abs), about 14.5 pounds per square inch absolute (psia), about 100 kilopascals absolute (kPa abs), or about 750 Torr) and about 99.999% of a perfect vacuum (about 0.0004 inHg abs, about 0.0002 psia, about 0.001 kPa abs, or about 0.01 Torr).

As an example, a port may be installed to the conditioning system and a vacuum may be drawn via the port to directly reduced pressure (e.g., remove gas from, etc.) around the thermal interface material inside the conditioning system. The vacuum may be applied to the thermal interface material for a desired period of time to achieve a desired pressure within the conditioning system (and around the thermal interface material). The resulting pressure (e.g., reduced pressure, vacuum, etc.) may be achieved substantially instantaneously around the thermal interface material following application of the vacuum. As an example, a vacuum of at least about 381 Torr (at least about 15 inHg abs, at least about 7.37 psia, or at least about 50.8 kPa abs) (gauge pressure) may be applied to the thermal interface material positioned in the conditioning system for at least about 5 minutes to achieve the desired reduced pressure.

Alternatively, reducing pressure around the thermal interface material can include reducing a temperature of the gas within the conditioning system around the thermal interface material while holding a volume of the conditioning system around the thermal interface material generally constant, or increasing a volume of the conditioning system around the thermal interface material while holding a temperature of the gas within the conditioning system around the thermal interface material generally constant, etc.

As an example, the conditioning system and the thermal interface material contained therein can be heated and then covered to create a low-pressure environment around the thermal interface material. More particularly, a container portion of the conditioning system and the thermal interface material contained therein can be heated to any desired temperature, and a lid can then be used to close the container portion while still heated, to thereby seal the thermal interface material therein. When the thermal interface material cools, a slight vacuum/gas-tight seal will form between the container portion and the lid. It should be appreciated that only a slight increase in temperature of the container portion and/or the thermal interface material may be required so that subsequently closing the container portion of the conditioning system with the lid and allowing the thermal interface material therein to cool will create the slight vacuum around the thermal interface material. However, the container portion and/or the thermal interface material can be heated to any desired temperature within the scope of the present disclosure (e.g., any temperature greater than an ambient air temperature around the conditioning system and/or the thermal interface material within the conditioning system, and up to a limit of the container portion of the conditioning system (e.g., about 80 degrees Celsius for a plastic container portion, etc.), etc.), depending on a desired level of vacuum to be achieved. Moreover, the container portion and/or the thermal interface material can be heated for any desired time frame (e.g., for about 30 seconds, for about 24 hours, etc.) depending on a desired level of vacuum to be achieved.

The operation 104 (of inhibiting ambient gas from contacting the conditioned thermal interface material) of the illustrated method 100 generally includes maintaining the conditioned thermal interface material in a generally sealed condition. This protects the conditioned thermal interface material from exposure to ambient gas until desired to use the thermal interface material or transfer the thermal interface material to another container (e.g., for packaging, storage, transport, etc.). The thermal interface material may then be retained in the generally sealed condition as desired, for example, until needed for use, for storage, for transport to an end user, etc. When transported to the end user in the generally sealed condition, the end user can unseal the thermal interface material (exposing the thermal interface material to ambient gas) and install the thermal interface material as desired (e.g., within a desired time frame, etc.). As previously described, the inventors hereof have unexpectedly discovered that if the conditioned thermal interface material is installed for use in components in thermal transfer systems (subject to cyclical changes in temperature during operation) within about 48 hours or less after unsealing the thermal interface material, such conditioning of the thermal interface material can help inhibit formation of cracks, voids, etc. in the thermal interface material during such use (thereby improving operational reliability of the thermal interface material).

Maintaining the conditioned thermal interface material in a generally sealed condition can include maintaining the conditioned thermal interface material within the conditioning system (e.g., within the container portion of the conditioning system in which the thermal interface material was conditioned, etc.) following application of the conditioning operation 102. For example, the thermal interface material may be maintained in the conditioning system under the reduced pressure (e.g., under continued vacuum, etc.). Or, the vacuum can be discontinued and any open portions of the conditioning system (e.g., any open portions of the container portion of the conditioning system, etc.) used to remove entrained gas from around the thermal interface material can be sealed using suitable operations to thereby inhibit ambient gas from contacting the conditioned thermal interface material. The thermal interface material may then be retained in the conditioning system (e.g., in the container portion of the conditioning system, etc.) as desired, for example, until needed for use, for storage, for transport to an end user, until desired to transfer the thermal interface material to other containers (e.g., for packaging, etc.), etc.

Alternatively, maintaining the conditioned thermal interface material in a generally sealed condition can include transferring (e.g., for packaging, etc.) the conditioned thermal interface material from the conditioning system to a desired container that can be sealed (e.g., hermetically sealed, hermetically packaged, etc.) to thereby hold the thermal interface material under conditions that inhibit contact of the conditioned thermal interface material with ambient gas. The container may include, for example, a hermetically sealable bucket (e.g., a five-gallon bucket, etc.), a sealable bag (e.g., a plastic heat-seal bag, etc.), at least one or more dispensing cartridges, at least one or more sealable tubes, any suitable sealable packaging or container, etc. within the scope of the present disclosure. The thermal interface material may then be retained in the sealed container as desired, for example, until needed for use, for storage, for transport to an end user, etc. When transported to the end user in the sealed container, the end user can open the sealed container (returning the pressure in the container to ambient pressure) and install the thermal interface material as desired.

As needed and/or desired, at least one or more of the operation 102 of conditioning the thermal interface material and the operation 104 of inhibiting ambient gas from contacting the conditioned thermal interface material can be repeated (at least one or more times) when processing the thermal interface material. For example, if the conditioned thermal interface material is exposed to ambient gas but is not used within about 48 hours or less after such exposure, the operation 102 (and possibly operation 104) may be repeated before the thermal interface material is used to recondition the thermal interface material and thus improve operational reliability as generally disclosed herein.

FIG. 2 illustrates an example system 220 configured to condition thermal interface materials in accord with the present disclosure. For example, the illustrated system 220 may be used in connection with method 100, and at least one or more of operations 102 and 104 thereof. In particular, the system 220 is configured to receive thermal interface materials therein (e.g., alone, already installed to thermal transfer surfaces, etc.), condition the thermal interface materials (e.g., remove entrained gases from the thermal interface materials, etc.), and then maintain the thermal interface materials under reduced pressure as desired.

As shown in FIG. 2, the illustrated system 220 generally includes a container 222, and first and second valve assemblies 224, 226 coupled to the container 222. The container 222 is configured to receive thermal interface materials therein. And, the first and second valve assemblies 224, 226 are configured to control (in conjunction with a vacuum source (not shown)) gas flow into and/or out of the container 222 (e.g., for reducing pressure within the container 222 and removing entrained gas from thermal interface material within the container 222, etc.). For example, valve assembly 224 operates to regulate the air pressure to the system 220. And, valve assembly 226 operates to monitor the air pressure flowing through line 228 to the container 222 (via gauge unit 226a), and to monitor the vacuum level inside the container 222 (via gauge unit 226b).

The container 222 includes a base 230 configured to hold the thermal interface materials therein, and a lid 232 configured to cover the base 230. A gasket (not visible) can be provided between the lid 232 and the base 230 to help substantially seal the thermal interface materials in the container 222 (when the lid 232 is positioned to cover the base 230). The lid 232 can be coupled to the base 230 by suitable operations (e.g., mechanical fasteners, etc.), and may include transparent and/or translucent material so that thermal interface materials in the container 222 can be viewed through the lid 232. The illustrated container 222 includes a generally cylindrical shape, but may include any other suitable shape within the scope of the present disclosure (e.g., cubic, spherical, etc.). In addition, the container 222 may include any desired size (e.g., 5 gallons, etc.) and/or may be formed from any desired material (e.g., a metallic material (e.g., steel, aluminum, combinations thereof, etc.), a plastic material, combinations thereof, etc.) within the scope of the present disclosure.

In operation of the illustrated system 220, thermal interface materials are positioned in the base 230, and the lid 232 is positioned over the base 230 to substantially seal the thermal interface materials in the container 222. The first and second valve assemblies 224, 226 are then operated to draw a vacuum in the container 222 and reduce pressure around the thermal interface materials in the container 222 (e.g., remove entrained gas from the thermal interface materials, etc.). For example, the first and second valve assemblies 224, 226 can be operated to draw a vacuum in the container 222 of at least about 381 Torr (about 15 inHg abs) for at least about 5 minutes to reduce pressure around the thermal interface materials in the container 222. Following application of the vacuum, the conditioned thermal interface materials may remain in the container 222 as desired. Or, the thermal interface materials may be removed from the container 222 for use, for subsequent packaging, etc. as disclosed herein. In other example embodiments, vacuums of less than about 381 Torr (about 15 inHg abs) may be drawn in systems to remove entrained gas from thermal interface materials, and/or vacuums may be drawn for less than about 5 minutes.

In some example embodiments of the present disclosure, thermal interface materials are provided suitable for use to fill gaps between thermal transfer surfaces in thermal transfer systems. Here, the thermal interface materials generally include base materials and thermally conductive particles dispersed within the base materials. The thermal interface materials are conditioned (e.g., prior to, while, or after installing the thermal interface materials in electrical components, etc.) by subjecting them to reduced pressures within about eight hours before being used to fill the gaps between the thermal transfer surfaces in the thermal transfer systems or before being stored under conditions that inhibit ambient gas from contacting the conditioned thermal interface materials. As described herein, this helps improve operational reliability of the thermal interface materials to transfer heat between the thermal transfer surfaces. In some example embodiments, the thermal interface materials are subjected to reduced pressures that are less than ambient air pressure. And in some example embodiments, the thermal interface materials are subjected to reduced pressures that are between about 0.01 Torr and about 750 Torr.

In some example embodiments of the present disclosure, the conditioned thermal interface materials are packaged within desired containers, for example, for storage, transport, etc. (e.g., alone, already installed to thermal transfer surfaces, etc.). The containers may be capable of being hermetically sealed with the thermal interface materials packaged therein under conditions that inhibit ambient gas from contacting the conditioned thermal interface materials. In some example embodiments, the thermal interface materials are shipped, stored, etc. in the hermetically sealed containers. In some example embodiments, the thermal interface materials are maintained under conditions that inhibit ambient gas from contacting the conditioned thermal interface materials until about 48 hours or less before being used (e.g., to transfer heat between thermal transfer surfaces, etc.). And more particularly, the thermal interface materials may be maintained under such conditions until about 24 hours or less before being used, or even more particularly until about 12 hours or less before being used, or still more particularly until about 8 hours or less before being used. In some example embodiments, the thermal interface materials may be removed from the hermetically sealed containers, and then subsequently reconditioned as needed (e.g., if the thermal interface materials are not used within about 48 hours or less of being exposed to ambient gas, etc.).

In some example embodiments, the thermal interface materials of the present disclosure are substantially free of cracks formed during use of the thermal interface materials to fill gaps between thermal transfer surfaces in thermal transfer systems. For example, the thermal interface materials may be substantially free of cracks following exposure of the thermal interface materials to thermal cycling between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius, etc. for at least about 10 cycles or more (e.g., 10 cycles, 20 cycles, 40 cycles, 50 cycles, 1,000 cycles, etc.). Also for example, the thermal interface materials may be substantially free of cracks following exposure of the thermal interface materials to thermal cycling comprising a temperature change of at least about 100 degrees Celsius, etc. for at least about 10 cycles or more (e.g., 10 cycles, 20 cycles, 40 cycles, 50 cycles, 1,000 cycles, etc.)

In some example embodiments, the thermal interface materials of the present disclosure are substantially free of cracks formed during exposure to thermal cycling analysis. In some example embodiments, the thermal interface materials are substantially free of cracks formed during exposure of the thermal interface materials to thermal cycles comprising a temperature change of at least about 100 degrees Celsius. In some example embodiments, the thermal interface materials of the present disclosure are substantially free of cracks formed during exposure of the thermal interface materials to thermal cycles of about −20 degrees Celsius to about 90 degrees Celsius. In some example embodiments, the thermal interface materials are substantially free of cracks formed during exposure of the thermal interface materials to thermal cycles of about −20 degrees Celsius to about 120 degrees Celsius. In some of these example embodiments, the thermal interface materials of the present disclosure are substantially free of cracks formed during exposure of the thermal interface materials to thermal cycles involving at least about 10 cycles or more (e.g., 10 cycles, 20 cycles, 40 cycles, 50 cycles, 1,000 cycles, etc.).

In one example embodiment, thermal interface materials of the present disclosure, at a first time period, are substantially free of cracks formed during exposure of the thermal interface materials to thermal cycling between a temperature of about −20 degrees Celsius and at temperature of about 160 degrees Celsius for at least about 10 cycles during use of the thermal interface material to fill a gap between at least two surfaces. However, at a second time period, after exposure of the thermal interface material (e.g., the same thermal interface material, a sample taken from the same bulk supply of the thermal interface material, etc.) to ambient air for at least about eight hours or more, the thermal interface material exhibits crack formation following exposure to thermal cycling between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius for at least about 10 cycles during use of the thermal interface material to fill a gap between at least two surfaces.

Example thermal interface materials suitable for use in accord with the present disclosure can include a wide range of materials including, but not limited to, thermally conductive putties, thermally conductive greases, thermally conductive gap pads, organic (e.g., polymeric) materials (as compared to an inorganic (e.g., metal solder) materials), cured self supporting or free standing pads or sheets (as contrasted to spreadable pastes or reflowable solders), etc.

The following examples are example in nature. Variations of the following examples are possible without departing from the scope of the disclosure.

In this example, presence of entrained gas was evaluated in four samples of a thermally conductive putty (a silicone thermal gap filler product). The thermally conductive putty had a thermal conductivity of about 3 Watts per meter-Kelvin (W/mK), and a density of about 2.4 grams per cubic centimeter (g/cc).

A first sample included a bulk sphere of the thermally conductive putty exposed to ambient laboratory conditions for about 24 hours. The sample was then submerged in degassed liquid silicone in a clear glass jar, and the jar was placed inside a vacuum chamber (with a clear window for viewing the sample). A progressively increasing vacuum was drawn inside the vacuum chamber, creating an ultimate reduced pressure in the chamber of about 127 Torr (about 5 inHg abs) (generating a gauge reading of about −25 inHg in the chamber). The sample was maintained at this reduced pressure in the chamber for about 1 hour, with the following observations. Gas bubbles began forming on the surface of the sample at a reduced pressure of about 254 Torr (about 10 inHg abs), and increased in quantity up to the ultimate reduced pressure of about 127 Torr (about 5 inHg abs). FIG. 3 shows the first sample (and the gas bubbles emerging therefrom) at about the time the reduced pressure of about 127 Torr (about 5 inHg abs) was achieved in the chamber. Cracks then began forming on the surface of the sample, with gas bubbles emerging from the cracks. After about 15 minutes at the reduced pressure of about 127 Torr (about 5 inHg abs), approximately 50 percent less gas bubbles were emerging from the sample. And, after about 1 hour at the reduced pressure of about 127 Torr (about 5 inHg abs), only a small fraction of the gas bubbles were still emerging from the sample, indicating that a significant percentage of the gas had been removed from the sample.

A second sample included a bulk sphere of the thermally conductive putty subjected to an initial vacuum conditioning operation (in accordance with the present disclosure) at a reduced pressure of about 127 Torr (about 5 inHg abs) (at a gauge reading of about −25 inHg) for about 15 minutes. The vacuum conditioned sample was then submerged (immediately following the vacuum condition operation) in degassed liquid silicone in a clear glass jar, and the jar was placed inside a vacuum chamber (with a clear window for viewing the sample). A vacuum was drawn in the vacuum chamber in substantially the same fashion as for the first sample, creating an ultimate reduced pressure in the chamber of about 127 Torr (about 5 inHg abs). The sample was then maintained at this reduced pressure for about 1 hour. FIG. 4 shows the second sample at about the time the reduced pressure of about 127 Torr (about 5 inHg abs) was achieved in the chamber. As shown in FIG. 4, the second sample demonstrated a drastically reduced amount of bubbling from its surface as compared to the first sample (FIG. 3). Specifically, the quantity of gas bubbles observed in connection with the second sample at about the time the reduced pressure of about 127 Torr (about 5 inHg abs) was achieved in the chamber was about the same as the quantity of gas bubbles observed in connection with the first sample after being exposed to the reduced pressure of about 127 Torr (about 5 inHg abs) for about 1 hour. Thus, the decreased gas bubbles associated with the second sample (in comparison to the first sample) demonstrates that the initial vacuum conditioning operation effectively removed entrained gases from the second sample.

A third sample included a bulk sphere of the thermally conductive putty subjected to an initial vacuum conditioning operation at a reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes. Following this vacuum conditioning operation, the sample sat at ambient laboratory conditions for about 12 hours. The sample was then submerged in degassed liquid silicone in a clear glass jar, and the jar was placed inside a vacuum chamber (with a clear window for viewing the sample). A vacuum was drawn in the vacuum chamber in substantially the same fashion as for the first sample, creating an ultimate reduced pressure in the chamber of about 127 Torr (about 5 inHg abs). The sample was then maintained at this reduced pressure for about 1 hour. FIG. 5 shows the third sample (and the gas bubbles emerging therefrom) at about the time the reduced pressure reached about 127 Torr (about 5 inHg abs) in the chamber. As shown in FIG. 5, large quantities of gas bubbles emerged from the sample in similar fashion to the first sample (FIG. 3), suggesting that removal of entrained gases in the sample by the initial vacuum conditioning operation is reversible if the sample is subsequently exposed to ambient gas as described herein.

A fourth sample included a bulk sphere of the thermally conductive putty subjected to an initial vacuum conditioning operation at a reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes. Following this vacuum conditioning operation, the sample was stored in a sealed bag with gas removed (to help inhibit the sample from coming into contact with ambient gas) for about 1 month. The sample was then submerged in degassed liquid silicone in a clear glass jar, and the jar was placed inside a vacuum chamber (with a clear window for viewing the sample). A vacuum was drawn in the vacuum chamber in substantially the same fashion as for the first sample, creating an ultimate reduced pressure in the chamber of about 127 Torr (about 5 inHg abs). The sample was then maintained at this reduced pressure for about 1 hour. FIG. 6 shows the fourth sample (and the gas bubbles emerging therefrom) at about the time the reduced pressure of about 127 Torr (about 5 inHg abs) was achieved in the chamber. As shown in FIG. 6, the fourth sample demonstrated a drastically reduced amount of bubbling from its surface as compared to the first sample (FIG. 3) and the third sample (FIG. 5), suggesting that no significant quantity of gas was entrained in the sample during the storage period.

In this example, thermal cycling analysis was performed on two samples of a thermally conductive putty (a silicone thermal gap filler product). The thermally conductive putty had a thermal conductivity of about 3 W/mK, and a density of about 1.5 g/cc.

A first sample of the thermally conductive putty was positioned in a container and subjected to a reduced pressure. In particular, gas was removed from the container (and entrained gas was removed from the sample in the container) via application of a vacuum of about 381 Torr (about 15 inHg abs) to the container and thermally conductive putty for about 5 minutes (such that the first sample was vacuum conditioned). A second sample of the thermally conductive putty was not subjected to the reduced pressure (and was thus not vacuum conditioned). Thermal cycling analyses were then immediately performed on the first and second samples. Each sample was placed between a pair of glass plates, so that effects of the thermal cycling analysis could be readily observed. Spacers separated the plates of each pair so that each sample had a substantially constant thickness of between about 40 mils and about 60 mils (between about 1 millimeter and about 1.5 millimeter). And, the plates of each pair were held together with spring clip clamps to help hold the samples at that thickness. Each sample was then placed in a cycling oven programmed to cycle the samples between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius for about 42 cycles (where each cycle had a duration of about 4 hours). FIG. 7 shows the vacuum conditioned first sample following analysis. And, FIG. 8 shows the unconditioned second sample following analysis. As can be seen by comparing FIG. 7 and FIG. 8, the vacuum conditioned first sample (FIG. 7) included substantially no visible cracks following analysis while the unconditioned second sample (FIG. 8) included substantial visible cracks.

In this example, thermal cycling analysis was performed on two samples of a thermally conductive putty (a silicone thermal gap filler product). The thermally conductive putty had a thermal conductivity of about 2 W/mK, and a density of about 3.0 g/cc.

A first sample of the thermally conductive putty was positioned in a container and subjected to a reduced pressure. In particular, gas was removed from the container (and entrained gas was removed from the sample in the container) via application of a vacuum of about 381 Torr (about 15 inHg abs) to the container and sample for about 5 minutes (such that the first sample was vacuum conditioned). A second sample of the thermally conductive putty was not subjected to the reduced pressure (and was thus not vacuum conditioned). Thermal cycling analyses were then immediately performed on the first and second samples. Each sample was placed between a pair of glass plates, so that effects of the thermal cycling analysis could be readily observed. Spacers separated the plates of each pair so that each sample had a substantially constant thickness of between about 40 mils and about 60 mils (between about 1 millimeter and about 1.5 millimeter). And, the plates of each pair were held together with spring clip clamps to help hold the samples at that thickness. Each sample was then placed in a cycling oven programmed to cycle the samples between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius for about 42 cycles (where each cycle had a duration of about 4 hours). FIG. 9 shows the vacuum conditioned first sample following analysis. And, FIG. 10 shows the unconditioned second sample following analysis. As can be seen by comparing FIG. 9 and FIG. 10, the vacuum conditioned first sample (FIG. 9) included substantially no visible cracks following analysis while the unconditioned second sample (FIG. 10) included substantial visible cracks.

In this example, thermal cycling analysis was performed on two samples of a thermally conductive putty (a silicone thermal gap filler product). The thermally conductive putty had a thermal conductivity of about 3 W/mK, and a density of about 2.4 g/cc.

A first sample of the thermally conductive putty was positioned in a container and subjected to a reduced pressure. In particular, gas was removed from the container (and entrained gas was removed from the sample in the container) via application of a vacuum of about 381 Torr (about 15 inHg abs) to the container and sample for about 5 minutes (such that the first sample was vacuum conditioned). A second sample of the thermally conductive putty was not subjected to the reduced pressure (and was thus not vacuum conditioned). Thermal cycling analyses were then immediately performed on the first and second samples. Each sample was placed between a pair of glass plates, so that effects of the thermal cycling analysis could be readily observed. Spacers separated the plates of each pair so that each sample had a substantially constant thickness of between about 40 mils and about 60 mils (between about 1 millimeter and about 1.5 millimeter). And, the plates of each pair were held together with spring clip clamps to help hold the samples at that thickness. Each sample was then placed in a cycling oven programmed to cycle the samples between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius for about 42 cycles (where each cycle had a duration of about 4 hours). FIG. 11 shows the vacuum conditioned first sample following analysis. And, FIG. 12 shows the unconditioned second sample following analysis. As can be seen by comparing FIG. 11 and FIG. 12, the vacuum conditioned first sample (FIG. 11) included substantially no visible cracks following analysis while the unconditioned second sample (FIG. 12) included substantial visible cracks.

In this example, thermal cycling analysis was performed on two samples of a thermally conductive grease (a silicone-based thermal grease having a thermal conductivity of about 3.8 W/mK, a density of about 2.6 g/cc, and suitable for use in high performance computer processing units, etc.). A first sample of the thermally conductive grease was positioned in a container and subjected to a reduced pressure. In particular, gas was removed from the container (and entrained gas was removed from the sample in the container) via application of a vacuum of about 381 Torr (about 15 inHg abs) to the container and sample for about 5 minutes (such that the first sample was vacuum conditioned). A second sample of the thermally conductive grease was not subjected to the reduced pressure (and was thus not vacuum conditioned). Thermal cycling analyses were then immediately performed on the first and second samples. Each sample was placed between a pair of glass plates, so that effects of the thermal cycling analysis could be readily observed. Spacers separated the plates of each pair so that each sample had a substantially constant thickness of between about 40 mils and about 60 mils (between about 1 millimeter and about 1.5 millimeter). And, the plates of each pair were held together with spring clip clamps to help hold the samples at that thickness. Each sample was then placed in a cycling oven programmed to cycle the samples between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius for 42 cycles (where each cycle had a duration of about 4 hours). FIG. 13 shows the vacuum conditioned first sample following analysis. And, FIG. 14 shows the unconditioned second sample following analysis. As can be seen by comparing FIG. 13 and FIG. 14, the vacuum conditioned first sample (FIG. 13) included few visible cracks following analysis while the unconditioned second sample (FIG. 14) included substantial visible cracks.

In this example, thermal cycling analysis was performed on four samples of a thermally conductive putty (a silicone thermal gap filler product). The thermally conductive putty had a thermal conductivity of about 3 W/mK, and a density of about 2.4 g/cc.

Each sample was prepared as follows prior to analysis. A first sample of the thermally conductive putty was exposed to ambient laboratory conditions for about 24 hours. A second sample of the thermally conductive putty was subjected to an initial vacuum conditioning operation at a reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes. A third sample of the thermally conductive putty was subjected to the initial vacuum conditioning operation at the reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes, and was then exposed to ambient laboratory conditions for about 24 hours. And, a fourth sample of the thermally conductive putty was subjected to the initial vacuum conditioning operation at the reduced pressure of about 127 Torr (about 5 inHg abs) for about 15 minutes, and was then packaged in a sealed container under vacuum (to help inhibit the sample from coming into contact with ambient gases) for about 1 month. The initial vacuum conditioning operation included positioning the subject samples in containers and then drawing a vacuum in the containers of about 127 Torr (about 5 inHg abs) for about 15 minutes.

Following the sample preparation, thermal cycling analyses were immediately performed on the four samples. Each sample was placed between a pair of generally square glass plates (having dimensions of about 2.5 inches by about 2.5 inches and a thickness of about 0.25 inches), so that effects of the thermal cycling analysis could be readily observed. Spacers separated the plates of each pair so that each sample had a substantially constant thickness of between about 40 mils and about 60 mils (between about 1 millimeter and about 1.5 millimeter). And, the plates of each pair were held together with spring clip clamps to help hold the samples at that thickness. Each sample was then placed in a cycling oven programmed to cycle the samples between a temperature of about −20 degrees Celsius and a temperature of about 160 degrees Celsius at a rate of about 1.5 degrees Celsius per minute for about 42 cycles (such that each cycle had a duration of about 4 hours, and analysis lasted about 7 days).

FIG. 15 shows the first sample following analysis, FIG. 16 shows the second sample following analysis, FIG. 17 shows the third sample following analysis, and FIG. 18 shows the fourth sample following analysis. As can be seen by comparing FIGS. 15-18, the second and fourth samples (FIG. 16 and FIG. 18, respectively), which were subjected to the initial vacuum conditioning operation within about 24 hours of analysis, exhibited substantially no visible cracks. The first and third samples (FIG. 15 and FIG. 17, respectively), however, which were exposed to ambient laboratory conditions for about 24 hours prior to analysis, exhibited substantial visible cracks. As such, the first sample (FIG. 15) shows the adverse effects of thermal cycling on the thermally conductive putty (when not initially subjected to the vacuum conditioning operation). The second sample (FIG. 16) shows the benefits (e.g., substantially reduced surface cracking, etc.) of the vacuum conditioning operation when applied to the thermally conductive putty. The third sample (FIG. 17) shows that the benefits of the vacuum conditioning operation when applied to the thermally conductive putty can wear off over time, such that subsequent use of the thermally conductive putty in applications involving thermal cycling can result in undesirable crack formation. And, the fourth sample (FIG. 18) shows that the benefits of the vacuum conditioning operation when applied to the thermally conductive putty can be maintained over time by packaging the vacuum conditioned thermally conductive putty in a sealed container under vacuum to protect it from exposure to ambient gas.

Example embodiments of the present disclosure can be used to condition bulk supplies of thermal interface materials. Such bulk supplies can include any desired volume of material.

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, systems, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

In addition, the disclosure of particular values (e.g., pressures, times, dimensions, etc.) herein is not exclusive of other values that may be useful in other example embodiments depending, for example, on particular thermal interface materials being processed, other factors, etc.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature\'s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

The disclosure herein of particular values and particular ranges of values for given parameters are not exclusive of other values and ranges of values that may be useful in one or more of the examples disclosed herein. Moreover, it is envisioned that any two particular values for a specific parameter stated herein may define the endpoints of a range of values that may be suitable for the given parameter. The disclosure of a first value and a second value for a given parameter can be interpreted as disclosing that any value between the first and second values could also be employed for the given parameter. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges.

The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.