The present disclosure relates to heat spreading and, in particular, to a clamped annealed pyrolytic graphite heat spreader
A heat spreader is an assembly that is used to transfer heat, which is generated by an electronic device or module, from the electronic device or module in a first direction and to spread that heat out in second directions. In some cases, the heat spreader includes the module, a cold plate or a heat exchanger, and a heat spreading element interposed between the module and the cold plate. The heat spreading element transfers heat generated by the module toward the cold plate and in doing so spreads the heat out.
In conventional heat spreaders, the heat spreading element was provided by monolithic copper spreaders. These monolithic copper spreaders tend to be heavy. As such, conventional heat spreaders that include monolithic copper spreaders tend to be heavy as well.
According to an aspect of the disclosure, a heat spreader is provided and includes a core of orthotropic material having first and second preferred directions of thermal conduction, a top plate, a bottom plate and pyrolytic graphite sheets (PGSs). The PGSs are interposed in a compressed state as a thermal interface material (TIM) between the core and the top plate and between the core and the bottom plate in a compression direction aligned with at least one of the first and second preferred directions of thermal conduction.
In accordance with additional or alternative embodiments, the orthotropic material includes annealed pyrolytic graphite (APG).
In accordance with additional or alternative embodiments, the first and second preferred directions of thermal conduction are in-plane directions of the core.
In accordance with additional or alternative embodiments, the top and bottom plates are aligned in a through-thickness direction and the core is rotated such that the at least one of the first and second preferred directions of thermal conduction is aligned with the through-thickness direction.
In accordance with additional or alternative embodiments, the PGSs include compressible PGSs that provide, in the compressed state, in-plane thermal conduction and coefficient of thermal expansion (CTE) matching of the core and the top and bottom plates.
In accordance with additional or alternative embodiments, the compressed state of the PGSs is characterized in that the PGSs are compressed to a predefined degree of compression and the heat spreader further includes stoppers configured to halt further compression of the PGSs in the compression direction beyond the predefined degree of compression.
In accordance with additional or alternative embodiments, the stoppers include pedestals extending upwardly from the bottom plate and toward the top plate and the heat spreader further comprises threaded screws that extend through the top plate to threadedly engage with the pedestals to draw the top plate toward the bottom plate until the top plate impinges on the pedestals.
In accordance with additional or alternative embodiments, the threaded screws include countersunk screws and the top plate is formed to define countersunk screw-holes through which the countersunk screws extend.
In accordance with additional or alternative embodiments, the heat spreader further includes additional PGS lining the stoppers.
According to an aspect of the disclosure, a heat spreader is provided and includes a core of orthotropic material having first and second preferred directions of thermal conduction, an encapsulant and pyrolytic graphite sheets (PGSs). The PGSs are interposed in a compressed state as a thermal interface material (TIM) between the core and the encapsulant in at least a compression direction aligned with at least one of the first and second preferred directions of thermal conduction.
In accordance with additional or alternative embodiments, the orthotropic material includes annealed pyrolytic graphite (APG).
In accordance with additional or alternative embodiments, the first and second preferred directions of thermal conduction are in-plane directions of the core.
In accordance with additional or alternative embodiments, the encapsulant has a global through-thickness direction and the core is rotated such that the at least one of the first and second preferred directions of thermal conduction is aligned with the through-thickness direction.
In accordance with additional or alternative embodiments, the PGSs comprise compressible PGSs that provide, in the compressed state, in-plane thermal conduction and coefficient of thermal expansion (CTE) matching of the core and the encapsulant.
In accordance with additional or alternative embodiments, the compressed state of the PGSs is characterized in that the PGSs are compressed to a predefined degree of compression and the heat spreader further includes stoppers configured to halt further compression of the PGSs in the compression direction beyond the predefined degree of compression.
In accordance with additional or alternative embodiments, the stoppers include pedestals extending upwardly from a bottom plate of the encapsulant and toward a top plate of the encapsulant and the heat spreader further includes threaded screws that extend through the top plate to threadedly engage with the pedestals to draw the top plate toward the bottom plate until the top plate impinges on the pedestals.
In accordance with additional or alternative embodiments, the threaded screws include countersunk screws and the top plate is formed to define countersunk screw-holes through which the countersunk screws extend.
In accordance with additional or alternative embodiments, the heat spreader further includes additional PGS lining the stoppers.
According to an aspect of the disclosure, a method of assembling a heat spreader is provided. The method includes providing a core of orthotropic material having first and second preferred directions of thermal conduction, arranging the core between top and bottom plates in a compression direction aligned with at least one of the first and second preferred directions of thermal conduction, interposing pyrolytic graphite sheets (PGSs) between the core and the top plate and between the core and the bottom plate in a compression direction and compressing the PGSs to a compressed state such that the PGSs provide a thermal interface material (TIM) between the core and the top plate and between the core and the bottom plate.
In accordance with additional or alternative embodiments, the PGSs include compressible PGSs that provide, in the compressed state, in-plane thermal conduction and coefficient of thermal expansion (CTE) matching of the core and the top and bottom plates, the compressed state of the PGSs is characterized in that the PGSs are compressed to a predefined degree of compression and the method further includes halting further compression of the PGSs in the compression direction beyond the predefined degree of compression.
Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed technical concept. For a better understanding of the disclosure with the advantages and the features, refer to the description and to the drawings.
For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts:
As will be described below, pyrolytic graphite sheet (PGS) material is used as a thermal interface material (TIM) between a bulk annealed pyrolytic graphite (APG) spreader and encapsulant. This allows for optimized APG preferred directions that balances compression and CTE mismatch while using a bolted joint design. The use of PGS material as a TIM leads to reduced fabrication complexity by avoiding hot isostatic press (HIP) operations or active solder welding processes and allows for expanded use of highly thermally conductive APG in product lines. In the resulting structure, one or more continuous or discontinuous PGSs can be used to join bulk thermal pyrolytic graphite (TPG) in a heat spreader with aluminum top and bottom clamping plates providing encapsulation. The APG orientation is optimized for heat transfer between the source and sink and for spreading in the bulk material with the two preferred directions in the spreader through thickness direction and one in-plane direction. PGS preferred directions are in the spreader in-plane direction, with the design goal of providing some spreading relief in the TPG unpreferred direction. Tight tolerances for wall and pedestal features control PGS compression and the encapsulated APG is sealed from the environment to protect from corrosion.
With reference to
In accordance with embodiments, the rigid PGS 120 can have a density of about 1200-1300 kg/m3 and the compressible PGS 110 can have a spongy quality with a density of about 400-500 kg/m3.
With reference to
As above, in accordance with embodiments, the rigid PGS 232 can have a density of about 1200-1300 kg/m3 and the compressible PGS 231 can have a spongy quality with a density of about 400-500 kg/m3.
The heat spreading element 230 is interposed between the module 210 and the cold plate 220 to provide for a transfer of the heat generated by the electronics 211 from the module 210 to the cold plate 220 in a first direction (i.e., an interleaving direction A with respect to the interleaving direction of the compressible PGS 231 and the rigid PGS 232). The heat spreading element 230 also spreads the heat out in a second direction (i.e., an in-plane direction B of the compressible PGS 231 and the rigid PGS 232) transverse with respect to the first direction. The clamp 240 can include screws 241 that are engageable with at least the cold plate 220 to draw the cold plate 220 toward the module 210. The clamp 240 can alternatively include or be provided with various other configurations that serve to draw the cold plate 220 toward the module 210. In any case, the clamp 240 serves to clamp the heat spreading element 230 between the module 210 and the cold plate 220 and to compress the compressible PGS 231 and the rigid PGS 232 in the first direction or the interleaving direction A (
In accordance with embodiments, the clamp 240 can be used to compress the compressible PGS 231 and the rigid PGS 232 to tune contact resistances between the compressible PGS 231 and the rigid PGS 232. This can optimize thermal performance of the heat spreading element 230 in general and to optimize thermal performance and the in-plane thermal conductivity of the compressible PGS 231 and the rigid PGS 232.
In accordance with further or alternative embodiments, it is to be understood that the compressible PGS 231 and the rigid PGS 232 need not be interleaved with one another in a 1:1 sequence and that other configurations are possible. These include configurations in which only the compressible PGS 231 are provided and/or configurations in which multiple compressible PGS 232 are interleaved with singular rigid PGS 232.
As shown in
With continued reference to
With reference to
In accordance with embodiments, a degree of compression can be about 5-60% of the height H2.
The compressibility of the compressible PGS 231 can provide for coefficient of thermal expansion (CTE) mismatch compliance among at least two or more of the module 210, the monolithic metallic element 250, the rigid PGS 232, and the cold plate 220.
With reference to
Although the transverse section 401 is illustrated in
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With reference to
With reference to
For purposes of clarity and brevity, the following description will relate to the case in which the compression direction is aligned with the first preferred direction of thermal conduction D1.
As shown in
The first PGSs 951 and the second PGSs 952 include or are provided as compressible PGSs that provide, in the compressed state, relatively high rates of in-plane thermal conduction and coefficient of thermal expansion (CTE) matching compliance of the core 910 and each of the top plate 920 and the bottom plate 930. As used herein, the compressed state of the first PGSs 951 and the second PGSs 952 is characterized in that the first PGSs 951 and the second PGSs 952 are compressed to a predefined degree of compression.
With this description, the heat spreader 901 also includes stoppers 960 that are configured to halt further compression of the first PGSs 951 and of the second PGSs 952 in the compression direction (i.e., the first preferred direction of thermal conduction D1 and the through-thickness direction D3) beyond the predefined degree of compression. The stoppers 960 can include or be provided as pedestals 961 that extend upwardly from the bottom plate 930 and toward the top plate 920. The heat spreader 901 further comprises threaded screws 962 that extend through the top plate 920 to threadedly engage with the pedestals 961 to draw the top plate 920 toward the bottom plate 930 until the top plate 920 impinges on the pedestals 961. In accordance with embodiments, the threaded screws 961 can include or be provided as countersunk screws and the top plate 920 is formed to define countersunk screw-holes 962 through which the countersunk screws extend.
During assembly of the heat spreader 901, as shown in
With reference to
As described above, the core 910, the first and second PGSs 951 and 952 and the additional PGS 970 exhibit in-plane thermal conductivity of greater than about 1000 W/m-K or about ˜400-1,500 W/m-K with a density of about 428-1,200 kg/m3. As such, the heat spreader 901 is capable of heat spreading at relatively high rates in the first preferred direction of thermal conduction D1 and the through-thickness direction D3 (owing to the rotation of the core 910 relative to the global frame of reference for the top plate 920 and the bottom plate 930 (and the encapsulant 940). The heat spreader 901 is also capable of heat spreading at the relatively high rates in the second preferred direction of thermal conduction D2 of the core 910 and of the in-plane thermal conduction of the first PGSs 951 and the second PGS 952 as well as the additional PGSs 960.
With reference to
Technical effects and benefits of the present disclosure are the provision of compressible PGSs that can be used as a TIM between an APG core and encapsulant providing a low thermal resistance contact and a compliant connection that limits thermal expansion induced strains.
The corresponding structures, materials, acts, and equivalents of all means or step-plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the technical concepts in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiments were chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
While the preferred embodiments to the disclosure have been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the disclosure first described.