WO2015026704A1 - Mechanically isolated thermal link - Google Patents

Mechanically isolated thermal link Download PDF

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Publication number
WO2015026704A1
WO2015026704A1 PCT/US2014/051443 US2014051443W WO2015026704A1 WO 2015026704 A1 WO2015026704 A1 WO 2015026704A1 US 2014051443 W US2014051443 W US 2014051443W WO 2015026704 A1 WO2015026704 A1 WO 2015026704A1
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WO
WIPO (PCT)
Prior art keywords
thermal
heat sink
substrate
management arrangement
link
Prior art date
Application number
PCT/US2014/051443
Other languages
French (fr)
Inventor
Alexander J. Augoustidis
Gregory P. Kramer
Jonathan A. Taylor
Original Assignee
Graftech International Holdings Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Graftech International Holdings Inc. filed Critical Graftech International Holdings Inc.
Publication of WO2015026704A1 publication Critical patent/WO2015026704A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
    • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/36—Selection of materials, or shaping, to facilitate cooling or heating, e.g. heatsinks
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/34—Arrangements for cooling, heating, ventilating or temperature compensation ; Temperature sensing arrangements
    • H01L23/42—Fillings or auxiliary members in containers or encapsulations selected or arranged to facilitate heating or cooling
    • H01L23/433—Auxiliary members in containers characterised by their shape, e.g. pistons
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L2224/28—Structure, shape, material or disposition of the layer connectors prior to the connecting process
    • H01L2224/29—Structure, shape, material or disposition of the layer connectors prior to the connecting process of an individual layer connector
    • H01L2224/29001—Core members of the layer connector
    • H01L2224/29099—Material
    • H01L2224/2919—Material with a principal constituent of the material being a polymer, e.g. polyester, phenolic based polymer, epoxy
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    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L2224/31—Structure, shape, material or disposition of the layer connectors after the connecting process
    • H01L2224/32—Structure, shape, material or disposition of the layer connectors after the connecting process of an individual layer connector
    • H01L2224/321—Disposition
    • H01L2224/32151—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/32221—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/32225—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being non-metallic, e.g. insulating substrate with or without metallisation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L2224/31—Structure, shape, material or disposition of the layer connectors after the connecting process
    • H01L2224/32—Structure, shape, material or disposition of the layer connectors after the connecting process of an individual layer connector
    • H01L2224/321—Disposition
    • H01L2224/32151—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/32221—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/32245—Disposition the layer connector connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic
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    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L2224/31—Structure, shape, material or disposition of the layer connectors after the connecting process
    • H01L2224/33—Structure, shape, material or disposition of the layer connectors after the connecting process of a plurality of layer connectors
    • H01L2224/331—Disposition
    • H01L2224/3318—Disposition being disposed on at least two different sides of the body, e.g. dual array
    • H01L2224/33181—On opposite sides of the body
    • H—ELECTRICITY
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    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L24/28—Structure, shape, material or disposition of the layer connectors prior to the connecting process
    • H01L24/29—Structure, shape, material or disposition of the layer connectors prior to the connecting process of an individual layer connector
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    • H01L24/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L24/31—Structure, shape, material or disposition of the layer connectors after the connecting process
    • H01L24/32—Structure, shape, material or disposition of the layer connectors after the connecting process of an individual layer connector
    • H—ELECTRICITY
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    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L24/31—Structure, shape, material or disposition of the layer connectors after the connecting process
    • H01L24/33—Structure, shape, material or disposition of the layer connectors after the connecting process of a plurality of layer connectors
    • H—ELECTRICITY
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    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/10—Details of semiconductor or other solid state devices to be connected
    • H01L2924/11—Device type
    • H01L2924/13—Discrete devices, e.g. 3 terminal devices
    • H01L2924/1304—Transistor
    • H01L2924/1305—Bipolar Junction Transistor [BJT]
    • H01L2924/13055—Insulated gate bipolar transistor [IGBT]
    • H—ELECTRICITY
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    • H01L2924/10—Details of semiconductor or other solid state devices to be connected
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    • H01L2924/13—Discrete devices, e.g. 3 terminal devices
    • H01L2924/1304—Transistor
    • H01L2924/1306—Field-effect transistor [FET]
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    • H01L2924/10—Details of semiconductor or other solid state devices to be connected
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    • H01L2924/14—Integrated circuits
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    • H01L2924/1433—Application-specific integrated circuit [ASIC]
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    • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
    • H01L2924/151—Die mounting substrate
    • H01L2924/156—Material
    • H01L2924/15793—Material with a principal constituent of the material being a solid not provided for in groups H01L2924/157 - H01L2924/15791, e.g. allotropes of carbon, fullerene, graphite, carbon-nanotubes, diamond

Definitions

  • the disclosure relates to thermal management for a heat source, and more particularly to a mechanically isolated thermal link between a heat generating electronic component and a heat sink.
  • Thermal management arrangements are disclosed for a device having a heat sink and an electronic component positioned on a substrate.
  • the heat sink is positioned proximate to, but not in contact with the substrate or the electronic component.
  • the thermal management arrangement includes a thermal link including at least one sheet of flexible graphite.
  • the sheet of flexible graphite is in thermal contact with the electronic component and the heat sink.
  • the thermal link is secured to the substrate and to the heat sink.
  • the thermal link includes a portion between the heat sink and the substrate that is curved and longer than required to bridge the gap between the substrate and the heat sink.
  • the thermal link includes a portion between the heat sink and the electronic component that is curved and longer than required to bridge the gap between the electronic component and the heat sink.
  • Figure 1 is a side view of a thermal management arrangement for a first electronic device
  • Figure 2 is a side view of a thermal management arrangement for a second electronic device. Detailed Description
  • Device 10 includes an electronic component 11 which may be, for example, a processor, memory module, application specific integrated circuits (ASIC), graphics processors, light emitting diodes (LED), or field effect transistors (Power FETs, IGBTs, etc.).
  • Electronic component 11 is mounted or secured to a substrate 12.
  • substrate 12 is a circuit board.
  • the substrate is a substantially polymeric material having relatively low thermal conductivity.
  • substrate 12 has a thermal conductivity less than 1 W/mK.
  • substrate 12 has a thermal conductivity less than about 0.5 W/mK.
  • substrate 12 has a thermal conductivity less than about 0.1 W/mK.
  • Substrate 12 may be generally planar and has a first major surface 14 and an opposed second major surface 16. As can be seen from Fig. 1, in one embodiment, electronic component 11 is positioned on the first major surface 14.
  • a thermal via 18 extends from the first major surface 14 to the second major surface 16 and provides a thermal pathway to move heat generated by electronic component 11 from the first major surface 14, where the electronic device is mounted in thermal contact with the thermal via, to the opposed second major surface 16. Accordingly, thermal via 18 advantageously has a relatively higher thermal conductivity than substrate 12.
  • Thermal via 18 advantageously has a thermal conductivity at least 20 W/mK, more advantageously at least 50 W/mK, still more advantageously at least 150 W/mK.
  • Exemplary materials for thermal via 18 may include copper, aluminum and alloys thereof. In other embodiments, thermal via 18 may a graphite material.
  • a heat sink 20 is located in proximity to, but not in physical contact with substrate 12 thereby forming a gap between the substrate and the heat sink.
  • heat sink 20 may be a thermally conductive housing or exterior facing element.
  • heat sink 20 is a thermally conductive internal structural support.
  • the heat sink 20 may be a dedicated heat sink.
  • the heat sink 20 may be a thermally conductive housing or frame for a display panel.
  • heat sink 20 may be a thermally conductive intermediate mounting plate.
  • Heat sink 20 is advantageously made of a metal such as, for example, aluminum, copper, steel, magnesium or alloys thereof. It should be appreciated, however, that heat sink 20 may be any thermally conductive material having sufficiently low thermal resistance to absorb and thereby dissipate heat generated by electronic device 10.
  • thermal link 30 is positioned at second major surface 16 and in thermal contact with electric or electronic component 11.
  • thermal contact may advantageously mean direct physical contact or may mean contact through an intermediate element that allows heat to flow through such as, for example, a thermal interface material, thermal grease, thermally conductive adhesive, or the like.
  • thermal contact is enabled by via 18.
  • the via 18 can be in direct physical contact with the electronic component 11 or in contact with the electronic component through an intermediate element, such as for example a thermal interface material, thermal grease, a thermally conductive adhesive, or the like.
  • the via 18 can be in direct physical contact with the thermal link 30 or in contact with the thermal link through an intermediate element, such as for example a thermal interface material, thermal grease, thermally conductive adhesive, or the like.
  • Thermal link 30 can be secured to the substrate 12.
  • thermal link 30 may advantageously be secured to the substrate 12 mechanically.
  • a mounting plate 32 secures thermal link 30 against via 18.
  • Mounting plate 32 may include anchors 34 that extend through thermal link 30 and into or through substrate 12 at opposite ends of the electronic component to secure thermal link 30 against substrate 12.
  • thermal link 30 may be adhesively secured to substrate 12 and via 18.
  • thermal link 30 may be mechanically secured and adhesively secured to substrate 12.
  • thermal link 30 may be mechanically secured and adhesively secured to substrate 12 and adhesively secured to via 18.
  • Thermal link 30 is also positioned in thermal contact with heat sink 20.
  • Thermal link 30 may advantageously be secured to the heat sink 20 mechanically.
  • mounting plate 32 secures thermal link 30 against heat sink 20.
  • Anchors 34 that extend through thermal link 30 and into or through heat sink 20 can be used to secure thermal link 30 against heat sink 20.
  • thermal link 30 can be secured to heat sink 20 by adhesively attaching it to the heat sink.
  • the thermal link 30 may be in thermal contact with heat sink 20 at more than one location.
  • Thermal link 30 is generally sheet- like and may extend laterally away from via 18 in, for example, at least two directions. In such a case, thermal link 30 may be secured to heat sink at spaced apart first and second locations 36 and 38, such as for example a first end and at a second end.
  • thermal link 30 is advantageously relatively flexible and non-structural to reduce the transmission of mechanical energy from the heat sink to the substrate or from the substrate to the heat sink.
  • Thermal link 30 further advantageously is secured so that the portion 40 of thermal link 30 spanning between substrate 12 and heat sink 20 is curved, forming a slackened portion that is longer than required to bridge the gap between substrate 12 and heat sink 20.
  • the thermal link 30 can be secured to the substrate 12 between the space apart first and second locations 36, 38 and spaced apart from the heat sink between these first and second locations so as to provide mechanical isolation.
  • the curved spanning portion 40 reduces the amount of mechanical energy, such as vibration, that is translated between substrate 12 and heat sink 20.
  • the portion 40 forms a flared or outwardly extending portion (as shown in Fig. 1).
  • the portion 40 may be in the form of a corrugated cross-section or serpentine cross-section.
  • the portion 40 of thermal link 30 can be disposed between a location at which the thermal link is in thermal contact with the heat sink 20 and a location at which the thermal link is in thermal contact with the electronic component, such as for example at the via 18. In this one example or another example, the portion 40 of thermal link 30 can be disposed between a location at which the thermal link is in thermal contact with the heat sink 20 and a location at which the thermal link is secured to the substrate 12.
  • FIG. 2 another embodiment of the device is shown generally at 100 with components similar to the components in Fig. 1 having similar reference numbers.
  • the device 100 includes an electronic component positioned on the second major surface 16 of the substrate 12.
  • the heat sink 20 is located in proximity to the substrate 12 and spaced apart from both the substrate and the electronic component 11 thereby forming a gap between the electronic component and the heat sink.
  • the thermal link 30 is positioned at second major surface 16 and in thermal contact with electric or electronic component 11 without using via 18.
  • the electronic device is disposed between the thermal link 30 and the substrate 12.
  • Thermal link 30 can be secured to the substrate 12.
  • thermal link 30 may advantageously be secured to the substrate 12 mechanically.
  • a mounting plate 32 secures thermal link 30 against electronic component 11.
  • Mounting plate 32 may include anchors 34 that extend through thermal link 30 and into or through substrate 12 at opposite ends of the electronic component 11 to secure thermal link 30 against electronic component 12.
  • thermal link 30 may also be adhesively secured to electronic component 11.
  • Thermal link 30 is also positioned in thermal contact with heat sink 20 and secured thereto in a similar manner as described above.
  • the thermal link 30 can be secured to the substrate 12 such that it is in contact with the electronic component 11 between the space apart first and second locations 36, 38 and spaced apart from the heat sink between the first and second locations so as to provide mechanical isolation.
  • Thermal link 30 is secured so that the portion 40 of thermal link 30 spanning between electronic component 11 and heat sink 20 is curved, forming a slackened portion that is longer than required to bridge the gap between electronic component 11 and heat sink 20.
  • the curved spanning portion 40 reduces the amount of mechanical energy, such as vibration, that is translated between substrate 12 and heat sink 20 or between substrate and electronic component 11.
  • the portion 40 forms a flared or outwardly extending portion (as shown in Fig. 2).
  • the portion 40 may be in the form of a corrugated cross-section or serpentine cross-section.
  • the thermal link 30 is formed of one or more sheets of flexible graphite.
  • flexible graphite may include compressed particles of exfoliated graphite.
  • the flexible graphite includes one or more layers of pyrolytic graphite with one or more support layers.
  • the flexible graphite may be formed of both pyrolytic graphite and one or more sheets of compressed particles of exfoliated graphite.
  • pyrolytic graphite is meant a graphitized graphitizable polymer, for instance, in U.S. Patent No. 5,091,025, the disclosure of which is incorporated herein by reference in its entirety.
  • the thermal link 30 may further include protective coatings on one or more sides.
  • Coatings may include a polymer or metal coating and may be, for example, PET films, acrylic films, and aluminum foil.
  • the flexible graphite may have a thickness of from between about 0.010 mm to 3.75 mm and a typical density of about 1.0 to 2.0 g/cc or higher.
  • the flexible graphite sheets have a thickness between about 0.025 mm to about 0.500 mm.
  • flexible graphite sheets have a thickness between about 0.050 mm to about 0.250 mm.
  • the flexible graphite sheet can have a density from between about 1.0 g/cc to about 2.0 g/cc.
  • the flexible graphite sheet can have a density from between about 1.2 g/cc and about 1.8 g/cc.
  • the flexible graphite can have a density of at least about 0.6 g/cc, more preferably at least about 1.1 g/cc. In another example, the flexible graphite can have a density of at least about 1.6 g/cc. The upper limit to the density of the graphite sheet is about 2.0 g/cc.
  • One graphite sheet suitable for use in the thermal bridge in the present disclosure is commercially available as eGRAF ® material, from GrafTech International Holdings Inc. of Parma, Ohio.
  • a plurality of graphite sheets may be laminated into a unitary article for use in the thermal link disclosed herein.
  • the sheets of compressed particles of exfoliated graphite may be laminated with a suitable adhesive, such as pressure sensitive or thermally activated adhesive, therebetween.
  • a suitable adhesive such as pressure sensitive or thermally activated adhesive
  • the adhesive chosen should balance bonding strength with minimizing thickness, and be capable of maintaining adequate bonding at the service temperature at which heat transfer is sought.
  • Suitable adhesives would be known to the skilled artisan, and include acrylic and phenolic resins.
  • the flexible graphite sheet(s) have an in-plane thermal conductivity of at least
  • the graphite sheet exhibits an in-plane thermal conductivity of at least 300 W/m*K. In still other embodiments the graphite sheet exhibits an in-plane thermal conductivity of at least 400 W/m*K. In still other embodiments the graphite sheet exhibits an in-plane thermal conductivity of at least 600 W/m*K. In still other embodiments the graphite sheet exhibits an in-plane thermal conductivity of at least 700 W/m*K. In still other embodiments, the graphite sheet exhibits an in-plane thermal conductivity of at least 1500 W/m*K. In one embodiment, the graphite sheet material may be from 10 to 1500 microns thick.
  • the flexible graphite sheet(s) may advantageously have a minimum bend radius of less than about 20.0 mm, more advantageously less than 10.0 mm and still more advantageously less than 6.0 mm.
  • the minimum bend radius may be from between about 1.0 mm to about 20.0 mm.
  • the flexible graphite sheets advantageously have a thickness between about 0.025 mm to about 0.500 mm, and more advantageously from between about .050 mm to about .250 mm.
  • the flexible graphite sheet advantageously has a density from between about 1.0 g/cc to about 2.0 g/cc and still more advantageously from between about 1.2 g/cc and about 1.8 g/cc.

Abstract

A thermal management arrangement for a device that includes a heat sink and an electronic component positioned on a substrate. The heat sink is positioned proximate to, but not in contact with the substrate and the thermal management arrangement includes a thermal link made of at least one sheet of flexible graphite. The sheet of flexible graphite is being in thermal contact with the electronic component and said heat sink. The thermal link includes a curved portion spanning a gap between the heat sink and the substrate or electronic component which is longer than required to bridge the gap to provide a slackened portion which reduces the transmission of mechanical energy between the heat sink and the substrate.

Description

Title
MECHANICALLY ISOLATED THERMAL LINK
Technical Field
[0001] The disclosure relates to thermal management for a heat source, and more particularly to a mechanically isolated thermal link between a heat generating electronic component and a heat sink.
Background
[0002] As electronic devices become more powerful and more ubiquitous, new challenges are presented, in particular when electronic devices are employed in difficult and hostile environments. A principle design concern in many electronic devices is the removal of excess heat to ensure proper performance and prevent damage to the components. This goal is made more difficult when the electronic device requires protection from other failure vectors such as, for example, vibration or electrical interference.
[0003] There is therefore a need in the art for a thermal management system capable of removing heat in difficult and hostile conditions.
Brief Description
[0004] Thermal management arrangements are disclosed for a device having a heat sink and an electronic component positioned on a substrate. The heat sink is positioned proximate to, but not in contact with the substrate or the electronic component. The thermal management arrangement includes a thermal link including at least one sheet of flexible graphite. The sheet of flexible graphite is in thermal contact with the electronic component and the heat sink. The thermal link is secured to the substrate and to the heat sink. In one example, the thermal link includes a portion between the heat sink and the substrate that is curved and longer than required to bridge the gap between the substrate and the heat sink. In another example, the thermal link includes a portion between the heat sink and the electronic component that is curved and longer than required to bridge the gap between the electronic component and the heat sink. Description of Drawings
[0005] Figure 1 is a side view of a thermal management arrangement for a first electronic device; and
[0006] Figure 2 is a side view of a thermal management arrangement for a second electronic device. Detailed Description
[0007] With reference to Fig. 1, a device is shown and generally indicated by the numeral 10. Device 10 includes an electronic component 11 which may be, for example, a processor, memory module, application specific integrated circuits (ASIC), graphics processors, light emitting diodes (LED), or field effect transistors (Power FETs, IGBTs, etc.). Electronic component 11 is mounted or secured to a substrate 12. In one embodiment, substrate 12 is a circuit board. In this or other embodiments, the substrate is a substantially polymeric material having relatively low thermal conductivity. In one embodiment, substrate 12 has a thermal conductivity less than 1 W/mK. In still further embodiments, substrate 12 has a thermal conductivity less than about 0.5 W/mK. In still further embodiments, substrate 12 has a thermal conductivity less than about 0.1 W/mK.
[0008] Substrate 12 may be generally planar and has a first major surface 14 and an opposed second major surface 16. As can be seen from Fig. 1, in one embodiment, electronic component 11 is positioned on the first major surface 14. A thermal via 18 extends from the first major surface 14 to the second major surface 16 and provides a thermal pathway to move heat generated by electronic component 11 from the first major surface 14, where the electronic device is mounted in thermal contact with the thermal via, to the opposed second major surface 16. Accordingly, thermal via 18 advantageously has a relatively higher thermal conductivity than substrate 12. Thermal via 18 advantageously has a thermal conductivity at least 20 W/mK, more advantageously at least 50 W/mK, still more advantageously at least 150 W/mK. Exemplary materials for thermal via 18 may include copper, aluminum and alloys thereof. In other embodiments, thermal via 18 may a graphite material.
[0009] A heat sink 20 is located in proximity to, but not in physical contact with substrate 12 thereby forming a gap between the substrate and the heat sink. In one embodiment, heat sink 20 may be a thermally conductive housing or exterior facing element. In other embodiments, heat sink 20 is a thermally conductive internal structural support. In still further embodiments, the heat sink 20 may be a dedicated heat sink. In still further embodiments, the heat sink 20 may be a thermally conductive housing or frame for a display panel. In still further embodiments heat sink 20 may be a thermally conductive intermediate mounting plate. Heat sink 20 is advantageously made of a metal such as, for example, aluminum, copper, steel, magnesium or alloys thereof. It should be appreciated, however, that heat sink 20 may be any thermally conductive material having sufficiently low thermal resistance to absorb and thereby dissipate heat generated by electronic device 10.
[0010] A thermal link 30 is positioned at second major surface 16 and in thermal contact with electric or electronic component 11. For purposes of this disclosure, thermal contact may advantageously mean direct physical contact or may mean contact through an intermediate element that allows heat to flow through such as, for example, a thermal interface material, thermal grease, thermally conductive adhesive, or the like.
[0011] In at least one embodiment, thermal contact is enabled by via 18. The via 18 can be in direct physical contact with the electronic component 11 or in contact with the electronic component through an intermediate element, such as for example a thermal interface material, thermal grease, a thermally conductive adhesive, or the like. The via 18 can be in direct physical contact with the thermal link 30 or in contact with the thermal link through an intermediate element, such as for example a thermal interface material, thermal grease, thermally conductive adhesive, or the like.
[0012] Thermal link 30 can be secured to the substrate 12. In one or more examples, thermal link 30 may advantageously be secured to the substrate 12 mechanically. In one embodiment a mounting plate 32 secures thermal link 30 against via 18. Mounting plate 32 may include anchors 34 that extend through thermal link 30 and into or through substrate 12 at opposite ends of the electronic component to secure thermal link 30 against substrate 12. In other embodiments, thermal link 30 may be adhesively secured to substrate 12 and via 18. In other embodiments, thermal link 30 may be mechanically secured and adhesively secured to substrate 12. In other embodiments, thermal link 30 may be mechanically secured and adhesively secured to substrate 12 and adhesively secured to via 18.
[0013] Thermal link 30 is also positioned in thermal contact with heat sink 20.
Thermal link 30 may advantageously be secured to the heat sink 20 mechanically. In one embodiment mounting plate 32 secures thermal link 30 against heat sink 20. Anchors 34 that extend through thermal link 30 and into or through heat sink 20 can be used to secure thermal link 30 against heat sink 20. In other embodiments, thermal link 30 can be secured to heat sink 20 by adhesively attaching it to the heat sink. In this or other embodiments, the thermal link 30 may be in thermal contact with heat sink 20 at more than one location. Thermal link 30 is generally sheet- like and may extend laterally away from via 18 in, for example, at least two directions. In such a case, thermal link 30 may be secured to heat sink at spaced apart first and second locations 36 and 38, such as for example a first end and at a second end. [0014] To compensate for potential vibration, and particularly relative vibration between heat sink 20 and substrate 12, thermal link 30 is advantageously relatively flexible and non-structural to reduce the transmission of mechanical energy from the heat sink to the substrate or from the substrate to the heat sink. Thermal link 30 further advantageously is secured so that the portion 40 of thermal link 30 spanning between substrate 12 and heat sink 20 is curved, forming a slackened portion that is longer than required to bridge the gap between substrate 12 and heat sink 20. In one example, the thermal link 30 can be secured to the substrate 12 between the space apart first and second locations 36, 38 and spaced apart from the heat sink between these first and second locations so as to provide mechanical isolation. The curved spanning portion 40 reduces the amount of mechanical energy, such as vibration, that is translated between substrate 12 and heat sink 20. In one embodiment, the portion 40 forms a flared or outwardly extending portion (as shown in Fig. 1). In other embodiments, the portion 40 may be in the form of a corrugated cross-section or serpentine cross-section.
[0015] In one example, the portion 40 of thermal link 30 can be disposed between a location at which the thermal link is in thermal contact with the heat sink 20 and a location at which the thermal link is in thermal contact with the electronic component, such as for example at the via 18. In this one example or another example, the portion 40 of thermal link 30 can be disposed between a location at which the thermal link is in thermal contact with the heat sink 20 and a location at which the thermal link is secured to the substrate 12.
[0016] Referring now to Fig. 2 another embodiment of the device is shown generally at 100 with components similar to the components in Fig. 1 having similar reference numbers. The device 100 includes an electronic component positioned on the second major surface 16 of the substrate 12. The heat sink 20 is located in proximity to the substrate 12 and spaced apart from both the substrate and the electronic component 11 thereby forming a gap between the electronic component and the heat sink.
[0017] The thermal link 30 is positioned at second major surface 16 and in thermal contact with electric or electronic component 11 without using via 18. In this embodiment the electronic device is disposed between the thermal link 30 and the substrate 12.
[0018] Thermal link 30 can be secured to the substrate 12. In one or more examples, thermal link 30 may advantageously be secured to the substrate 12 mechanically. In one embodiment a mounting plate 32 secures thermal link 30 against electronic component 11. Mounting plate 32 may include anchors 34 that extend through thermal link 30 and into or through substrate 12 at opposite ends of the electronic component 11 to secure thermal link 30 against electronic component 12. In other embodiments, thermal link 30 may also be adhesively secured to electronic component 11.
[0019] Thermal link 30 is also positioned in thermal contact with heat sink 20 and secured thereto in a similar manner as described above. In one example, the thermal link 30 can be secured to the substrate 12 such that it is in contact with the electronic component 11 between the space apart first and second locations 36, 38 and spaced apart from the heat sink between the first and second locations so as to provide mechanical isolation.
[0020] Thermal link 30 is secured so that the portion 40 of thermal link 30 spanning between electronic component 11 and heat sink 20 is curved, forming a slackened portion that is longer than required to bridge the gap between electronic component 11 and heat sink 20. The curved spanning portion 40 reduces the amount of mechanical energy, such as vibration, that is translated between substrate 12 and heat sink 20 or between substrate and electronic component 11. In one embodiment, the portion 40 forms a flared or outwardly extending portion (as shown in Fig. 2). In other embodiments, the portion 40 may be in the form of a corrugated cross-section or serpentine cross-section. [0021] Referring now to Figs. 1 and 2, in some embodiments the thermal link 30 is formed of one or more sheets of flexible graphite. In one embodiment, flexible graphite may include compressed particles of exfoliated graphite. In other embodiments, the flexible graphite includes one or more layers of pyrolytic graphite with one or more support layers. In still other embodiments, the flexible graphite may be formed of both pyrolytic graphite and one or more sheets of compressed particles of exfoliated graphite. By "pyrolytic graphite" is meant a graphitized graphitizable polymer, for instance, in U.S. Patent No. 5,091,025, the disclosure of which is incorporated herein by reference in its entirety.
[0022] The thermal link 30 may further include protective coatings on one or more sides. Coatings may include a polymer or metal coating and may be, for example, PET films, acrylic films, and aluminum foil.
[0023] The flexible graphite may have a thickness of from between about 0.010 mm to 3.75 mm and a typical density of about 1.0 to 2.0 g/cc or higher. In one example, the flexible graphite sheets have a thickness between about 0.025 mm to about 0.500 mm. In another example, flexible graphite sheets have a thickness between about 0.050 mm to about 0.250 mm. In one example, the flexible graphite sheet can have a density from between about 1.0 g/cc to about 2.0 g/cc. In another example, the flexible graphite sheet can have a density from between about 1.2 g/cc and about 1.8 g/cc. In one example, the flexible graphite can have a density of at least about 0.6 g/cc, more preferably at least about 1.1 g/cc. In another example, the flexible graphite can have a density of at least about 1.6 g/cc. The upper limit to the density of the graphite sheet is about 2.0 g/cc. One graphite sheet suitable for use in the thermal bridge in the present disclosure is commercially available as eGRAF® material, from GrafTech International Holdings Inc. of Parma, Ohio.
[0024] In certain embodiments, a plurality of graphite sheets may be laminated into a unitary article for use in the thermal link disclosed herein. The sheets of compressed particles of exfoliated graphite may be laminated with a suitable adhesive, such as pressure sensitive or thermally activated adhesive, therebetween. The adhesive chosen should balance bonding strength with minimizing thickness, and be capable of maintaining adequate bonding at the service temperature at which heat transfer is sought. Suitable adhesives would be known to the skilled artisan, and include acrylic and phenolic resins.
[0025] The flexible graphite sheet(s) have an in-plane thermal conductivity of at least
150 W/m*K. In still other embodiments, the graphite sheet exhibits an in-plane thermal conductivity of at least 300 W/m*K. In still other embodiments the graphite sheet exhibits an in-plane thermal conductivity of at least 400 W/m*K. In still other embodiments the graphite sheet exhibits an in-plane thermal conductivity of at least 600 W/m*K. In still other embodiments the graphite sheet exhibits an in-plane thermal conductivity of at least 700 W/m*K. In still other embodiments, the graphite sheet exhibits an in-plane thermal conductivity of at least 1500 W/m*K. In one embodiment, the graphite sheet material may be from 10 to 1500 microns thick.
[0026] The flexible graphite sheet(s) may advantageously have a minimum bend radius of less than about 20.0 mm, more advantageously less than 10.0 mm and still more advantageously less than 6.0 mm. In this or other embodiments, the minimum bend radius may be from between about 1.0 mm to about 20.0 mm.
[0027] The flexible graphite sheets advantageously have a thickness between about 0.025 mm to about 0.500 mm, and more advantageously from between about .050 mm to about .250 mm. The flexible graphite sheet advantageously has a density from between about 1.0 g/cc to about 2.0 g/cc and still more advantageously from between about 1.2 g/cc and about 1.8 g/cc.
[0028] The various embodiments described herein can be practiced in any combination thereof. The above description is intended to enable the person skilled in the art to practice the invention. It is not intended to detail all of the possible variations and modifications that will become apparent to the skilled worker upon reading the description. It is intended, however, that all such modifications and variations be included within the scope of the invention that is defined by the following claims. The claims are intended to cover the indicated elements and steps in any arrangement or sequence that is effective to meet the objectives intended for the invention, unless the context specifically indicates the contrary.

Claims

Claims What is claimed is:
1. A thermal management arrangement for a device having a heat sink and an electronic component positioned on a substrate, the heat sink being positioned proximate to, but not in contact with the substrate thereby forming a gap between the substrate and the heat sink, the thermal management arrangement comprising:
a thermal link comprising at least one sheet of flexible graphite, the flexible graphite being in thermal contact with the electronic component and the heat sink, said thermal link being secured to said substrate and to said heat sink, said thermal link including a portion spanning between the heat sink and the substrate, wherein the portion is curved and longer than required to bridge the gap between the substrate and the heat sink.
2. The thermal management arrangement according to claim 1 wherein said portion includes at least one of a serpentine cross-section and an outwardly extending flare.
3. The thermal management arrangement according to claim 1 wherein said flexible graphite comprises one or more sheets of compressed particles of exfoliated graphite.
4. The thermal management arrangement according to claim 1 wherein said flexible graphite comprises one or more sheets of pyrolytic graphite.
5. The thermal management arrangement according to claim 1 wherein said thermal link further comprises a protective coating.
6. The thermal management arrangement according to claim 1 wherein said flexible graphite has a thickness from between about 0.025 mm to about 0.500 mm and a density from between about 0.6 g/cc to about 2.0 g/cc.
7. The thermal management arrangement according to claim 1 wherein said flexible graphite has a minimum bend radius of about 1.0 mm to about 20.0 mm
8. The thermal management arrangement according to claim 1 wherein said flexible graphite has an in-plane thermal conductivity of at least 150 /m*K.
9. The thermal management arrangement according to claim 1 wherein said portion is disposed between a location at which the thermal link is in thermal contact with the heat sink and a location at which the thermal link is secured to the substrate.
10. The thermal management arrangement according to claim 1 wherein said thermal link is secured to the heat sink at spaced apart first and second locations on the thermal link and said thermal link is secured to the substrate and spaced apart from the heat sink between the first and second locations.
11. A thermal management arrangement for a device having a heat sink and an electronic component positioned on a substrate, the heat sink being positioned proximate to the substrate and spaced apart from the substrate and the electronic component, the thermal management arrangement comprising:
a thermal link comprising at least one sheet of flexible graphite, the flexible graphite being in thermal contact with the electronic component and the heat sink, said thermal link being secured to said substrate and to said heat sink, said thermal link including a portion spanning between the heat sink and the electronic component, wherein the portion is curved and longer than required to bridge the gap between the electronic component and the heat sink.
12. The thermal management arrangement according to claim 11 wherein said portion includes at least one of a serpentine cross-section and an outwardly extending flare.
13. The thermal management arrangement according to claim 11 wherein said flexible graphite comprises one or more sheets of compressed particles of exfoliated graphite.
14. The thermal management arrangement according to claim 11 wherein said flexible graphite comprises one or more sheets of pyrolytic graphite.
15. The thermal management arrangement according to claim 11 wherein said thermal link further comprises a protective coating.
16. The thermal management arrangement according to claim 11 wherein said flexible graphite has a thickness from between about 0.025 mm to about 0.500 mm and a density from between about 0.6 g/cc to about 2.0 g/cc.
17. The thermal management arrangement according to claim 11 wherein said flexible graphite has a minimum bend radius of about 1.0 mm to about 20.0 mm
18. The thermal management arrangement according to claim 11 wherein said flexible graphite has an in-plane thermal conductivity of at least 150 /m*K.
19. The thermal management arrangement according to claim 11 wherein said portion is disposed between a location at which the thermal link is in thermal contact with the heat sink and a location at which the thermal link is secured to the substrate.
20. The thermal management arrangement according to claim 11 wherein said thermal link is secured to the heat sink at spaced apart first and second locations on the thermal link and said thermal link is in thermal contact with the electronic component and spaced apart from the heat sink between the first and second locations.
PCT/US2014/051443 2013-08-21 2014-08-18 Mechanically isolated thermal link WO2015026704A1 (en)

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