WO2014149189A1 - Thermal interfaces - Google Patents

Thermal interfaces Download PDF

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Publication number
WO2014149189A1
WO2014149189A1 PCT/US2014/013721 US2014013721W WO2014149189A1 WO 2014149189 A1 WO2014149189 A1 WO 2014149189A1 US 2014013721 W US2014013721 W US 2014013721W WO 2014149189 A1 WO2014149189 A1 WO 2014149189A1
Authority
WO
WIPO (PCT)
Prior art keywords
graphite
thermal
management system
sheet
component
Prior art date
Application number
PCT/US2014/013721
Other languages
French (fr)
Inventor
Alexander J. Augoustidis
Richard Allen BEYERLE II
Gregory P. Kramer
Robert A. Reynolds Iii
David G. Rich
Martin D. Smalc
Bret Alan Trimmer
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 WO2014149189A1 publication Critical patent/WO2014149189A1/en

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    • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
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    • H01L23/367—Cooling facilitated by shape of device
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    • H01L23/373—Cooling facilitated by selection of materials for the device or materials for thermal expansion adaptation, e.g. carbon
    • H01L23/3737—Organic materials with or without a thermoconductive filler
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Definitions

  • the field of the disclosure relates to electronic thermal management.
  • One particular application of the embodiments disclosed herein is as a thermal interface. RELATED BACKGROUND
  • An embodiment disclosed herein includes an electronic device which includes an electronic component and a thermal management system in thermal contact with the electronic component.
  • the system includes at least one sheet of a graphite formed in a three dimensional shape other than its unaltered form.
  • the graphite comprises at least one sheet of a graphitized polyimide, compressed particles of exfoliated graphite or combinations thereof.
  • the electronic device may further include a third component in thermal contact with the thermal management system and it is disposed above the thermal management system.
  • an electronic device which includes an electronic component and a thermal management system in thermal contact with the electronic component.
  • the system further includes at least one sheet of a graphite formed in a three dimensional shape other than its native sheet form thereby forming a graphite article, the graphite article comprising at least one of graphitized polyimide, compressed particles of exfoliated graphite or combinations thereof.
  • a third component is in thermal contact with the thermal management system and is disposed above the thermal management system.
  • a further embodiment of an electronic device described herein includes an electronic component and a thermal management system in thermal contact with the electronic component.
  • the system includes at least one sheet of a graphite formed in a three dimensional shape other than its unaltered form forming a graphite article, the graphite article comprising at least a graphitized polyimide sheet.
  • a third component is in thermal contact with the thermal management system and is disposed above the thermal management system. Additionally, the thermal management system has a height of at least 125 microns and a void space.
  • Figure 1 is a schematic view of an embodiment of a thermal interface disclosed herein in an electronic device.
  • Figure 2 is a second schematic view of the thermal interface shown in figure 1.
  • Figure 3 is a side view of a different embodiment of a thermal interface disclosed herein.
  • Figure 4 is a side view of another embodiment of a thermal interface disclosed herein.
  • Figure 5 is a side view of a further embodiment of a thermal interface disclosed herein.
  • Figures 6 A and 6B are side views of additional embodiments of thermal interfaces disclosed herein.
  • Figure 7 is a side view of a further embodiment of a thermal interface.
  • Figure 8 is a schematic view of the embodiment shown in figure 7 in use.
  • Figure 9 is a schematic view of another particular embodiment of a thermal management system.
  • Figure 10 is a schematic view of an alternative embodiment shown in figure 8.
  • Figure 11 is a further schematic view of a further embodiment of a thermal management system.
  • Figure 12 is a top view of two graphite articles which are incorporated into the thermal management system shown in figures 13A and 13B.
  • Figures 13A and 13B are side views of the thermal management system using the graphite articles of figure 12.
  • the embodiments disclosed herein include designs and description how flexible graphite can be used as a thermal interface.
  • Typical graphite materials applicable to the disclosed embodiments include one or more sheets of compressed particles of exfoliated graphite; a method of making such graphite particles is disclosed in US Patent 3404061 which is incorporated fully herein in its entirety.
  • Another type of graphite which may be used in the disclosed embodiments may include one or more sheets of graphitized polyimide.
  • a method of making such sheets is disclosed in US Patent 5091025 which is incorporated fully herein in its entirety.
  • a third option may be a combination of a graphitized polyimide and the compressed particles of exfoliated graphite.
  • a further example of a suitable type of graphite is a graphite which has an anisotropic ratio of at least about 40:1, preferably at least about 50:1, more preferably at least about 75:1, and even more preferably at least about 100 : 1.
  • the graphite sheet may include a plastic layer, a polymeric layer , a metallic layer, a cermet layer or combinations thereof on at least one of the major surfaces of the sheet.
  • the sheet may include such a layer on each major surface.
  • the layer may be on the major surface and one or more the edge surfaces with or without being on the second major surface.
  • the layer may be the same material or different.
  • a thermal interface is a material or an article which functions to move heat in the z-direction away from the heat source, dissipating a desired amount of heat from the heat source. Such an interface may spread heat in the x-y direction also but the required direction of heat movement is to dissipate the heat in the z-direction.
  • the graphite article as described above may have anyone of shapes as shown in the figures.
  • the graphite article is generally coiled into a cylinder.
  • the cylinder is aligned horizontally, the length dimension of cylinder extends in the horizontal direction, whereas the axial direction provides the height of the cylinder.
  • the portions of the sheet located in the interior of the cylinder may be attached to the immediate outer portion of the sheet, conversely it may be unattached or any variation of the two.
  • the graphite article may comprise one or more sheets of the afore graphite.
  • the graphite article has a generally chevron type shape, preferably multiple chevrons.
  • the chevrons may be made from different sheets of graphite, all the same sheet of graphite, or any combination thereof.
  • the article of figure 3 is not limited to any number of chevrons, however it is preferred that the article includes at least two (2) chevrons. Stated another way, preferably the graphite article includes a plurality of chevrons, more preferred the plurality includes on even number of chevrons.
  • the graphite article includes a plurality of bowed sections.
  • the bowed sections of the graphite article of figure 4 may be formed by a plurality of graphite sheets, a single sheet of graphite coiled into a cylinder which is compressed, or a combination of each.
  • the graphite article may have a honeycomb shaped orientation.
  • the graphite article may be formed from one or more graphite sheets.
  • each circular segment which makes up the honeycomb is formed from a different sheet.
  • the honeycomb is formed from more than one sheet of graphite, however a particular sheet of graphite may form more than one of the circular sections.
  • the graphite article has a substantially rectangular shape.
  • suitable substantially rectangular shapes include substantially square, substantially parallelogram, or substantially rectangular.
  • the graphite article may be formed from one or more sheets of graphite.
  • the interior of the graphite article represents a void space; which may also be referred to as an unfilled or open section.
  • the substantially rectangular shape may have straight corners, rounded corners (AKA rounded corners), or a combination of a desired corner having straight connections and the other desired corners having rounded corner(s).
  • a filler may inserted into the void space to provide the article with "structure" for the vertically aligned pieces of graphite and/or strength the thermal management system.
  • Benefits of including a filler may include improving the ability of the graphite article to maintain its shape during any of placement, attachment, device manufacture or device use.
  • An additional benefit of the filler is that it may be selected to provide adhesion to one or more surfaces.
  • One example of a suitable filler may be a gap pad.
  • the described graphite article may be used as a thermal interface in an electronic device.
  • embodiment 10 shows how graphite article 20 may be used as a thermal interface.
  • Graphite article 20 may be part of the thermal management system for the electronic device.
  • the graphite article has a three dimensional shape other than its native form of a sheet.
  • Native form of a sheet may also be known as its unaltered sheet form.
  • An example of native form or unaltered form is the same as that of a sheet of paper lying on a counter top without any folds or creases in the sheet.
  • the three dimensional shape may also be described as other than its unaltered sheet form.
  • article 20 has the shape of the afore described coiled cylinder.
  • the electronic device will further include at least one electronic component 30.
  • the thermal management system is in thermal contact with the electronic component 30.
  • the electronic device may include a third component 32 in thermal contact with the thermal management system.
  • the third component 32 is disposed above the thermal management system.
  • the third component 32 is an Rf can.
  • the third component may be a heat dissipation element. Examples of such dissipation elements include cold plate, heat sinks or heat pipes.
  • article 20 and component 30 An alternate way to describe the relationship between article 20 and component 30 is that the axis of article 20 is aligned parallel to the top surface of component 30. Further the radial aspect of article 20 extends in the normal direction from the top surface of component 30 to component 32. Applying this terminology to figures 3 and 4, in such figures, articles 20a and 20b extend in the normal direction from the top surface of component 30 (not shown) to component 32 (not shown).
  • the embodiment shown in figure 1 may be incorporated into an electronic device of choice, such as but not limited to a cellular telephone, a note book computer, a tablet, an e- reader, a desk top computer, laptop computer, or any other desired electronic device which dissipating heat from an electronic component or components may be advantageous.
  • an electronic device of choice such as but not limited to a cellular telephone, a note book computer, a tablet, an e- reader, a desk top computer, laptop computer, or any other desired electronic device which dissipating heat from an electronic component or components may be advantageous.
  • Electronic component 30 is not limited to any particular component.
  • a PoP is an integrated circuit packaging method to combine vertically discrete logic and memory ball grid array (BGA) packages.
  • BGA memory ball grid array
  • a benefit of the PoP design is the savings of space on the motherboard.
  • the PoP may include any combination of semiconductor and non- semiconductor components stacked in the PoP configuration.
  • the PoP may include any suitable semiconductor package for chips and may further be a BGA.
  • the thermal management system may further include a contact element 34 between the electronic component and the graphite article.
  • the contact element 34 may be conductive grease, phase change material, conductive adhesive, or any other material which will reduce contact resistance between the graphite article 20 and the element adjacent to it.
  • Another optional element may include a second contact element 36.
  • Contact element 36 will have the same function as contact element 34 except between the article 20 and the third component 32 instead of article 20 and component 30.
  • the choice of materials for contact elements 34 and 36 may be the same or different for any particular embodiment.
  • the graphite article may have the shape substantially similar to the article 20a, in the form of one or more chevrons 40. In a particular embodiment, it is preferred that the chevrons 40 are used in pairs.
  • Another alternative configuration for the graphite article is shown in Figure 4 as 20b, in the shape of one or more bowed or concave segments 42. In a particular embodiment, it is preferred that the concave segments are used in pairs. Neither of the proposed embodiments is limited to any particular number of chevrons 40 or concaved segments 42.
  • the graphite article has a substantially honeycombed shape 44.
  • the honeycombed graphite article may be formed as described above.
  • the graphite article may have a substantially rectangular shape 46.
  • the shape 46 may have round or radius corners 46r or straight corners 46s.
  • Figure 7 a sheet of graphite 50 is wound into a substantially circular shape 52 such as a circle or an oval.
  • the graphite sheet is a sheet of graphitized polyimide as described above.
  • Figure 8 shows graphite article having the shape 52 in between two contact elements 34, 36.
  • the electronic device includes a display in the same section of the device as the electronic component and preferably the display is not in thermal contact with the thermal management system.
  • Another embodiment disclosed herein includes an electronic device comprising an electronic component and a thermal management system in thermal contact with the electronic component.
  • the system includes at least one sheet of a graphite formed in a three dimensional shape other than its unaltered form.
  • the graphite article comprises at least a sheet of graphitized polyimide.
  • the device includes a third component in thermal contact with the thermal management system and disposed above the thermal management system.
  • the thermal management system may have a height of at least 125 microns and a void space.
  • the thermal system may further include a potting agent (A.K.A.
  • the potting agent may provide structural support to the thermal management system for the graphite article.
  • the potting agent may be spongy, compliant, resilient, firm, or soft.
  • the potting agent may stabilize the geometry of the graphite article in the thermal management system.
  • Some examples of potting agents include silicon cement, foaming agent, urethane foam or a foam rubber.
  • the electronic device may include a second electronic component having a differing height than the electronic component as well as a second thermal interface in thermal contact with the second electronic component.
  • the second thermal interface may be in thermal contact with the third component.
  • the second thermal interface will have a three dimensional shape other than the second interface material in its unaltered sheet form.
  • the shape of the second thermal interface may further comprise a void space.
  • the second thermal interface may comprise at least one of sheet graphitized polyimide.
  • the second thermal interface may include other materials of construction than the graphitized polyimide, such as compressed particles of exfoliated graphite, aluminum, copper and combinations thereof.
  • the height of the second thermal interface will differ from the height of the thermal interface.
  • the height of the second thermal interface may be greater or lesser than the height of the thermal interface.
  • the electronic device may include multiple heat generating components, as shown three (3) different electronic components 60, 62 and 64, though the embodiment should not be limited to any particular number of heat generating components.
  • the thermal management system it may also include multiple graphite articles, as shown, it include three (3) separate graphite articles 70, 72 and 74; just as the number of electronic components, the embodiment is not limited to any particular number of graphite articles.
  • each graphite article 70, 72 and 74 is in thermal contact with the third component 32a; as shown third component 32a is a heat sink.
  • the illustrated embodiment may further include one contact element 36a in thermal contact with each graphite article 70, 72 and 74 and in thermal contact with third component 32a.
  • Contact element 36a may be any known type of planar thermal interface material, such as but not limited to aluminum, copper, compressed sheet of exfoliated graphite, sheet of graphitized polyimide, phase change material, etc.
  • the embodiment shown may further include contact elements 34a, 34b and 34c.
  • Each contact element 34a, 34b and 34c may be in thermal contact with a heat source and a graphite article; for example contact element 34a may be in thermal contact with heat source 60 and graphite article 70.
  • Contact elements 34a, 34b and 34c may be anyone of the afore noted planar thermal interfaces as well as the afore noted conductive greases or conductive adhesives. Any such contact elements may have a smooth or rough surface, whichever is desired. Further if so desired, the contact elements may be curved or may be able to accommodate a curved surface.
  • a further alternate nomenclature is that the contact elements are aligned parallel to the heat sources. This may be true for each embodiment disclosed herein.
  • the electronic device may include one or more additional thermal interfaces 80, 82 and 84, wherein each thermal interface is in thermal contact with the electronic component (not shown) and a heat dissipation element (not shown), as shown in Figure 11.
  • each thermal interface is in thermal contact with the electronic component (not shown) and a heat dissipation element (not shown), as shown in Figure 11.
  • a heat dissipation element not shown
  • FIG 11 is the afore noted positioning or potting agents 85 as well as the afore noted planar contact elements, indicated as elements 34 and 36.
  • the graphite article for the thermal management system shown in figure 13 may comprise a first sheet of graphite 90 or it may comprise the first sheet of graphite 90 and a second sheet of graphite 92. Both or either sheets of graphite 90 and 92 may be the same graphite as described above. As illustrated each sheet of graphite 90 and 92 may include a main body section 94 and a first wing section 96 and a second wing section 98. In the embodiments shown, each wing section 96 and 98 extend from a side of main body section 94 and is integral to the main body section 94. Further for each sheet of graphite 90 and 92, the wing sections 96 and 98 are opposed from each other. The dimensions of any of sheets 90, 92, main bodies 94, and wings 96 and/or 98 can be adjusted for the particular application.
  • FIG. 13A is a side view of thermal management system 100.
  • thermal management system 100 includes graphite sheet 92, a filler 102, a top surface 104 of the filler 102 adjacent main body section 94 of sheet 92 and a bottom surface (not shown) of filler 102 adjacent main body section 94 of graphite sheet 90.
  • Wings 96 and 98 extend from main body 94 of sheet 90 along any exterior surface of filler 102 to main body section 94 of sheet 92.
  • the wings 96 and 98 of sheet 90 are aligned generally about 180° apart from one another, or stated another the wings are disposed to each other in a substantially opposed relationship to one another.
  • each wing 96 and 98 of sheet 90 is in thermal contact with main body 94 of sheet 92.
  • Thermal management system 100 is further described in figure 13B.
  • thermal management system 100 is rotated 90° from the view shown in figure 13 A.
  • the wings 96 and 98 of sheet 92 extend from main body 94 of sheet 92 along the external surface of filler 102 to the main body 94 of sheet 90.
  • wings 96 and 98 of sheet 92 are in thermal contact with the main body section 94 of sheet 90.
  • main body section 94 of either sheet 90 or sheet 92 is in thermal contact with a heat source such as one of the afore mentioned electronic components.
  • the other main body section 94 of the sheet not in thermal contact with the heat source is in thermal contact with a heat dissipation element, such as but not limited to a chassis with in the device, an internal surface of a part which forms an exterior surface of the device, Rf can, a heat pipe, a heat sink, cold plate or a heat conduit.
  • filler 102 may be adhered to either one or both of the main body sections 94 of sheets 90 and/or 92.
  • thermal management system 100 may extend from the heat source to the heat dissipation element through an Rf can.
  • thermal management system 100 may extend through an opening in a surface of the Rf can.
  • filler 102 may be incorporated to other embodiments disclosed herein if so desired.
  • filler 102 may be used with chevrons 40 of figure 3.
  • graphite articles 20a having substantially chevron 40 may be arranged radially around filler 102, with one end section of each chevron in thermal contact with one of the heat source or the heat dissipation element and the other end section of the chevron in thermal contact with the opposite of which the first end section of the chevron is in thermal contact.
  • One or more of the disclosed embodiments may be used to direct the heat generated in specific vectors, thereby directing a certain amount of heat in a desired direction.
  • one or more of the disclosed embodiments will include thermal interfaces that have conductivity and conductance levels exceeding that of grease, resin or gap pad thermal interfaces while minimizing unwanted heat convection along the selected path associated with metal thermal interfaces. Further the disclosed embodiments of one or more of the thermal interfaces are lighter and have a longer useful life than greases, resins and gap pads.
  • Electronic devices which include one of the disclosed embodiments may exhibit one or more of the following advantages:
  • Increased performance - thermal loops reduce device performance when any thermal limit is reached.
  • CPU frequency may be scaled back, maximum radio transmit power may be reduced resulting in dropped calls or decreased bandwidths (radio protocol specific), and display brightness may be limited. Being able to redirect desired amounts of heat to more preferred surfaces would allow devices to operate at full performance longer.

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Abstract

Sheets of flexible graphite may be used as thermal interfaces in various ways. The flexible graphite sheets may consist of compressed particles of exfoliated graphite, graphitized polyimide sheets, or combinations thereof. The sheets in their unaltered form are standard planar sheets. The sheets are manipulated to create a three dimensional graphite article. The article is used to dissipate heat away from a heat source to a heat dissipation element. The article can take anyone of the shapes included herein or other three dimensional shapes other than a standard sheet of paper. Such a graphite article may be incorporated into a thermal management system.

Description

THERMAL INTERFACES
TECHNICAL FIELD
[001] The field of the disclosure relates to electronic thermal management. One particular application of the embodiments disclosed herein is as a thermal interface. RELATED BACKGROUND
[002] In Smartphones, Tablets and Notebooks, for example, many heat sources are dissipated onto a non-preferred surface. As a first example, smartphones, tablets and notebook OEMs are using Package-on-Package ("PoP") configurations wherever possible due to limited PCB area; these stacked components can have mismatched temperature requirements. One such instance is the PoP memory on top of a CPU. Current CPUs can maintain rated frequency until a junction temperature of 92-105 °C, while the PoP memories are limited to 85°C (i.e., DRAM ~ high temperature increases refresh rate requirements; Flash ~ reliability due to tunneling of electrons at higher temperatures). System performance must be curbed (reduce f to f/2 or lower (f is used as an abbreviation for frequency)) when any thermal limit is reached. As a second example, heat from CPUs, radio power amplifiers, and other hot components is mostly redirected back into the PCB. In the case of double-sided PCBs with back-to-back hot components, the PCB's thermal spreading and dissipation effectiveness is severely limited. As a result, un-optimized PCB design rules must be utilized that increase industrial design size, limit onboard functionality options, and/or strain device temperature and component reliability.
BRIEF DESCRIPTION
[003] An embodiment disclosed herein includes an electronic device which includes an electronic component and a thermal management system in thermal contact with the electronic component. The system includes at least one sheet of a graphite formed in a three dimensional shape other than its unaltered form. The graphite comprises at least one sheet of a graphitized polyimide, compressed particles of exfoliated graphite or combinations thereof. The electronic device may further include a third component in thermal contact with the thermal management system and it is disposed above the thermal management system.
[004] Also disclosed herein is an electronic device which includes an electronic component and a thermal management system in thermal contact with the electronic component. The system further includes at least one sheet of a graphite formed in a three dimensional shape other than its native sheet form thereby forming a graphite article, the graphite article comprising at least one of graphitized polyimide, compressed particles of exfoliated graphite or combinations thereof. A third component is in thermal contact with the thermal management system and is disposed above the thermal management system.
[005] A further embodiment of an electronic device described herein includes an electronic component and a thermal management system in thermal contact with the electronic component. The system includes at least one sheet of a graphite formed in a three dimensional shape other than its unaltered form forming a graphite article, the graphite article comprising at least a graphitized polyimide sheet. A third component is in thermal contact with the thermal management system and is disposed above the thermal management system. Additionally, the thermal management system has a height of at least 125 microns and a void space.
[006] It is to be understood that both the foregoing general description and the following detailed description provide embodiments of the disclosure and are intended to provide an overview or framework of understanding the nature and character of the invention as it is claimed.
DESCRIPTION OF THE DRAWINGS
[007] Figure 1 is a schematic view of an embodiment of a thermal interface disclosed herein in an electronic device.
[008] Figure 2 is a second schematic view of the thermal interface shown in figure 1.
[009] Figure 3 is a side view of a different embodiment of a thermal interface disclosed herein.
[010] Figure 4 is a side view of another embodiment of a thermal interface disclosed herein.
[011] Figure 5 is a side view of a further embodiment of a thermal interface disclosed herein.
[012] Figures 6 A and 6B are side views of additional embodiments of thermal interfaces disclosed herein.
[013] Figure 7 is a side view of a further embodiment of a thermal interface.
[014] Figure 8 is a schematic view of the embodiment shown in figure 7 in use.
[015] Figure 9 is a schematic view of another particular embodiment of a thermal management system.
[016] Figure 10 is a schematic view of an alternative embodiment shown in figure 8. [017] Figure 11 is a further schematic view of a further embodiment of a thermal management system.
[018] Figure 12 is a top view of two graphite articles which are incorporated into the thermal management system shown in figures 13A and 13B.
[019] Figures 13A and 13B are side views of the thermal management system using the graphite articles of figure 12.
DETAILED DESCRIPTION
[020] The embodiments disclosed herein include designs and description how flexible graphite can be used as a thermal interface. Typical graphite materials applicable to the disclosed embodiments include one or more sheets of compressed particles of exfoliated graphite; a method of making such graphite particles is disclosed in US Patent 3404061 which is incorporated fully herein in its entirety. Another type of graphite which may be used in the disclosed embodiments may include one or more sheets of graphitized polyimide. A method of making such sheets is disclosed in US Patent 5091025 which is incorporated fully herein in its entirety. A third option may be a combination of a graphitized polyimide and the compressed particles of exfoliated graphite. An example of this material is disclosed in WO 2012-040148, this publication is fully incorporated herein its entirety. A further example of a suitable type of graphite is a graphite which has an anisotropic ratio of at least about 40:1, preferably at least about 50:1, more preferably at least about 75:1, and even more preferably at least about 100 : 1.
[021] Optionally the graphite sheet may include a plastic layer, a polymeric layer , a metallic layer, a cermet layer or combinations thereof on at least one of the major surfaces of the sheet. Alternatively, the sheet may include such a layer on each major surface.
Optionally, the layer may be on the major surface and one or more the edge surfaces with or without being on the second major surface. In the case of having a layer on each major surface, the layer may be the same material or different.
[022] As used herein a thermal interface is a material or an article which functions to move heat in the z-direction away from the heat source, dissipating a desired amount of heat from the heat source. Such an interface may spread heat in the x-y direction also but the required direction of heat movement is to dissipate the heat in the z-direction.
[023] The graphite article as described above may have anyone of shapes as shown in the figures. In one such embodiment, the graphite article is generally coiled into a cylinder. As shown in figures 1 and 2, the cylinder is aligned horizontally, the length dimension of cylinder extends in the horizontal direction, whereas the axial direction provides the height of the cylinder. The portions of the sheet located in the interior of the cylinder may be attached to the immediate outer portion of the sheet, conversely it may be unattached or any variation of the two.
[024] In another embodiment, the graphite article may comprise one or more sheets of the afore graphite. As shown in figure 3, the graphite article has a generally chevron type shape, preferably multiple chevrons. The chevrons may be made from different sheets of graphite, all the same sheet of graphite, or any combination thereof. The article of figure 3 is not limited to any number of chevrons, however it is preferred that the article includes at least two (2) chevrons. Stated another way, preferably the graphite article includes a plurality of chevrons, more preferred the plurality includes on even number of chevrons.
[025] An alternate embodiment is shown in figure 4. The graphite article includes a plurality of bowed sections. The bowed sections of the graphite article of figure 4 may be formed by a plurality of graphite sheets, a single sheet of graphite coiled into a cylinder which is compressed, or a combination of each.
[026] In a further embodiment as shown in figure 5, the graphite article may have a honeycomb shaped orientation. The graphite article may be formed from one or more graphite sheets. In a particular embodiment, each circular segment which makes up the honeycomb is formed from a different sheet. In another particular embodiment, the honeycomb is formed from more than one sheet of graphite, however a particular sheet of graphite may form more than one of the circular sections.
[027] Additional embodiments are shown in figures 6 A and 6B in which the graphite article has a substantially rectangular shape. Examples of suitable substantially rectangular shapes include substantially square, substantially parallelogram, or substantially rectangular. The graphite article may be formed from one or more sheets of graphite. Preferably the interior of the graphite article represents a void space; which may also be referred to as an unfilled or open section. Further the substantially rectangular shape may have straight corners, rounded corners (AKA rounded corners), or a combination of a desired corner having straight connections and the other desired corners having rounded corner(s).
[028] In the case of the graphite article in the form of a three dimensional structure having a void space, optionally a filler may inserted into the void space to provide the article with "structure" for the vertically aligned pieces of graphite and/or strength the thermal management system. Benefits of including a filler may include improving the ability of the graphite article to maintain its shape during any of placement, attachment, device manufacture or device use. An additional benefit of the filler is that it may be selected to provide adhesion to one or more surfaces. One example of a suitable filler may be a gap pad.
[029] Other examples of suitable shapes for the graphite article include a pleated fold or a step configuration.
[030] As stated above, the described graphite article may be used as a thermal interface in an electronic device. As shown in figure 1, embodiment 10 shows how graphite article 20 may be used as a thermal interface. Graphite article 20 may be part of the thermal management system for the electronic device. Preferably the graphite article has a three dimensional shape other than its native form of a sheet. Native form of a sheet may also be known as its unaltered sheet form. An example of native form or unaltered form is the same as that of a sheet of paper lying on a counter top without any folds or creases in the sheet. The three dimensional shape may also be described as other than its unaltered sheet form. As shown in figure 1 , article 20 has the shape of the afore described coiled cylinder.
[031] The electronic device will further include at least one electronic component 30.
Preferably the thermal management system is in thermal contact with the electronic component 30. The electronic device may include a third component 32 in thermal contact with the thermal management system. Preferably the third component 32 is disposed above the thermal management system. In one particular embodiment, the third component 32 is an Rf can. In an alternate embodiment, the third component may be a heat dissipation element. Examples of such dissipation elements include cold plate, heat sinks or heat pipes.
[032] An alternate way to describe the relationship between article 20 and component 30 is that the axis of article 20 is aligned parallel to the top surface of component 30. Further the radial aspect of article 20 extends in the normal direction from the top surface of component 30 to component 32. Applying this terminology to figures 3 and 4, in such figures, articles 20a and 20b extend in the normal direction from the top surface of component 30 (not shown) to component 32 (not shown).
[033] The embodiment shown in figure 1 may be incorporated into an electronic device of choice, such as but not limited to a cellular telephone, a note book computer, a tablet, an e- reader, a desk top computer, laptop computer, or any other desired electronic device which dissipating heat from an electronic component or components may be advantageous.
[034] Electronic component 30 is not limited to any particular component. One example of such component includes a package over package ("PoP"). In one embodiment a PoP is an integrated circuit packaging method to combine vertically discrete logic and memory ball grid array (BGA) packages. In many cases, two or more packages are installed atop each other, i.e. stacked, with a standard interface to route signals between them. A benefit of the PoP design is the savings of space on the motherboard. The PoP may include any combination of semiconductor and non- semiconductor components stacked in the PoP configuration. In another embodiment, the PoP may include any suitable semiconductor package for chips and may further be a BGA.
[035] Optionally, the thermal management system may further include a contact element 34 between the electronic component and the graphite article. The contact element 34 may be conductive grease, phase change material, conductive adhesive, or any other material which will reduce contact resistance between the graphite article 20 and the element adjacent to it. Another optional element may include a second contact element 36. Contact element 36 will have the same function as contact element 34 except between the article 20 and the third component 32 instead of article 20 and component 30. The choice of materials for contact elements 34 and 36 may be the same or different for any particular embodiment.
[036] As shown in Figure 2, when the third component 32 is brought in contact with printed circuit board "PCB" 37, thereby compressing graphite article 20.
[037] As shown in Figure 3, the graphite article may have the shape substantially similar to the article 20a, in the form of one or more chevrons 40. In a particular embodiment, it is preferred that the chevrons 40 are used in pairs. Another alternative configuration for the graphite article is shown in Figure 4 as 20b, in the shape of one or more bowed or concave segments 42. In a particular embodiment, it is preferred that the concave segments are used in pairs. Neither of the proposed embodiments is limited to any particular number of chevrons 40 or concaved segments 42.
[038] In Figure 5, the graphite article has a substantially honeycombed shape 44. The honeycombed graphite article may be formed as described above. As shown in Figures 6A and 6B, the graphite article may have a substantially rectangular shape 46. As shown in the in the figures, the shape 46 may have round or radius corners 46r or straight corners 46s. A further alternative embodiment is shown in Figure 7. In this embodiment, a sheet of graphite 50 is wound into a substantially circular shape 52 such as a circle or an oval. Preferably, the graphite sheet is a sheet of graphitized polyimide as described above. Figure 8 shows graphite article having the shape 52 in between two contact elements 34, 36.
[039] In a further embodiment, the electronic device includes a display in the same section of the device as the electronic component and preferably the display is not in thermal contact with the thermal management system. [040] Another embodiment disclosed herein includes an electronic device comprising an electronic component and a thermal management system in thermal contact with the electronic component. The system includes at least one sheet of a graphite formed in a three dimensional shape other than its unaltered form. The graphite article comprises at least a sheet of graphitized polyimide. The device includes a third component in thermal contact with the thermal management system and disposed above the thermal management system. The thermal management system may have a height of at least 125 microns and a void space.
[041] Optionally the thermal system may further include a potting agent (A.K.A.
positioning agent) or phase change material 78 as shown in Figure 10. Optionally contact elements (34, 36) may be disposed in conjunction with the potting agent or phase change material. The potting agent may provide structural support to the thermal management system for the graphite article. The potting agent may be spongy, compliant, resilient, firm, or soft. Preferably, the potting agent may stabilize the geometry of the graphite article in the thermal management system. Some examples of potting agents include silicon cement, foaming agent, urethane foam or a foam rubber.
[042] In another optional embodiment, the electronic device may include a second electronic component having a differing height than the electronic component as well as a second thermal interface in thermal contact with the second electronic component. The second thermal interface may be in thermal contact with the third component. Preferably, the second thermal interface will have a three dimensional shape other than the second interface material in its unaltered sheet form. The shape of the second thermal interface may further comprise a void space. The second thermal interface may comprise at least one of sheet graphitized polyimide. Alternatively the second thermal interface may include other materials of construction than the graphitized polyimide, such as compressed particles of exfoliated graphite, aluminum, copper and combinations thereof. Typically the height of the second thermal interface will differ from the height of the thermal interface. The height of the second thermal interface may be greater or lesser than the height of the thermal interface.
[043] As illustrated in Figure 9, the electronic device may include multiple heat generating components, as shown three (3) different electronic components 60, 62 and 64, though the embodiment should not be limited to any particular number of heat generating components. As for the thermal management system it may also include multiple graphite articles, as shown, it include three (3) separate graphite articles 70, 72 and 74; just as the number of electronic components, the embodiment is not limited to any particular number of graphite articles. Further as shown, each graphite article 70, 72 and 74 is in thermal contact with the third component 32a; as shown third component 32a is a heat sink. The illustrated embodiment may further include one contact element 36a in thermal contact with each graphite article 70, 72 and 74 and in thermal contact with third component 32a. Contact element 36a may be any known type of planar thermal interface material, such as but not limited to aluminum, copper, compressed sheet of exfoliated graphite, sheet of graphitized polyimide, phase change material, etc. The embodiment shown may further include contact elements 34a, 34b and 34c. Each contact element 34a, 34b and 34c may be in thermal contact with a heat source and a graphite article; for example contact element 34a may be in thermal contact with heat source 60 and graphite article 70. Contact elements 34a, 34b and 34c may be anyone of the afore noted planar thermal interfaces as well as the afore noted conductive greases or conductive adhesives. Any such contact elements may have a smooth or rough surface, whichever is desired. Further if so desired, the contact elements may be curved or may be able to accommodate a curved surface. A further alternate nomenclature is that the contact elements are aligned parallel to the heat sources. This may be true for each embodiment disclosed herein.
[044] In another alternate embodiment, the electronic device may include one or more additional thermal interfaces 80, 82 and 84, wherein each thermal interface is in thermal contact with the electronic component (not shown) and a heat dissipation element (not shown), as shown in Figure 11. Optionally illustrated in Figure 11 is the afore noted positioning or potting agents 85 as well as the afore noted planar contact elements, indicated as elements 34 and 36.
[045] As shown in figure 12, the graphite article for the thermal management system shown in figure 13 may comprise a first sheet of graphite 90 or it may comprise the first sheet of graphite 90 and a second sheet of graphite 92. Both or either sheets of graphite 90 and 92 may be the same graphite as described above. As illustrated each sheet of graphite 90 and 92 may include a main body section 94 and a first wing section 96 and a second wing section 98. In the embodiments shown, each wing section 96 and 98 extend from a side of main body section 94 and is integral to the main body section 94. Further for each sheet of graphite 90 and 92, the wing sections 96 and 98 are opposed from each other. The dimensions of any of sheets 90, 92, main bodies 94, and wings 96 and/or 98 can be adjusted for the particular application.
[046] Figure 13A is a side view of thermal management system 100. As depicted, thermal management system 100 includes graphite sheet 92, a filler 102, a top surface 104 of the filler 102 adjacent main body section 94 of sheet 92 and a bottom surface (not shown) of filler 102 adjacent main body section 94 of graphite sheet 90. Wings 96 and 98 extend from main body 94 of sheet 90 along any exterior surface of filler 102 to main body section 94 of sheet 92. The wings 96 and 98 of sheet 90 are aligned generally about 180° apart from one another, or stated another the wings are disposed to each other in a substantially opposed relationship to one another. Preferably each wing 96 and 98 of sheet 90 is in thermal contact with main body 94 of sheet 92.
[047] Thermal management system 100 is further described in figure 13B. In figure 13B, thermal management system 100 is rotated 90° from the view shown in figure 13 A. In the same manner as shown in figure 13A, depicted in figure 13B, the wings 96 and 98 of sheet 92 extend from main body 94 of sheet 92 along the external surface of filler 102 to the main body 94 of sheet 90. Preferably wings 96 and 98 of sheet 92 are in thermal contact with the main body section 94 of sheet 90.
[048] Regarding thermal management system 100, preferably one of main body section 94 of either sheet 90 or sheet 92 is in thermal contact with a heat source such as one of the afore mentioned electronic components. The other main body section 94 of the sheet not in thermal contact with the heat source is in thermal contact with a heat dissipation element, such as but not limited to a chassis with in the device, an internal surface of a part which forms an exterior surface of the device, Rf can, a heat pipe, a heat sink, cold plate or a heat conduit. Furthermore, filler 102 may be adhered to either one or both of the main body sections 94 of sheets 90 and/or 92.
[049] In a further optional application of thermal management system 100, may extend from the heat source to the heat dissipation element through an Rf can. In this embodiment, thermal management system 100 may extend through an opening in a surface of the Rf can.
[050] The use of filler 102 may be incorporated to other embodiments disclosed herein if so desired. For example, filler 102 may be used with chevrons 40 of figure 3. In such an embodiment graphite articles 20a having substantially chevron 40 may be arranged radially around filler 102, with one end section of each chevron in thermal contact with one of the heat source or the heat dissipation element and the other end section of the chevron in thermal contact with the opposite of which the first end section of the chevron is in thermal contact.
[051] One or more of the disclosed embodiments may be used to direct the heat generated in specific vectors, thereby directing a certain amount of heat in a desired direction.
Additionally one or more of the disclosed embodiments will include thermal interfaces that have conductivity and conductance levels exceeding that of grease, resin or gap pad thermal interfaces while minimizing unwanted heat convection along the selected path associated with metal thermal interfaces. Further the disclosed embodiments of one or more of the thermal interfaces are lighter and have a longer useful life than greases, resins and gap pads.
[052] Electronic devices which include one of the disclosed embodiments may exhibit one or more of the following advantages:
1. Faster design cycle time - layout options for thermal, their "last" consideration would be minimized by using this invention. ;
2. Flexible design material options - effectively reducing touch temperature through heat redirection grants OEMs wider industrial design and materials' choices ... a metal back cover (UL max of 55°C) vs. plastic (UL max of 75°C) without exceeding UL touch temp limits.;
3. Increased performance - thermal loops reduce device performance when any thermal limit is reached. CPU frequency may be scaled back, maximum radio transmit power may be reduced resulting in dropped calls or decreased bandwidths (radio protocol specific), and display brightness may be limited. Being able to redirect desired amounts of heat to more preferred surfaces would allow devices to operate at full performance longer.
4. Safety - Being able to redirect heat to desirable surfaces will make them more fault tolerant without the risks of exceeding UL (or equivalent) touch temperatures. E.g., latchup in one or more components could result in unexpected heat levels
(reference BB 9000 at Dokomo in 2009) that exceed.; and
5. Reduced BOM costs - By ensuring heat is more effectively removed from specific components, OEMs may be able to choose less-expensive components. For example, radio power amplifiers that can withstand higher junction temperatures are not only more expensive, but have lower gain due to increased number of base-emitter resistors. BOM cost increases and talk-time per unit of battery energy decreases.
[053] 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

What is claimed is:
1. A graphite article in the form of a sheet having the general shape as shown in one of figure 1, figure 3, figure 4, figure 5, figure 6A, figure 6B or figure 7, the article comprised of at least one of: graphitized polyimide, compressed particles of exfoliated graphite or combinations thereof, the graphite article further comprising a plastic, polymeric metallic or cermet layer on at least one of the major surfaces of the sheet.
2. The graphite article of claim 1 wherein the shape comprises a generally coiled cylinder.
3. The graphite article of claim 1 further comprising more than one sheet and the shape of each sheet comprising a chevron.
4. The graphite article of claim 1 wherein the shape comprises a generally honeycombed configuration.
5. The graphite article of claim 1 wherein the shape comprises a generally rectangular shape.
6. An electronic device comprising electronic component and a thermal management system in thermal contact with the electronic component, wherein the system includes at least one sheet of a graphite formed in a three dimensional shape other than its native sheet form thereby forming a graphite article, the graphite article comprising at least one of graphitized polyimide, compressed particles of exfoliated graphite or combinations thereof, a third component in thermal contact with the thermal management system and disposed above the thermal management system.
7. The electronic device of claim 6 wherein the shape comprises at least one of a coiled cylinder, a wound circle, a chevron, a pleated fold, a step configuration, a honeycomb or substantially rectangular.
8. The electronic device of claim 6 wherein in the electronic component comprises a package over package and the third component comprises an Rf can.
9. The electronic device of claim 6 wherein the thermal management system further comprises a contact element between the electronic component and the graphite article.
10. The electronic device of claim 6 wherein the third component comprises a heat dissipation element.
11. The electronic device of claim 6 wherein the graphite article has an anisotropic ratio of at least 100:1.
12. The electronic device of claim 6 further comprising a display in the same section of the device as the component and wherein the display not in thermal contact with the thermal management system.
13. An electronic device comprising electronic component and a thermal management system in thermal contact with the electronic component, wherein the system includes at least one sheet of a graphite formed in a three dimensional shape other than its unaltered form thereby forming a graphite article, the graphite article comprising at least one of graphitized polyimide, compressed particles of exfoliated graphite or combinations thereof, a third component in thermal contact with the thermal management system and disposed above the thermal management system.
14. The electronic device of claim 13 wherein in the electronic component comprises a package over package and the third component comprises an Rf can.
15. The electronic device of claim 13 wherein the shape comprises at least one of a coiled cylinder, substantially wound circle, a chevron, a pleated fold, a step configuration, a honeycomb or substantially rectangular.
16. The electronic device of claim 13 further comprising a display in the same section of the device as the component and wherein the display not in thermal contact with the thermal management system.
17. An electronic device comprising electronic component and a thermal management system in thermal contact with the electronic component, wherein the system includes at least one sheet of a graphite formed in a three dimensional shape other than its unaltered form thereby forming a graphite article, the graphite article comprising at least a graphitized polyimide sheet, a third component in thermal contact with the thermal management system and disposed above the thermal management system, the thermal management system having a height of at least 125 microns and a void space.
18. The electronic device of claim 17 wherein the system further includes at least a potting agent.
19. The electronic device of claim 17 further comprising a second electronic component having a differing height than the electronic component, a second thermal interface in thermal contact with the second electronic component and the third component in thermal contact with the second thermal interface, wherein the second thermal interface having a three dimensional shape other than the second interface material in its unaltered sheet form, the shape further comprising a void space, wherein the second thermal interface comprises at least one of sheet graphitized polyimide, and having a differing height than the graphite article.
20. The electronic device of claim 17 further comprising one or more additional thermal interfaces, wherein each thermal interface in thermal contact with the electronic component.
PCT/US2014/013721 2013-03-15 2014-01-30 Thermal interfaces WO2014149189A1 (en)

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