Thermally insulated electronic device

Abstract

Disclosed are thermally insulated devices and components having a heat-generating electrical component and a thermal insulation component. The thermal insulation component includes a porous polymer layer comprising a polymer matrix material defining pores and having an empty pore volume. The thickness of the porous polymer layer is between 20 and 300 microns; and the porosity of the porous polymer layer is at least 50%.

Description

THERMALLY INSULATED ELECTRONIC DEVICEField of the Invention

[0001] The invention relates to the field of thermal insulation, in particular to the thermal management of electronic devices.Background to the Invention

[0002] Electronic devices include electrical components that generate heat, such as RF transceivers (e.g. relatively high frequency 5G mobile phone antennae), CPUs, batteries and associated control circuitry, wireless charging induction coils and the like.

[0003] Portable and hand held devices in particular are desirably as compact or thin and lightweight as possible. The configuration of such devices can therefore require close packaging between a heat-generating component and another component within the device (which may be temperature sensitive) or between a heat-generating component and a device housing or casing. Heat flow to a housing or casing must be limited to ensure that a device, particularly if hand-held or portable, remains at a safe or comfortable temperature.

[0004] Thin insulating sheet materials in current use typically utilize aerogel technology. An “aerogel” is a gel material (where the gel is a particulate disordered structure) formed from a microporous solid in which the dispersed phase is a gas (PAC, 2007, 79, 1801 “Definitions of terms relating to the structure and processing of sols, gels, networks, and inorganic-organic hybrid materials, IUPAC Recommendations 2007, page 1806). Aerogels are known to be excellent thermal insulators, and can be included in laminate structures, for example deposited on or between polymer membranes or sheets, for use as ultra-thin insulation layers for electronics applications. Aerogels can also be incorporated into the pores of fabrics or porous materials to improve their mechanical properties, such as disclosed in US2021351501A1 or US2021351501A1 to W. L. Gore & Associates, Inc. the contents of which are incorporated herein in their entirety.

[0005] Aerogels are brittle materials, and the ultra-thin layers (less than 500 microns or in some cases less than 200 microns) used in insulation for electronic devices can be prone to particulation, which can limit the working lifetime of aerogel insulation and resulting dust can also cause damage to electrical components. Particulation can also result from handling of aerogel-based insulation during manufacture.

[0006] Mechanical robustness and lifetime can be improved by protective layers and / or by impregnating the aerogel into a supporting membrane or fabric, but particulation remains problematic for some applications - particularly where the insulation is subjected to mechanical stresses such as caused by compression or flexing of a device, for example.Summary of the Invention

[0007] Disclosed herein is thermal insulation for use in electronic devices. Aspects and embodiments relate to electronic devices, electronic components and casing for electronic devices comprising said thermal insulation layer.

[0008] A first aspect of the invention is an electronic device, comprising:a heat-generating electrical component; anda thermal insulation component, the thermal insulation component comprising a porous polymer layer comprising a polymer matrix material defining pores and having an empty pore volume and wherein the porous polymer layer has;a thickness of between 20 and 300 microns; anda porosity of at least 50%.

[0009] The thermal insulation component can be simply and cost effectively manufactured without the use of brittle materials, or materials prone to particulation during manufacture or use of an electronic device.

[0010] The thermal insulation component of the various aspects disclosed herein is described in further detail as follows.

[0011] Reference herein to the pore volume of the pores of the porous polymer layer being “empty” or the pores being “unfilled” means that all or substantially the pores are free of any other material, other than air or ambient gas. That is to say, all or substantially all of the pores of the porous polymer layer are free of other condensed phase material (in particular aerogel or any other non-gaseous insulating medium) and the porous polymer layer has not been through a process such as wetting or imbibing whereby the pores are filled with any such material. It will be understood that some infilling of pores, for example proximate to an outer face of the porous polymer layer, may occur in some embodiments. For example, some adhesive may be present in some embodiments, as disclosed below.

[0012] The porous polymer layer may accordingly consist essentially of the polymer matrix material. It will be understood that trace amounts of plasticizers, flow agents, or other additives as used in manufacture of polymer material may be present.

[0013] The thermal insulation component desirably has a largest pore size of less than about 5.0 microns. The largest pore size may be less than about 4.5 microns, less than about 4.0 microns, less than about 3.5 microns, less than about 3.0 microns or less than about 2.0 microns. The largest pore size may be between around 0.1-4.5 microns, between around 0.1-4.0 microns, between around 0.1 to 3.5 microns, between around 0.1 to 3.0 microns, or between around 0.1 to 2.0 microns.

[0014] The term “largest pore size” herein refers to a pore size diameter derived from gasliquid bubble point pressure measurement. A capillary flow porometer is used. The “bubblepoint pressure” is lowest gas pressure under which a wetting fluid is driven through a porous polymer layer. For an oil wetting fluid having a surface tension of y = 20.1 dynes / cm (i.e. 20.1 mN / m), a largest pore size diameter is determined by the following equation (1):Where d is diameter in microns and BP is bubble point pressure in kN / m2

[0015] In the examples set out below, a silicone oil with y = 20.1 dynes / cm was used.

[0016] It has been surprisingly found that a lower largest pore size may be associated with an improved crush resistance (or compression rate, as disclosed herein) at higher porosities.

[0017] The thermal insulation component, or the porous polymer layer thereof, desirably has a low thermal conductivity. The thermal insulation component, or the porous polymer layer thereof, may have a non-contact thermal conductivity of less than about 0.08 kW / m.K, or of less than about 0.07 kW / m.K, or of less than about 0.06 kW / m.K, or of less than about 0.05 kW / m.K. The thermal insulation component, or the porous polymer layer thereof, may have a non-contact thermal conductivity of less than about 0.040 kW / m.K, or of less than about 0.035 kW / m.K, or of less than about 0.030 kW / m.K, or of less than about 0.025 kW / m.K. The thermal insulation component may have a non-contact thermal conductivity of about.040 kW / m.K, or about 0.035 kW / m.K, or about 0.030 kW / m.K, or about 0.025 kW / m.K.

[0018] The porous polymer layer may have a porosity of greater than around 60%, greater than around 65%, or greater than around 70%. The porous polymer layer may have a porosity of between around 55%-98%, between around 60%-98%, between around 65%-98%, between around 60%-95%, between around 70%-95%, or between around 70%-90%.

[0019] The porosity of the porous polymer layer may be determined from the bulk density of non-porous polymer of the polymer matrix forming the porous polymer layer, and the density of the porous polymer layer as in equation (2):P = iooWhere porosity, P, is the void fraction %Dbuik is the bulk density of the polymer material of the porous polymer layer Dppi is the density of the polymer material of the porous polymer layer.Dbuik may be derived from areal weight of the porous polymer layer and non-contact thickness.

[0020] The thermal insulation component, and in particular the porous polymer layer thereof is advantageously crush resistant, so as to resist deformation and reduced thermalperformance in use of an electronic device comprising the thermal insulation component. Crush resistance may be measured by the % compressive strain through the thickness of the porous polymer layer, which may also be referred to as “compression rate”. The compression rate of the thermal insulation component, or the porous polymer layer thereof, at 41.4 kN / m2(6 psi) may be below around 45%, below around 40%, below around 30%, below around 25%, below around 20%, or below around 15%. The compression rate of the thermal insulation component, or the porous polymer layer thereof, may be between around 3%-30%, or between around 3%-25%, or between around 3-20%, or between around 3-15%. The compression rate of the thermal insulation component, or the porous polymer layer thereof, at 41.4 kN / m2(6 psi) may be around 14% or around 20%.

[0021] For some applications, the porous polymer layer of the thermal insulation component may have a desirable combination of these properties.

[0022] In some embodiments the porous polymer layer has: a porosity of between around 70%-95%; and a largest pore size of less than around 1.5 microns. The thermal conductivity may be less than around 0.045 kW / m.K.

[0023] The porous polymer layer may have: a porosity of between around 70%-95%; and a largest pore size of less than around 1.0 microns. The thermal conductivity may be less than around 0.045 kW / m.K, or less than around 0.040 kW / m.K, or less than around 0.035 kW / m.K, 0.030 kW / m.K.

[0024] The porous polymer layer may have: a porosity of between around 70%-95%; and a largest pore size of less than around 0.6 microns. The thermal conductivity of the porous polymer layer may be less than around 0.045 kW / m.K, or less than around 0.040 kW / m.K, or less than around 0.035 kW / m.K, 0.030 kW / m.K.

[0025] The porous polymer layer may have: a porosity of between around 70%-90%; a largest pore size of less than around 1.0 or 0.6 microns; a thermal conductivity less than around 0.040 kW / m.K, or less than around 0.035 kW / m.K; and a compression rate less than around 25%, or less than around 20%.

[0026] The porous polymer layer may have: a porosity of between around 70%-90%; and a largest pore size of less than around 1.5, 1.0 or 0.6 microns. The thermal conductivity of the porous polymer layer may be less than around 0.045 kW / m.K, or less than around 0.040 kW / m.K, or less than around 0.035 kW / m.K, 0.030 kW / m.K. The compression rate may be less than around 25%, or less than around 20%.

[0027] Unless otherwise stated, the thermal conductivity referred to herein relates to a measurement taken on a thermal component or porous polymer layer thereof that has not been subjected to any compressive force. That is to say, unless otherwise stated the thermal conductivity values provided can be considered as “non-contact” values.

[0028] The thickness of the thermal insulation component or the porous polymer layer thereof may be selected according to a particular purpose. For example, the thickness may be determined by an available space within an electronic device, or by other factors such as susceptibility to radio frequency radiation. The thickness may for example be between around 20-200 microns, between around 20-150 microns or between around 20-100 microns. The thickness of the thermal insulation component or the porous polymer layer thereof may be between around 15-25 microns, between around 40-60 microns, between around 45-55 microns, or between around 60-80 microns. The thickness of the thermal insulation component or the porous polymer layer thereof may be around 20 microns, 50 microns, 70 microns or 100 microns.

[0029] Unless otherwise stated, the thickness of the thermal component or porous polymer layer refers to a value of a thermal component or porous polymer layer that has not been subjected to any compressive force. That is to say, unless otherwise stated the thickness values provided can be considered as “non-contact” thickness values.

[0030] The porous polymer layer may be any suitable type of porous polymer layer, including but not limited to an expanded polymer layer or an electrospun polymer layer.

[0031] Materials which can be used for the porous polymer layer include, but are not limited to, fibrillated structures, such as expanded fluoropolymers (for example, expanded polytetrafluoroethylene (ePTFE)) or expanded polyethylene (as described in U.S. Patent 6,743,388 and incorporated herein by reference); fibrous structures (such as woven or braided fabrics; non-woven mats of fibers, microfibers, or nanofibers; materials made from processes such as electrospinning or flash spinning; polymer materials consisting of melt or solution processable materials such as fluoropolymers, polyamides, polyurethanes, polyolefins, polyesters, polyglycolic acid (PGA), polylactic acid (PLA), and trimethylene carbonate (TMC), and the like; films with openings created during processing (such as laser- or mechanically-drilled holes); open cell foams; microporous membranes made from materials such as fluoropolymers, polyamides, polyurethanes, polyolefins, polyesters, PGA, PLA, TMC, and the like; porous polyglycolide-co-trimethylene carbonate (PGA:TMC) materials (as described in U.S. Patent 8,048,503 and incorporated herein by reference); or combinations of the above. In another embodiment, said materials comprise micropores between nodes interconnected by fibrils, such as in ePTFE. In another embodiment, said material comprises micropores in an essentially nodeless ePTFE, as described in U.S. Patent 5,476,589, which is hereby incorporated by reference in its entirety for all purposes.

[0032] Properties of a porous polymer layer can be selected by adjusting parameters, and known in the art. For example, an expanded porous polymer layer can be made by passing tape through a sequence heated pinch rollers, with the expansion ratio being determined by the relative speed of the rollers in sequence. Parameters such as thickness, porosity and poresize etc. may be controlled via, inter alia the temperature, speed, relative speed (and thus expansion ratio), number of expansion steps performed, and / or whether expansion is uni-axial or biaxial.

[0033] The porous polymer layer in some embodiments comprises a polyoefin, such as polyethylene (PE) or polypropylene (PP), or a fluoro or perfluoro polymer, such as polyetrafluoroethylene (PTFE), perfluoromethylvinylether (PMVE) or fluorinated ethylenepropylene (FEP). In some embodiments the porous polymer layer comprises PE or PTFE, in particular expanded PE or PTFE (ePE, ePTFE).

[0034] The thermal insulation component may comprise further layers or materials, such as adhesive on one or more faces thereof. The adhesive may be used to attach the thermal insulation component within an electronic device, for example. The adhesive may be applied as a continuous layer or may be discontinuous (e.g. in a pattern of spots or discontinuous regions).

[0035] The adhesive may be directly against one or both faces of the porous polymer layer, and may be applied as a film, by spraying or dip coating or the like. It will be understood that application of adhesive may result in adhesive being present in some pores of the porous polymer layer (e.g. those proximate to the adhesive layer).

[0036] The thermal insulation component may include additional protective layer or layers, such as a non-porous polymer layer, e.g. a protective film.

[0037] The thermal insulation component may be of form part of a thermal management component, and comprise a thermally conductive component. A thermally conductive component in use may function to conduct heat away from a heat-generating electrical component, such that heat can be exhausted from the device across a wider surface area to reduce peak temperature increases transferred via the thermal management component. The porous polymer layer may be disposed between the thermally conductive component and a device casing or another heat-sensitive component of the electronic device, e.g. a human interface device (e.g. touch pad) or LCD or LED screen. The porous polymer layer may be disposed between the heat-generating component and the thermally conductive component. The thermally conductive component may be disposed between the porous polymer layer and a casing or heat sensitive component. The thermally conductive component may be disposed between each of two porous polymer layers (which may be the same as one another or different). A said porous polymer layer may be disposed between thermally conductive layers.

[0038] The thermal insulation component may comprise multiple layers, The thermal insulation component may comprise multiple porous polymer layers, for example laminated or bonded together and / or to other layers, such as one or more thermally conductive layer.

[0039] The thermal insulation component may serve additional functions as part of the electronic device, such as a covering (e.g. of an antenna) or as an electrically insulatingcomponent. The thermal insulation component may for example comprise a non-porous polymer layer (which may comprise the same polymer or polymers, or a different polymer or polymers as the porous polymer layer) adjacent to the porous polymer layer. One or both outer surfaces of the thermal insulation component (or porous polymer layer thereof) may be adjacent to a non-porous polymer layer.

[0040] In some embodiments, the thermal insulation component may function as a spacer, and define an air gap within the electronic device. Air gaps may be provided in electronic devices for heat management or electrical isolation between electrical components, electrical components and a casing, a human interface device or the like. Conventionally, a mesh may be used to define an air gap, however such conventional solutions provide a comparatively high conductivity pathway via the material from which the mesh is formed. In accordance with some embodiments, the thermal insulation component may comprise insulating regions and void regions therebetween (the void regions providing the air gap). The parts of the electronic device being spaced apart by the air gap are thus only connected via the very low thermal conductivity of the insulating regions.

[0041] The thermal insulation component may comprise a continuous or a discontinuous pattern of insulating regions. A continuous pattern may for example be formed by cutting into a mesh pattern, a pattern of lines or strips of the porous polymer layer (and any other layers present). A discontinuous pattern may for example be formed from an array discrete regions (e.g. circles, squares or the like) of porous polymer material (and any other layers present).

[0042] The thermal insulation component may be disposed between the heat-generating electrical component and a human interface device, such as a touchpad, keyboard, fingerprint senor, physical buttons for power, volume or the like. The thermal insulation component may be disposed between the heat-generating electrical component and a temperature-sensitive component, such as a display screen. The thermal insulation component may be disposed between the heat-generating electrical component and a casing part. The thermal insulation component may define a part of an external surface of the electronic device. The thermal insulation component may form or be part of a cover, e.g. across an opening of a casing, for example adjacent an antenna or a speaker). The thermal insulation may cover a part of an external surface of a casing or casing part.

[0043] The thermal insulation component may be attached or bonded (e.g. via adhesive as discussed herein) one or more of: the heat-generating electronic component, a casing part, a structural member (e.g. a keyboard carriage), a temperature-sensitive component, part of a heat management system, a can covering one or more electrical components.

[0044] The heat-generating electronic component may be any electronic component of, in particular portable, electronic devices that generate heat. The heat-generating electronic component may be a processor, such as a graphics processor (GPU), central processor (CPU)or the like. The heat-generating electronic component may be a transmitter or transceiver, such as a RF transmitter or transceiver (Wi-Fi, 4G, 5G, Bluetoothtm, ANT+ etc). The heat generating component may be a transformer, such as for charging a battery or regulating an input to an electronic device. The heat-generating component may be an induction coil. The heat-generating electronic component may be a power amplifier, or a baseband component that process signal for transmissions. In some embodiments, the heat-generating electronic component may be a memory module (e.g. SSD drives or the like), a speaker, a camera module, or a light source (such as an LED or an LED bar).

[0045] The electronic device may comprise more than one thermal insulation component. The heat-generating electronic component may be associated with more than one thermal insulation component, for example having a thermal insulation component against more than one face of the electronic component.

[0046] The electronic device may comprise more than one heat-generating electrical component. Each of a plurality of heat-generating electrical components may be associated with a corresponding thermal insulation component.

[0047] A given thermal insulation component may be associated with more than one heatgenerating electronic device. For example, a thermal insulation component may line all or a portion of a casing part for an electronic device, and be associated with multiple heatgenerating electronic components within the electronic device.

[0048] The electronic device may comprise a heat management system, to manage heat generated by the one or more heat-generating electrical components. A heat management system may for example comprise a heat sink, e.g. a metallic (typically copper) block, from which absorbed heat can be exhausted in a controlled manner. A heat management system may comprise a can (as disclosed herein) covering one or more electrical components. A heat management system may include a heat conduit, comprising a thermally conductive material (e.g. copper) to conduct heat away from a heat-generating electrical component. The heat management system may comprise a fluid conduit, to convey a heat exchange fluid. The heat management system may comprise a cooling circuit, comprising a said fluid conduit, optionally a heat exchanger, vapour chamber or the like as known in the art. The heat management system may comprise a fan, or radiator (e.g. heat conductive block with multiple fins).

[0049] A thermal insulation component as disclosed herein may be associated with one or more parts of the heat management system. A thermal insulation component may for example desirably contain heat energy within a part of the heat management system and / or contribute to directing flow of heat energy; thereby desirably mitigating temperatures elsewhere in the electronic device. A heat sink, heat conduit or fluid conduit may for example be covered by the thermal insulation component.

[0050] A second aspect of the invention is an insulated electronic unit comprising an heatgenerating electronic component and a thermal insulation component;wherein the thermal insulation component comprises a porous polymer layer, the porous polymer layer comprising a polymer matrix material defining pores and having an empty pore volume and wherein the porous polymer layer has;a thickness of between 20 and 300 microns; anda porosity of at least 50%.

[0051] The thermal insulation component may be disposed against at least a part of an external surface of the heat-generating electronic component.

[0052] In some applications, heat-generating electronic components (such as processors) are provided with a protective cover, known as a “can”. A can is typically a metallic cover (e.g. aluminium) attached to an underlying base board, to provide mechanical protection and in some cases also electromagnetic isolation to the electrical component. The thermal insulation component may be disposed against some or all of an external surface of the can.

[0053] The electronic unit may include multiple heat-generating components and / or one or more non-heat generating components (by which we mean components that do not generate sufficient heat to require insulation, or which do not generate sufficient heat to increase their temperature above ambient temperature in use). The electronic unit may for example comprise a PCB with multiple electronic components, more than one of which may be a heatgenerating electrical component, mounted thereon, wherein the thermal insulation component covers some or all of the multiple electronic components. A can may cover the or each heatgenerating electrical component and optionally other electrical components.

[0054] The heat-generating electrical component may be any electronic component, as disclosed herein

[0055] A third aspect of the invention is an insulated casing part for an electronic device, the casing part having an external surface and an internal surface, and a thermal insulation component against at least a part of the external surface and / or the internal surface;wherein the thermal insulation component comprises a porous polymer layer, the porous polymer layer comprising a polymer matrix material defining pores and having an empty pore volume and wherein the porous polymer layer has;a thickness of between 20 and 300 microns; anda porosity of at least 50%.

[0056] A fourth aspect of the invention is a method of insulating an electronic device; comprising providing a thermal insulation component as disclosed herein, and applying said thermal insulation component to one or more of:an external part of a heat-generating electronic component;at least a part of an external or internal surface of a casing part;between a casing part and a heat-generating electrical component;between a structural component and a heat-generating electrical component;a part of a heat management system.

[0057] The method will typically form part of manufacture of the electronic device, or of an electronic unit, which will later be incorporated into an electronic device.

[0058] The method may comprise bending the thermal insulation component, for example to conform to a shape of a casing part, or to wrap or partially wrap the thermal insulation component over or around a heat-generating electrical component, a structural member or any other element of the electrical device as disclosed herein. The thermal insulation component may for example be bent through an angle of at least around 30, 45, 60, or 90 degrees, over a length of below around 10 mm, 8 mm, 5 mm or 2 mm, in order to conform to a required shape or configuration.

[0059] The method may comprise cutting the thermal insulation component to size from a thermal material blank, for example from a sheet of thermal insulation material comprising a porous polymer layer as disclosed herein. Cutting to size may be automated, for example by laser cutting apparatus as known in the art.

[0060] The method may comprise placing the thermal insulation component that has been cut to size against one or more of: an external part of a heat-generating electronic component; at least a part of an internal surface of a casing part; a structural component, a part of a heat management system.

[0061] The method may comprise covering the heat-generating component with the thermal insulation component. The method may comprise covering more than one heat-generating component with one or more thermal insulation components.

[0062] The method may comprise use of a pick and place machine, as known in the art, in an automated step to pick up the thermal insulation component that has been cut to size and place said thermal insulation component against one or more of: an external part of a heatgenerating electronic component; at least a part of an internal surface of a casing part; a structural component.

[0063] The method may comprise attaching or bonding the thermal insulation component to one or more of: an external part of a heat-generating electronic component; at least a part of an internal surface of a casing part; a structural component.

[0064] The method may comprise providing the porous polymer layer by expanding a non-porous polymer sheet or tape, wherein the porous polymer layer is an expanded porous polymer membrane. The method may comprise forming the porous polymer layer by electrospinning.

[0065] The method may comprise applying adhesive to one or both faces of the porous polymer layer. The adhesive may be printed onto, e.g. in a discontinuous pattern, or sprayedonto the or each face of the porous polymer layer. The adhesive may be applied by dipping the porous polymer layer into adhesive or adhesive solution. The adhesive may be applied by laminating, for example by providing a film of adhesive and laminating the film and the porous polymer layer together.

[0066] Further features of each aspect of the invention correspond to features described in relation to any other aspect of the invention. It is also intended that the features and options described in relation to any embodiments disclosed herein are exemplary and that the invention encompasses embodiments with other combinations of the various features and options disclosed.

[0067] The phrases “in one embodiment”, “in an embodiment” and “in some embodiments” etc. as used herein do not necessarily refer to the same embodiment(s), though they may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, though they may. All embodiments of the disclosure are intended to be combinable.

[0068] Unless stated otherwise, the terms “comprises” and “comprising” mean to consist of, consist substantially of, or to include but not be limited to, such that further features may be present.

[0069] It is to be noted that all ranges described herein are exemplary in nature and include any and all values in between. Measurements that are reasonably close to the stated measurement deviate from the stated measurement by a reasonably small amount as understood and readily ascertained by individuals having ordinary skill in the relevant arts. In the event it is determined that individuals having ordinary skill in the relevant arts would not readily ascertain values for such reasonably small differences, the terms “substantially,” “approximately,” and “about” can 10 be understood to mean plus or minus 10% of the stated value.Brief Description of the Drawings

[0070] Non-limiting example embodiments will now be described with reference to the following figures in which:Fig. 1(a) is a photograph of a sheet of known thermally insulating material used in electronic devices;Fig. 1(b) is an SEM image through a thickness of a non-woven PET fabric imbibed with silica aerogel;Fig. 2 shows the relationship between areal weight and porosity of example porous polymer layers;Fig. 3 shows the relationship between non-contact thermal conductivity and porosity of example porous polymer layers;Fig. 4 shows the relationship between predicted non-contact thermal conductivity based on a linear regression fit to the data in Table 1 and the measured non-contact thermal conductivity values;Fig. 5 shows the relationship between contact thermal conductivity and porosity of example porous polymer layers;Fig. 6 shows the relationship between predicted contact thermal conductivity based on a linear regression fit to the data in Table 1 and the measured contact thermal conductivity values; Fig. 7 shows the relationship between compression rate and porosity of example porous polymer layers;Fig. 8 shows the relationship between largest pore size, porosity and thermal conductivity of example porous polymer layers;Fig. 9 shows the relationship between largest pore size, porosity and compression rate of example porous polymer layers;Fig. 10 shows a schematic cross sectional view of an example electronic device;Fig. 11 shows a schematic cross sectional view of an example insulated circuit board;Figs. 12(a)-12(e) show schematic perspective views of the stages of making an insulated casing part for an electronic device; andFig. 13 is a flow chart of an example method of making an insulated casing part.Detailed Description of Example Embodiments

[0071] Electronic devices, such as hand-held or portable devices (mobile telephones, tablets, laptop computers and the like) typically have target specifications for thermal performance. For example, for a hand held device, casing temperature (including touch scree surface) should not exceed 40-42 Celsius for user comfort.

[0072] The challenge posed to insulate increasingly compact electronic devices can be understood by reference to the Fourier conduction heat transfer equation (3):Where Q is the thermal conduction, or power (kW)k is thermal conductivity (kW / m.K)AT is the temperature difference (Kelvin)I is distance of which the heat is flowing (metres).

[0073] In the present context, I is the thickness of the thermal insulation component and Q is related to the rate of heat output from the heat-generating electrical component. If the available thickness I is reduced, then for a given power Q, and all other factors being equal, thetemperature reduction provided across the thermal insulation will fall. In order to achieve a required temperature drop, a thinner insulation must therefore be compensated for by improvements in the thermal conductivity of the insulating material.

[0074] By way of example, to meet performance requirements, a thermal insulation component within a mobile phone device must typically have a thermal conductivity in the range 0.02-0.07 kW / m.K (i.e. comparable to or lower than the thermal conductivity of an equivalent air gap) within a volume with a thickness of between 50-150 microns.

[0075] Known technical solutions typically utilize aerogels. However, aerogels are fragile materials and render the thermal insulation component susceptible to damage and particulation during handling or use.

[0076] Fig. 1(a) is a photograph of a sheet of known thermally insulating material used in electronic devices, in which a PET film is coated on one side with silica aerogel. The material has an overall thickness of around 70 microns and a thermal conductivity of less than around 0.09 W / m.K. The upper layer shown has been subjected to light mechanical abrasion, resulting in fracture of the aerogel layer. The aerogel layers of such material is also known to fracture on bending / wrapping of this type of insulation material. Fig. 1 (b) shows an SEM image through a thickness of a non-woven PET fabric imbibed with silica aerogel. The nominal thickness of the material is 400 microns and, typical of fabric-based insulation materials of this general type, the thickness across the layer is variable; reflecting the difficulty in controlling thickness during manufacture of such materials. It is clear that the sample preparation has resulted in the aerogel particulation visible in the image, and indeed the insulating material shown in Fig. 1(b) was found to be dusty when handling and prone to particulation when bending, when compressed or from contact with the surface. Consequently, in many applications a protective outer layer must be used to provide at least some degree of containment of the aerogel dust. Moreover, the comparatively high thickness of 400 microns is required to achieve suitable thermal insulating performance for some applications.

[0077] Candidate material for a thermal insulation component were prepared, consisting of porous polymer sheet material for use as a porous polymer layer of a thermal insulation component, in which the polymer matrix material thereof define pores having an empty pore volume, i.e. the pores are unfilled.

[0078] Physical properties of the porous polymer sheet material were measured and are set out in Table 1 below.TABLE 1

[0079] The relationship between areal weight (mass per area) and porosity of the porous polymer layers (based upon the nominal thicknesses quoted by the manufacturer of each material) is shown in Fig. 2.

[0080] The relationship between thermal conductivity and porosity of the examples of Table 1 is shown in Fig. 3. There is a relatively strong linear correlation shown, as illustrated by a low root mean square error (RMSE) and P-value of the best linear fit to the calculated data (see Fig. 4). The correlation was also observed, but was somewhat weaker, showing a higher RMSE (see Fig. 5 and Fig. 6). This indicates that other factors are also relevant to membrane performance.

[0081] Tables 2 and 3 provide statistical values of the correlations between non-contact TC and contact TC, for the parameters listed in Table 1. In Tables 2 and 3, The logworth value is -loglO(P-value) and the P-value is the probability of obtaining the observed data (or more extreme data) when the null hypothesis is true. This value was calculated using JMP data analysis software, published by JMP Statistical Discovery LLC (JMP is a trade mark).Table 2> >> > > >> &>>Table 3< >>

[0082] Notably, it was observed that the correlation between largest pore size and contact TC is significantly better in comparison to the other parameters (Table 3) than the correlation between largest pore size and non-contact TC (Table 2). Moreover, the multiple of porosity and largest pore size showed a closer correlation to contact TC than any parameter taken alone.

[0083] A general correlation between increased porosity and increased compression rate was observed (Fig. 7), however the scatter in these data again infer that the compression rate depends on multiple parameters.

[0084] This inter-relationship is shown in the contour plots of Figs. 8 and 9. Fig. 8 shows the relationship between largest pore size, porosity and thermal conductivity. Fig. 9 shows the relationship between largest pore size, porosity and compression rate. Some technical applications of a thermal insulation component will emphasise the requirements, for example, of thickness and thermal conductivity. Whereas, other applications may place greater emphasis on the thermal insulation component’s resistance to mechanical damage and thus compression rate may be of comparatively, greater importance. Figs. 8 and 9 show certain combinations of parameters for which one or both of an unexpectedly high thermal conductivity or compression rate may be achieved. An improved balance between these properties may be achieved within the regions marked generally as “A” on the figures.Experimental

[0085] CONTACT THERMAL CONDUCTIVITY:

[0086] Contact thermal conductivity was measured by a modified ASTM C518 test standard, using a TA Instruments FOX 50 heat flow meter. Thickness measurements used to calculate TC were obtained using an Instron Model 5565 Tensile tester. Each sample was placed between two plates, one heated and one cooled, and heat flow measured through the sample. In accordance with this test standard, the heat flow is measured using heat flux transducers, and the temperature difference between the plates is measured using thermocouples. The thermal conductivity is then calculated using Fourier's law of heat conduction.

[0087] NON-CONTACT THERMAL CONDUCTIVITY:Non-contact thermal conductivity was derived from differences in heat flow rate between a sample cell with and without a porous polymer layer present, using the same instrumentation and methods. The sample cell of the FOX 50 instrument was modified to provide an annular spacer between the upper and lower plates, such that a volume is defined within the circumference of the spacer. Measurements were taken with and without a sample in the volume, to obtain heat flow measurements of an air gap at the ambient conditions, and an air gap plus sample in the same ambient conditions. Non-contact thermal conductivity of the porous polymer layer sample kppiis calculated from equations (3a) and (3b):Rppl ~Rtotal ~Ralr (3a)WhereRppiis calculated heat flow rate of the porous polymer layer (m2K / W)totai is measured heat flow rate of the porous polymer layer and air gap within the spacer (m2K / W)Rair is measured heat flow rate of the air gap within the spacer (m2K / W)AndWherekppi is non-contact thermal conductivity of the porous polymer layer (W / m.K)A is cross sectional area of volume within the spacer (m2)AT is the temperature difference between the upper and lower plates (K)L is sample thickness (m)

[0088] BUBBLE POINT:

[0089] The bubble pointof a sample is the measured minimum pressure at which a gas bubble is forced through a liquid-filled pore. Bubble point was measured according to the general teachings of ASTM F31 6-03 using a capillary flow Porometer, Model CFP 1500AEXL from Porous Materials, Inc., Ithaca NY, USA. The sample membrane was placed into the sample chamber and wet with silicone oil (Silwick oil, available from Porous Materials, Inc.) having a surface tension of about 20.1 dynes / cm. The bottom clamp of the sample chamber had an about 2.54 cm diameter hole.

[0090] COMPRESSION RATE:

[0091] Compression rate was measured using an Instron Model 5565 Tensile tester with 0.5kN (1001b) load cell installed.

[0092] Non contact thickness was measured optically using a Keyence LS-7010 high-accuracy digital micrometer, by which thickness was measured to an accuracy of ±0.5 microns by comparing reflected and transmitted light. This technique enabled rapid, non-destructive measurements without physically contacting the film surface.

[0093] Fig. 10 shows a schematic cross sectional view of an electronic device 1, in the example shown a laptop, having a casing 2 formed from an upper casing part 3 and a lower casing part 5. The upper casing includes a carriage 7, which is a supporting structure for a human interface device, keyboard and touch pad 9. Various electronic components (indicated generally as 20) are housed within the casing 2 on a printed circuit board 22.

[0094] One or more of the components 20 may be heat-generating in use, such as the central processing unit 24. A battery 26 (or charging apparatus associated therewith, not shown) may be heat generating.

[0095] The device 1 includes, in the embodiment shown, a plurality of thermal insulation components 30, 32, 34, 36 are provided. The thermal insulation component 30, comprising aporous polymer layer as disclosed herein bonded to the upper casing part 3 via an adhesive film (not shown). Thermal insulation component 32 also is bonded to the lower casing part 5, and forms an insulating layer on the inner face 5a thereof. During application of the insulating layer of the component 32, the porous polymer layer is bent or wrapped to conform to the shape of the inner surface 5a, for example around tightly radiused corner section 5b. The pores of the porous polymer layer are empty and unfilled, and thus the application of the thermal insulation component 32 does not risk participation of any insulative material. Moreover, thin porous polymer layers of materials such as PE, PTFE, PP are far more flexible and able to conform to internal contours of an electronic device than other known thin-film insulation material.

[0096] The thermal insulation component 34 is similarly bonded to the internal face of the upper casing portion 3, around the radiused region 3b.

[0097] The thermal insulation component 36 is a thermal management component including a porous polymer layer 37 and a thermally conductive graphite layer 38 bonded by adhesive (not shown). The thermal management component 36 is itself bonded to the carriage 7. In use of the electronic device 1 , the thermal insulation components 30, 32, 34, 36 maintain the temperature of an outer surface of the casing 2 or the keyboard 9 to an acceptable level, for example less than around 40 Celsius. Heat generated by heat-generating electrical components such as the processor 24 and the battery 26 is transferred via the porous polymer layer 37 and radiated over a wider area by the thermally conducting layer 38, so as to further moderate the temperature of the interface device, keyboard 9.

[0098] Fig. 11 shows a view of an electronic unit, an insulated printed circuit board 40, with a PCB 22 to which are mounted electronic components 20 (which may be heat-generating or not heat-generating) and a processor 24. An thermal insulation component 42 is bonded to a face of the processor 24 and, in the embodiment shown, the electronic components 20. The thermal insulation component has been made to conform to the shape of the upper surfaces to which it is bonded.

[0099] An exemplary method is illustrated in Figs. 12 and 13. In step 1000, a casing part 50 is provided. It will be understood that the methods disclosed herein can be applied to other parts of an electronic device, as disclosed herein.

[0100] In step 1010, a sheet of thermally insulating material 60 is provided. The thermally insulating material can include a porous polymer layer such as an expanded polymer layer as disclosed herein and an adhesive backing (not shown).

[0101] The casing part 50 (such as a mobile telephone casing) has an internal face 52 with a back-plate 54 and curved transitions to side faces 56 (Fig. 12(a)). In step 1020, the thermal insulation sheet is cut to a template 62 corresponding to the internal face 52, with the tabs 66 corresponding to the side faces 56. The template 62 may be cut using a CNCcontrolled precision cutting apparatus, such as a laser cutting apparatus. As illustrated in Fig.12(b), the sheet may be sized such that multiple templates 62 may be cut therefrom.

[0102] In step 1030, a said template 62 is lifted, e.g. with a pick and place machine, from the sheet 60 (Fig. 12(c)) and, in step 1040, moved over the casing part 50 (Fig. 12(d))

[0103] In step 1050, the template 62 is bonded to the inner face 52, for example using a forming tool, such that the tabs 66 bend and conform to the curvature between the back plate 54 and side faces 56, and line the inner face 52. An insulating casing part 58 is thereby formed, having a thermal insulation component 68 bonded to the inner face 52.

[0104] It will be understood that the reference numerals applied to the exemplary method are not limiting upon the sequence of steps encompassed by the present disclosure, and that variations to the sequence and number of steps are envisaged.

[0105] The above described examples embodiments are intended to be illustrative only and in no way limiting. The described embodiments are susceptible to many modifications of form, arrangement of parts, details and order of operation. The disclosure is intended to encompass all such modification within its scope, as defined by the following claims.

Claims

CLAIMS1. An electronic device, comprising:a heat-generating electrical component; anda thermal insulation component, the thermal insulation component comprising a porous polymer layer comprising a polymer matrix material defining pores and having an empty pore volume and wherein the porous polymer layer has;a thickness of between 20 and 300 microns; anda porosity of at least 50%.

2. The electronic device of claim 1, wherein the thermal insulation component has a largest pore size of less than about 5.0 microns, less than about 3.5 microns, or less than about 2.0 microns.

3. The electronic device of claim 1 or 2, wherein the thermal insulation component, or the porous polymer layer thereof, has a non-contact thermal conductivity of less than about 0.08 kW / m.K, or of less than about 0.07 kW / m.K, or of less than about 0.040 kW / m.K, or of less than about 0.025 kW / m.K.

4. The electronic device of any preceding claim, wherein the porous polymer layer has a porosity of between around 55%-98%, or around 70%-95%, or between around 70%-90%.

5. The electronic device of any preceding claim, wherein the compression rate of the thermal insulation component, or the porous polymer layer thereof, below around 30%, or below around 20% at 41.4 kN / m2.

6. The electronic device of any preceding claim, wherein the porous polymer layer has:a porosity of between around 70%-95%; anda largest pore size of less than around 1.0 microns.

7. The electronic device of claim 6, wherein the thermal conductivity of the porous polymer layer is less than around 0.040 kW / m.K; and / or the compression rate is less than around 25%.

8. The electronic device of any preceding claim, wherein the thickness of the thermal insulation component or the porous polymer layer thereof is between around 20-150 microns.

9. The electronic device of any preceding claim, wherein the porous polymer layer is an expanded polymer layer or an electrospun polymer layer.

10. The electronic device of any preceding claim, wherein, wherein the porous polymer layer comprises polyethylene (PE) or polyetrafluoroethylene (PTFE).

11. The electronic device of claim 10, wherein the porous polymer layer comprises expanded polyethylene (ePE) or expanded polyetrafluoroethylene (ePTFE).

12. The electronic device of any preceding claim, wherein the thermal insulation component comprises adhesive and / or a protective layer on one or more faces thereof.

13. The electronic device of any preceding claim, wherein the thermal insulation component is, or forms part of, a thermal management component, and comprises a thermally conductive component, wherein the porous polymer layer is disposed between the thermally conductive component and a device casing or a heat-sensitive component of the electronic device; or wherein the porous polymer layer is disposed between the heat-generating component and the thermally conductive component.

14. The electronic device of any preceding claim, wherein the thermal insulation component is disposed between one or more of:the heat-generating electrical component and a human interface device;the heat-generating electrical component and a temperature-sensitive component; the heat-generating electrical component and a casing part.

15. The electronic device of any preceding claim, wherein the thermal insulation component is attached or bonded to one or more of:the heat-generating electronic component;a casing parta structural member;a temperature-sensitive component;a part of a heat management system;a can, covering one or more electrical components.

16. The electronic device of any preceding claim, wherein the heat-generating electronic component is selected from: a processor, a transmitter or transceiver, a transformer, aninduction coil, a power amplifier, a baseband component, a memory module, a speaker, a camera module, a light source.

17. The electronic device of any preceding claim, comprising a heat management system, and comprising one or more thermal insulation components, wherein the said one or more thermal insulation components is associated with one or more parts of the heat management system; and wherein the one or more thermal insulation component functions to contain heat energy within a part of the heat management system and / or contributes to directing flow of heat energy.

18. An insulated electronic unit comprising:an heat-generating electronic component; anda thermal insulation component;wherein the thermal insulation component comprises a porous polymer layer, the porous polymer layer comprising a polymer matrix material defining pores and having an empty pore volume and wherein the porous polymer layer has;a thickness of between 20 and 300 microns; anda porosity of at least 50%.

19. The insulated electronic unit of claim 17, comprising more than one heat-generating component and / or one or more non-heat generating components.

20. An insulated casing part for an electronic device, the casing part having an external surface and an internal surface, and a thermal insulation component against at least a part of the external surface and / or the internal surface;wherein the thermal insulation component comprises a porous polymer layer, the porous polymer layer comprising a polymer matrix material defining pores and having an empty pore volume and wherein the porous polymer layer has;a thickness of between 20 and 300 microns; anda porosity of at least 50%.

21. The insulated electronic unit of claim 18 or 19, or the insulated casing part of claim 20, wherein the thermal insulation component has a largest pore size of less than about 5.0 microns, less than about 3.5 microns, or less than about 2.0 microns.

22. The insulated electronic unit of claim 18, 19 or 21, or the insulated casing part of claim 20 or 21, wherein the thermal insulation component, or the porous polymer layer thereof, hasa non-contact thermal conductivity of less than about 0.08 kW / m.K, or of less than about 0.07 kW / m.K, or of less than about 0.040 kW / m.K, or of less than about 0.025 kW / m.K.

23. The insulated electronic unit of any one or claims 17, 18 or 20-21, or the insulated casing part of any one of claims 19 to 21 , wherein the porous polymer layer has a porosity of between around 55%-98%, or around 70%-95%, or between around 70%-90%.

24. The insulated electronic unit of any one or claims 18, 19 or 21-23, or the insulated casing part of any one of claims 20-23, wherein the compression rate of the thermal insulation component, or the porous polymer layer thereof, is below around 45%, or below around 30%, or below around 20% at 41.4 kN / m2.

25. A method of insulating an electronic device; comprising:providing a thermal insulation component as disclosed herein, and applying said thermal insulation component to one or more of:an external part of a heat-generating electronic component;at least a part of an internal surface of a casing part;between a casing part and a heat-generating electrical component;between a structural component and a heat-generating electrical component;a part of a heat management system.

Images