Excessive heat generation caused by the operation of small handheld personal electronic devices, such as cell phones, e-readers and other such devices, is an increasingly challenging problem as the size of such devices continue to shrink, while their performance, and thus heat output, continues to grow. The heat generated by internal electronic components can lead to high external surface temperatures on the outside surface of such devices and result in user discomfort, such as discomfort in a person's lap or palm. Such discomfort can lead to customer complaints, warranty claims and a diminished reputation in the market place. Thus, the thermal management of the sealed electronic enclosures of such devices presents an increasing challenge to the designers and engineers involved in the development of such products.
An exemplary embodiment provides a better heat dissipation device for electronic enclosures to aid in reducing the overheating of internal components of such devices and therefore their concomitant external surface temperature.
Some embodiments are directed to a device comprising a heat dissipation composite that uses two or more heat dissipation mechanisms to enhance heat dissipation and reduce the external surface temperature of an electronic device. The composite of some embodiments can have applications in various electronic devices such as computers, cellular phones, LCD or LED display panels, LED lights used in conjunction with printed circuit boards (PCBs), LCD backlight units (BLU) and the like.
In one embodiment, the device comprise a heat dissipation composite, comprising a reflective film configured to reflect heat or thermal energy and an anisotropic component, wherein the reflective film forms an outer major surface boundary of the composite. In another embodiment, the device comprises a heat dissipation composite, comprising a reflective film configured to reflect thermal energy; a metal layer; and a graphite sheet, wherein the metal layer is interposed between the reflective film and the graphite sheet.
the heat dissipation composite is a multi-layer structure, comprising a heat reflective film with a reflectivity of at least 70%; an electroplated metal layer selected from copper, nickel, chromium, gold, silver, tin, platinum, or combinations thereof; a flexible exfoliated graphite sheet; and one or more adhesives, wherein the electroplated metal layer is interposed between the adhesive and the graphite sheet, the adhesive is interposed between the reflective film and the electroplated metal layer.
In another embodiment, the device comprising a means for managing heat energy, comprising means for reflecting heat energy; and means for dissipating heat having an anisotropic property.
Embodiments are also directed to methods of dissipating heat and reducing the external surface temperature of an electronic device using the heat dissipation composite. The method includes the following steps:
Other utilities of some embodiments will become apparent in the following detailed description of the embodiments, with reference to the accompanying drawings, in which:
As employed above and throughout the disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings.
As used herein, the singular forms “a,” “an,” and “the” include the plural reference unless the context clearly indicates otherwise.
As used herein, the term “about,” when referring to a measurable value such as a thickness, and the like, is meant to encompass variations of ±10%, ±5%, ±1%, and/or ±0.1% from the specified value, as such variations are appropriate to the thickness of the reflective film, unless otherwise specified. As used herein, the term “about,” when referring to a range, is meant to encompass variations of ±10% within the difference of the range, ±5%, ±1%, and/or ±0.1% from the specified value.
An exemplary heat dissipation composite comprises an anisotropic component that has a higher thermal conductivity in a planar direction (e.g., in the x-y direction as illustrated, for example, in
In an exemplary embodiment, the reflective component reflects about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or more of the incident radiation.
In one group of embodiments, the anisotropic component of the heat dissipation composite is graphite. In another group of embodiment, the anisotropic component of the heat dissipation composite comprises a metal layer and an insulating film. In yet another group of embodiment, the anisotropic component of the heat dissipation composite comprises a metal layer and an insulating film, and is devoid of graphite.
In one group of embodiments, the heat dissipation composite comprises a reflective film configured to reflect heat energy and a graphite sheet, substantially free of thermoplastic polyester foamed material. In another embodiment, the heat dissipation composite consists essentially of reflective film, a metal layer and a graphite sheet.
In an exemplary embodiment, the heat dissipation composite further comprises a metal layer, as illustrated in
In one embodiment, the metal layer 3 is electroplated onto the graphite sheet 4 according to the method disclosed in U.S. Pub. No. 2010/0243230, which teachings pertaining to electroplating are incorporated herein by reference in their entirety. In an exemplary embodiment, the graphite sheet 4 is cleaned with an acid solution or plasma solution at atmospheric pressure, followed by electroplating the metal on the graphite sheet 4. In another embodiment, the metal layer 3 is adhered to the graphite sheet 4 using a double-sided adhesive or other means. In an exemplary embodiment, the metal layer is in direct physical contact with one of the major surfaces of the graphite sheet layer and does not cover any of the edges of the graphite sheet. The metal layer 3 prevents the flaking of and provides stiffness to the graphite sheet 4.
In another group of embodiments, the heat dissipation composite comprises a reflective film 2, a metal layer 3 and an insulating film 5, placed adjacent to one another. (See
In another embodiment, the heat dissipation composite 1 further comprises an adhesive 6 or other means for adhering the reflective film to the metal layer (e.g., as in
In an exemplary embodiment, the insulating film is in direct physical contact with one of the major surfaces of the metal layer and does not cover any of the edges of the metal layer.
The heat dissipation composite 1 is adhered to an electronic device's casing using an adhesive 6 (e.g., as in
In one embodiment, the heat dissipation composite 1 reduces the external surface temperature of an electronic device by about 7.5° C. to about 20° C. relative to no heat dissipation composite. In another embodiment, the heat dissipation composite 1 reduces the external surface temperature of an electronic device by about 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19° C. relative to no heat dissipation composite.
The reflective film used in some embodiments attenuates heat radiation. As illustrated in
In an exemplary embodiment, the performance characteristics detailed herein are related to heat radiation/heat energy that corresponds to the infrared part of the electromagnetic spectrum. In an exemplary embodiment, the performance characteristics detailed herein are related to heat radiation/heat energy that corresponds to radiation having a wavelength of more than about 750 nm and/or between about 750 nm to about 1 mm.
The reflective film comprises a base material with a reflective layer. A protection layer is optionally disposed on the reflective coating to avoid oxidation of the reflective coating.
The base material can be a glass, a plastic or a metal such as aluminum. A wide variety of reflective layers can be used as the reflective film. Examples of reflective coatings useful in at least some embodiments include, but are not limited to, indium, tin, gold, platinum, zinc, silver, copper, titanium, lead, an alloy of gold and beryllium, an alloy of gold and germanium, nickel, an alloy of lead and tin and an alloy of gold and zinc. In an exemplary embodiment, the reflective coating is made of silver. In another exemplary embodiment, the reflective coating is substantially free of optical fiber.
The protection layer can comprise an antioxidant such as metal oxides, silicon oxides, metal nitrides, silicon nitrides and other appropriate antioxidants.
The reflective film can have, in some embodiments, a reflectivity of at least 70% as measured by CIR l*a*b* using D65 light source (6500K) and/or a reflectivity as otherwise detailed herein and the thickness is about 0.05 mm to about 0.5 mm.
The reflective film faces the heat source directly, i.e., there is no interposing layer between the reflective film and the heat source.
The graphite sheet in the heat dissipation composite can be prepared from natural, synthetic or pyrolytic graphite particles. An example of natural graphite used in at least some embodiments includes, but is not limited to, flexible exfoliated graphite (made by treating natural graphite flakes with substances that intercalate into the crystal structure of the graphite). The thermal conductivity of the graphite sheet is anisotropic, i.e., high in the direction parallel to the major faces of the flexible graphite sheet (in-plane conductivity) and substantially less in the direction transverse to the major surfaces of the graphite sheet (through-plane conductivity). In an exemplary embodiment, anisotropic ratio of the graphite sheet, defined as the ratio of in-plane conductivity to through-plane conductivity, is between about 2 to about 800. The graphite sheet can be about 0.01 mm to about 0.5 mm.
The metal layer 3 in some embodiments is isotropic in nature, i.e., it has a higher thermal conductivity in a through direction (e.g., in the z direction as illustrated, for example, in
In some embodiments, the metal layer 3 includes two metal films wherein a cooper film having a thickness ranging from 8 μm to 10 μm is formed on the graphite sheet 4, and a nickel film having a thickness ranging from 2 μm to 5 μm is formed on the copper film.
Suitable materials for the insulating film 5 include, but are not limited to, resin, polyester (e.g., polyethylene terephthalate or PET) and polyimide materials. An exemplary material is PET, with a thickness of about 0.001 mm to about 0.05 mm. The insulating film can be applied to the metal layer by various methods known in the field, such as by coating, using a hot laminating process, or by adhesion.
An adhesive 6 is disposed between the reflective film 2 and the metal layer 3, and/or between the heat dissipation composite and the electronic device's casing or a heat sink. The adhesive is a double-sided adhesive tape, including a pressure sensitive adhesive coating and a release liner. The thickness of the adhesive is about 0.005 mm to about 0.05 mm. Examples of suitable adhesives useful in at least some embodiments include, but are not limited to, 3M 6T16 adhesive and 3M 6602 adhesive, both are commercially available from 3M, USA. In one exemplary embodiment, the refractive index is above about 1.30.
By juxtaposition of the metal layer 3 and the insulating layer 5, an anisotropic composite is formed whereby the heat can spread across the planar direction of the metal layer 3.
In some instances of executing the above methods, there can be less heat transferred to the heat dissipation composite 1 because the reflective film 2 reflects a portion of the heat away from the composite 1 (pathway B). The reflected heat is then dissipated in the ambient air through radiation. In addition, less heat reaches the external surface of the electronic device as heat is spread out through the anisotropic composite (pathways D and E). By using various cooling mechanisms, the heat dissipation composite of at least some embodiments can increase heat dissipation and reduce the external surface temperature of the electronic device as compared to more conventional approaches.
The following examples further illustrate some embodiments. These examples are intended merely to be illustrative and are not to be construed as being limiting.
A computer laptop was modeled for this study and three types of heat dissipation devices were used: a reflective film (Toray E6ZA100, commercially available from Toray, Japan), a flexible graphite sheet electroplated with a metal layer (flexible graphite sheet+metal), and a heat dissipation composite (reflective film+metal+flexible graphite sheet).
The heat dissipation device was about 100 mm×100 mm in size and interposed between the heat source and the laptop's plastic casing. The study was conducted at room temperature (25° C.)
The heater was pre-heated to 80° C. prior to the commencement of the study. The external surface temperature of the laptop casing was measured every 30 seconds for 10 minutes using a thermometer (Model TM-946 from Lutron, Taiwan). The temperature was measured at the “surface temperature” point in
The study results are summarized in Table 1. The maximum recorded external surface temperature was 71.3° C. in the group without any heat dissipation device, 69.8° C. in the reflective film group, 67.9° C. in the graphite sheet+metal layer group, and 52.3° C. for the heat dissipation composite. Using the maximum external surface temperature in the group without any heat dissipation device as a reference, the reflective film reduced the external surface temperature by 1.5° C., the graphite sheet+metal layer reduced the external surface temperature by 3.4° C. and the heat dissipation device according to this embodiment reduced the external surface temperature by 19.0° C.
The results show that the heat dissipation composite according to this embodiment is more efficient in dissipating heat in an electronic device compare to a reflective film or a graphite sheet alone.
This application claims priority to U.S. Provisional Patent Application No. 61/669,140, filed Jul. 9, 2012, the contents of which is incorporated herein by reference in its entirety.
Number | Date | Country | |
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61699140 | Sep 2012 | US |