Patent Application
20150043162
Electromagnetic (EM) radiation generated by internal electronic components can interrupt electronic operations and cause electronic devices to malfunction. This is electromagnetic interference (EMI). As operating frequencies increase and the electronic devices become more complex, they may be more susceptible to electromagnetic interference (EMI).
EMI shields are commonly implemented in a design to isolate one component or section of an electronic device from another or to protect circuitry in an electronic component from a source external to the component (including other electronic components). The EMI shield can either be soldered to or clip on to the contact points on the component.
To ensure a reliable and robust electromagnetic seal, the EMI shield encloses the entire electromagnetic radiation component of the electronic device, such as a central processing unit (CPU) or an integrated circuit. The heat generated by the internal component, such as a CPU, will accumulate in the EMI shield and adversely affect the performance of the internal component. Openings or apertures on the EMI shields provide ventilation addresses the problem of heat accumulation. However, these features can undermine shielding effectiveness. Thus, there is a need for EMI shields that have improved heat dissipation property and shielding effectiveness.
Some embodiments provide an EMI shield, wherein the shield is configured to substantially uniformly distribute heat throughout the shield when one side of the shield is exposed to a heat source that creates a temperature imbalance between the side of the shield more exposed to the heat source and an opposite side of the shield less exposed to the heat source. In one exemplary embodiment, the EMI shield comprises a first layer configured to shield EMI and a second layer configured to dissipate heat.
Some embodiments provide an apparatus comprising an EMI shield.
Some embodiments are directed to an apparatus comprising a means for shielding electromagnetic interference (EMI) and substantially uniformly dissipating heat; and an electronic component at least one of shielded by the means for shielding EMI or emitting EMI that is shielded by the means for shielding EMI. The means substantially uniformly dissipate heat when one side of the means is exposed to the electronic component that creates a temperature imbalance between the side of the means more exposed to the electronic component and an opposite side of the means less exposed to the electronic component.
Another embodiment provides a portable electronic device, such as a laptop computer, a desktop computer, a hand-held communications device, etc., comprising: a motherboard; a central processing unit (CPU) supported on a first side of the motherboard; and an EMI shield surrounding the sides of the CPU not surrounded by the motherboard, the shield including: a first layer configured to shield EMI; and a second layer configured to dissipate heat, wherein the shield is configured to substantially uniformly distribute heat throughout the shield when one side of the shield is exposed to a heat source that creates a temperature imbalance between the side of the shield more exposed to the heat source and an opposite side of the shield less exposed to the heat source, wherein the shield is configured such that when the CPU outputs 2.5 watts of thermal energy over a time period where heat transfer from the CPU to the shield has reached saturation and such that the CPU has a surface temperature of 68.5 degrees C. at a first location about 0.5 mm from the shield, a temperature distribution of the shield is such that the closest point to the first location on an opposite side of the shield having 60×60 mm2 geometrically centered about the first location and facing away from the shield is at about 50 degrees C. and locations of the shield on that side furthest away from the closest point have a temperature within the range of about 48 to about 50 degrees C.
Embodiments are also directed to methods of reducing external surface temperature of an electronic component and reducing EMI to and from the component using the EMI and impact resistant shield. The method includes the following actions:
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 illustrated in
In another exemplary embodiment, as illustrated in
In some embodiments, the EMI shielding layer 2 and the heat dissipation layer 3 are connected at 4, by one of the following processes: lamination, coating (requires one or more interfaces 4A) and electroplating (requires one or more interfaces 4A). The thickness of the EMI shield 1 is at least 20 um in some embodiments. In one embodiment, the thickness of the EMI shielding layer 2 and heat dissipation layer 3 of the EMI shield 1 are the same. In another embodiment, the thickness of the EMI shielding layer 2 and heat dissipation layer 3 of the EMI shield 1 are different.
In one embodiment, by forming the EMI shield 1 in this manner, anisotropic thermal conductivity is achieved by the juxtaposition of an EMI shielding layer 2 and isotropic heat dissipation layer 3.
In one exemplary embodiment, as illustrated in
Referring to
Referring to
In one group of embodiments, the EMI shield 1 uniformly distributes the heat over the shield 1 when one side of the shield is exposed to a heat source that creates a temperature imbalance between the side of the shield more exposed to the heat source and an opposite side of the shield less exposed to the heat source.
In one embodiment, the EMIS shield 1 is configured such that a heat source outputting 2.5 watts of thermal energy having a surface saturation temperature of 68.5 degrees C. at a location closest to the EMI shield 1 and about 0.5 mm from the EMIS shield 1 results in a temperature distribution of the shield such that the closest point to the location on an opposite side of the EMI shield 1 having 60×60 mm2 geometrically centered about the location and facing away from the EMI shield 1 is at about 50 degrees C. and locations of the EMI shield 1 on that side furthest away from the closest point have a temperature within the range of about 48 to about 50 degrees C.
In some embodiments, the EMI shield 1 has a shield effectiveness for EMI over a range of about 50 MHz to about 4.2 GHz falls within a range of about 88 dB to about 75 dB.
In an exemplary embodiment, there is a portable electronic device, such as a laptop, having a housing/casing, having an interior height of less than 2 inches, less than 1.5 inches, less than 1.0 inches, less than 0.75 inches, less than 0.5 inches or any vale or range of values therebetween in 0.1 inch increments (e.g., 1.8 inches, 0.7 inches, 0.6 inches to 1.2 inches, etc), and a width and length of larger dimensions, in which housing any or all of the components detailed herein are located with the respective height, width and length at least substantially aligned in the same manner. An example of such housing or casing is the base of a laptop having a keyboard or other user interface, where, in an exemplary embodiment of such exemplary housing, the base is movably attached a liquid crystal display.
In one exemplary embodiment, EMI Shielding layer 2 shields EMI and is substantially flat.
The term “substantially flat” as used herein to describe surfaces of the EMI shielding layer 2 or heat dissipation layer 3 refers to a surface that does not touch the side of the electronic component 5 surrounded by the EMI shield 1. A substantially flat surface can include a flat surface having various surface characteristics that do not touch the side of the electronic component 5 surrounded by the EMI shield 1. In addition, the substantially flat surfaces can have slight curvature as long as such curvature does not cause the EMI shield 1 to touch the side of the electronic component 5 surrounded by the EMI shield 1. The substantially flat surfaces of the EMI shielding layer 2 or heat dissipation layer 3 can have defined or rounded edges.
In an exemplary embodiment, the thickness of the EMI shielding layer 2 is equal to or more than about 10 μm. In another exemplary embodiment, the EMI shielding layer 2 has one or more of the following characteristics: heat dissipation, ductility, elasticity, forming or spinning property.
In one exemplary embodiment, the EMI shielding layer 2 is selected from stainless steel, aluminum, nickel silver, tin plate, tin coated steel, bass, an alloy, or a combination thereof. In another exemplary embodiment, the EMI shielding layer 2 is stainless steel.
In one exemplary embodiment, heat dissipation layer 3 substantially uniformly dissipates heat throughout the EMI shield 1 and is substantially flat. In some embodiments, the heat dissipation layer 3 dissipates heat in an anisotropic direction, i.e., high in the direction parallel to the major faces of the heat dissipation layer 3 (in-plane conductivity) and substantially less in the direction transverse to the major surfaces of the heat dissipation layer 3 (through-plane conductivity).
In an exemplary embodiment, the thickness of the heat dissipation layer 3 is equal to or more than about 10 μm.
In one exemplary embodiment, the heat dissipation layer 3 is selected from copper, aluminum, nickel silver, tin plate, tin coated steel, bass, an alloy, or a combination thereof. In another exemplary embodiment, the heat dissipation layer 3 is copper.
An interface 4A is disposed between the EMI shielding layer 2 and the heat dissipation layer 3. Suitable interfaces 4A include, but are not limited to, adhesive and graphite. The adhesive is a double-sided adhesive tape, including a pressure sensitive adhesive coating and a release liner. 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 some embodiments, the graphite interface 4A 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. 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.
Methods of reducing external surface temperature of an electronic component and reducing EMI from the electronic component using the EMI shield 1 are provided in some embodiments. The method includes the following actions:
In some embodiments, the methods further comprise the action of reducing the EMI from the ambient environment into the component relative to that which would be the case in the absence of the EMI shield.
In one embodiment, heat from the internal component 5 is then transferred to the EMI shield 1, wherein the heat spreads across the planar direction (i.e. anisotropic direction) of the EMI shield 1. In another embodiment, heat from the internal component 5 is then transferred to the EMI shield 1, wherein the heat spreads across the planar direction (i.e. anisotropic direction) of the heat dissipation layer 1 (pathways A in
In one exemplary embodiment, by juxtaposition of an EMI shield layer 2 and an isotropic heat dissipation layer 3 (such as copper), the heat dissipation layer 5 becomes anisotropic whereby the heat can spread across the planar direction of the heat dissipation layer 3 (pathways A in
In one exemplary embodiment, the EMI shield 1 uniformly distributes the heat over the EMI shield 1 if its temperature distribution ratio is less than about 15% when one side of the EMI shield 1 is exposed to the electronic component with a surface temperature of 60° C. or higher and the other side of the EMI shield is exposed to no more than 50% of the heat of the electronic component. In another exemplary embodiment, the EMI shield 1 uniformly distributes the heat if its temperature distribution ratio is equal to or less than about 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1% or any value or range of values therebetween in 0.1% increments (e.g., about 2.5%, about 4.5%, about 2.6% to about 4.6%, etc.). The temperature distribution ratio based on a 6 cm×6 cm EMI shield is defined as follows: (maximum measured temperature of the EMI shield 1−minimum measured temperature of the EMI shield 1)/minimum measured temperature of the EMI shield 1.
In another exemplary embodiment, the EMI shield 1 uniformly distribute the heat over the shield 1 if the difference of the maximum measured temperature of the EMI shield 1 and the minimum measured temperature of the EMI shield 1 is equal to or less than about 10° C., 9° C., 8° C., 7° C., 6° C., 5° C., 4° C., 3° C., 2° C., 1° C. and/or any value or range of values therebetween in 0.1° C. increments (e.g., about 2.2° C., about 4.4° C., about 2.2° C. to about 3.3° C., etc.).
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 heat source 5 was placed in direct contact with a mother board 6 for this study and three types of EMI shields 1 were used:
In this study, the heat source 5 was about 25.4 mm(length)×25.4 mm(width)×0.5 mm (height) and the heat power was about 2.5 watts. The EMI shield 1 was about 60 mm(length)×60 mm(width)×1 mm(height) and interposed between the heat source 5 and an outer casing 10. The distance between the inner surface of the EMI shield 1 and the outer surface of the heat source 5 was about 0.5 mm, and the distance between the outer surface of the EMI shield 1 and the inner surface of the outer casing 10 was about 2 mm.
The heater source 5 was pre-heated to 80° C. prior to the commencement of the study. The temperature was measured after 2 hours using a thermometer (YOKOGAWA DX-2048, Tokyo, Japan). The temperature was measured at points H, L, M, R, and O in
The results show that the stainless steel+copper EMI shield according to one embodiment has a temperature distribution ratio of about 4.6% and is more efficient in heat dissipation compare to a stainless steel EMI shield or a copper EMI shield. In addition, heat is uniformly distributed over the EMI shield using the stainless steel+copper EMI shield according to one embodiment. This is illustrated by a small temperature difference (from about 0.7° C. to about 2.3° C.) on the EMI shield at 2 hours. In addition, the stainless steel+copper EMI shield according to one embodiment is effective in shielding the EMI.
