Apparatus including a heat-dissipating apparatus, and method for forming same

The present invention provides an apparatus (200) that includes a heat-generating component (202) and a heat-dissipating apparatus (120). The heat-generating component (202) is mounted on a substrate (204). The heat-dissipating apparatus (120) includes a housing piece (100) that includes a sealed chamber (102) and a phase change material (106) disposed within the sealed chamber (102). The heat-dissipating apparatus (120) is thermally coupled to the heat-generating component (202) and provides for heat dissipation by an endothermic process of changing phase from solid to liquid, thereby lowering the operating temperature of the heat-generating component (202).

FIELD OF THE INVENTION
 The present invention relates generally to an apparatus that includes a
 heat-generating component, and more particularly to an apparatus that
 includes a heat-dissipating apparatus.
 BACKGROUND OF THE INVENTION
 Electronic components, such as exciters, power amplifiers, transistors, and
 others, generate heat as they perform their normal functions. Although
 these components are able to continue working effectively while
 experiencing some increase in their temperature, they cannot be allowed to
 have their temperature raised above a certain temperature, as this can
 lead to failure in the component or can severely lessen the life of the
 electronic component.
 Electronic devices that include such components typically include means for
 removing some of the heat from the heat-generating components. Such
 methods currently include heat sinks, fans, and liquid cooling. Although
 each of these techniques is effective in lowering the temperature of the
 components, they are not easily integrated into hand-held electronic
 equipment, mainly due to the size of these components.
 In addition, when dealing with hand-held electronic devices, not only do
 you have to worry about the life of the component and its failure, but you
 also need to provide a comfortable operating temperature for the user of
 the electronic device. For instance, if a heat-generating component is
 included in a cellular telephone, and the excess heat buildup is not
 removed, the heat generated by the heat-generating component can be
 transferred to a user of the device, leading to discomfort for the user.
 Consequently, a need exists for a heat-dissipating device that can
 effectively remove heat from a heat-generating device, and particularly in
 a handheld electronic device.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
 The present invention provides a heat-dissipating apparatus that is
 effective in removing heat from a heat-generating component. An apparatus,
 such as a cellular telephone, includes a heat-generating component mounted
 on a substrate. The apparatus also includes a heat-dissipating apparatus
 that is thermally coupled to the heat-generating component. The
 heat-dissipating apparatus includes a housing piece that includes a sealed
 chamber and a phase change material disposed within the sealed chamber.
 The phase change material is effective in absorbing heat generated by the
 heat-generating component, whereby the phase change material changes phase
 from a solid phase to a liquid phase. This process is endothermic.
 Consequently, the liquefaction of the phase change material is effective
 to remove heat from the heat-generating component and to lower the
 temperature of the heat-generating component.
 The present invention can be better understood with reference to FIGS. 1-3.
 FIGS. 1A-1D depict a cross-sectional view of a method for forming a
 heat-dissipating apparatus in accordance with the present invention. FIG.
 1A depicts a housing piece 100. Housing piece 100 is preferably formed of
 a thin sheet of metal, preferably aluminum. Cavity 102 is formed in
 housing piece 100, preferably by stamping. Cavity 102 is preferably formed
 in a generally cylindrical shape, but can alternately be formed in a
 rectangular shape or any shape that is effective in dissipating heat.
 FIG. 1B depicts an alternate embodiment of the present invention. In the
 alternate embodiment of the present invention, a heat transfer enhancement
 agent 104 is disposed within cavity 102 of housing piece 100. Heat
 transfer enhancement agent 104 is effective in spreading heat within
 cavity 102 to provide for more uniform distribution of heat incident upon
 housing 100. Heat transfer enhancement agent 104 is preferably formed of a
 porous aluminum foam, but any material that is capable of spreading heat
 throughout cavity 102 would be effective as well.
 FIG. 1C depicts a phase change material 106 dispensed into cavity 102. In
 the preferred embodiment of the present invention, phase change material
 106 is dispensed into an empty cavity 102. In the alternate embodiment, as
 depicted in FIG. 1C, phase change material 106 is dispensed into cavity
 102 with a heat transfer enhancement agent 104 disposed therein. Cavity
 102 has a volume. A predetermined volume of phase change material 106 is
 dispensed into cavity 102. In the preferred embodiment of the present
 invention, the predetermined volume of phase change material 106 dispensed
 is less than the volume of cavity 102. In this manner, cavity 102 is not
 completely filled with phase change material 106. It is important to not
 completely fill cavity 102 with phase change material 106, because most
 phase change materials expand when changing from a solid phase to a liquid
 phase. Paraffin waxes expand in volume by about 10% when melting, while
 metals typically expand by about 2.5% upon melting. By leaving volume
 unfilled in cavity 102, room is left for expansion of phase change
 material 106.
 Phase change material 106 comprises a material that changes phase, from
 solid to liquid, upon heat being applied. In the preferred embodiment,
 phase change material 106 is formed of a material that is solid at room
 temperature.
 In the preferred embodiment, phase change material 106 is formed of an
 organic paraffin compound. Some examples of an organic paraffin compound
 include n-eicosene, n-octadecane, and n-dotriacontane. In an alternate
 embodiment of the present invention, phase change material 106 is formed
 of a low-temperature solder alloy, such as the eutectic
 bismuth-lead-tin-indium alloy. In a further alternate embodiment, phase
 change material 106 is formed of a low-temperature metal, such as gallium.
 Each of the metallic phase change materials will greatly increase the
 thermal conductivity of phase change material 106, and consequently will
 preferably not need a heat transfer enhancement agent 104 as depicted in
 FIG. 2.
 FIG. 1D depicts a lid piece 108 disposed onto housing piece 100. Lid piece
 108 is preferably formed of a thin sheet of metal, preferably aluminum.
 Lid piece 108 is preferably planar and is placed onto housing piece 100
 such that lid piece 108 completely overlies and covers cavity 102.
 Lid piece 108 is then attached to housing piece 100 to form
 heat-dissipating apparatus 120. In the preferred embodiment, lid piece 108
 is sealed to housing piece 100 via a low-temperature process, preferably
 conducted at a temperature below the melting temperature of phase change
 106. In this manner, phase change material 106 will not melt during
 attachment of lid piece 108 to housing piece 100, thereby ensuring that
 phase change material 106 will remain within cavity 102 during attachment.
 It should be understood that the temperature at which lid piece 108 is
 attached to housing piece 100 can be accomplished at a temperature
 slightly higher than the melting temperature of phase change material 106,
 as long as the temperature at phase change material 106 does not exceed
 its melting temperature. In the preferred embodiment of the present
 invention, lid piece 108 is attached to housing piece 100 via a crimping
 process. In an alternate embodiment of the present invention, lid piece
 108 is attached to housing piece 100 via an ultrasonic welding process or
 via an adhesive bonding process, with an adhesive such as an epoxy resin.
 Regardless of the method for attaching lid piece 108 to housing piece 100,
 it is critical that lid piece 108 be attached to housing piece 100 such
 that a seal is formed therebetween. This is important because the seal
 provides for the containment of phase change material 106 when phase
 change material 106 changes into liquid form upon heating.
 Heat-dissipating apparatus 120 includes a heat-transfer surface 110.
 Heat-transfer surface 110 is effective to transfer heat from a
 heat-generating component to phase change material 106. In the preferred
 embodiment of the present invention, heat-transfer surface 110 is planar
 and opposite cavity 102. In an alternate embodiment of the present
 invention, heat-transfer surface 110 is shaped in such a way as to conform
 to a heat-generating component, as depicted below in FIG. 3.
 FIG. 2 depicts an apparatus 200. In the preferred embodiment of the present
 invention, apparatus 200 comprises a wireless communication device, such
 as a cellular telephone or a two-way radio. Apparatus 200 can alternately
 comprise an apparatus that includes a heat-generating component where it
 is desired to remove some of the heat from the heat-generating component.
 Apparatus 200 includes a heat-generating component 222 that is mounted on
 a substrate 224. Heat-generating component 222 is preferably an exciter,
 but can alternately be a high-power RF transistor, a DC/DC converter, an
 AC/DC converter, a Digital Signal Processor, or any other electronic
 component that generates heat during operation. Substrate 224 is
 preferably formed of a glass-epoxy laminate commonly referred to as FR-4,
 but can alternately be formed of ceramic or other suitable substrate
 materials. In the preferred embodiment, apparatus 200 also includes an ear
 piece 226.
 In current hand-held communication devices, the optimal placement for
 exciter 222 is toward the top portion of apparatus 200. By placing
 heat-generating device 222 near the top portion of apparatus 200,
 heat-generating component 222 is closer to the antenna of apparatus 200,
 which is typically located at the top of apparatus 200. However, one
 downside of this arrangement is that heat-generating component 222 is
 located directly behind ear piece 226. For short calls, this arrangement
 is not disadvantageous. However, during long calls, as exciter 222 heats
 up during normal use, the temperature of ear piece 226 begins to rise.
 After a period of time, this increase in temperature of ear piece 226 can
 lead to discomfort by the user of apparatus 200.
 In the preferred embodiment of the present invention, heat-dissipating
 apparatus 120 is thermally coupled to heat-generating component 222. As
 depicted in FIG. 2, heat generated by heat-generating component 222 is
 transferred through substrate 224 to heat-dissipating apparatus 120.
 The following process would happen during a call utilizing the present
 invention. As the call begins, and heat-generating apparatus 222 begins to
 function normally, heat-generating apparatus 222 begins to heat up. After
 a few minutes of heating up, as the temperature of heat-generating
 apparatus 222 continues to increase, the heat generated by apparatus 222
 is transferred to heat-dissipating apparatus 120 through substrate 224.
 Phase change material 106 located within cavity 102 of heat-dissipating
 apparatus 120 begins to change phase from a solid phase to a liquid phase.
 During the time while phase change material 106 is melting (changing phase
 from solid to liquid), a constant operating temperature is ensured, since
 phase change material 106 melts isothermally. This isothermal reaction
 allows for even absorption of heat from heat-generating component 222.
 This even absorption of heat by phase change material 106 will continue
 until phase change material 106 is completely in a liquid state.
 After the call, when heat-generating component 222 is no longer generating
 heat, phase change material 106 will re-solidify by radiating heat to the
 surrounding atmosphere. In this manner, phase change material 106 will
 re-solidify to be ready to absorb more heat during the next call, or when
 heat-generating component 222 starts generating heat again.
 FIG. 3 depicts an apparatus 300 in accordance with an alternate embodiment
 the present invention. Apparatus 400 includes a heat-generating component
 322 attached to a substrate 324. Apparatus 400 also includes a
 heat-dissipating apparatus 320. Heat-dissipating apparatus 320 comprises a
 housing piece 301 that includes a cavity 302 formed therein. The cavity is
 filled with a liquid phase change material 306, and prior to phase change
 material 306 changing to a solid phase, a lid piece 308 is placed into
 phase change material 306 within cavity 302. The lid piece 308 has an
 impression that is of the same size and shape as heat-generating component
 322. The impression within lid piece 308 is preferably formed prior to
 attachment. Alternately, lid piece 308 is formed of a conformable
 material, such as a very thin aluminum sheet, and the impression is formed
 by pressing heat-generating component 322 into the conformable lid piece.
 Phase change material 306 is then allowed to solidify.
 Housing piece 300 can alternately be formed in a shape such that the cavity
 extends through housing piece 300. This generally donut shape allows for
 phase change material to be disposed within the cavity, and the cavity to
 surround the heat-generating component, but the heat-dissipating apparatus
 will not make the apparatus any thicker, since it does not add any depth
 to the apparatus.
 Lid piece 308 is then attached to housing piece 300 to seal cavity 302. As
 stated with regard to the preferred embodiment, the attachment process is
 done such that the temperature within cavity 302 does not exceed the
 melting temperature of phase change material 306 within cavity 302. This
 is preferably done by crimping, but can also be done by ultrasonic
 welding, adhesive bonding, or other suitable processes.
 Heat-generating component 322, which is attached to substrate 324, is then
 coupled to heat-dissipating apparatus 320 such that heat-generating
 component 322 fits into the depression formed in lid piece 308. Upon
 heating during normal operation, the heat generated by component 322 is
 transferred through heat-transfer surface 310 of lid piece 308 to phase
 change material 306. Phase change material 306 will, upon sufficient heat,
 begin to liquefy, which will remove heat from component 322.
 One advantage to the alternate embodiment is that there is a buffer layer
 between heat-generating component 322 and ear piece 326. This provides for
 additional comfort for the user of apparatus 300.
 The present invention provides an apparatus that includes a
 heat-dissipating apparatus. The heat-dissipating apparatus removes heat
 from a heat-generating component, thereby prolonging the life of the
 heat-generating component and lowering the operating temperature of the
 apparatus. This provides for increased comfort to the user of the
 apparatus. By providing the phase change material in a sealed cavity, the
 phase change material is allowed to liquefy and solidify with damaging
 component of the apparatus when in a liquid state.
 While this invention has been described in terms of certain examples
 thereof, it is not intended that it be limited to the above description,
 but rather only to the extent set forth in the claims that follow.