Abstract:
The present invention relates to a thermal solution for hand-held devices. In an embodiment, the present invention implements a thermal gap filler and a system enclosure for effective thermal management of high performance hand-held devices. In an embodiment, a hand-held device of the present invention increases the thermal power dissipation capability by reducing its system thermal resistance.

Description:
BACKGROUND 
     Currently, hand-held products such as cell phones and PDA&#39;s are equipped with features to provide multiple modes of communication, organization, storage, etc. 
     Additional features boost power consumption, which increases the challenge of thermal solutions for hand-held devices subject to ever-increasing size constraints. As a result, package and system power densities increase leading to significant temperature elevation. This may also lead to performance deterioration, package delamination, and reliability issues. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a hand-held device, which features a thermal gap filler above an electronic package and enclosed by a thermally conductive casing according to an embodiment of the present invention. 
         FIG. 2  is an illustration of a hand-held device, which features a thermal gap filler encompassing the entire area enclosed by the thermally conductive casing not occupied by the electronic package or other system components according to an embodiment of the present invention. 
         FIG. 3  is a cross-sectional view of a hand-held device featuring a heat spreader and a thermal gap filler above an electronic package according to an embodiment of the present invention. 
         FIG. 4  is a cross-sectional view of a hand-held device featuring an electronic package and an EMI shield exterior to the electronic package according to an embodiment of the present invention. 
         FIG. 5A  is a chart of the maximum power dissipation ratio of a hand-held device according to varying embodiments of the present invention. 
         FIG. 5B  is a chart, corresponding with the embodiments in  FIG. 5A , listing key thermal dissipation components and their thermal conductivities according to embodiments of the present invention. 
         FIG. 6  is a chart which exhibits the use of a thermal gap filler and system enclosure with increasing thermal conductivities to decrease the electronic package and system enclosure temperatures according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In an embodiment, the present invention includes a passive thermal solution for hand-held devices. In an embodiment, the passive thermal solution may comprise a gap filler and a thermally conductive casing to dissipate heat produced by mechanical and/or electronic components in the hand-held device. In an embodiment, the gap filler used in the hand-held device is a thermal gap filler. In an embodiment, the thermal conductivity of the thermally conductive casing may be approximately 2.0 W/m-K or greater. 
       FIG. 1  is a cross-sectional view of hand-held device  101 , which may feature thermally conductive casing  120 , thermal gap filler  110 , electronic package  100 , mechanical and electronic components  140 . As illustrated, thermally conductive casing  120  may enclose embedded components of hand-held device  101 .  FIG. 1  also illustrates thermal gap filler  110  positioned flush between electronic package  100  and a portion of thermally conductive casing  120 . In other embodiments, thermally conductive casing  120  may at least partially enclose, but not fully enclose, components of hand-held device  101 . In some embodiments, hand-held device  101  may include a power supply such as a battery and may not operate for periods of time while not connected to an external source of power. Under such conditions, the power supply may provide limited power so that use of active cooling solutions, such as fans, etc, may be impractical. 
     In an embodiment, the operation of hand-held device  101  produces heat. The production of heat within hand-held device  101  can have a detrimental effect on the functionality of the embedded components. In an embodiment of the present invention, heat may dissipate to an ambient exterior to hand-held device  101  via conduction through thermal gap filler  110  and thermally conductive casing  120 . 
     In an embodiment of the present invention, thermal gap filler  110  may be positioned between a portion of thermally conductive casing  120  and electronic package  100 . In an embodiment, thermal gap filler  110  passively facilitates heat transfer from electronic package  100  to thermally conductive casing  120 . In an embodiment, thermal gap filler  110  comprises acrylate resin. In an embodiment when thermal gap filler  110  comprises an acrylate resin, the thermal conductivity of thermal gap filler  110  is approximately 1 W/m-K. In an embodiment when thermal gap filler comprises silicone, the thermal conductivity of thermal gap filler  110  is approximately 10 W/m-K. In an embodiment, thermal gap filler  110  may have a thermal conductivity in the range of 1 W/m-K to 10 W/m-K. In another embodiment, the thermal gap filler  110  may have a thermal conductivity in a range between about 5 W/m-K to about 15 W/m-K. In other embodiments, the thermal gap  110  filler may have a different thermal conductivity. 
     In an embodiment, a thermal gap filler  110  with a thermal conductivity of at least 1 W/m-K may sufficiently facilitate heat transfer to thermally conductive casing  120 . In this embodiment, thermal gap filler  110  transfers heat to thermally conductive casing  120  well. In an embodiment when the temperature of electronic package  100  is greater than the temperature of thermal gap filler  110 , heat is transferred from electronic package  100  to thermal gap filler  110 . In an embodiment, thermal gap filler  110  acts as a heat conduit from which heat produced from electronic package  100  is transferred to thermally conductive casing  120  through thermal gap filler  110 . 
     In an embodiment of the present invention, thermally conductive casing  120  may serve as the system enclosure to fully or partially enclose the embedded components of hand-held device  101  as illustrated in  FIG. 1 . In an embodiment, thermally conductive casing  120  comprises a polycarbonate material which features a thermal conductivity of approximately 0.2 W/m-K. Thermally conductive casing  120  may comprise a liquid crystalline polymer. In an embodiment when thermally conductive casing comprises a liquid crystalline polymer, the thermal conductivity of thermally conductive casing  120  is approximately 2.0 W/m-K. In an embodiment, thermally conductive casing  120  may comprise a polyphenylene sulfide, which may have a thermal conductivity of approximately 20 W/m-k. In other embodiments, the thermally conductive casing  120  may comprise a polybutene terephthalate, polypropylene, thermoplastic elastomer, polyamide, magnesium or another material. In an embodiment, thermally conductive casing  120  may have a thermal conductivity in the range from 2.0 to 20 W/m-K although other thermal conductivities are also possible in other embodiments. 
     In an embodiment, thermally conductive casing  120  with a thermal conductivity of at least 2.0 W/m-K is sufficient to transfer heat to an ambient outside of hand-held device  101 . In an embodiment, the temperature of thermal gap filler  110  is greater than the temperature of thermally conductive casing  120  such that heat is transferred from thermal gap filler  110  to thermally conductive casing  120 . In an embodiment, heat is transferred from thermal gap filler  110  to a thermally conductive casing  120  and is subsequently transferred to an ambient outside of hand-held device  101 . 
     In an embodiment, an electronic package  100  may provide all or part of the electronic functionality of hand-held device  101 . In an embodiment when electronic package  100  is a microprocessor and is active, heat  130  is conducted through thermal gap filler  110  throughout the inner area of hand-held device  101 . In  FIG. 1 , heat  130  is conducted through thermal gap filler  110  but may also be conducted through other components and in different directions throughout hand-held device  101 . In an embodiment, heat  130  may increase the temperature of hand-held device  101 . In an embodiment, the use of thermal gap filler  110  and thermally conductive casing  120  prevents the temperature of hand-held device  101  from elevating to affect the electrical or mechanical functions of the device. In an embodiment, without the passive thermal solution provided by thermal gap filler  110  and thermally conductive casing  120  the temperature of hand-held device  101  may increase so much as to adversely affect the operation of the device. 
       FIG. 2  is a cross-sectional view of hand-held device  200 , which features thermal gap filler  210  substantially filling the volume enclosed by thermally conductive casing  220  not filled by other mechanical or electronic components within thermally conductive casing  220 . In an embodiment as illustrated in  FIG. 2 , thermal gap filler  210  may be positioned flush with electronic package  201  providing a path for heat  250  to thermally conductive casing  220  for subsequent dissipation from hand-held device  200 .  FIG. 2  further illustrates mechanical and electronic components  240  in contact with thermal gap filler  210 . 
     In yet another embodiment of the present invention, a thermal gap filler may partially fill the volume of thermally conductive casing  120 . In an embodiment, a thermal gap filler may fill more of the volume of thermally conductive casing  120  than filled by thermal gap filler  110  in  FIG. 1 , but not fill as much of the volume of thermally conductive casing as illustrated by thermal gap filler  210  in  FIG. 2 . 
     In an embodiment of the present invention, a heat spreader may be incorporated in the hand-held device. In an embodiment, a heat spreader may be incorporated to increase the thermal dissipation capabilities of hand-held devices. 
     In an embodiment as illustrated in  FIG. 3 , heat spreader  340  is positioned above electronic package  301  and between thermal gap filler  310  and thermally conductive casing  320 . In an embodiment, a thermal interface material  325  may span a portion of thermally conductive casing  320  as illustrated. Also, electronic package  301  may be positioned on substrate  330  according to an embodiment of the present invention. 
     In an embodiment of the present invention, the hand-held device may incorporate an EMI shield. In an embodiment as illustrated in  FIG. 4 , EMI shield  445  may be incorporated in hand-held device  400  to protect an ambient surrounding hand-held device  400  from the effects of electromagnetic waves. In an embodiment as illustrated in  FIG. 4 , EMI shield  445  may be positioned above electronic package  400  and between two sections of thermal gap filler  410 . In an embodiment, EMI shield  445  is positioned between two sections of thermal gap filler  410  to minimize contact resistance. In an embodiment, EMI shield  445  may comprise metal and have a thermal conductivity of 150-400 W/m-K. 
     In an embodiment, the hand-held device of the present invention may exhibit better heat dissipation ability than hand-held devices currently in the art.  FIG. 5A  features chart  500 , which exhibits the thermal dissipation power (TDP) of current hand-held devices and that of multiple hand-held device embodiments of the present invention.  FIG. 5B  features chart  501 , which corresponds to chart  500  and provides the setup of a hand-held device according to varying embodiments along with the corresponding thermal conductivities (k) of the system enclosure and thermal gap filler. 
     Chart  500  of  FIG. 5A  and chart  501  of  FIG. 5B  illustrate the thermal dissipation power of hand-held devices of the current state of the art and multiple embodiments of the present invention. In an embodiment, an electronic package produces the same quantity of heat in the hand-held device embodiments listed in chart  500  and chart  501 . In an embodiment as exhibited in chart  500  of  FIG. 5A , Case  1  (Baseline) may represent a hand-held device of the current state of the art. In an embodiment, Baseline may represent a hand-held device which features a system enclosure with a thermal conductivity of 0.2 W/m-K. In an embodiment, Case  2  may represent a hand-held device which features a system enclosure, a thermal gap filler with a thermal conductivity of 1 W/m-K, and a copper heat spreader. In an embodiment, Case  3  may represent a hand-held device which features a system enclosure and a thermal gap filler with thermal conductivities of 20 W/m-K, 1 W/m-K respectively. In an embodiment, Case  4  may represent a hand-held device which features a system enclosure and a thermal gap filler, with a thermal conductivity of 20 W/m-K, 1 W/m-K respectively, and a copper heat spreader. In an embodiment, Case  5  may represent a hand-held device which features a system enclosure and a thermal gap filler with thermal conductivities of 20 W/m-K, 10 W/m-K respectively. 
     In an embodiment as illustrated in  FIG. 5A , the thermal dissipation power (TDP) of a hand-held device may be greater by the use of a thermal gap filler and thermally conductive casing as exhibited by Case  2 , Case  3 , Case  4 , and Case  5  in chart  500 . In an embodiment as further illustrated in chart  500 , the thermal dissipation power (TDP) of a hand-held device may be greater with the use of a heat spreader as illustrated in Case  3  and Case  4 . 
     In an embodiment as illustrated in chart  600  of  FIG. 6 , the die junction temperature, T j , and system enclosure temperature, T skin , may be less in a hand-held device comprising a thermal gap filler and system enclosure with increasing thermal conductivity properties. In an embodiment, chart  600  corresponds with chart  500  and chart  501  in  FIG. 5A  and  FIG. 5B  with the exception of Case  5 . As exhibited in chart  600 , the die junction temperature and temperature of the system enclosure decreases with the use of a thermal gap filler and a system enclosure with increasing thermal conductivities. Also, the use of a heat spreader within a hand-held device aids to decrease the temperature of both die and system enclosure as exhibited by Case  3  and Case  4  in chart  600 . In an embodiment, the present invention&#39;s ability to dissipate heat outside the hand-held device may allow the device to function better. 
     In an embodiment, the hand-held device of the present invention may be manufactured such that the hand-held device of the present invention features a thermally conductive casing with a thermal conductivity greater than 2.0 W/m-k, an electronic package embedded inside the thermally conductive casing, and a thermal gap filler positioned between the thermally conductive casing and the electronic package. In an embodiment, the hand-held device may be manufactured such that the thermal gap filler provides a heat path from the electronic package to the thermally conductive casing. In an embodiment, the heat path created by the thermal gap filler is substantially free from air gaps. In yet another embodiment, the hand-held device of the present invention may be manufactured such that the thermal gap filler substantially fills the volume enclosed by said thermally conductive casing not filled by other components within said thermally conductive casing.