Patent Publication Number: US-2009236707-A1

Title: Electronic devices with enhanced heat spreading

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application entitled “Electronic Devices with Enhanced Heat Spreading,” Ser. No. 11/763,630, filed on Jun. 15, 2007, which claims the priority of U.S. provisional application Ser. No. 60/827,222, filed on Sep. 28, 2006, the entirety of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to electronic devices, and more particularly to electronic devices with enhanced heat spread or dissipation from chips and electrostatic discharge protection therein. 
     2. Description of the Related Art 
     Generally, as performance of chips (integrated circuits) is promoted, heat generated thereby increases commensurately. Effective removal or spread of the heat generated by the chips (integrated circuits) during operation is thus critical. 
     Referring to  FIG. 1 , a conventional electronic device  1  comprises a casing  11 , a printed circuit board  12 , a chip  13 , a heat sink  14 , and a fan  15 . The printed circuit board  12 , chip  13 , heat sink  14 , and fan  15  are disposed in the casing  11 . The chip  13  is disposed on the printed circuit board  12  and may be a chip with lead-frame package or ball grid array package. Here, the chip  13  shown in  FIG. 1  is illustrated by a chip with lead-frame package and comprises a plurality of leads  13   a , a die  13   b , and a molding plastic  13   c . The die  13   b  is covered by the molding plastic  13   c  and is connected to the leads  13   a . The leads  13   a  are electrically connected to the printed printed circuit board  12  by soldering. The heat sink  14  is disposed on the chip  13 . The fan  15  is disposed on the heat sink  14 . 
     Heat generated by the die  13   b  of the chip  13 , during operation, is transferred to the heat sink  14  through the molding plastic  13   c . The heat is then dissipated to the interior or exterior of the casing  11  from the heat sink  14  by the fan  15 . 
     The electronic device  1  as shown in  FIG. 1 , however, has many drawbacks regarding to heat spreading. A formula of thermal conduction is described as follows: 
     
       
         
           
             
               
                 Q 
                 t 
               
               = 
               
                 
                   k 
                   × 
                   A 
                   × 
                   Δ 
                    
                   
                       
                   
                    
                   T 
                 
                 L 
               
             
             , 
           
         
       
     
     wherein, Q denotes conducted heat, t denotes conducted time, Q/t denotes thermal conduction rate, k denotes a coefficient of thermal conduction, A denotes thermal contact area, ΔT denotes temperature difference, and L denotes conducted distance. In general, the temperature difference (ΔT) between the chip  13  and the heat sink  14  is often insignificant and the value of the coefficient (k) of thermal conduction of the molding plastic  13   c  is quite small. Thus, the heat dissipation from the chip is poor because of the thermal conduction rate (Q/t) at which the heat generated by the die  13   b  conducted to the heat sink  14  through the molding plastic  13   c  is low. Additionally, the current disposition of the heat sink  14  and fan  15  in the electronic device  1  is not only taking a large space from the device but also increasing the manufacturing costs. Another drawback of the current system is that the issues of electrostatic discharge (ESD). 
     Specially, the electronic device  1  has the same aforementioned drawbacks when the chip  13  is presented in the form of a ball grid array package. 
     Hence, there is a need for an electronic device providing enhanced heat spread or dissipation and electrostatic discharge protection. 
     BRIEF SUMMARY OF THE INVENTION 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     An exemplary embodiment of the invention provides an electronic device comprising a casing, a printed circuit board, and a chip. The printed circuit board is disposed in the casing and comprises a first metal ground layer, a second metal ground layer, and a metal connecting portion. The first metal ground layer is disposed on the printed circuit board opposite the second metal ground layer. The metal connecting portion is connected between the first and second metal ground layers. The second metal ground layer is connected to the casing. The chip is electrically connected to the printed circuit board and comprises a die and a heat-conducting portion connected to the die and soldered with the first metal ground layer. Heat generated by the chip is conducted to the casing through the heat-conducting portion, first metal ground layer, metal connecting portion, and second metal ground layer. 
     The electronic device further comprises a conductive element connected between the casing and the second metal ground layer. 
     The conductive element comprises conductive glue, a conductive tape, or a thermal pad. 
     The first metal ground layer comprises a top solder mask opening through which the heat-conducting portion is soldered with the first metal ground layer. 
     The second metal ground layer comprises a bottom solder mask opening through which the conductive element is connected to the second metal ground layer. 
     The metal connecting portion comprises a through hole with an inner wall coated with metal. 
     The casing comprises a protrusion to which the second metal ground layer is connected. 
     The electronic device further comprises a conduction base connected between the second metal ground layer and the casing. 
     The chip comprises a chip with lead-frame package, and the heat-conducting portion comprises an exposed die pad. 
     The chip comprises a chip with ball grid array package, and the heat-conducting portion comprises a thermal ground ball. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  is a partial side view and cross section of a conventional electronic device; 
         FIG. 2  is a partial side view and cross section of an electronic device of a first embodiment of the invention; 
         FIG. 3  is a partial side view and cross section of an electronic device of a second embodiment of the invention; 
         FIG. 4  is a partial side view and cross section of an electronic device of a third embodiment of the invention; 
         FIG. 5  is a partial side view and cross section of an electronic device of a fourth embodiment of the invention; 
         FIG. 6  is a partial side view and cross section of an electronic device of a fifth embodiment of the invention; 
         FIG. 7  is a partial side view and cross section of an electronic device of a sixth embodiment of the invention; 
         FIG. 8  is a partial side view and cross section of an electronic device of a seventh embodiment of the invention; and 
         FIG. 9  is a partial side view and cross section of an electronic device of an eighth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     First Embodiment 
     Referring to  FIG. 2 , an electronic device  100  comprises a casing  110 , a printed circuit board  120 , a chip  130 , and a conductive element  140 . 
     The printed circuit board  120  is disposed in the casing  110  and comprises a first metal ground layer  121 , a second metal ground layer  122 , and a plurality of metal connecting portions  123 . The first metal ground layer  121  is disposed on the printed circuit board  120  opposite the second metal ground layer  122 . The metal connecting portions  123  are respectively connected between the first metal ground layer  121  and the second metal ground layer  122 . The second metal ground layer  122  is connected to the casing  110 . In this embodiment, the casing  110  comprises a protrusion  111  to which the second metal ground layer  122  is connected. Moreover, each metal connecting portion  123  may be a through hole with an inner wall coated with metal. Additionally, the printed circuit board  120  may be a multilayer printed circuit board. 
     The chip  130  is electrically connected to the printed circuit board  120  and comprises a die  131 , a heat-conducting portion  132 , and a molding plastic  133 . The heat-conducting portion  132  is connected to the die  131  and is soldered with the first metal ground layer  121  of the printed circuit board  120 . The molding plastic  133  covers the die  131 . Specifically, the first metal ground layer  121  is often coated with a solder mask S. To solder the heat-conducting portion  132  of the chip  130  with the first metal ground layer  121 , the first metal ground layer  121  comprises a top solder mask opening  121   a  formed thereon. The heat-conducting portion  132  is soldered with the first metal ground layer  121  through the top solder mask opening  121   a.    
     The conductive element  140  is connected between the protrusion  111  of the casing  110  and the second metal ground layer  122  of the printed circuit board  120 . Similarly, the second metal ground layer  122  is often coated with a solder mask S. The second metal ground layer  122  comprises a bottom solder mask opening  122   a  formed thereon. The conductive element  140  is connected to the second metal ground layer  122  through the bottom solder mask opening  122   a . Additionally, the conductive element  140  may comprise electric and/or thermal conductors. For example, the conductive element  140  may comprise conductive glue, a conductive tape, or a thermal pad. 
     Moreover, the chip  130  may be a chip with lead-frame package or ball grid array package. Specifically, when the chip  130  is a chip with lead-frame package, such as a chip with low profile plastic quad flat package (LQFP), the heat-conducting portion  132  thereof is an exposed die pad connected to the die  131 . Here, the exposed die pad is composed of metal, such as aluminum. In another aspect, when the chip  130  is a chip with ball grid array package, such as a chip with flip chip ball grid array package (FCBGA package), the heat-conducting portion  132  thereof is formed by a plurality of thermal ground balls connected to the die  131 . 
     When the die  131  of the chip  130  is in operation, heat generated thereby is conducted to the casing  110  sequentially through the heat-conducting portion  132 , first metal ground layer  121 , metal connecting portions  123 , second metal ground layer  122 , and conductive element  140  and is further transmitted to the exterior of the electronic device  100 . 
     Accordingly, as the heat generated by the die  131  is not distributed over the molding plastic  133  but conducted to the casing  110  through the heat-conducting portion  132 , first metal ground layer  121 , metal connecting portions  123 , second metal ground layer  122 , and conductive element  140 , the value of the coefficient (k) of thermal conduction is significantly increased. Additionally, the temperature difference (ΔT) between the die  131  and the casing  110  is larger than the temperature difference between the die  131  and the molding plastic  133 . Thus, the thermal conduction rate (Q/t) is increased and the ability of heat spread or dissipation from the die  131  (or chip  130 ) is enhanced. Moreover, neither a heat sink nor a fan is required for the disclosed electronic device. Thus, the overall size and manufacturing costs of the electronic device  100  are significantly reduced. 
     More specifically, as the first metal ground layer  121  is connected to the second metal ground layer  122  through a shortest conduction path (metal connecting portions  123 ) and the second metal ground layer  122  is connected to the casing  110 , static electricity in the printed circuit board  120  is easily conducted to the casing  110 , effectively enhancing electrostatic discharge (ESD) protection in the electronic device  100 . Thus, time, effort, and test equipment for solving issues of electrostatic discharge (ESD) are not required, further reducing the manufacturing costs of the electronic device  100 . 
     Moreover, the electronic device  100  may selectively omit the conductive element  140 . Namely, the protrusion  111  of the casing  110  may be directly connected to the second metal ground layer  122  through the bottom solder mask opening  122   a , achieving the effect described. 
     Second Embodiment 
     Elements corresponding to those in the first embodiment share the same reference numerals. 
     Referring to  FIG. 3 , the protrusion  111  of the electronic device  100  of the first embodiment is replaced by a conduction base  150  of an electronic device  100 ′ in this embodiment. Specifically, the conduction base  150  is connected between the second metal ground layer  122  of the printed circuit board  120  and the casing  110  and may comprise electric and/or thermal conductors. 
     When the conduction base  150  comprises an electric conductor, such as metal, heat spread or dissipation from the die  131  (or chip  130 ) and electrostatic discharge (ESD) protection in the electronic device  100 ′ are effectively enhanced. In another aspect, when the conduction base  150  comprises a thermal conductor, such as an insulating thermal pad, heat spread or dissipation from the die  131  (or chip  130 ) is effectively enhanced. 
     Similarly, the electronic device  100 ′ may selectively omit the conductive element  140 . Namely, the conduction base  150  may be directly connected to the second metal ground layer  122  through the bottom solder mask opening  122   a , achieving the effect described. 
     Structure, disposition, and function of other elements in this embodiment are the same as those in the first embodiment, and explanation thereof is omitted for simplicity. 
     Third Embodiment 
     Referring to  FIG. 4 , an electronic device  300  comprises a casing  310 , a printed circuit board  320 , a chip  330 , and a plurality of metal connecting members  340 . 
     The printed circuit board  320  is disposed in the casing  310  and comprises a first metal ground layer  321 , a second metal ground layer  322 , and a plurality of metal connecting portions  323 . The first metal ground layer  321  is opposite the second metal ground layer  322 . The metal connecting portions  323  are respectively connected between the first metal ground layer  321  and the second metal ground layer  322 . In this embodiment, each metal connecting portion  323  may be a through hole with an inner wall coated with metal. Additionally, the printed circuit board  320  may be a multilayer printed circuit board. 
     The chip  330  is electrically connected to the printed circuit board  320  and comprises a die  331 , a heat-conducting portion  332 , and a molding plastic  333 . The heat-conducting portion  332  is connected to the die  331  and is soldered with the first metal ground layer  321  of the printed circuit board  320 . The molding plastic  333  covers the die  331 . Specifically, the first metal ground layer  321  is often coated with a solder mask S. To connect the heat-conducting portion  332  of the chip  330  with the first metal ground layer  321 , the first metal ground layer  321  comprises a solder mask opening  321   a  formed thereon. The heat-conducting portion  332  is soldered with the first metal ground layer  321  through the solder mask opening  321   a.    
     The metal connecting members  340  are fit in the printed circuit board  320  and connect the first metal ground layer  321  and second metal ground layer  322  to the casing  310 . Specifically, the metal connecting members  340  may be screws fixing the printed circuit board  320  to the casing  310 , in addition to connecting the first metal ground layer  321  and second metal ground layer  322  to the casing  310 . 
     Similarly, the chip  330  may be a chip with lead-frame package or ball grid array package. When the chip  330  is a chip with lead-frame package, such as a chip with low profile plastic quad flat package (LQFP), the heat-conducting portion  332  thereof is an exposed die pad connected to the die  331 . Here, the exposed die pad is composed of metal, such as aluminum. In another aspect, when the chip  330  is a chip with ball grid array package, such as a chip with flip chip ball grid array package (FCBGA package), the heat-conducting portion  332  thereof is formed by a plurality of thermal ground balls connected to the die  331 . 
     When the die  331  of the chip  330  is in operation, heat generated thereby is conducted to the casing  310  through the heat-conducting portion  332 , first metal ground layer  321 , metal connecting portions  323 , second metal ground layer  322 , and metal connecting members  340  and is further transmitted to the exterior of the electronic device  300 . 
     Accordingly, as the heat generated by the die  331  is not distributed over the molding plastic  333  but conducted to the casing  310  through the heat-conducting portion  332 , first metal ground layer  321 , metal connecting portions  323 , second metal ground layer  322 , and metal connecting members  340 , the value of the thermal conduction coefficient (k) is significantly increased. Additionally, the temperature difference (ΔT) between the die  331  and the casing  310  is larger than the temperature difference between the die  331  and the molding plastic  333 . Thus, the thermal conduction rate (Q/t) at which the heat generated by the die  331  is conducted to the casing  310  is high, enhancing heat spread or dissipation from the die  331  (or chip  330 ). Similarly, as neither a heat sink nor a fan is required, the overall size and manufacturing costs of the electronic device  300  are significantly reduced. 
     More specifically, as the first metal ground layer  321  is connected to the second metal ground layer  322  through a shortest conduction path (metal connecting members  340  and metal connecting portions  323 ), and the second metal ground layer  322  is connected to the casing  310  through a shortest conduction path (metal connecting members  340 ), static electricity in the printed circuit board  320  is easily conducted to the casing  310 , effectively enhancing electrostatic discharge (ESD) protection in the electronic device  300 . Thus, time, effort, and test equipment for solving issues of electrostatic discharge (ESD) can be omitted, further reducing the manufacturing costs of the electronic device  300 . 
     Moreover, the printed circuit board  320  may selectively omit the metal connecting portions  323 . At this point, heat generated by the die  331  is conducted to the casing  310  through the heat-conducting portion  332 , first metal ground layer  321 , and metal connecting members  340  and is further transmitted to the exterior of the electronic device  300 . Accordingly, heat spread or dissipation from the die  331  (or chip  330 ) and electrostatic discharge (ESD) protection in the electronic device  300  are also enhanced. 
     Fourth Embodiment 
     Referring to  FIG. 5 , an electronic device  400  comprises a casing  410 , a printed circuit board  420 , a chip  430 , and a conductive element  440 . 
     The printed circuit board  420  is disposed in the casing  410  and comprises a metal ground layer  421  connected to the casing  410 . In this embodiment, the casing  410  comprises a protrusion  411  to which the metal ground layer  421  is connected. Additionally, the printed circuit board  420  may be a multilayer printed circuit board. 
     The chip  430  is electrically connected to the printed circuit board  420  and comprises a die  431 , a heat-conducting portion  432 , and a molding plastic  433 . The heat-conducting portion  432  is connected to the die  431  and is soldered with the metal ground layer  421  of the printed circuit board  420 . The molding plastic  433  covers the die  431 . 
     Specifically, the metal ground layer  421  is often coated with a solder mask S. To connect the heat-conducting portion  432  of the chip  430  with the metal ground layer  421 , the metal ground layer  421  comprises a top solder mask opening  421   a  formed thereon. The heat-conducting portion  432  is soldered with the metal ground layer  421  through the top solder mask opening  421   a.    
     The conductive element  440  is connected between the protrusion  411  of the casing  410  and the metal ground layer  421  of the printed circuit board  420 . Specifically, the metal ground layer  421  further comprises a bottom solder mask opening  421   b  formed thereon. The conductive element  440  is soldered with the metal ground layer  421  through the bottom solder mask opening  421   b . Additionally, the conductive element  440  may comprise electric and/or thermal conductors. For example, the conductive element  440  may comprise conductive glue, a conductive tape, or a thermal pad. 
     Similarly, the chip  430  may be a chip with lead-frame package or ball grid array package. When the chip  430  is a chip with lead-frame package, such as a chip with low profile plastic quad flat package (LQFP), the heat-conducting portion  432  thereof is an exposed die pad connected to the die  431 . Here, the exposed die pad is composed of metal, such as aluminum. In another aspect, when the chip  430  is a chip with ball grid array package, such as a chip with flip chip ball grid array package (FCBGA package), the heat-conducting portion  432  thereof is formed by a plurality of thermal ground balls connected to the die  431 . 
     When the die  431  of the chip  430  is in operation, heat generated thereby is conducted to the casing  410  sequentially through the heat-conducting portion  432 , metal ground layer  421 , and conductive element  440  and is further transmitted to the exterior of the electronic device  400 . 
     Accordingly, as the heat generated by the die  431  is not distributed over the molding plastic  433  but conducted to the casing  410  through the heat-conducting portion  432 , metal ground layer  421 , and conductive element  440 , the value of the thermal conduction coefficient (k) is significantly increased comparing to the traditional packaging structure. Additionally, the temperature difference (ΔT) between the die  431  and the casing  410  is larger than the temperature difference between the die  431  and the molding plastic  433 . Thus, the thermal conduction rate (Q/t) at which the heat generated by the die  431  distributing over the casing  410  has a higher conducting rate than traditional devices, and thus the efficiency of heat spread or dissipation from the die  431  (or chip  430 ) is improved. As disclosed, neither a heat sink nor a fan is required, the overall size and manufacturing costs of the electronic device  400  are significantly reduced. 
     More specifically, as the metal ground layer  421  is connected to the casing  410  through a shortest conduction path, static electricity in the printed circuit board  420  is easily transmitted to the casing  410 , effectively enhancing electrostatic discharge (ESD) protection in the electronic device  400 . Thus, time, effort, and test equipment for solving issues of electrostatic discharge (ESD) can be omitted, further reducing the manufacturing costs of the electronic device  400 . 
     Moreover, the electronic device  400  may selectively omit the conductive element  440 . Namely, the protrusion  411  of the casing  410  may be directly connected to the metal ground layer  421  through the bottom solder mask opening  421   b , achieving the effect described. 
     Fifth Embodiment 
     Elements corresponding to those in the fourth embodiment share the same reference numerals. 
     Referring to  FIG. 6 , the protrusion  411  of the electronic device  400  of the fourth embodiment is replaced by a conduction base  450  of an electronic device  400 ′ in this embodiment. Specifically, the conduction base  450  is connected between the metal ground layer  421  of the printed circuit board  420  and the casing  410 , and it may comprise electric and/or thermal conductors. 
     When the conduction base  450  comprises an electric conductor, such as metal, heat spread or dissipation from the die  431  (or chip  430 ) and electrostatic discharge (ESD) protection in the electronic device  400 ′ are effectively enhanced. In another aspect, when the conduction base  450  comprises a thermal conductor, such as an insulating thermal pad, heat spread or dissipation from the die  431  (or chip  430 ) is effectively enhanced. 
     Similarly, the electronic device  400 ′ may selectively omit the conductive element  440 . Namely, the conduction base  450  may be directly connected to the metal ground layer  421  through the bottom solder mask opening  421   b , achieving the effect described. 
     Structure, disposition, and function of other elements in this embodiment are the same as those in the fourth embodiment, and explanation thereof is omitted for simplicity. 
     Sixth Embodiment 
     Referring to  FIG. 7 , an electronic device  600  comprises a casing  610 , a printed circuit board  620 , a chip  630 , and a plurality of metal connecting members  640 . 
     The printed circuit board  620  is disposed in the casing  610  and comprises a metal ground layer  621 . Additionally, the printed circuit board  620  may be a multilayer printed circuit board. 
     The chip  630  is electrically connected to the printed circuit board  620  and comprises a die  631 , a heat-conducting portion  632 , and a molding plastic  633 . The heat-conducting portion  632  is connected to the die  631  and is soldered with the metal ground layer  621  of the printed circuit board  620 . The molding plastic  633  covers the die  631 . Specifically, the metal ground layer  621  is often coated with a solder mask S. To connect the heat-conducting portion  632  of the chip  630  with the metal ground layer  621 , the metal ground layer  621  comprises a solder mask opening  621   a  formed thereon. The heat-conducting portion  632  is soldered with the metal ground layer  621  through the solder mask opening  621   a.    
     The metal connecting members  640  are fit in the printed circuit board  620  and connect the metal ground layer  621  to the casing  610 . Specifically, the metal connecting members  640  may be screws fixing the printed circuit board  620  to the casing  610 , in addition to connecting the metal ground layer  621  to the casing  610 . 
     Similarly, the chip  630  may be a chip with lead-frame package or ball grid array package. When the chip  630  is a chip with lead-frame package, such as a chip with low profile plastic quad flat package (LQFP), the heat-conducting portion  632  thereof is an exposed die pad connected to the die  631 . Here, the exposed die pad is composed of metal, such as aluminum. In another aspect, when the chip  630  is a chip with ball grid array package, such as a chip with flip chip ball grid array package (FCBGA package), the heat-conducting portion  632  thereof is formed by a plurality of thermal ground balls connected to the die  631 . 
     When the die  631  of the chip  630  is in operation, heat generated thereby is transmitted to the casing  610  through the heat-conducting portion  632 , metal ground layer  621 , and metal connecting members  640  and is further transmitted to the exterior of the electronic device  600 . 
     Accordingly, as the heat generated by the die  631  is not distributed over the molding plastic  633  but conducted to the casing  610  through the heat-conducting portion  632 , metal ground layer  621 , and metal connecting members  640 , the value of the thermal conduction coefficient (k) is significantly increased. Additionally, the temperature difference (ΔT) between the die  631  and the casing  610  is larger than the temperature difference between the die  631  and the molding plastic  633 . Thus, the thermal conduction rate (Q/t) is increased, and the heat spread or dissipation from the die  631  (or chip  630 ) is enhanced as well. The embodiment as disclosed requires neither a heat sink nor a fan. Thus, the overall size and manufacturing costs of the electronic device  600  are significantly reduced. 
     More specifically, as the metal ground layer  621  is connected to the casing  610  through a shortest conduction path (metal connecting members  640 ), static electricity in the printed circuit board  620  is easily conducted to the casing  610 , effectively enhancing electrostatic discharge (ESD) protection in the electronic device  600 . Thus, time, effort, and test equipment for solving issues of electrostatic discharge (ESD) are not required, and the manufacturing costs of the electronic device  600  are further reduced as well. 
     Seventh Embodiment 
     Referring to  FIG. 8 , an electronic device  700  comprises a casing  710 , a printed circuit board  720 , a chip  730 , and a conductive element  740 . 
     The casing  710  comprises a protrusion  711 . The printed circuit board  720  is disposed in the casing  710 . Additionally, the printed circuit board  720  may be a multilayer printed circuit board. 
     The chip  730  is electrically connected to the printed circuit board  720  and comprises a die  731 , a heat-conducting portion  732 , and a molding plastic  733 . The heat-conducting portion  732  is connected between the die  731  and the protrusion  711  of the casing  710 . The molding plastic  733  covers the die  731 . Specifically, the chip  730  of this embodiment is a chip with lead-frame package and the heat-conducting portion  732  thereof is a reverse exposed die pad connected to the die  731 . Here, the reverse exposed die pad is composed of metal, such as aluminum. 
     The conductive element  740  is connected between the protrusion  711  of the casing  710  and the heat-conducting portion  732 . Additionally, the conductive element  740  may comprise electric and/or thermal conductors. For example, the conductive element  740  may comprise conductive glue, a conductive tape, or a thermal pad. 
     When the die  731  of the chip  730  is in operation, heat generated thereby is conducted to the casing  710  through the heat-conducting portion  732  and conductive element  740  and is further transmitted to the exterior of the electronic device  700 . 
     Since the heat generated by the die  731  is not conducted to the molding plastic  733  but conducted to the casing  710  through the heat-conducting portion  732  and conductive element  740 , the value of the coefficient (k) of thermal conduction is significantly increased. Additionally, the temperature difference (ΔT) between the die  731  and the casing  710  is also increased. Thus, the thermal conduction rate (Q/t) at which the heat generated by the die  731  conducting to the casing  710  is increased, and the heat spread or dissipation from the die  731  (or chip  730 ) is enhanced. The embodiment as disclosed requires neither a heat sink nor a fan. Thus, the overall size and manufacturing costs of the electronic device  700  are significantly reduced. 
     Moreover, when the conductive element  740  comprises conductive glue or a conductive tape, static electricity in the printed circuit board  720  is easily conducted to the casing  710 , effectively enhancing electrostatic discharge (ESD) protection in the electronic device  700 . Thus, time, effort, and test equipment for solving issues of electrostatic discharge (ESD) are not required, further reducing the manufacturing costs of the electronic device  700 . 
     Moreover, the electronic device  700  may selectively omit the conductive element  740 . Namely, the protrusion  711  of the casing  710  may be directly connected to the heat-conducting portion  732 , achieving the effect described. 
     Eighth Embodiment 
     Elements corresponding to those in the seventh embodiment share the same reference numerals. 
     Referring to  FIG. 9 , the protrusion  711  of the electronic device  700  of the seventh embodiment is replaced by a conduction base  750  of an electronic device  700 ′ in this embodiment. Specifically, the conduction base  750  is connected between the heat-conducting portion  732  and the casing  710  and may comprise electric and/or thermal conductors. 
     Specifically, when the conduction base  750  comprises an electric conductor, such as metal, heat spread or dissipation from the die  731  (or chip  730 ) and electrostatic discharge (ESD) protection in the electronic device  700 ′ are effectively enhanced. In another aspect, when the conduction base  750  comprises a thermal conductor, such as an insulating thermal pad, heat spread or dissipation from the die  731  (or chip  730 ) is effectively enhanced. 
     Similarly, the electronic device  700 ′ may selectively omit the conductive element  740 . Namely, the conduction base  750  may be directly connected to the heat-conducting portion  732 , achieving the effect described. 
     Structure, disposition, and function of other elements in this embodiment are the same as those in the seventh embodiment, and explanation thereof is omitted for simplicity. 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.