Abstract:
The disclosed embodiments relate to a system that facilitates thermal conductance in a system that includes a module comprising a circuit board with integrated circuits, such as a solid-state drive. A thermal-coupling material between one side of the circuit board and an adjacent baseplate is used to increase thermal conduction between the circuit board and the baseplate. Furthermore, the module may include another thermal-coupling material between the baseplate and a housing that at least in part surrounds the circuit board, thereby increasing thermal conduction between the baseplate and the housing. In these ways, the baseplate and/or the housing may be used as a heat-transfer surfaces or heat spreaders that reduce hotspots associated with operation of the integrated circuits.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/683,955 filed Nov. 21, 2012, which claims the benefit of U.S. Provisional Application No. 61/657,489 filed Jun. 8, 2012, and to U.S. Provisional Application No. 61/656,747 filed Jun. 7, 2012, the contents of each are incorporated by reference herein in their entireties. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The described embodiments relate to techniques for cooling integrated circuits. 
         [0004]    2. Related Art 
         [0005]    A solid-state drive is a type of memory that stores information on multiple integrated circuits. For example, the integrated circuits may include a solid-state non-volatile memory, such as flash memory chips or dynamic-random-access-memory (DRAM) chips. Solid-state drives are increasingly popular because, unlike hard-disk drives, they do not contain moving parts, and are therefore more reliable, have reduced power consumption and generate less noise. 
         [0006]    However, flash memory chips, such as NAND flash devices, are susceptible to memory wear after repeated program-erase cycles. In particular, stored information can be lost if a specified maximum number of program-erase cycles (such as 1,000,000 program-erase cycles) is exceeded. This memory wear can be exacerbated by the temperature increase associated with the heat generated during operation of a flash memory chip. 
         [0007]    More expensive, solid-state drives based on DRAM chips offer reduced latency and are not susceptible to memory wear. However, DRAM chips also generate heat during operation. The temperature increase associated with this heat can adversely impact other components in electronic devices that include solid-state drives. 
         [0008]    More generally, the computational performance of integrated circuits has increased significantly in recent years. This increased performance has been accompanied by an increase in power consumption and associated heat generation. Furthermore, this additional heat generation has made it harder to maintain acceptable operational temperatures in these integrated circuits. 
         [0009]    Cooling integrated circuits that include wireless-communication circuits (which are sometimes referred to as ‘wireless-communication integrated circuits’) can be especially challenging. This is because these integrated circuits are often enclosed in electromagnetic-interference shields to reduce interference. 
         [0010]    Existing approaches to cooling a wireless-communication integrated circuit often use an electromagnetic-interference shield as a heat sink. Thus, a thermal-interface material is often included between electromagnetic-interference shield and wireless-communication integrated circuit to increase the thermal conductance between them. However, there are limits to the thermal power that can be conducted away from wireless-communication integrated circuits via this thermal path, which can constrain the performance of wireless-communication integrated circuits. 
       SUMMARY 
       [0011]    Some of the described embodiments facilitate thermal conductance in a system that includes a module with a circuit board, having a top surface and a bottom surface, and integrated circuits disposed on the top surface and the bottom surface. Moreover, the module includes a baseplate, having a top surface and a bottom surface, mechanically coupled to an edge of the circuit board. Furthermore, a first thermal-coupling material is mechanically coupled to the bottom surface of the circuit board and the top surface of the baseplate. This first thermal-coupling material increases a thermal conductance between the circuit board and the baseplate. 
         [0012]    Note that the integrated circuits may include memory, such as flash memory. 
         [0013]    Additionally, the first thermal-coupling material may include a thermal pad and/or a thermal gel. 
         [0014]    In some embodiments, the module includes a housing enclosing the circuit board, the baseplate and the first thermal-coupling material. Moreover, the module may include a second thermal-coupling material mechanically coupled to the bottom surface of the baseplate. This second thermal-coupling material may include a thermal pad. Additionally, the housing may enclose the circuit board, the baseplate, the first thermal-coupling material and the second thermal-coupling material. 
         [0015]    Furthermore, the baseplate may be made of metal. 
         [0016]    Another embodiment provides a portable electronic device. This portable electronic device may include an external housing and the module. In the portable electronic device, the second thermal material may be mechanically coupled to the bottom surface of the baseplate and the external housing, and may increase a thermal conductance between the baseplate and the external housing. 
         [0017]    Another embodiment provides a method for transferring heat from integrated circuits. During the method, heat is transferred from the integrated circuits disposed on surfaces of a circuit board to the baseplate mechanically coupled to the edge of the circuit board using the first thermal-coupling material disposed between the circuit board and the baseplate, where the first thermal-coupling material increases the thermal conductance between the circuit board and the baseplate. Then, heat is transferred from the baseplate to the external housing of the portable electronic device that includes the circuit board, the integrated circuits and the baseplate using the second thermal-coupling material disposed between the baseplate and the external housing, where the second thermal-coupling material increases the thermal conductance between the baseplate and the external housing. 
         [0018]    Additional described embodiments facilitate thermal conductance in a second module with a circuit board, having a top surface and a bottom surface, and an integrated circuit disposed on the top surface. Moreover, the second module includes a second circuit board, having a top surface, mechanically coupled to the circuit board. Furthermore, the bottom surface of the circuit board is separated from the top surface of the second circuit board by a gap, and a thermal-interface material in the gap between the bottom surface of the circuit board and the top surface of the second circuit board thermally couples the circuit board and the second circuit board so that heat generated during operation of the integrated circuit is conducted to the second circuit board. 
         [0019]    In some embodiments, the second module includes an electromagnetic-interference shield disposed on the top surface of the circuit board and at least partially enclosing the integrated circuit. For example, the circuit board may include a wireless-communication circuit board. 
         [0020]    Alternatively, the integrated circuit may include a solid-state memory. For example, the circuit board may include a solid-state drive. 
         [0021]    Note that the thermal-interface material may include: a foam, a thermal gel, a thermal pad, thermal grease, and/or an elastomeric material. 
         [0022]    In some embodiments, the second module includes components disposed on the bottom surface of the circuit board, where a surface of the thermal-interface material facing the bottom surface of the circuit board includes pre-compressed regions so that a contact area between the surface of the thermal-interface material and the bottom surface of the circuit board is increased relative to a thermal-interface material without the pre-compressed regions. 
         [0023]    Another embodiment provides a second portable electronic device that includes the second module. 
         [0024]    Another embodiment provides a second method for transferring heat from an integrated circuit. During the second method, heat generated by the integrated circuit disposed on the top surface of the circuit board is transferred to the bottom surface of the circuit board. Then, the heat is conducted to a top surface of the second circuit board, which is thermally coupled to the circuit board by the thermal-interface material. Note that the bottom surface of the circuit board is separated from the top surface of the second circuit board by the gap, and the thermal-interface material is in the gap between the bottom surface of the circuit board and the top surface of the second circuit board. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0025]      FIG. 1  is a block diagram illustrating a side view of a module in accordance with an embodiment of the present disclosure. 
           [0026]      FIG. 2  is a block diagram illustrating a side view of the module of  FIG. 1  in a portable electronic device in accordance with an embodiment of the present disclosure. 
           [0027]      FIG. 3  is a flowchart illustrating a method for transferring heat from integrated circuits in accordance with an embodiment of the present disclosure. 
           [0028]      FIG. 4  is a block diagram illustrating a side view of a module in accordance with an embodiment of the present disclosure. 
           [0029]      FIG. 5  is a block diagram illustrating a side view of the module of  FIG. 1  in a portable electronic device in accordance with an embodiment of the present disclosure. 
           [0030]      FIG. 6  is a flowchart illustrating a method for transferring heat from an integrated circuit in accordance with an embodiment of the present disclosure. 
       
    
    
       [0031]    Note that like reference numerals refer to corresponding parts throughout the drawings. Moreover, multiple instances of the same part are designated by a common prefix separated from an instance number by a dash. 
       DETAILED DESCRIPTION 
       [0032]      FIG. 1  presents a block diagram illustrating a side view of a module  100 . This module includes a circuit board  110 , having a top surface  112  and a bottom surface  114 , and integrated circuits  116  disposed on top surface  112  and bottom surface  114 . For example, integrated circuits  116  may include memory, such as flash memory or dynamic-random-access memory (DRAM). Therefore, module  100  may include a solid-state drive. More generally, module  100  may include another type of volatile or non-volatile computer-readable memory. 
         [0033]    Moreover, module  100  includes a baseplate  118 , having a top surface  120  and a bottom surface  122 , mechanically coupled to an edge  124  of circuit board  110 . For example, baseplate  118  may be made of metal. Furthermore, a thermal-coupling material  126  is mechanically coupled to bottom surface  114  and top surface  120 . This thermal-coupling material may increase a thermal conductance (defined as κ·A/L, where κ is the thermal conductivity of thermal-coupling material  126 , A is a cross-sectional area, and L is a thickness) between circuit board  110  and baseplate  118  so that baseplate  118  can be used as a heat-transfer surface or heat spreader for integrated circuits  116 . For example, thermal-coupling material  126  may include a thermal pad and/or a thermal gel. In an exemplary embodiment, the thermal gel is Gel 30 (from Chomerics North America of Woburn, Mass.) and/or the thermal pad is the Gap Pad VO Ultra Soft (from The Bergquist Company of Chanhassen, Minn.). 
         [0034]    In some embodiments, module  100  includes an optional housing  130  (such as a housing made of metal or plastic) that at least partially encloses circuit board  110 , baseplate  118  and thermal-coupling material  126 . Moreover, module  100  may include optional thermal-coupling material  128  mechanically coupled to bottom surface  122 . This optional thermal-coupling material may include a thermal pad, such as the Gap Pad VO Ultra Soft. Note that optional housing  130  may also partially enclose optional thermal-coupling material  128 . 
         [0035]    Module  100  may be included in an electronic device, such as a portable electronic device. This is shown in  FIG. 2 , which presents a block diagram illustrating a side view of module  100  ( FIG. 1 ) in a portable electronic device  200 . In particular, portable electronic device  200  may include an external housing  210  and module  100 . In portable electronic device  200 , thermal-coupling material  128  may be mechanically coupled to bottom surface  122  and external housing  210 , and may increase a thermal conductance between baseplate  118  and external housing  210  so that external housing  210  can be used as a heat-transfer surface or heat spreader for integrated circuits  116 . In addition, thermal-coupling material  128  may provide additional thermal inertia or thermal mass to circuit board  110  and integrated circuits  116 . This thermal inertia may reduce temperature increases of circuit board  110  and integrated circuits  116  that occur during episodic operation of integrated circuits  116 , such as during read or write operations. 
         [0036]    By including thermal-coupling materials  126  and/or  128 , hotspots in portable electronic device  200  that are associated with heat generated during operation of integrated circuits  116  may be reduced or eliminated. For example, during operation of portable electronic device  200 , the maximum temperature associated with integrated circuits  116  may be less than 55 C. 
         [0037]    Portable electronic device  200  may include: one or more program modules or sets of instructions stored in an optional memory subsystem, such as module  100 . These sets of instructions may be executed by an optional processing subsystem (such as one or more processors) on a motherboard (not shown). Note that the one or more computer programs may constitute a computer-program mechanism. Moreover, instructions in the various modules in the optional memory subsystem may be implemented in: a high-level procedural language, an object-oriented programming language, and/or in an assembly or machine language. Furthermore, the programming language may be compiled or interpreted, e.g., configurable or configured, to be executed by the optional processing subsystem. 
         [0038]    In some embodiments, functionality in these circuits, components and devices may be implemented in one or more: application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and/or one or more digital signal processors (DSPs). Moreover, the circuits and components may be implemented using any combination of analog and/or digital circuitry, including: bipolar, PMOS and/or NMOS gates or transistors. Furthermore, signals in these embodiments may include digital signals that have approximately discrete values and/or analog signals that have continuous values. Additionally, components and circuits may be single-ended or differential, and power supplies may be unipolar or bipolar. 
         [0039]    Portable electronic device  200  may include one of a variety of devices that can include memory, including: a laptop computer, a media player (such as an MP3 player), an appliance, a subnotebook/netbook, a tablet computer, a smartphone, a cellular telephone, a network appliance, a personal digital assistant (PDA), a toy, a controller, a digital signal processor, a game console, a device controller, a computational engine within an appliance, a consumer-electronic device, a portable computing device, a personal organizer, and/or another electronic device. 
         [0040]    While portable electronic device  200  was used as an illustration in the preceding discussion, in other embodiments module  100  is included in an electronic device, such as a server, a desktop computer, a mainframe computer and/or a blade computer. Moreover, alternative passive heat transfer components and/or materials may be used in thermal-coupling material  126  and/or  128 . In some embodiments, circuit board  110  only includes integrated circuits  116  on top surface  112  and/or thermal-coupling mechanism  126  is pre-stressed with cavities corresponding to components on back surface  114  so that a contact area between thermal-coupling mechanism  126  and back surface  114  is maximized. Furthermore, in some embodiments there is a gap between optional thermal-coupling material  128  and external housing  210  in  FIG. 2 , so that heat is transferred to external housing  210  by radiation or conduction through air in the gap. 
         [0041]    Additionally, one or more of the components may not be present in the  FIGS. 1 and 2 . In some embodiments, the preceding embodiments include one or more additional components that are not shown in  FIGS. 1 and 2 . Also, although separate components are shown in  FIGS. 1 and 2 , in some embodiments some or all of a given component can be integrated into one or more of the other components and/or positions of components can be changed. 
         [0042]    We now describe embodiments of a method that can be performed using the preceding embodiments.  FIG. 3  presents a flowchart illustrating a method  300  for transferring heat from integrated circuits, such as those in module  100  ( FIG. 1 ). During the method, heat is transferred from the integrated circuits disposed on surfaces of a circuit board to a baseplate mechanically coupled to an edge of the circuit board using a first thermal-coupling material disposed between the circuit board and the baseplate (operation  310 ), where the first thermal-coupling material increases the thermal conductance between the circuit board and the baseplate. Then, heat is transferred from the baseplate to an external housing of a portable electronic device (which includes the circuit board, the integrated circuits and the baseplate) using a second thermal-coupling material disposed between the baseplate and the external housing (operation  312 ), where the second thermal-coupling material increases the thermal conductance between the baseplate and the external housing. 
         [0043]    In some embodiments of method  300 , there may be additional or fewer operations. Moreover, the order of the operations may be changed, and/or two or more operations may be combined into a single operation. 
         [0044]    We now describe embodiments of thermal-management technique for a wireless-communication integrated circuit.  FIG. 4  presents a block diagram illustrating a side view of a module  400 . This module includes a circuit board  410 , having a top surface  412  and a bottom surface  414 , and at least an integrated circuit  416  disposed on top surface  412 . For example, integrated circuit  416  may include a wireless-communication integrated circuit, and circuit board  410  may include a wireless-communication circuit board. Therefore, in some embodiments integrated circuit  416  may be at least partially enclosed by an optional electromagnetic-interference (EMI) shield  418 . Alternatively, integrated circuit  416  may include a solid-state memory, such as flash memory, dynamic-random-access memory (DRAM) or, more generally, another type of volatile or non-volatile computer-readable memory. Thus, circuit board  410  may include a solid-state drive. 
         [0045]    Moreover, module  400  includes a circuit board  420 , having a top surface  422 , mechanically coupled to an edge  424  of circuit board  410 . Bottom surface  414  of circuit board  410  may be separated from top surface  422  of circuit board  420  by a gap  426 , and a thermal-interface material  428  in gap  426  may thermally couple circuit board  410  and circuit board  420  so that heat generated during operation of integrated circuit  416  is conducted to circuit board  420 . The ground plane(s) and copper traces in circuit board  420  can then function as a heat sink for circuit board  110  and integrated circuit  116 . In addition, thermal-interface material  428  may provide additional thermal inertia or thermal mass to circuit board  410  and integrated circuit  416 . This thermal inertia may reduce temperature increases of circuit board  410  and integrated circuit  416  that occur during episodic operation of integrated circuit  416 , such as during read or write operations. 
         [0046]    In particular, thermal-interface material  428  may increase a thermal conductance (defined as κ·A/L, where κ is the thermal conductivity of thermal-interface material  428 , A is a cross-sectional area, and L is a thickness) between circuit board  410  and circuit board  420  so that circuit board  420  can be used as a heat-transfer surface or heat spreader for integrated circuit  416 . For example, thermal-interface material  428  may include: a foam, a thermal gel, a thermal pad, thermal grease, and/or an elastomeric material. In an exemplary embodiment, the thermal gel is Gel 30 (from Chomerics North America of Woburn, Mass.) and/or the thermal pad is the Gap Pad VO Ultra Soft (from The Bergquist Company of Chanhassen, Minn.). 
         [0047]    In an exemplary embodiment, circuit board  410  has a thickness  430  of 0.8 mm, gap  426  has a thickness  432  of 1.6 mm, and circuit board  420  has a thickness  440  of 1.0 mm. Moreover, during operation, integrated circuit  416  may have a power consumption of approximately 3.5 W. 
         [0048]    In some embodiments, module  400  includes optional components  434  (such as capacitors) disposed on bottom surface  414  of circuit board  410 , where a surface  436  of thermal-interface material  428  facing bottom surface  414  includes optional pre-compressed regions  438  so that a contact area between surface  436  and bottom surface  414  is increased relative to a thermal-interface material without optional pre-compressed regions  438 . In addition, optional pre-compressed regions  438  may ensure that the stress applied to optional components  434  by thermal-interface material  428  does not exceed a strain limit of circuit board  410 , so that optional components  434  do not detach from bottom surface  414 . 
         [0049]    Module  400  may be included in an electronic device, such as a portable electronic device. This is shown in  FIG. 5 , which presents a block diagram illustrating a side view of module  400  ( FIG. 4 ) in a portable electronic device  500 . 
         [0050]    By including thermal-interface material  428 , hotspots in portable electronic device  500  that are associated with heat generated during operation of integrated circuit  416  may be reduced or eliminated. For example, during operation of portable electronic device  500 , the maximum temperature associated with integrated circuit  416  may be less than 55 C. 
         [0051]    Portable electronic device  500  may include: one or more program modules or sets of instructions stored in an optional memory subsystem, such as module  500 . These sets of instructions may be executed by an optional processing subsystem (such as one or more processors) on a motherboard, such as circuit board  420 . Note that the one or more computer programs may constitute a computer-program mechanism. Moreover, instructions in the various modules in the optional memory subsystem may be implemented in: a high-level procedural language, an object-oriented programming language, and/or in an assembly or machine language. Furthermore, the programming language may be compiled or interpreted, e.g., configurable or configured, to be executed by the optional processing subsystem. 
         [0052]    In some embodiments, functionality in these circuits, components and devices may be implemented in one or more: application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and/or one or more digital signal processors (DSPs). Moreover, the circuits and components may be implemented using any combination of analog and/or digital circuitry, including: bipolar, PMOS and/or NMOS gates or transistors. Furthermore, signals in these embodiments may include digital signals that have approximately discrete values and/or analog signals that have continuous values. Additionally, components and circuits may be single-ended or differential, and power supplies may be unipolar or bipolar. 
         [0053]    Portable electronic device  500  may include one of a variety of devices that can include memory, including: a laptop computer, a media player (such as an MP3 player), an appliance, a subnotebook/netbook, a tablet computer, a smartphone, a cellular telephone, a network appliance, a personal digital assistant (PDA), a toy, a controller, a digital signal processor, a game console, a device controller, a computational engine within an appliance, a consumer-electronic device, a portable computing device, a personal organizer, and/or another electronic device. 
         [0054]    While portable electronic device  500  was used as an illustration in the preceding discussion, in other embodiments module  400  is included in an electronic device, such as a server, a desktop computer, a mainframe computer and/or a blade computer. Furthermore, alternative passive heat transfer components and/or materials may be used in thermal-interface material  528 . 
         [0055]    Additionally, one or more of the components may not be present in  FIGS. 4 and 5 . In some embodiments, the preceding embodiments include one or more additional components that are not shown in  FIGS. 4 and 5 . Also, although separate components are shown in  FIGS. 4 and 5 , in some embodiments some or all of a given component can be integrated into one or more of the other components and/or positions of components can be changed. 
         [0056]    We now describe embodiments of a method that can be performed using the embodiments in  FIGS. 4 and 5 .  FIG. 6  presents a flowchart illustrating a method  600  for transferring heat from an integrated circuit, such as that in module  400  ( FIG. 4 ). During the method, heat generated by the integrated circuit disposed on the top surface of the circuit board is transferred to the bottom surface of the circuit board (operation  410 ). Then, the heat is conducted to a top surface of the second circuit board, which is thermally coupled to the circuit board by the thermal-interface material (operation  412 ). Note that the bottom surface of the circuit board is separated from the top surface of the second circuit board by the gap, and the thermal-interface material is in the gap between the bottom surface of the circuit board and the top surface of the second circuit board. 
         [0057]    In some embodiments of method  600 , there may be additional or fewer operations. Moreover, the order of the operations may be changed, and/or two or more operations may be combined into a single operation. 
         [0058]    In the preceding description, we refer to ‘some embodiments.’ Note that ‘some embodiments’ describes a subset of all of the possible embodiments, but does not always specify the same subset of embodiments. 
         [0059]    The foregoing description is intended to enable any person skilled in the art to make and use the disclosure, and is provided in the context of a particular application and its requirements. Moreover, the foregoing descriptions of embodiments of the present disclosure have been presented for purposes of illustration and description only. They are not intended to be exhaustive or to limit the present disclosure to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Additionally, the discussion of the preceding embodiments is not intended to limit the present disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.