Patent Publication Number: US-2017374744-A1

Title: Heat-sinking components mounted on printed boards

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of co-pending U.S. patent application Ser. No. 14/487,922, filed on Sep. 16, 2014, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to heat sinks, and more particularly, to methods of heat sinking components mounted on printed boards. 
     BACKGROUND 
     Solid state drives (SSDs) store information using solid state memory devices, such as flash memory devices. In order to achieve performance targets (e.g., data transfer rates), SSDs may utilize a plurality of flash memory devices electrically connected to a controller using a plurality of data channels. Read and write speeds to and from the flash memory devices may be affected by the number of data channels and the frequencies at which the controller and flash memory devices operate. Increasing the frequencies of the controller and flash memory devices may increase an amount of heat generated by the controller and the individual flash memory devices, other factors, such as process node and transistor type, being equal. Further, increasing the number of flash memory devices in a SSD may increase the total amount of heat generated, other factors, such as process node, transistor type, and operating frequency, being equal. 
     SUMMARY 
     In some examples, the disclosure describes a method including coupling a printed board assembly (PBA) to a fixture. In some examples, the PBA may include a printed board (PB) and a plurality of components electrically and mechanically coupled to the PB, and each component of the plurality of components may define a respective surface. The method may further include planarizing at least one of the respective surfaces of the plurality of components using an abrasive tool. The method may further include attaching a heat sink to the respective surfaces of the plurality of components. 
     In some examples, the disclosure describes a system including a fixture configured to restrain a PBA and an abrasive tool. In accordance with these examples, the PBA may include a PB and a plurality of components electrically and mechanically coupled to the PB, and each component of the plurality of components may define a respective surface. At least one of the fixture or the abrasive tool may be configured to be moved relative to the other of the abrasive tool or the fixture to planarize at least one of the respective surfaces of the plurality of components such that the respective surfaces of the plurality of components lie in a substantially flat plane after planarization. 
     In some examples, the disclosure describes a system including means for restraining a PBA. The may include a PB and a plurality of components electrically and mechanically coupled to the PB, and each component of the plurality of components may define a respective surface. In accordance with these examples, the system also may include means for planarizing at least one of the respective surfaces of the plurality of components such that the respective surfaces of the plurality of components lie in a substantially flat plane after planarization. 
     The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a conceptual and schematic diagram illustrating a side view of an example printed board assembly and an example system including a fixture and an abrasive tool. 
         FIG. 2  is a conceptual and schematic diagram illustrating a side view of an example printed board assembly and an example system including a fixture and an abrasive tool. 
         FIG. 3  is a conceptual and schematic diagram illustrating a side view of an example solid state drive including a printed board assembly, at least one heat sink, and a housing. 
         FIG. 4  is a flow diagram illustrating an example technique for planarizing a surface of at least one component of a printed board assembly. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure describes techniques and systems for planarizing a surface of at least one component mounted to a printed board (PB) to facilitate coupling of a heat sink to the at least one component. Printed board assemblies (PBAs) include a PB and a plurality of components. In some examples, the components may include a plurality of active devices, such as controllers, flash memory devices, buffer memory devices, or the like. The techniques and systems may planarize the at least some respective surfaces of the components to facilitate coupling of a single heat sink to at least one of the components. In this way, the techniques and systems may facilitate assembly of a PBA and a heat sink, compared to requiring a separate heat sink for each component to be heat-sinked. 
     In some examples, a system for planarizing a plurality of components mounted to a PB may include a fixture and an abrasive tool. The fixture may be configured to hold or restrain the PB, and may include a material or shape that facilitates holding the PB substantially flat (planar) during the planarization technique. In some examples, a compliant film may be disposed between a rigid support of the fixture and the PB assembly. The compliant film may conform to non-planar features on a back side of the PB, such as solder bumps, while allowing the rigid fixture to hold the PB substantially planar during the planarization technique. 
     The abrasive tool may include any tool that defines a substantially planar surface and includes or utilizes an abrasive material to abrade material from a respective surface of one or more of the plurality of components to result in the respective surfaces lying in a substantially flat plane after the planarization technique. This may facilitate formation of a substantially uniform planar surface for attaching a heat sink to a plurality of components of the PBA. A substantially uniform planar surface for multiple components may facilitate more efficient assembly of the PBA and one or more heat sinks, while allowing sufficient thermal contact between the components and the heat sink. Similarly, the substantially uniform planar surface for multiple components may improve thermal contact between respective surfaces of the multiple components and the heat sink compared to instances where multiple components do not include the substantially uniform planar surface. 
     Planarizing respective surfaces for multiple components to lie in substantially the same plane may be facilitated by performing the planarization after the components are attached to the PB compared to individually planarizing surfaces prior to attaching the components to the PB. For example, the PB may not lie substantially in a plane, such that, even if the individual surfaces of the components are substantially planar, after connecting the components to the PB, the component surfaces may not lie in a substantially flat plane. Planarizing the respective surfaces after the components are attached to the PB also may result in the component surfaces lying in a substantially flat plane, even if the PB does not lie substantially in a plane. 
       FIG. 1  is a conceptual and schematic diagram illustrating a side view of an example PBA  100  and a system including a fixture and an abrasive tool. PBA  100  may include a PB  102  and a plurality of components  104 . In some examples, components  104  may be mechanically coupled to PB  102  and electrically coupled to electrically conductive traces or layers in or on PB  102 . Components  104  may include electrical and electronic components, such as actives devices, passive devices, or both. Examples of active devices may include a controller, a host interface chip, a buffer memory (which may be part of the controller), flash memory devices, power delivery components, or the like. Examples of passive devices may include capacitors, resistors, inductors, or the like. In some examples, components  104  may be surface mounted, through-hole mounted, or a mixture of surface mounted and through-hole mounted. In some examples, components  104  may be attached to PB  102  using soldering, brazing, electrically conductive adhesive, or the like. 
     In some examples, PBA  100  may be part of a solid state drive (SSD) (e.g., SSD  200 ,  FIG. 3 ). A SSD stores information using active devices such as flash memory. In some examples, the storage space of the SSD may be increased by increasing the number of flash memory devices. In some examples, increasing the number of flash memory devices also may increase the read/write speeds of the SSD, e.g., compared to an SSD with fewer flash memory devices and fewer data channels. In some examples, the performance (e.g., read/write speeds) also may be increased by increasing the operating frequency at which the active devices operate (including the controller, the flash memory devices, or both). Operation of components  104  may generate heat, and additional components  104 , increased operating frequencies, or both, may increase a total heat generated by components  104  and PB  102  of PBA  100 , when other factors are consistent. 
     PB  102  includes a plurality of surfaces, including a first PB surface  106 A and a second PB surface  106 B. First PB surface  106 A may be substantially opposite to and substantially parallel to second PB surface  106 B. First and second PB surfaces  106 A and  106 B may be the major (e.g., largest) surfaces of PB  102 . In some examples, the plurality of components  104  may be attached to first PB surface  106 A, to second PB surface  106 B, or both. As illustrated in  FIG. 1 , in some examples, the plurality of components  104  may be attached only to second PB surface  106 B. 
     In some examples, one or both of first PB surface  106 A and second PB surface  106 B may include surface features, non-uniformities, or non-planarity. In some examples, the surface features or non-uniformities may include solder bumps from soldering components  104  to PB  102 , e.g., in through-hole mounting techniques. In some examples, the surface features or non-uniformities additionally or alternatively may include one or more components  104  attached to the respective PB surface  106 A or  106 B. For example, second PB surface  106 B may include one or more passive or active components, one or more solder bumps, curvature such that second PB surface  106 B is not substantially planar, or the like. As illustrated in  FIG. 1 , in some examples, first PB surface  106 A may include surface features or non-uniformities such that first PB surface  106 A is not substantially planar. 
     In some examples, one or more surfaces of at least one of components  104  may include surface non-uniformities. Each component  104  includes a respective first component surface  108 A proximate to PB  102  and a respective second component surface  108 B opposite of first component surface  108 A and PB  102 . In some examples, at least one of the respective second component surfaces  108 B includes one or more surface non-uniformities, such as surface roughness or curvature that deviates from planarity. Surface non-uniformities of second component surfaces  108 B may hinder thermal coupling between second component surfaces  108 B and a heat sink thermally coupled to components  104 . 
     In accordance with one or more examples of the disclosure, a system that includes a fixture  114  and an abrasive tool  120  may be used to substantially remove surface non-uniformities from one or more of second component surfaces  108 B of components  104 . Fixture  114  may be configured to restrain or hold PBA  100 , e.g., during the planarization technique. In some examples, fixture  114  also may be configured to maintain PB  102  substantially planar when PBA  100  is restrained by fixture  114 . In this way, fixture  114  may be configured to maintain components  104  substantially motionless relative to each other during the planarization technique. 
     In some examples, fixture  114  may include a substantially rigid support  118  and a compliant film  110 . Substantially rigid support  118  may include a substantially rigid material, which may exhibit substantially no deformation (e.g., no deformation or nearly no deformation) under the forces exerted on substantially rigid support  118  during the planarization techniques described herein. Example materials from which substantially rigid support  118  may be formed include wood, metal, an alloy, a polymer or mixture of polymers, or the like. 
     In some examples, compliant film  110  may be disposed between PBA  100  and substantially rigid support  118 . For example, as shown in  FIG. 1 , a first film surface  112 A of compliant film  110  may be positioned adjacent to substantially rigid support  118  while a second film surface  112 B of compliant film  110  may be opposite from first surface  112 A and may be positioned to receive first PB surface  106 A. 
     Compliant film  110  may include flexible and conforming material. For example, compliant film  110  may deform in response to contact with surface features, non-uniformities, or non-planarity of first PB surface  106 A when PBA  100  is pressed against compliant film  110  during planarization of second component surfaces  108 B. The material(s) from which compliant film  110  is formed may be selected to be sufficiently flexible to deform in response to contact with first PB surface  106 A while being sufficiently resilient to exert a force against first PB surface  106 A during the planarization technique. For example, compliant film  110  may be sufficiently inflexible that none of the surface features, non-uniformities, or non-planar portions of first PBA surface  106 A contact substantially rigid support  118  during the planarization technique. 
     In some examples, compliant film  110  may possess adhesive properties, such that compliant film  110  at least partially restrains PBA  100  with respect to substantially rigid support  118 . Compliant film  110  may be made of any suitable flexible material, including, wax, a foam tape, a polyurethane, or the like. 
     In other examples, instead of including compliant film  110 , fixture  114  may include alternative mechanisms to support PBA  100  and, optionally, restrain PBA  100  relative to fixture  114 . For example, fixture  114  may include a plurality of pillars or protrusions that extend from fixture surface  116 A. The pillars or protrusions may be located at selected locations of fixture surface  116 A such that the pillars or protrusions contact first PB surface  106 A of PB and do not contact any components  104  that are attached to first PB surface  106 A. Additionally, the pillars or protrusions may be sized such that any components  104  attached to first PB surface  106 A do not contact fixture surface  116 A when PBA  100  is pressed against the pillars or protrusions during the planarization technique. 
     As another example, fixture surface  116 A may define a complementary shape to first PB surface  106 A of PBA  100 . In other words, fixture surface  116 A may define a topology that is opposite to the surface topology of first PB surface  106 A, such that the surface features of the first PB surface  106 A substantially fit within the topology of fixture surface  116 A and second PB surface  106 B is maintained as a substantially flat plane during the planarization technique. 
     In some examples, fixture  114  may include one or more restraining devices, such as clamps, fasteners, clips, or the like. The one or more restraining devices may restrain PBA  100  relative to fixture  114  during the planarization technique. In some examples, the one or more restraining devices restrain movement of PBA  100  relative to fixture  114  in one or more of the x-, y-, and z-axes (where orthogonal x-y-z axes are shown in  FIG. 1  for ease of description only). 
     The system also may include an abrasive tool  120 . Abrasive tool  120  may define a substantially planar surface, such that abrasive tool  120  facilitated planarizing one or more of second component surfaces  108 B. In some examples, abrasive tool  120  includes an abrasive film or layer, such as a lapping film  122 , attached to a substantially rigid, substantially planar plate  124 , as shown in  FIG. 1 . 
     In other examples, as shown in  FIG. 2 , abrasive tool  120  may include an abrasive slurry  126  and a substantially planar plate  128 . In some examples, abrasive slurry  126  may include abrasive particles or powder carried by a fluid. In some examples, lapping film  122  or abrasive slurry  126  may include materials such as aluminum oxide, emery, silicon carbide, diamond, or another abrasive material. In some examples, rigid plate  124  or substantially planar plate  128  may include a metal or charged composite plate. 
     The apparatus or device including abrasive tool  120  and fixture  114  may be used to reduce or substantially remove the surface non-uniformities of second component surfaces  108 B of components  104  to result in second component surfaces  108 B being disposed along a substantially flat plane. In some examples, one or both of abrasive tool  120  (e.g., substantially planar plate  124  or  128 ) or fixture  114  is configured to move relative to the other of abrasive tool  120  or fixture  114 . In other examples, both abrasive tool  120  and fixture  114  are configured to move relative to one another. 
     As abrasive tool  120  moves relative to PBA  100 , lapping film  122  or abrasive slurry  126  moves over the respective second component surfaces  108 B of a plurality of components  104  and planarizes one or more of the respective second component surfaces  108 B of the plurality of components  104 . In some examples, abrasive tool  120  may be applied to individual components  104  to reduce or remove surface non-uniformities of that individual component. However, in some examples, abrasive tool  120  may be simultaneously or sequentially applied to the respective second component surfaces  108 B of a plurality of electrical components  104 , such that the plurality of electrical components  104  are polished or planarized as part of the same process. Not only may this be more efficient, this may facilitate formation of a substantially planar surface across multiple second component surfaces  108 B. 
     By planarizing multiple second component surfaces  108 B to lie in the same plane, a single heat sink may be thermally coupled to multiple (e.g., at least two) second component surfaces  108 B while having desirable thermal contact between the heat sink and the respective second component surfaces  108 B. This may allow simpler and/or faster assembly of PBA  100  with a heat sink compared to using a respective heat sink for each respective component of the plurality of components  104 . Similarly, the substantially uniform planar surface for multiple components may improve thermal contact between respective surfaces of the multiple components and the heat sink compared to instances where multiple components do not include the substantially uniform planar surface. 
     Planarizing multiple second component surfaces  108 B to lie in the same plane may be facilitated by performing the planarization after components  104  are attached to PB  102  compared to individually planarizing second components surfaces  108 B prior to attaching components  104  to PB  102 . For example, PB  102  may not lie substantially in a plane, such that, even if second component surfaces  108 B are individually substantially planar, after connecting components  104  to PB  102 , second component surfaces  108 B may not lie in a substantially flat plane. Planarizing the respective second component surfaces  108 B after components  104  are attached to PB  102  also may result in the respective second component surfaces  108 B lying in a substantially flat plane, even if PB  102  does not lie substantially in a plane. 
     Although three components  104  are illustrated in  FIG. 1 , in other examples, PBA  100  may include more than three components  104 . Generally PBA  100  may include a plurality of components  104 . The planarization of multiple components  104  using fixture  114  and abrasive tool  120  may be performed on all of components  104  or a subset of components  104 . Generally, fixture  114  and abrasive tool  120  may be used to planarize at least two second component surfaces  108 B, and a single heat sink may be thermally coupled to at least two components  104 . The heat sink may be thermally coupled to all of components  104  or a subset of components  104 . In this way, a single heat sink may be used for multiple components  104 , which may facilitate assembly, and the apparatus including fixture  114  and abrasive tool  120  may be used to form substantially planar surfaces of the multiple components  104  to facilitate thermal coupling of the heat sink to the components  104 . 
       FIG. 3  is a conceptual and schematic diagram illustrating a side view of an example SSD  200  including PBA  100 , at least one heat sink  202 , and a housing  204 . PBA  100  may be similar to or substantially the same as PBA  100  illustrated in  FIGS. 1 and 2 , and may include PB  102  and a plurality of components  104 . Components  104  may include second component surfaces  108 B, which have been planarized to lie in a substantially flat plane. In the example illustrated in  FIG. 3 , PBA  100  includes three components  104 . In general, PBA  100  may include a plurality of components  104  (e.g., at least two components  104 ). 
     SSD  200  also includes at least one heat sink  202 . In some examples, a single heat sink  202  may be thermally coupled to all of components  104 . In other examples, heat sink  202  may be thermally coupled to a subset of components  104 . In some examples, SSD  200  may include a plurality of heat sinks  202 , each of which may be coupled to at least two components  104 . 
     In some examples, heat sink  202  may be thermally coupled to the at least two components  104  using a thermal interface material such as thermal paste, a thermal adhesive, a thermal tape, or the like. In some examples, heat sink  202  may be mechanically coupled to at least PB  102  using clips, pins, compression springs, or other similar devices to retain heat sink  202  relative to PB  102  and components  104 . 
     Heat sink  202  may include a thermally conductive material such as aluminum, copper, or the like. Heat sink  202  may be configured to transfer heat generated by components  104  to cool components  104 . For example, heat sink  202  may have greater thermal mass than components  104 , may have greater volume than components  104 , may include geometric features such as fins that facilitate increased heat transfer, or may be thermally coupled to another component to which the heat may be transferred. In this way, heat sink  202  may facilitate cooling of components  104 . Heat sink  202  may be passive cooled, actively cooled, or both. Passive cooling may include conduction of heat to another component, such as housing  204 , passive convection, radiation, or the like. Active cooling may include forced air convection, liquid cooling using a pumped fluid, or the like. 
     SSD  200  also includes housing  204 . Housing  204  may include a plurality of sides and defines an internal volume in which PBA  100  and heat sink  202  are disposed. In some examples, housing  204  may include a thermally conductive material, such as a metal, an alloy, a thermally conductive ceramic, a thermally conductive polymer or polymer doped to be thermally conductive, or the like. In some examples, heat sink  202  may be thermally coupled to housing  204  by a thermal interface material such as a thermal paste, a thermal adhesive, a thermal tape, or the like. In some examples, housing  204  may act as an extension of heat sink  202  to further dissipate heat from components  104 . 
     Housing  204  may include one of several sizes, and may conform to one or various size standards for SSDs. In some examples, housing  204  may be sized as a 1.8 inch, 2.5 inch, or 3.5 inch form factor. However, in general, housing  204  may be any size. 
       FIG. 4  is a flow diagram illustrating an example technique for planarizing components of a PBA. For purposes of description only, the technique of  FIG. 4  will be described with reference to the system of  FIG. 1 . However, the technique  FIG. 4  may be implemented with other systems, and the system of  FIG. 1  may be formed using other techniques. 
     In some examples, the technique may include coupling PBA  100  to fixture  114  ( 402 ). As described in  FIG. 1 , in some examples, fixture  114  may include a substantially rigid support  118  and a compliant film  110 . Coupling PBA  100  to fixture  114  ( 402 ) may include positioning compliant film  110  between PBA  100  and substantially rigid support  118 . For example, as shown in  FIG. 1 , first film surface  112 A of compliant film  110  may be positioned adjacent to substantially rigid support  118  while a second film surface  112 B of compliant film  110  may be opposite from first surface  112 A and may be positioned to receive first PB surface  106 A. Thus, PBA  100  may be coupled to fixture  114  ( 402 ) by positioning first film surface  112 A of compliant film  110  on fixture surface  116 A, positioning a first PB surface  106 A on second film surface  112 B, and applying a force on PBA  100  and/or fixture  114  to couple PBA  100  to fixture  114 . In some examples, compliant film  110  may include adhesive properties that help restrain PBA  100  relative to fixture  114 . Compliant film  110  may deform in response to contact with surface features, non-uniformities, or non-planarity of first PB surface  106 A when PBA  100  is pressed against compliant film  110 . 
     In some examples, coupling PBA  100  to fixture  114  ( 402 ) may include alternative or additional mechanisms to support PBA  100  and, optionally, restrain PBA  100  relative to fixture  114 . For example, fixture  114  may include a plurality of pillars or protrusions that extend from fixture surface  116 A. The pillars or protrusions may be located at selected locations of fixture surface  116 A such that the pillars or protrusions contact first PB surface  106 A of PB  102  and do not contact any components  104  that are attached to first PB surface  106 A. 
     In other examples, coupling PBA  100  to fixture  114  ( 402 ) may include positioning a first PB surface  106 A of PBA  100  directly on fixture surface  116 A. Fixture surface  116 A may define a complementary shape to first PB surface  106 A of PBA  100 . In other words, fixture surface  116 A may define a topology that is opposite to the surface topology of first PB surface  106 A, such that the surface features of the first PB surface  106 A substantially fit within the topology of fixture surface  116 A and second PB surface  106 B is maintained as a substantially flat plane during the planarization technique. Thus, PBA  100  may fit directly within fixture  114 . 
     In some examples, fixture  114  may include one or more restraining devices, such as clamps, fasteners, clips, or the like. The one or more restraining devices may restrain PBA  100  relative to fixture  114  during the planarization technique. In some examples, the one or more restraining devices restrain movement of PBA  100  relative to fixture  114  in one or more of the x-, y-, and z-axes (where orthogonal x-y-z axes are shown in  FIG. 1  for ease of description only). In these examples, coupling PBA  100  to fixture  114  ( 402 ) may include restraining PBA  100  relative to fixture  114 . 
     After PBA  100  has been coupled to fixture  114  ( 402 ), at least one surface of at least one component  104  may be planarized using abrasive tool  120  ( 404 ). In some examples, abrasive tool  120  may include an abrasive film or layer, such as a lapping film  122 , attached to a substantially rigid, substantially planar plate  124 , as shown and described in  FIG. 1 . In other examples, as shown and described in  FIG. 2 , abrasive tool  120  may include an abrasive slurry  126  and a substantially planar plate  128 . 
     In some examples, planarizing the respective surfaces of the plurality of components  104  ( 404 ) involves moving one or both of abrasive tool  120  or fixture  114  relative to the other of abrasive tool  120  or fixture  114 . As abrasive tool  120  moves relative to PBA  100  or vice versa, lapping film  122  or abrasive slurry  126  moves over the respective second component surfaces  108 B of plurality of components  104  and planarizes the respective second component surfaces  108 B of the plurality of components  104 . The planarization of multiple components  104  using fixture  114  and abrasive tool  120  may be performed on all of components  104  or a subset of components  104 . In some examples, abrasive tool  120  may be applied to individual components  104  to reduce or remove surface non-uniformities of that individual component. However, in some examples, abrasive tool  120  may be simultaneously or sequentially applied to the respective second component surfaces  108 B of a plurality of components  104 , such that the plurality of components  104  are polished or planarized as part of the same process. Not only may this be more efficient, this may facilitate formation of a substantially planar surface across multiple second component surfaces  108 B. 
     After planarization, in some examples, the technique of  FIG. 4  includes thermally coupling at least one heat sink  202  a respective surface of at least two of the plurality of components  104  ( 406 ). In some examples, heat sink  202  may be thermally coupled to all of components  104 , or to a subset of components  104 . In some examples, a plurality of heat sinks may be thermally coupled to components  104 ; each heat sink  202  may couple to at least two planarized components  104 . In some examples, heat sink  202  may be thermally coupled to components  104  by a machine in an automated process. In some examples, the at least one heat sink  202  may be thermally coupled to the respective components  104  ( 406 ) using a thermal interface material, such as a thermal paste, a thermal adhesive, a thermal tape, or the like. 
     In some examples, the technique of  FIG. 4  optionally may include enclosing PBA  100  and heat sink  202  within a housing ( 408 ). In some examples, heat sink  202  may be thermally coupled to housing  204  ( FIG. 3 ). In some examples, heat sink  202  may be thermally coupled to housing  204  using a thermal interface material, such as a thermal paste, a thermal adhesive, a thermal tape, or the like. PBA  100  may be mechanically coupled to housing  204  via screws, pins, clips, or the like. Heat sink  202  may be thermally coupled to housing  204 . Housing  204  may protect PBA  100  from the external environment, and also may facilitate dissipation of heat generated by components  104 . 
     Various examples have been described. These and other examples are within the scope of the following claims.