Abstract:
Socketable flexible circuit based electronic device modules and sockets for electrically and mechanically connecting the electronic device modules to an interconnect substrate are described. The systems provide ways in which the electronic device module may be positioned accurately and securely on an interconnect carrier, while allowing the electronic device modules to be replaced easily without having to resort to laborious desoldering and resoldering operations to remove the modules and connect new modules in their place.

Description:
TECHNICAL FIELD 
     This invention relates to schemes for connecting flexible circuit based electronic device modules to an interconnect substrate through a socket connection. 
     BACKGROUND 
     The use of flexible printed circuits has become quite widespread because of their low cost, ease of assembly in interconnection systems, and the low volumes that they occupy. A flexible printed circuit (or “flex circuit”) typically includes a strip or cable with a plurality of embedded electrically conductive lines. The conductive lines may be formed on a relatively thin base layer of insulative material, such as a polyimide sheet or the like. The conductive lines are covered by an overlying layer of insulative material to form an elongated and relatively flexible circuit structure. Apertures may be formed in one of the insulation layers to expose portions of the conductive lines for electrical connection to other electronic components (e.g., the conductors of a complementary mating connecting device, which may be a second flat flexible circuit, a printed circuit board or the terminals of a mating connector). A zero insertion force (ZIF) connector typically provides an electrical interface between the flexible printed circuit and a printed circuit board. 
     Electronic components may be mounted on flexible printed circuits that, in turn, may be incorporated into electronic device modules, such as charged coupled device (CCD) sensors and complementary metal-oxide-semiconductor (CMOS) sensors. In some cases, a flexible printed circuit may be connected to an interconnect substrate (e.g., a printed circuit board) through a multi-layer ceramic dual-in-line (DIP) package (see, e.g., U.S. Pat. Nos. 5,072,084 and 5,311,007). In other cases, a flexible printed circuit may be connected to an interconnect substrate through a zero insertion force connector. For example, U.S. Pat. No. 6,011,294 discloses a charged coupled device packaging in which an image sensor is housed within a ring frame and is mounted on a flexible circuit board that may be connected to a printed circuit board through a standard zero insertion force connector, an anisotropic adhesive, or a traditional solder butt joint. 
     SUMMARY 
     The invention features socketable flexible circuit based electronic device modules and sockets for electrically and mechanically connecting the electronic device modules to an interconnect substrate. These systems provide inventive ways in which the electronic device modules may be positioned accurately and securely on an interconnect carrier, while allowing the electronic device modules to be replaced easily without having to resort to laborious desoldering and resoldering operations to remove the modules and connect new modules in their place. 
     In one aspect, the invention features an electronic device module socket that includes a support frame, a retainer, and an electrical connector. The support frame is constructed and arranged to receive the electronic device module. The retainer is constructed and arranged to engage and thereby mechanically hold the electronic device module in place. The electrical connector is constructed and arranged to electrically connect the plurality of elongated flexible circuit board conductors to a corresponding plurality of electrical conductors of the interconnect substrate. 
     Embodiments in accordance with this aspect of the invention may include one or more of the following features. 
     The electrical connector preferably is constructed and arranged to be biased against the plurality of elongated flexible circuit board conductors when the electronic device module is mechanically held in place by the retainer. The electrical connector may comprise a plurality of electrically conductive spring fingers or an elastomeric anisotropic electrically conductive film. 
     The retainer preferably has a latch portion that is configured to yield during insertion of the electronic device module into the socket and to snap back over an edge of the electronic device module when fully inserted into the socket. The support frame and the retainer may be incorporated within a unitary structure. 
     In another aspect, the invention features a socketable electronic device module that includes a housing, one or more electronic components, and a flexible circuit board. The housing is constructed and arranged to be inserted within an electronic device module socket for electrical and mechanical connection to an interconnect substrate. The flexible circuit board comprises a flexible substrate having a component portion supporting the one or more electronic components and a contact portion supporting a plurality of elongated electrical conductors and coupled to the component portion through a curved portion. The component portion of the flexible substrate is disposed within the housing and the contact portion of the flexible substrate is disposed outside of the housing and is exposed for electrical contact with an electrical connector of the electronic device module socket. 
     Embodiments in accordance with this aspect of the invention may include one or more of the following features. 
     In some embodiments, the one or more electronic components may be supported on one surface of the flexible substrate and at least a portion of the electrical conductors may be supported on an opposite surface of the flexible is substrate. In these embodiments, the contact portion of the flexible substrate may be substantially orthogonal to the component portion of the flexible substrate. 
     In other embodiments, the one or more electronic components and the electrical conductors are supported on the same surface of the flexible substrate. In these embodiments, the contact portion of the flexible substrate may be substantially parallel to the component portion of the flexible substrate, and the flexible substrate may be folded at the curved portion. 
     In another aspect, the invention features a socket-based system for electrically and mechanically connecting an interconnect substrate and an electronic device module. 
     Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 is a diagrammatic perspective top view of a flexible circuit based electronic device module that is plugged into a socket. 
     FIG. 2A is a diagrammatic perspective view of the electronic device module socket of FIG.  1 . 
     FIG. 2B is a diagrammatic perspective view of the flexible circuit based electronic device module of FIG. 1 without a top housing portion. 
     FIG. 2C is a diagrammatic perspective view of the flexible circuit based electronic device module of FIG. 2B plugged into the socket of FIG.  2 A. 
     FIG. 2D is a diagrammatic cross-sectional side view of an electrical socket conductor with a spring finger portion biased against a contact portion of the electronic device module of FIG.  1 . 
     FIG. 3 is a diagrammatic perspective top view of an alternative flexible circuit based electronic device module that is plugged into a socket. 
     FIG. 4A is a diagrammatic perspective top view of the electronic device module socket of FIG.  3 . 
     FIG. 4B is a diagrammatic perspective bottom view of the electronic device module socket of FIG.  3 . 
     FIG. 5A is a diagrammatic perspective side view of the flexible circuit based electronic device module of FIG. 3 without a top housing portion. 
     FIG. 5B is a diagrammatic perspective bottom view of the flexible circuit based electronic device module of FIG. 5A, and an electrical connector of the socket of FIG. 3 coupled to a contact portion of the electronic device module. 
     FIG. 6 is a diagrammatic perspective top view of an electronic device module socket. 
    
    
     DETAILED DESCRIPTION 
     In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
     Referring to FIGS. 1,  2 A,  2 B,  2 C and  2 D, in one embodiment, a socket-based electrical and mechanical circuit connection system  10  includes a socket  12  and a socketable flexible circuit based electronic device module  14 . 
     Socket  12  is constructed and arranged to electrically and mechanically connect electronic device module  14  to an interconnect substrate (e.g., a printed circuit board). In particular, socket  12  includes a support frame  16 , a pair of retainers  18 ,  20 , and a pair of electrical connectors  22 ,  24 . Support frame  16  has four sidewalls that define a recess for receiving electronic device module  14 . Each retainer  18 ,  20  includes a respective latch portion  26 ,  28  that is configured to yield during insertion of electronic device module  14  into socket  12  and to snap back over a respective edge of electronic device module  14  when electronic device module  14  is fully seated within socket  12 . In this way, retainers  18 ,  20  operate to mechanically hold electronic device module  14  in place with respect to socket  12 . In some embodiments, support frame  16  and retainers  18 ,  20  may be incorporated into a unitary structure, which may be formed from a plastic material that is molded by a conventional injection molding process. In other embodiments, support frame  16  and retainers  18 ,  20  may be formed as separate components from any of a wide variety of different materials. 
     Electrical connectors  22 ,  24  each includes a plurality of resilient electrical conductors  29 , each of which includes a spring finger portion  31  that protrudes into the recess defined by the sidewalls of support frame  16 . Each spring finger portion  31  is biased (or spring loaded) against a corresponding electrical conductor of a contact portion of electronic device module  14  (described in detail below) when the electronic device module is held in place by retainers  18 ,  20 . Each spring finger  29  preferably contacts the corresponding electrical conductor of electronic device module  14  over a relatively small area so that the contact pressure exerted by the spring fingers is relatively high. As shown in FIG. 2D, in this embodiment, each spring finger portion  31  forms an “S”-shaped curve with the distal end extending away from the recess defined by the socket sidewalls. In other embodiments, each spring finger portion may form a “C”-shaped curve with the distal end extending toward the recess defined by the socket sidewalls. Still other spring finger arrangements are possible. 
     Socket  12  may be connected to an interconnect substrate by any conventional surface mount process (e.g., an infrared solder reflow process). 
     Electronic device module  14  includes a housing  30 , one or more electronic components  32  and a flexible circuit board  34 . 
     Housing  30  includes a top housing portion  36  that has a pair of tabs  38 ,  40  (FIG. 1) that are configured to engage a pair of mating latches  42 ,  44  of a bottom housing portion  46 . Top housing portion  36  also includes a pair of slots (not shown) that are configured to receive a pair of flanges  48 ,  50  that protrude from one end of bottom housing portion  46 . Top housing portion  36  and bottom housing portion  46  each may be formed from a plastic material that is molded by a conventional injection molding process. In operation, flanges  48 ,  50  slide into the slots of top housing portion  36  and latches  42 ,  44  snap down over tabs  38 ,  40  to hold top housing portion  36  and bottom housing portion  46  together. 
     The electronic components  32  may be semiconductor-based devices (e.g., integrated circuits and sensors) and other active or passive devices. In the illustrated embodiment, electronic components  32  correspond to the components of an image sensor (e.g., a CMOS image sensor available from Agilent Technologies, Inc. of Palo Alto, Calif., USA), including an image sensor chip and a number of peripheral electrical devices. 
     Electronic components  32  are coupled mechanically and electrically by flexible circuit board  34 . Flexible circuit board  34  may include a pattern of elongated electrical conductors formed on a plastic (e.g., polyimide) substrate surface. The electrical conductors may be formed from any one of a wide variety of electrically conductive materials, such as the electrically conductive materials that are used commonly in the circuit board industry. In one embodiment, the electrical conductors are formed, from copper with nickel and gold plating. Electronic components  32  may be connected to the electrical conductor pattern of flexible circuit board  34  by a conventional wire bonding process. In the embodiments of FIGS. 1-2D, flexible circuit board  34  includes a component portion  52 , a pair of contact portions  54 ,  56 , and a pair of curved portions  58 ,  60  that physically couple contact portions  54 ,  56  to component portion  52 . Component portion  52  is substantially planar and corresponds to the area where electronic components  32  are mounted to flexible circuit board  34 . Contact portions  54 ,  56  are electrically coupled to the electronic components  32  by a plurality of electrical conductors that extend from the contact portions  54 ,  56 , through curved portions  58 ,  60 , to the pattern of electrical conductors formed in component portion  52 . In this embodiment, contact portions  54 ,  56  are oriented substantially orthogonally to component portion  52  and extend outside of housing  30  (as shown in FIGS. 1 and 2D) to enable electronic component module  14  to electrically couple to the electrical connectors  22 ,  24  of socket  12 . To this end, the electrical conductors of contact portions  54 ,  56  are formed on a surface of flexible circuit board  34  that is opposite the surface on which electronic components  32  are mounted. The backsides of contact portions  54 ,  56  are supported by top housing portion  36  to resist the contact force exerted by the socket spring finger portions  31  when electronic device module  14  is fully seated within socket  12 . 
     Referring to FIGS. 3,  4 A,  4 B,  5 A and  5 B, in another embodiment, a socketbased electrical and mechanical circuit connection system  70  includes a socket  72  and a socketable flexible circuit based electronic device module  74 . In this embodiment, socket  72  is configured to electrically connect to a contact portion of a flexible circuit board that is disposed at the bottom side of electronic device module  74 . 
     As shown in FIGS. 4A and 4B, socket  72  is constructed and arranged to electrically and mechanically connect electronic device module  74  to an interconnect substrate (e.g., a printed circuit board). In particular, socket  72  includes a support frame  76 , a retainer  78 , and an electrical connector  82 . Support frame  76  has two adjacent sidewalls that, together with retainer  78 , define a recess for receiving electronic device module  74 . Retainer  78  includes a latch portion  86  that is configured to yield during insertion of electronic device module  74  into socket  72  and to snap back over a respective edge of electronic device module  74  when electronic device module  74  is fully seated within socket  72 . In this way, retainer  78  operates to mechanically hold electronic device module  74  in place with respect to socket  72 . In some embodiments, support frame  76  and retainer  78  may be incorporated into a unitary structure, which may be formed from a plastic material that is molded by a conventional injection molding process. In other embodiments, support frame  76  and retainer  78  may be formed as separate components from any of a wide variety of different materials. Electrical connector  82  includes a plurality of resilient electrical conductors  89 , each of which includes a spring finger portion  91  that protrudes into the recess defined by the sidewalls of support frame  76 . Each spring finger portion  91  is biased (or spring loaded) against a corresponding electrical conductor of a contact portion of electronic device module  74  (described in detail below) when the electronic device module  74  is held in place by retainer  78 . Each spring finger  89  preferably contacts the corresponding electrical conductor of electronic device module  74  over a relatively small area so that the contact pressure exerted by the spring fingers is relatively high. Socket  72  may be connected to an interconnect substrate by any conventional surface mount process (e.g., an infrared solder reflow process). 
     Referring to FIGS. 3,  5 A and  5 B, electronic device module  74  includes a housing  90 , one or more electronic components  92  and a flexible circuit board  94 . 
     Housing  90  may include a top portion and a bottom portion that may be constructed and arranged in a way that is similar to the construction and arrangement of electronic module housing  30  (described above). Housing  90  may be formed from a plastic material that is molded by a conventional injection molding process. 
     The electronic components  92  may be semiconductor-based devices (e.g., integrated circuits and sensors) and other active or passive devices. In the illustrated embodiment, electronic components  92  correspond to the components of an image sensor (e.g., a CMOS image sensor available from Agilent Technologies, Inc. of Palo Alto, Calif., USA), including an image sensor chip and a number of peripheral electrical devices. 
     Electronic components  92  are coupled mechanically and electrically by flexible circuit board  94 . Flexible circuit board  94  may include a pattern of elongated electrical conductors formed on a plastic (e.g., polyimide) substrate surface. The electrical conductors may be formed from any one of a wide variety of electrically conductive materials that are used conventionally in the circuit board industry. In one embodiment, the electrical conductors are formed from copper with nickel and gold plating. Electronic components  92  may be connected to the electrical conductor pattern of flexible circuit board  94  by a conventional wire bonding process. In the embodiments of FIGS. 3-5B, flexible circuit board  94  includes a component portion  112 , a contact portion  114 , and a curved portion  118  that physically couple contact portion  114  to component portion  112 . Component portion  112  is substantially planar and corresponds to the area where electronic components  92  are mounted to flexible circuit board  94 . Contact portion  114  is electrically coupled to the electronic components  92  by a plurality of electrical conductors that extend from the contact portion  114 , through curved portion  118 , to the pattern of electrical conductors formed in component portion  112 . In this embodiment, contact portion  114  is oriented substantially parallel to component portion  112  and extends outside of housing  90  to enable electronic component module  74  to electrically couple to the electrical connector  82  of socket  72 . To this end, flexible circuit board  94  is folded at curved portion  118 , and the electrical conductors of contact portion  114  and electronic components  92  are disposed on the same surface of flexible circuit board  94 . The backside of contact portion  114  is supported by housing  90  to resist the contact force exerted by the socket spring finger portions  91  when electronic device module  74  is fully seated within socket  72 . 
     In sum, the above-described socket-based electrical and mechanical circuit connection systems provide unique ways in which electronic device modules may be positioned accurately and securely on an interconnect carrier, while allowing the electronic device modules to be replaced easily without having to desolder the modules and resolder new modules in their place. 
     Other embodiments are within the scope of the claims. 
     For example, in some embodiments, the spring loaded electrical conductors of the socket electrical connectors may be replaced by a conventional anisotropic electrically conductive film. 
     See, for example, socket  120  of FIG. 6, which corresponds to socket  72  of FIG. 4A with electrical connector  82  replaced by an elastomeric anisotropic electrically conductive film  122 . In these embodiments, the retaining force applied by the socket retainers would be sufficient to hold the anisotropic electrically conductive film in electrical contact with the contact portions of the electronic device modules.