Patent Publication Number: US-9836683-B2

Title: Microelectronics device with exposed user interfaces

Description:
TECHNICAL FIELD 
     The present disclosure relates to microelectronic devices. Example embodiments related to exposing interfaces, including a user interface, on a microelectronic device package intended to be installed in a host. 
     BACKGROUND 
     Secure Digital (SD™) refers to a standard maintained by the SD Association covering nonvolatile memory card technology. SD cards are used primarily in portable devices (known as “hosts”) such as mobile phones, Global Positioning System (GPS) navigation devices, and digital cameras. The SD standard describes four performance-based families: SD Standard Capacity (SDSC™), SD High Capacity (SDHC™), SD eXtended-Capacity (SDXC™) and SD Input Output (SDIO™). The SD standard also describes three form factors of increasingly smaller size: SD, miniSD™, and microSD™. Electrically passive adapters allow a smaller card to fit and function in a device built for a larger card. 
     Cards in the SCSC, SDHC, and SDXC families are used as regular memory cards and offer increased capacity progressing through -SC to -HC to -XC. Cards in the SDIO family can provide input/output functionality, such as geolocation, radio and television reception, barcode reading, and external interfaces such as Wi-Fi and IrDA when the card is inserted into a host. 
       FIG. 1  presents two outline views of the form factor of a microSD card  100 —a top perspective view  110 , and a bottom perspective view  120  (rotated 180 degrees away from the viewer about the long axis of the top perspective view  110 ). The overall dimensions of the microSD card are 15 mm long, by 11 mm wide, by 1 mm thick. Asymmetrical profiles on the long sides of the microSD card prevent inserting it in a host microSD slot upside down. 
     A thumb ridge  112  forms an arc concave to a first short side, in part to assist in removal of the card  100  from a host. Conductive electrical contacts  132  are exposed in the bottom view  120  proximate the second short side for electrical interface (both data communication and power) with a host. The notch  114  formed in one of the long sides interfaces with a corresponding retention device in the host to physically secure the card during operation. 
     Traditional thermoset plastic overmolding involves molding one thermoplastic material over another to form a single part. Traditional packaging of electronics includes a printed circuit board assembly containing passive and active elements, along with interface components inside a clamshell housing. A form of overmolding can be applied to electronics packages, eliminating the need for the clamshell housing. After creating a PCB assembly (PCBA), the PCBA can be inserted into a mold, and injected thermoset plastic can surround the PCBA. Properties of the thermoset plastic are chosen for various reasons, including to prevent inadvertent interactions with any of the materials being molded over, and to under fill electrical components such as flip chip devices. This approach can provide mechanical and moisture protection, vibration resistance; and also can reduce the number of manufacturing steps. 
     SUMMARY 
     In certain example aspects described herein, an electronic device includes an electronics assembly and an enclosure. The electronics assembly includes a host interface and a direct user input interface. The direct user input interface remains exposed when the device is connected to a host via the host interface. The enclosure, substantially in the form factor of a microSD device (for example, having host interface surfaces compatible with the microSD standard, but a longer body to accommodate user interfaces), forms the outer boundary of the electronic device, overmolded on the electronics assembly. 
     In some embodiments, the direct user input interface is a touch sensitive surface. In some such embodiments, the device is a trusted computing device. In some such embodiments, the device, when connected to a host via the host interface, is operative to execute a challenge-response protocol requiring user input to the touch sensitive surface as the response. 
     In some embodiments, the touch sensitive surface is a single surface. In some such embodiments, the single touch sensitive surface is located on or adjacent to the thumb ridge plateau of the microSD form factor. In some embodiments where a single touch sensitive surface is located on the thumb ridge plateau of the microSD form factor, at least one additional user interface is positioned beneath the touch sensitive surface. In some such embodiments, the additional user interface includes at least one of a light emitting diode (LED) and a transmit/receive Infrared Data Association (IrDA) interface. 
     In some embodiments, the touch sensitive surface includes multiple portions that are non-contiguous at the surface of the electronic device. In some such embodiments, each non-contiguous portion of the touch sensitive surface is a wire bond exposed by singulation of the device from a mirror symmetry device connected thereto during manufacture. 
     These and other aspects, objects, features, and advantages of the example embodiments will become apparent to those having ordinary skill in the art upon consideration of the following detailed description of illustrated example embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  presents two outline views of the form factor of a microSD card—a top perspective view, and a bottom perspective view (rotated 180 degrees away from the viewer about the long axis of the top perspective view). 
         FIG. 2  is a block diagram depicting a trusted computing device, in accordance with certain example embodiments. 
         FIG. 3  is an exploded perspective view of a microSD card, in accordance with certain example embodiments. 
         FIG. 4  is a top perspective view of a microSD card, in accordance with certain example embodiments. 
         FIG. 5  is a partial view of the thumb ridge side of the top of a microSD card, in accordance with certain example embodiments. 
         FIG. 6  is a partial view of the thumb ridge side of the top of a microSD card in accordance with certain example embodiments. 
         FIG. 7  illustrates a touch contact interface, along with transmit (Tx) and receive (Rx) infrared Data Association (IrDA) interface, in accordance with certain example embodiments. 
         FIG. 8  illustrates a touch contact interface attached to a PCB using wire bond, in accordance with certain example embodiments. 
         FIG. 9  is a block flow diagram depicting a method for preparing a microSD card, in accordance with certain example embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS 
     Turning now to the drawings, in which like numerals indicate like (but not necessarily identical) elements throughout the figures, example embodiments are described in detail. 
     Overview 
     Given the small form factor of microSD cards, limited space is available for non-radio frequency interfaces on the card surface, especially direct user interfaces. Direct user interfaces are those that do not require intermediate hardware or software to receive input from, or to present output to, a user. For example, an LED or a touch sensitive surface is a direct user interface. 
     Further, conventional clamshell enclosures may not be sufficient to protect the electronics of a microSD card, which can be subject to rough treatment outside the host. More specifically, certain user interface components, such as an LED or IrDA interface, can be subject to damage during manufacture. Additionally, manufacturing cost for incorporating components of interfaces that must be exposed may be prohibitive. 
     Example embodiments of the present technology include overmolded microSD card assemblies comprising both direct user interfaces and user input device interfaces that 1) remain exposed during microSD card operation, and that 2) do not extend significantly beyond the standard form factor of the microSD card. 
     Example Architectures 
     Consider, as an example use case of the present technology, a trusted computing device  230  implemented on a microSD card, such as shown in the block diagram  200  of  FIG. 2 . In such embodiments, the trusted computing device  230  includes an isolated environment  238 , a host interface  232  (the primary interface), a plurality of user interfaces  237 , and a computer program product  239  that is distributed across the components of the trusted device  230 . 
     The isolated environment  238  includes an isolated environment processor  235 , zero or more auxiliary processors  235   a , and memory  236 . The memory  236  is connected for data communication with the isolated environment processor  235 . Each auxiliary processor  235   a  is connected for data communication with the isolated environment processor  235  and the memory  236 . Each auxiliary processor  235   a  and the memory  236  communicate with the host outside the isolated environment  238  only through the isolated environment processor  235 . 
     Each user interface  237  and the host interface  232  are in data communication with the isolated environment processor  235 . The computer program product  239  includes non-transitory computer-readable media having computer-executable program instructions embodied thereon. When executed by the trusted computing device  230 , the program instructions cause the trusted computing device  230  to perform a variety of trusted computing operations. The program instructions of the computer program product  239  can cause the trusted computing device  230  to provision itself, such as for cryptographic operations, in cooperation with an external device, such as user input device  210 , via user interface  237 . Using the program instructions of the computer program product  239 , the trusted device  230  presents a first file system partition via the host interface  232  from the isolated environment processor  235 . 
     In some embodiments of the trusted device  230 , the user interfaces  237  can be used, in combination with the computer program product  239  and the isolated environment  238 , for implementing a challenge-response protocol. In a challenge-response protocol, a “challenge” is presented that requires a valid “response” in order to proceed with a given activity. For example, in a trusted device  230  having a first user interface  237   a  including an light emitting diode (LED) visible to a user, and a second user interface  237   b  that responds to touch, program instructions of the computer program product  239  can be executed to illuminate the LED  237   a , signaling to a user that the user must touch the second user interface  237   b  in order to proceed with a given activity of the trusted device  230 . In some embodiments, the user interface  237   b  is a capacitive sensor that takes human body capacitance as input. In some embodiments, a resistive touch sensor or a piezoelectric touch sensor is used. 
     As another example use of a user interface  237 , the user interface device  210  is in data communication with the isolated environment  238  via user interface  237   c . Data communication between the user interface device  210  and the trusted device  230  can employ any one or a combination of a variety of connections (preferably wireless), including an Infrared Data Association (IrDA) link, a BLUETOOTH® wireless technology standard link, and a Near Field Communication (NFC) link. The trusted device  230  issues a challenge, such as lighting an LED on the user interface  237   a  on the trusted device  230  (a direct user interface), or sending a message to a display of user input device  210 . The user may responds to the challenge using the user interface device  210 . In some embodiments, the response is a fingerprint response input to the user interface device  210 . In some embodiments, the response is an answer to an authentication question presented on a display of the user interface device  210 . In some embodiments, the user interface device  210  can be a mobile communication device such as a mobile phone. In some embodiments, the user interface device  210  can be an NFC-enabled fob. In some embodiments, the response can be a direct user input to a touch sensitive user interface  237   b.    
     Referring to  FIG. 3 , and continuing to refer to prior figures for context, an exploded view  300  of a notional PCBA of the example use case is shown. The view is a simplified version of the PCBA to emphasize placement of the user interfaces  237 . Note that the contacts  122  of the host interface  232  are shown in the lowest layer of the exploded view  300 . These contacts  122  will be partially exposed on the bottom of the device. An LED  237   a  constitutes the first user interface  237   a . A series of conductive contacts for capacitive touch constitute the second user interface  237   b . Both a transmit (Tx) IrDA and receive (Rx) IrDA diode constitute the third user interface  237   c . While a series of discrete contacts  237   b  are shown, the third secure interface can be formed as one or more continuous contact surfaces. 
     Referring to  FIG. 4 , and continuing to refer to prior figures for context, a perspective view of an example completed trusted computing device  400  is shown with the outline of features, shown as dashed lines, that are hidden through overmolding (shown as solid lines  410  forming the outline of the microSD form factor trusted computing device  400 ). Note that the top surface of the Tx/Rx IrDA diode  237   c  and the top surface of the LED  237   a  are exposed on the plateau of the thumb ridge  112 . Also note that each of the seven (7) touch contacts  237   b  are exposed both on the plateau of the thumb ridge  112  and on the short side face  440  proximate to the thumb ridge  112 . The overmolding  410  protects the PCBA from moisture, shock, vibration, and impact damage, while exposing the user interfaces  237   a ,  237   b , and  237   c.    
     Referring to  FIG. 5 , and continuing to refer to prior figures for context, a partial view of the thumb ridge  112  side of the top of a microSD card  500  in accordance with example embodiments of the present technology is shown. In such embodiments, die film assisted molding can be used to expose user interface  237   b  (shown as a single touch surface in  FIG. 5 ). 
     Referring to  FIG. 6 , and continuing to refer to prior figures for context, a partial view of the thumb ridge  112  side of the top of a microSD card  600  in accordance with example embodiments of the present technology is shown. In such embodiments, the exposed user touch interface  237   b  is formed by multiple touch-sensitive surfaces  620 ,  630  separated by an insulator  610 . As with  FIG. 5  die film assisted molding can be used to expose user interface  237   b.    
     Referring to  FIG. 7 , and continuing to refer to prior figures, a side view  700  of a Tx/Rx IrDA diode interface  237   c  protected by a touch contact interface  237   b  for an overmolded microSD card in accordance with example embodiments of the present technology is shown. In such embodiments, a single surface touch contact interface  237   b  is formed in an inverted “U” shape, with surface  730  being substantially flush with the thumbnail ridge  112  of the microSD device after overmolding has been completed. This surface  730  can be exposed via die film assisted molding on the top, and a sacrificial cut on the rear edge. Tx and Rx infrared diodes  237   c  are protected underneath the touch contact interface  237   c —with the intervening space filled with epoxy  720  either post-mold or via transfer molding depending on the specific process parameters. In a variant to the approach of  FIG. 7 , the U-shaped structure can be interrupted along its top section by an insulator, similar to the approach shown in  FIG. 6 . 
     Referring to  FIG. 8 , and continuing to refer to prior figures for context, a cross section of an overmolded microSD card  800  in accordance with example embodiments of the present technology is shown. The card  800  includes a stair step shaped touch contact interface  837   c . In some embodiments, the touch contact interface can be attached to the PCB using epoxy, and then conductively connected using a wire bond  910 . The overmold cap  820  would then be applied to protect the wire bond  810  connection. At least a portion of such a touch contact interface is exposed at the thumbnail ridge  122 , and along the microSD card short side face  830  adjacent the thumbnail ridge  122 . In another variation, the stair shaped touch contact interface  837   c  can be mounted to the PCB via surface mount technology (SMT) techniques. 
     In an additional variation, a subassembly integrating each of the interfaces (Tx/Rx IrDA, LED, and touch contact)  237  can be produced that can be wire bonded or surface mounted to the PCB. 
     In yet a further variation, where microSD cards of the present technology are manufactured in rows, with mirror symmetry across each pair of rows, sacrificial wire bonds across mirrored cards can be used. Corresponding cards on opposite sides of a row can be exposed during the singulation process. This approach has the advantage of the precision placement available with standard wire bond techniques. The same effect can be achieved using the lead frame manufacturing process. 
     Example Processes 
     Referring to  FIG. 9 , a block flow diagram depicting a method  900  for preparing a microSD card, in accordance with certain example embodiments, is shown. A trusted computing device  230  in microSD card form, including an isolated environment  238 , an LED  237   a , an IrDA port  237   c , and a touch interface  237   b , is used as an example device. 
     While other methods can be used, a PCB can be fabricated by baking and screen printing, photoengraving, milling, or laser resist abrasion of interconnections—Block  910 . In many instances, panelization, where a number of PCBs are grouped for manufacturing into a “panel,” can be employed. The panels can be broken apart (“depaneling” or “singulation”) through methods such as laser cutting. 
     Trusted computing device microSD card  230  PCBA assembly can begin with mounting and soldering circuit elements such as the host interface  232 , LED  237   a , IrDA port  237   c , and touch interface  237   b , along with miscellaneous other components to the fabricated PCB—Block  920 . As an example, interface elements  237   a ,  237   b , and  237   c  of  FIG. 3  can be placed on the trusted computing device  230  PCB, and soldered into place. 
     In parallel to the processes represented by Block  910  and Block  920 , the isolated environment  238  can be processed from a set of isolated environments, for example an array, fabricated on a silicon wafer—Block  930 . This process results in an inspected singulated isolated environment  238  for integration into the trusted computing device  230  PCBA. 
     The complete PCBA can be assembled (Block  940 ) by physically mounting the isolated environment  238 , for example, using epoxy, and the and electrically interconnecting the isolated environment  238 , for example by wire bonding, to the PCBA. 
     At this point, assembled PCBAs can be placed in a mold array and overmolded—Block  950 . For example, using the sacrificial wire bond approach for secure interfaces  237  described above, assembled PCBAs can be placed in rows, with mirror symmetry across each pair of rows, using sacrificial wire bonds across mirrored cards. A thermosetting plastic can be molded around the assembled PCBAs and cured. 
     Post-molding, the array of trusted computing devices  230  can be finished—Block  960 . For example, after curing, and while still in the array, the devices can be marked. Then corresponding trusted computing device  230  micro SD cards on opposite sides of a row can separated. Where sacrificial wire bonds are used for the touch interface  237   b , these can be exposed during the separation process. The individual trusted computing devices, with secure interfaces  237  exposed, can be chamfered, inspected, and tested. 
     The example systems, methods, and acts described in the embodiments presented previously are illustrative, and, in alternative embodiments, certain acts can be performed in a different order, in parallel with one another, omitted entirely, and/or combined between different example embodiments, and/or certain additional acts can be performed, without departing from the scope and spirit of various embodiments. Accordingly, such alternative embodiments are included in the technology described herein. 
     Although specific embodiments have been described above in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects described above are not intended as required or essential elements unless explicitly stated otherwise. 
     For example, while a microSD form factor is used in example embodiments described above, other form factors can incorporate a direct user input and overmolding, along with non-contact interfaces protected by a contact interface as described herein. In some embodiments, the protection of non-contact interfaces under a contact interface is contemplated regardless of form factor or overmolding. In some embodiments, the form factor of the device can be an elongated microSD form factor, in part to accommodate user interfaces such as those described herein. In some embodiments, an interface assembly comprising a contiguous or non-contiguous contact interface protecting diode-based interfaces (for example an LED, an IrDA transceiver) can be assembled separately and epoxied/wire bonded or surface mounted to the device substrate. 
     Modifications of, and equivalent components or acts corresponding to, the disclosed aspects of the example embodiments, in addition to those described above, can be made by a person of ordinary skill in the art, having the benefit of the present disclosure, without departing from the spirit and scope of embodiments defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures.