Abstract:
A biometric sensor apparatus and method are disclosed, which may comprise a flexible substrate comprising a first side surface and a second side surface opposing the first side surface; a biometric sensor portion comprising biometric image sensing elements formed on the second side surface forming at least part of a biometric sensor array sensing capacitively induced changes induced by a biometric in the vicinity of the biometric image sensing elements; a biometric sensor controller integrated circuit mounted to the flexible substrate on one of the first side surface and the second side surface of the flexible substrate; an edge surface of the flexible substrate including at least one conductively plated perforation in the flexible substrate; and an electro-static discharge element formed on or as part of the flexible substrate and electrically connected to the at least one conductively plated perforation.

Description:
CROSS-REFERENCE 
       [0001]    This application is a continuation of Ser. No. 12/716,122, filed Mar. 2, 2010, entitled Apparatus and Method for Electrostatic Discharge Protection by Armando Leon Perezelsky, et al., which is incorporated herein by reference in its entirety and to which application priority is claimed under 35 USC §120. 
     
    
     BACKGROUND 
       [0002]    Electrostatic discharge (ESD) is a serious problem for many types of solid state electronics, such as integrated circuits (ICs). Electronic components such as ICs can be exposed to ESD from various different sources, such as the human body, assembly equipment, or basic packaging materials. Contact between the sources and a grounded IC can generate large enough currents through the IC to significantly damage its internal circuitry. 
         [0003]    The effects of ESD create special problems with touch electronics, i.e., electronics intended for touching by the body. For example, electronic fingerprint sensors allow a user to swipe or press a finger over some portion of the circuit in order to read the user&#39;s fingerprint. It would be impractical or inconvenient for a user to have to ground his or her body prior to touching the sensor in order to dissipate an electrostatic charge. 
         [0004]    Conventional fingerprint sensors include a silicon chip with an exposed surface fir receiving human touch. These fingerprint sensors can be easily damaged physically or mechanically because of the exposed surface, reducing the durability and/or reliability of the sensor. The conventional fingerprint sensors as well as newer, more advanced “flexible” fingerprint sensors, which enable a user to swipe a finger across a polyimide surface without directly contacting the sensor circuitry, are both susceptible to ESD damage. For example, electrostatic charge can build up on the polyimide surface of the flexible fingerprint sensor as a user swipes his or her finger. This charge can continue to increase in potential until the path of least resistance is found and the charge dissipated. In certain cases, the charge can discharge to the sensor circuitry, causing damage to sensitive electronic components such as IC input/output cells. 
         [0005]    The current ESD protection used in the fingerprint sensor industry uses a metal ring surrounding the perimeter of the sensor. This arrangement requires an additional metal layer in the sensor manufacture, thus increasing the cost of the sensor. The inventions disclosed herein teach a new kind of ESD protection for touch electronics that reduces the manufacture cost and increase the durability of the electronics. 
       SUMMARY 
       [0006]    Some embodiments of the invention provide a substrate capable of receiving electrostatic discharge. The substrate includes an edge surface including at least one plated castellation capable of conducting the electrostatic discharge. The substrate also includes a bottom surface, a top surface, and a circuit trace along at least one of the bottom surface and the top surface, the circuit trace electrically connected to the at least one plated castellation. 
         [0007]    Some embodiments of the invention provide a method of constructing a substrate with electrostatic discharge protection. The method includes providing a substrate array including a plurality of substrates, punching holes along at least a portion of a perimeter of each of the plurality of substrates, and plating the holes with a conductive material. The method also includes cutting each of the plurality of substrates along cut lines that bisect at least some of the holes and connecting the conductive material on each of the plurality of substrates to a known potential. 
         [0008]    It will be understood that biometric sensor apparatus and method are disclosed, which may comprise a flexible substrate comprising a first side surface and a second side surface opposing the first side surface; a biometric sensor portion comprising biometric image sensing elements formed on the second side surface forming at least part of a biometric sensor array sensing capacitively induced changes induced by a biometric in the vicinity of the biometric image sensing elements; a biometric sensor controller integrated circuit mounted to the flexible substrate on one of the first side surface and the second side surface of the flexible substrate; an edge surface of the flexible substrate including at least one conductively plated perforation in the flexible substrate; and an electro-static discharge element formed on or as part of the flexible substrate and electrically connected to the at least one conductively plated perforation. The at least one conductively plated perforation may be plated with a conductive material including one of copper, aluminum, nickel, and gold. The at least one conductively plated perforation may comprise a plurality of conductively plated perforations positioned on the periphery of the flexible substrate. At least one of the plurality of conductively plated perforations may be electrically connected to a known potential. The sensor and method may comprise at least one other biometric image sensing element formed on the other of the first side surface and the second side surface of the flexible substrate remote from the biometric sensor controller integrated circuit and electrically coupled to the biometric sensor controller integrated circuit, wherein the at least one other biometric image sensing element transmits information to the biometric sensor controller integrated circuit. The biometric may comprise a fingerprint. The first side surface may provide an area for a finger to be swiped. 
         [0009]    The biometric object image sensor and method may comprise a flexible substrate comprising a first side surface and a second side surface opposing the first side surface; a biometric image sensor portion comprising biometric image sensing elements formed on one of the first side surface and the second side surface forming at least part of a biometric sensor element trace array sensing capacitively induced changes induced by a biometric in the vicinity of the biometric image sensing element trace array; a biometric sensor controller integrated circuit mounted to the flexible substrate on one of the first side surface and the second side surface of the flexible substrate; the flexible substrate mounted on a connecting substrate, comprising a ball grid array mounting for connecting the biometric sensor controller to an apparatus utilizing the biometric object image sensor. The biometric object image sensor and method may comprise the connecting substrate comprising a printed circuit board. The flexible substrate may comprise an area for a biometric object to be brought into proximity to the biometric object sensing element traces. The biometric object image sensor and method may comprise the image sensor traces comprising an array of capacitive gap biometric object image pixel elements, e.g., a linear array. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a side view of a fingerprint sensing circuit according to one embodiment of the invention. 
           [0011]      FIG. 2  is a perspective bottom view of a top substrate of the fingerprint sensing circuit of  FIG. 1 . 
           [0012]      FIG. 3  is a perspective top view of a top substrate of the fingerprint sensing circuit of  FIG. 1 . 
           [0013]      FIG. 4  is a bottom view of a bottom substrate of the fingerprint sensing circuit of  FIG. 1 . 
           [0014]      FIG. 5  is a top view of a top substrate of the fingerprint sensing circuit of  FIG. 1 . 
           [0015]      FIG. 6A  is a top view of the fingerprint sensing circuit of  FIG. 1 . 
           [0016]      FIG. 6B  is an exploded side view of the fingerprint sensor of  FIG. 1 . 
           [0017]      FIG. 6C  is another side view of the fingerprint sensing circuit of  FIG. 1 . 
           [0018]      FIG. 7  is a top view of a substrate array for use with a fingerprint sensing circuit according to one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0020]    The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention. 
         [0021]      FIG. 1  illustrates a fingerprint sensing circuit  10  according to one embodiment of the invention. The fingerprint sensing circuit  10  can have a two-substrate architecture including a top substrate  12  and a bottom substrate  14 . The top substrate  12  can be constructed of a flexible or rigid material suitable for applying a. circuit thereon. In one embodiment, the top substrate  12  can be constructed of a flexible polyimide material, such as Kapton®, with a thickness of between about  5  and about  100  micrometers. The bottom substrate  18  can be a conventional printed circuit board (PCB). 
         [0022]      FIGS. 2 and 3  illustrate the top substrate  12 . The top substrate  12  can have a circuit side  16 , as shown in  FIG. 2 , and a sensing side  18 , as shown in  FIG. 3 . The circuit side  16  of the top substrate  12  can be attached to the bottom substrate  14  via a chip-on-flex (COF) process, wire bonding, anisotropic conductive film (ACF), etc. 
         [0023]    In some embodiments, the fingerprint sensing circuit  10  can include an image sensor  20  to detect the ridges and valleys of a fingerprint as a finger moves across the image sensor  20 . The fingerprint sensing circuit  10  can also include a velocity sensor  22  to detect the speed of a finger moving across the image sensor  20 . The image sensor  20  and/or the velocity sensor  22  can be bonded to the circuit side  16  of the fingerprint sensing circuit  10 . For example, the image sensor  20  and/or the velocity sensor  22  can be constructed of conductive traces (e.g., copper traces) printed or applied to the circuit side  16  using a lithographic technique, as shown in FIG.  2 . In some embodiments, the image sensor  20  can be implemented as an array of capacitive sensors capable of sensing the ridges and valleys of a finger as it travels over the sensor  20 . In addition, the velocity sensor  22  can be implemented using two or more capacitive detectors at intervals along the direction of travel of the finger. 
         [0024]    Fingerprint information sensed by the image sensor  20  and the velocity sensor  22  can be transmitted to one or more sensor integrated circuits (ICs)  24  connected to the circuit side  16  of the top substrate  12 . The sensor IC  24  can be bonded to the top substrate  12  using a suitable technique such as a chip-on-flex (COF) process, wirebond, flip chip, anisotropic conductive film (ACF) adhesive, underfil, glob-top, etc. The sensor IC  24  can include drive and sense electronics for interpreting the fingerprint information from the image sensor  20  and the velocity sensor  22 . In one embodiment, the sensor IC  24  can be a silicon chip or die. In addition, in some embodiments, the image sensor  20  and the velocity sensor  22  can be contained within the sensor IC  24  (e.g., rather than being positioned external to the sensor IC  24 , as described above). 
         [0025]    During use, a user&#39;s finger can be swiped along the sensing side  18  of the top substrate  12 . On the circuit side  16  of the top substrate  12 , the image sensor  20  and the velocity sensor  22  can detect changes in capacitance as the finger is swiped. As a result of having a separate sensing side  18  and circuit side  16 , the top substrate  12  can substantially electrically and mechanically isolate the user&#39;s finger from the image sensor  20 , the velocity sensor  22 , and the sensor IC  24 , thereby providing some degree of protection from electrostatic discharge (ESD) and mechanical abrasion. 
         [0026]    In some embodiments, the top substrate  12  can include interconnect pads  26  that allow the sensor IC  24  to interface with the bottom substrate  14 . The bottom substrate  14  can include, for example, power supply circuitry, external communication circuitry, etc. for the sensor IC  24 .  FIG. 4  illustrates the bottom substrate  14  according to one embodiment of the invention. As shown in  FIG. 4 , the underside of the bottom substrate  14  can include a ball grid array (BGA)  28  to electrically connect the fingerprint sensing circuit  10  to a substrate of a product. 
         [0027]    In one embodiment, the fingerprint sensing circuit  10  can have a single-substrate architecture, where the single. substrate has a sensing side and an opposite circuit side. Thus, the substrate can include a sensor IC on its circuit side and a user&#39;s finger can be swiped along the opposite, or sensing side. As the user&#39;s finger is swiped along the sensing side, the sensor IC, with separate or integral image and velocity sensors, can detect the user&#39;s fingerprint through the substrate using techniques such as capacitive, thermal, radio frequency (RF), infrared (IR), light-gathering, and/or ultrasonic techniques. The single substrate can also include other circuitry, such as power supply circuitry, external communications circuitry, etc. on its circuit side. 
         [0028]    In another embodiment, the fingerprint sensing circuit  10  can have a single-substrate architecture, where the single substrate has a combined circuit and sensing side. Thus, the substrate can include a sensor IC on the same side that the user&#39;s finger is swiped. An epoxy “glob-top” over the sensing side can protect the sensor IC from mechanical damage and/or contamination. The sensor IC, including an integral image sensor and/or a velocity sensor, can sense and collect fingerprint information by coming in direct contact with the user&#39;s finger through the epoxy. The sensor IC can detect the user&#39;s fingerprint using techniques such as capacitive, thermal, RF, IR, light-gathering and/or ultrasonic techniques. 
         [0029]    In yet another embodiment, the fingerprint sensing circuit  10  can have a single-substrate or two-substrate architecture, where both sides of the top substrate can include sensing circuitry. The top substrate can include an image sensor and a velocity sensor on the sensing side (i.e., same side that the user&#39;s finger is swiped). An epoxy glob-top or an ink, layer can be applied over the sensing side to protect the image sensor and the velocity sensor from mechanical damage and/or contamination. The sensor IC can be applied to the opposite, circuit side. The image sensor and the velocity sensor can sense fingerprint information by coming in direct contact with the user&#39;s finger through the epoxy or ink layer and transmit the fingerprint information to the sensor IC through, for example, RF transmissions. Other circuitry, or a bottom substrate, can also be coupled to the circuit side of the top substrate. 
         [0030]    In some embodiments, the one or more substrates of the fingerprint sensing circuit  10  (i.e., the substrate of the single-substrate architecture or one or both of the substrates of the two-substrate architecture) can include a plated portion around its outside edge surface. The plated portion can be plated with a conductive plating (e.g., copper, aluminum, gold, nickel, etc.) and can be connected to a circuit trace along a top, bottom, or inner surface of the one or more substrates. The circuit trace can be connected to a low impedance path to a known potential, such as power source ground. As a result, the outside edge of the one or more substrates can allow a controlled path for ESD to be removed from the fingerprint sensing circuit  10  (Le., from the plated portion, along the circuit trace, to power source ground). 
         [0031]    For example, ESD can build up on the sensing side as a user swipes his or her finger. This charge can continue to increase in potential until the path of least resistance is found and the charge dissipated. The plated outside edge and the circuit trace can create the shortest discharge path for ESD, thus preventing ESD from discharging to the sensor IC or any other components of the circuit side or bottom substrate and potentially damaging them. In some embodiments, the plated portion can completely surround the outside edge of the one or more substrates. In other embodiments, the plated portion can partially surround the outside edge of the one or more substrates. In addition, the plated portion can extend down the entire thickness, or only a portion of the thickness, of the outside edge of the one or more substrates. 
         [0032]    In one embodiment, the plated portion can be in the form of plated castellations  30 , or perforations. For example,  FIGS. 4-6C  illustrate a fingerprint sensing circuit with the two-substrate architecture according to one embodiment of the invention. As shown in  FIGS. 6B and 6C , the substrates  12 ,  14  can include the plated castellations  30  down their outside edge surfaces  32 . The castellations  30  can be interconnected by a circuit trace  34  along a top surface of the top substrate  12 , as shown in  FIG. 5 , and/or a bottom surface of the bottom substrate  12 , as shown in FIG. . 4 . The circuit trace  3 . 4  can be connected to power source ground. As a result, the plated castellations  30  and the circuit trace can create the shortest discharge path for ESD. In one embodiment, each of the plated castellations  30  can be directly connected to power source ground, rather than interconnected through the circuit trace. 
         [0033]    In some embodiments, the castellations  30  can completely surround the outside edge  32  of one or both of the substrates  12 ,  14  at a constant or varying pitch. In other embodiments, the castellations  30  can partially surround the outside edge  32  of one or both of the substrates  12 ,  14 .  FIGS. 4 and 5  illustrate the castellations with a smooth, semi-circular cross-section. In other embodiments, the castellations can have semi-circular, semi-square, semi-rectangular, and/or semi-triangular cross-sections. 
         [0034]    In some embodiments, multiple substrates can be created from a single substrate array  36 . For example,  FIG. 7  illustrates a substrate array  36  including nine separate substrates  12  (and/or substrates  14 ) fir nine fingerprint sensing circuits  10 . As shown in  FIG. 7 , prior to stamping out individual substrates  12 , via holes  38  can be punched around a perimeter of each substrate  12  and plated. In some embodiments, the via holes  38  can be punched and plated around only a portion of the perimeter of each substrate  12  (not shown). In addition, the via holes  38  can be all through holes, all blind holes, or some combination of through holes and blind holes. Further, the via holes  38  can have a circular cross-section, as shown in  FIG. 7 , or a square, rectangular, and/or triangular cross-section. 
         [0035]    After the via holes  38  have been punched and plated around each perimeter, the substrates  12  can be cut or stamped out. Cut lines  40  made by the cutting or stamping mechanism can divide the via holes  38 , thereby creating the castellations  30 , as shown in  FIG. 5 . Accordingly, each castellation  30  can be a fraction of a via hole  38 . For example,  FIG. 5  shows some castellations  30  created from via holes  38  that have been bisected and some castellations  30  created from via holes  38  that have been quartered (e.g., at corners of the substrate  12 ). After the via holes  38  are punched, and before or after the substrates  12  are stamped from the substrate array  36 , other layers or coatings  42 , such as an epoxy glob-top or an ink layer, can be coupled to the substrate  12 , as shown in  FIGS. 6A-6C . When the fingerprint sensing circuit  10  is viewed from above, as shown in  FIG. 6A , the coating  42  can substantially hide the castellations  30 . 
         [0036]    The fingerprint sensing circuits  10  described above can be applied to products other than fingerprint sensors, such as sensing circuits for touchpads and molded plastics having a variety of shapes and contours. In addition, the plated outside edge or castellation method described above can be applied to various other devices to protect circuitry from ESD. For example, the plated outside edge or castellation method can be used to protect sensitive circuitry associated with devices intended for human touch, including but not limited to PCBs for touch pads, touch screens, touch panels, keyboards, keypads, mice, joysticks, trackballs, etc. which can be collectively referred to as “touch electronics circuits” herein. 
         [0037]    It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein. Various features and advantages of the invention are set forth in the Wowing claims.