Abstract:
The present invention is directed to a method of making flexible interconnect packaging, in particular, packaging for fingerprint sensor chips. The chip is mounted on a flexible substrate having conductive traces leading to a connector at an end of the substrate. Wires are used to connect contact pads with the conductive traces, and a rigid frame is mounted below the substrate and chip. The conductive traces are preferably internal within the substrate and are exposed by forming a cavity in the substrate adjacent to the chip. Also disclosed are electronic devices which incorporate the foregoing fingerprint sensing apparatus.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority as a division of allowed U.S. patent application Ser. No. 10/160,438, filed May 31, 2002, now U.S. Pat. No. 6,924,496. This application also related to commonly owned U.S. Pat. No. 6,653,723, issued on Nov. 25, 2003, entitled “System For Providing An Open-Cavity Low Profile Encapsulated Semiconductor Package.” The disclosures of the above parent application and related patent are incorporated by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to packaging systems, and more particularly, to a flexible interconnect packaging system. 
   BACKGROUND OF THE INVENTION 
   Given the reduced size of many consumer electronic devices, packaging systems are becoming increasingly important. For example, cellular telephones are becoming smaller and smaller to satisfy consumer&#39;s desires for portable lightweight telephones that are easy to carry. Such devices must still provide all the features and functions consumers require. It is typical for a cellular telephone to have a keypad, display, and a sound generator. It is anticipated that the newest telephones will include an infrared (IR) interface, video capability and a fingerprint sensor for added security. Furthermore, the progression to smaller and smaller consumer devices with advanced features is extending beyond cellular telephone technology to such technologies as Personal Digital Assistants (PDAs) and notebook computers. 
   The migration to smaller and smaller devices has placed great emphasis on the various packaging systems used to integrate the various internal system components together within the device housing. However, conventional packaging techniques make use of rigid circuit boards to secure components and to electrically coupled the components together. As a result, limitations exist as to where and how the components can be arranged within the housing and how they are presented at the external surface of the housing to the consumer. 
   One of the most important issues in electronic packaging is that of packaging and interconnecting integrated circuits (ICs). The ICs are the heart of electronic system controls, and since they are typically sensitive to electrical, mechanical, physical, and chemical influences, they require careful consideration by the packaging engineer. As such, IC packaging is the middle link of the process that produces today&#39;s systems. 
     FIG. 1  shows three levels of electronic packaging. The first level of packaging (IC packaging) is where an IC chip  120  is assembled into an IC package  122 . The IC package is the housing that assures environmental protection to the IC chip, and provides for complete testing and high-yield assembly to the next level of interconnection. The IC package provides the first order of interconnection to the IC chip. The IC chip is coupled to external package pins via wire bonding, tape automated bonding (TAB), or using a flip-chip bumping method. 
   The second level of packaging can be described as IC package assembly onto a carrier circuit board  124 . The carrier circuit board is typically made up of a single or multi-layered rigid substrate and is designed to carry the IC package to provide the next level of interconnection to a main printed circuit board (PCB) or back-plane  126 . 
   The interconnecting joints between the IC package  122  and the carrier circuit board  124  is typically made possible via solder balls, IC sockets, and/or solder joint pads. A third level of packaging is accomplished when the carrier circuit board  124  is finally connected to the main (PCB)  126 . Thus, current packaging systems provide a system of rigid packaging structures to package and interconnect electronic components. 
     FIG. 2  shows another conventional technique used to couple an electrical component to a main circuit board. For example, the electrical component may be a fingerprint sensor. The electrical component  102  is mounted to a small rigid printed circuit board  104  that includes a connector  106 . The main circuit board  108  also includes a connector  110 . An interface cable  112  couples the small circuit board  104  to the main circuit board  108 . The interface cable  112  includes mating connectors  114 ,  116  that mate to connectors  106  and  110 , respectively. Thus, the small circuit board  104  and associated connectors  106 ,  114  are used to couple the component  102  to the main circuit board  108 . 
   Given the above-described packaging system it is easy to see that several limitations exist. For example, connecting the component  102  to the main circuit board  108  is expensive because it requires the small circuit board  104  on which to mount the component  102 , and connectors  106 ,  114  to mate with the interface cable  112 . Furthermore, the technique results in size and flexibility limitations because the size of the circuit board  104  and the associated connectors ( 106 ,  114 ) limit how and where the component  102  may be located in a housing, and how such components are presented to the user at the outside surface of the device. 
   Therefore, it would be desirable to have a packaging system that allows components to be coupled together without the restrictions and limitations that are present in currently available packaging systems. 
   SUMMARY OF THE INVENTION 
   The present invention includes a flexible interconnect packaging system. The system makes use of a flexible printed circuit board as the main substrate material. In one embodiment, components are mounted or attached to the substrate using standard die attachment adhesive (conductive or non-conductive). Bonding pads of the components are connected to conductive trace pads of the flexible substrate using techniques such as, wire bonding, ball/bump methods, tape automated bonding (TAB), or any other applicable bonding methodology for integrated circuits. The packaging includes a plastic transfer molding in the form of a pre-molded package that provides physical support and protection, and enables reliable connection between the component and the substrate. 
   Using the packaging system included in the present invention provides several advantages over convention systems. In conventional systems, IC devices generally must follow the orientation of the main circuit board. However, the packaging system included in the present invention allows the circuit to bend, thus providing a way for devices to be placed in virtually any orientation. For example, a component may be located away from a main circuit board and orientated in virtually any orientation with regards to the main circuit board. For example, the component may be a fingerprint sensor that is used in a cell phone. The packaging system included in the present invention allows the fingerprint sensor to be located away from the main circuit board and orientated and exposed at an outside surface of the cell phone to provide the best sensor position for use by the cell phone user. 
   Furthermore, the packaging system allows devices to be coupled to the main circuit board via a single socket connector located on the circuit board, thereby providing easy access and quick connect and disconnect of the device from the circuit. This allows easy replacement by the user without the need to return the device to the manufacturer. The packaging system is applicable to all types of electronic devices, optical devices, touch/pressure devices and any other type of sensor or electrical component. 
   Thus, the limitations on sensor placement onto a given enclosure (cell phone, PDA and etc.) has been eliminated. For example, with the advantages offered by one or more embodiments of the present the invention, cell phone designers now have freedom to select the mounting location for sensor components at any location on the enclosure. Due to the easy connection and disconnection of the packaging system from the main circuit board, the sensor can be replaced either by the end user or at a field service location. Thus, the device does not have to be returned to a service center and users do not have to wait for days to repair the device. 
   In one embodiment included in the present invention, a flexible interconnect apparatus is provided for coupling to an electrical component. The electrical component has at least one contact pad and the interconnect apparatus comprises a flexible substrate, and at least one conductive trace in the flexible substrate, wherein the at least one conductive trace has an exposed contact region that is directly electrically coupled to the at least one contact pad. 
   In another embodiment of the present invention, a flexible interconnect apparatus is provided for flexibly coupling a fingerprint sensor to an external circuit. The interconnect apparatus includes a flexible substrate having one or more conductive traces that form a connector at one end. The connector mates with a corresponding connector that is coupled to the external circuit. A fingerprint sensor is attached to the substrate and has a sensor surface. The fingerprint sensor has sensor contacts that are wire-bonded to the conductive traces. The apparatus also includes a molded package coupled to a bottom portion of the substrate below the fingerprint sensor, the molded package forming an open top cavity that allows the sensor surface of the fingerprint sensor to be exposed for access by a user. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and the attendant advantages of this invention will become more readily apparent by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  shows three levels of electronic packaging; 
       FIG. 2  shows a diagram of a conventional packaging system; 
       FIG. 3  shows a diagram of one embodiment of a flexible interconnect packaging system constructed in accordance with the present invention; 
       FIG. 4  shows a side view of one embodiment of a packaging system constructed in accordance with the present invention; 
       FIG. 5  shows a diagram for a third embodiment of a flexible interconnect packaging system constructed in accordance with the present invention; 
       FIG. 6  shows a diagram for a fourth embodiment of a flexible interconnect packaging system constructed in accordance with the present invention; 
       FIG. 7  shows a diagram for a fifth embodiment of a flexible interconnect packaging system constructed in accordance with the present invention; and 
       FIG. 8  shows three devices that use a flexible interconnect packaging system in accordance with the present invention. 
   

   DETAILED DESCRIPTION 
   The present invention includes a flexible interconnect packaging system that overcomes the limitations of conventional packaging systems. For example, in one embodiment, a flexible packaging system is provided that includes a flexible substrate and a pre-molded or post-assembly molded plastic package that forms an open cavity for receiving a fingerprint sensor. Such a flexible packaging system can be used within the housing of a cellular telephone, or other portable electronic device, to provide the sensor at an outside surface of the device housing, while electrically coupling the sensor to an internal circuit board that has an orientation that is different from the sensor&#39;s orientation. 
   The packaging system as described above fits into very small form factor devices and is producible at a relatively low cost. Furthermore, the packaging system is easily replaceable in case of damage to the sensor. For example, the fingerprint sensor may be damaged by a hard material such as a key or coins as they are being carried within the same pocket that the is carrying the cell phone. 
   EXEMPLARY EMBODIMENTS 
     FIG. 3  shows a diagram of one embodiment of a flexible interconnect packaging system  200  constructed in accordance with the present invention. The system  200  includes a substrate material, shown generally at  202 . The substrate  202  is comprised of a top substrate portion  204  and a bottom substrate portion  206 . An electronic component  208  is shown affixed to the top substrate portion  204 . In one embodiment, the component  208  is affixed to the substrate  204  using a high temperature die attachment epoxy (conductive or non-conductive). In another embodiment, the component  208  is affixed using a conductive or non-conductive high temperature adhesive tape. However, any suitable attachment means may be used to affix the component  208  to the substrate  204 . 
   A set of conductive traces, shown generally at  210 , is located between the top  204  and bottom  206  substrate portions. The conductive traces transmit electrical signals between the component  208  and an edge connector  212 . The edge connector  212  is constructed to connect to a mating connector (not shown) that is located on a main circuit board. The conductive traces are comprised of copper or other suitable conductive material. In one embodiment, the traces are laminated between the top and bottom substrate portions. However, other processes may be used to incorporate conductive traces with the substrate. For example, it is possible to embed conductive traces into a single substrate portion. 
   In the embodiment shown in  FIG. 3 , there exists only one layer of conductive traces. However, it is possible to incorporate multiple layers of conductive traces, where each layer is separated and/or isolated by additional substrate material or other suitable flexible material. Thus, it is possible to create complex circuits that route signals using multiple layers of conductive traces that have conductive vias to electrically couple traces on different layers. 
   At the edge connector  212 , the top substrate portion is partially removed to expose contact regions  214  of the conductive traces. The contact regions  214  mate with corresponding contact regions of the mating connector to allow electrical signals to be transmitted from the packaging system  200  to the main circuit board. The contact regions may be gold plated if desired. The edge connector  212  includes a stiffener  216  that is attached to the bottom substrate portion  206  under the contact regions  214 . The stiffener operates to reinforce the edge connector and keep it in a relatively flat or straight alignment. 
   The top substrate portion also includes a break where a section of the top substrate is removed, as shown at  218 . The removed section of the top substrate  204  exposes regions of the traces  210  that are referred to as trace pads  220 . The removed section of the top substrate portion is located in close proximity to the component  208 . 
   The component  208  includes contact pads  222  that are coupled to the internal circuitry of the component  208  and are used to interface the component to other circuits. In one embodiment of the invention, bonding wires  224  are bonded between the contact pads  222  and the trace pads  220 . The bonding wires are connected using typical bonding techniques. Wire bonding technology is the preferred method for device interconnection for several reasons. First, bonding wires are low cost since the cost of gold wire per connection is the lowest compared to any interconnection method. Second, gold wires are flexible and can be shaped or profiled according to a desired looping sequence, loop height, or other shape that other technologies can not offer. Third, bonding pads can be plated. The copper pads on the flexible substrate are very well suited for gold plating or deposition. This allows 100% compatibility with the gold wire so that gold to gold bonding accomplished through a thermosonic process is very reliable. Lastly, bonding machines are readily available, since they are standard machines available at any given assembly foundry and the processes are standard and low cost, whereby unlimited volume demand can be supported. 
   In order to withstand the temperature requirements of the bonding process, the flexible substrate portions  204  and  206  are comprised of a high temperature substrate material. In one embodiment, the substrate portions are comprised of a polyimide material. For example, the polyimide material may be a material known as “Kapton” that has a service temperature range of approximately −200 to +300 degrees Celsius. Another material that is suitable for use as the flexible substrate portions  204  and  206  is referred to as “Adhesiveless Kapton.” This material has a service temperature range of approximately −200 to +350 degrees Celsius. However, the flexible substrate material is not limited to the above-identified materials and may be comprised of any flexible material having a service temperature that can withstand the wire bonding process or solder processes. Thus, in one embodiment, the flexible substrate material is basically a polyimide substrate base material with laminated layer(s) of copper traces for interconnection between a silicon device and the external edge contacts. 
   After the bonding wires are installed, an encapsulation (not shown in  FIG. 3 ) is provided to cover and protect the bonding wires  224 , the contact pads  222 , and the trace contacts  220 . The encapsulation is discussed in more detail in another section of this document. Furthermore, the packaging system of  FIG. 3  is not shown to scale since the portion of the packaging system shown at  226  may be much longer than shown, thereby allowing the component to be located at varying distances from the edge connector  212 . This allows for the packaging system to provide the most flexibility since the substrate portions are flexible and allow for bending and twisting so that the component  208  can be orientated as desired independently from the orientation of the edge connector  212 . 
     FIG. 4  shows a side view of one embodiment of a packaging system  300  constructed in accordance with the present invention. The packaging system  300  includes top and bottom substrate portions  302  and  304 , respectively. The system  300  also includes a conductive trace region  306 , an electrostatic discharge region  308  and a pre-molded package  310 . 
   The packaging system  300  includes a sensor component  312 . In one embodiment, the sensor component is a fingerprint sensor and includes a sensor region  314  and one or more sensor contacts  316 . The one or more sensor contacts  316  allow data obtained from the sensor region to be transmitted to another circuit. The sensor component may also comprise other types of IC sensors as desired. 
   The conductive trace region  306  includes one or more conductive traces  326  that have one or more trace contacts  318 . For example, the top substrate portion  302  includes an opening that exposes the one or more trace contacts. The sensor contacts and the trace contacts are coupled together with bonding wires  320 . As a result, signals from the fingerprint sensor are transmitted via the bonding wires  320  from the sensor contacts  316  to the trace contacts  318  for transmission over the conductive traces  326 . 
   The conductive traces  326  include edge contacts  321  that form part of an edge connector  322  that allows the packaging system  300  to be coupled to a mating connector that is part of another circuit. Thus, it is possible for signals from the fingerprint sensor to be transmitted to another circuit via the edge connector. The edge connector  322  may also include a stiffener (not shown in  FIG. 4 ) to support the alignment of the edge connector  322 . 
   The pre-molded package  310  solves various limitations and problems that might occur in the actual packaging process. Due to the added stiffening support provided by the package  310  underneath the flexible substrate, the total chip bonding surface area and bondable trace contact  318  are well supported. This operates to counter any flexing action that may occur during the bonding process, and thereby avoid severe packaging and/or assembly quality problems such as those described below. 
   A) Wire bonding defects and failures encountered in wire bonding to a flexible substrate due to its material surface “softness” as compared to other conventional hard substrate material like metal lead-frame and organic substrate PC boards. For example, when a capillary wire bonding tool touches the flexible substrate bonding pads, in order to make a complete wire bond interconnect from the silicon chip bond pads, the softness of the flexible substrate inherently experience “bouncing” action from the tip of the wire bond capillary. This phenomena is called a “bouncing capillary” and would thereby result in wire bonding imperfections and quality defects known in various degrees and forms, such as broken wire, non-stick on pad, smashed ball bond, over sized ball, or undersized ball and etc. 
   B) Handling problems while in packaging assembly process where the device is mounted onto the flexible substrate without any reinforcement or stiffener materials such as described in this invention. Danger of damaging the device due to accidental bumps, shocks, or miscarriage of the single strip or many strips of devices attached onto the flexible substrate may potentially suffered deformation, bending and crumple the flexible substrate. Thus, several quality defects related to handling and miscarriage of the devices may directly result in reliability failures of the devices. 
   The pre-molded package included in the present invention operates to reduce or eliminate the above-identified defects so that reliable connection between the device and the substrate is achieved. The pre-molded package  310  achieves this result by providing support to the bottom and side of the substrate material. In effect, the pre-molded package  310  provides an open cavity that allows the component to be mounted on the top portion of the substrate. By providing this open cavity, the component may be a sensor device, such as a fingerprint sensor, that reads user data when touched by a user. Mounting such a sensor would not be possible where the pre-molded package fully encapsulates the substrate material so that there would be no access to the sensor surface. 
   Also included in the packaging system  300  is an encapsulation region  324  that covers and protects the bonding wires  320 , the sensor contacts  316 , and the trace contacts  318 . The encapsulation  324  may comprise a plastic epoxy material (glob top, molded, etc.) or other suitable material. Thus, the packaging system  300  provides a way to package a fingerprint sensor  312  using a flexible substrate, and to electrically coupled the sensor to another circuit without the use of a separate circuit board and additional interface connectors. The length of the substrate  302 ,  304  and contact  306  regions may be selected to accommodate folding and twisting to orientate the fingerprint sensor to a desired position independent from the orientation of the edge connector  322 . 
   In accordance with the invention, the packaging system  300  has the advantage of providing an assembled sensor package ready for mounting in a final product assembly application (i.e., cell phone, PDA, remote key lock, etc.). Since the construction of the package includes reinforcements built around the sides and bottom surface of the fingerprint sweep sensor device, the final mounting can be easily located and fixed onto any part of a given enclosure of the device. For example, the pre-molded package can be fastened, secured, or snapped into a slot provided in the device housing allowing the sensor surface to be exposed on the enclosure. The unique construction of the pre-molded package allows the use of the fingerprint sensor in the packaging system, since the package provides an “open top cavity” molding process that results in access to the sensor, instead of a complete encapsulation of the device, which would not allow access to the sensor. 
     FIG. 5  shows a diagram for another embodiment of a flexible interconnect packaging system  400  constructed in accordance with the present invention. The system  400  includes top  402  and bottom  404  substrate portions and a conductive trace region  406 . The system  400  is used to flexibly package a fingerprint sensor component  408  that has a sensor region  410  and sensor contacts  412 . Trace contacts  414  are exposed by a break in sections of the top substrate portion  402 . 
   Bonding wires  416  are used to couple the sensor contacts  412  to the trace contacts  414 . An encapsulation material  418  is used to cover and protect the bonding wires and the associated contacts. Conductive contacts  420  are provided so that signals from the fingerprint sensor  408  may be transmitted via the sensor contacts  412 , bonding wires  416  and trace contacts  414 , through the conductive contacts  420  to an external circuit. 
     FIG. 6  shows a diagram for another embodiment of a flexible interconnect packaging system  500  constructed in accordance with the present invention. In this embodiment, a gold ball bump technique is used to couple a fingerprint sensor component to a flexible interconnect package. 
   The system  500  includes flexible substrate portions  502  and  504  that surround a conductive trace region  506 . The trace region  506  includes trace contacts shown at  508  and  510 . The trace region includes internal conductive traces that couple together corresponding trace contacts. For example, one conductive trace couples together one trace contact shown at  510  with one trace contact shown at  508 . 
   A component  512  mounted to the flexible packaging includes a component contacts  514 . The component contacts  514  are coupled to the trace contacts  510  using a conductive ball  516  technique. An encapsulation  518  is used to cover the component and trace contacts and to reinforce the attachment of the component to the flexible package. 
   The flexible packaging system  500  forms an edge connector as shown at  520 . In one embodiment, the edge connector  520  is reinforced with a stiffener (not shown). The edge connector  520  connects to a mating connector coupled to an external circuit. For example, the mating connector may be on a main circuit board that includes a main processing circuit. Signals transmitted from the component via the component contacts and the conductive traces are input to the external circuit through the edge connector. Since the packaging system  500  is flexible, the substrate portions  502 ,  504  and the conductive trace region  506  may be folded, bent or twisted to allow the component  512  to be orientated in virtually any orientation with respect to the main circuit board. Thus, the component location within a housing (i.e., a cellular telephone housing) is not restricted by the location or orientation of the main circuit board. Furthermore, since the flexible packaging system  500  does not require a small circuit board to couple to the component, additional size, space and cost savings are realized. 
     FIG. 7  shows a diagram for another embodiment of a flexible interconnect packaging system  600  constructed in accordance with the present invention.  FIG. 7  illustrates how the flexible packaging system may comprise multiple components that are interconnected within the packaging system itself. 
   The system  600  comprises top  602  and bottom  604  flexible substrate portions that surround a flexible conductive trace region  606 . Components  608  and  610  are attached to the top substrate  602 . The components include component contacts  612  that are used to transmit information signals from the components. 
   The conductive trace region  606  includes conductive traces  616  that are used to carry signals from the components to an edge connector, shown generally at  626 . A portion of the top substrate is removed, as shown at  624 , to expose trace pads  614  of the conductive traces. 
   In the system  600 , a conductive trace  618  is shown that couples together trace pad  620  to trace pad  622 . The trace pads ( 614 ,  620 ,  622 ) are coupled to the contact pads  612  via bonding wires  632 . Signals flowing to and from the components flow through the bonding wires. 
   With regards to trace  618 , this trace operates to couple signals between the components  608  and  610 . For example, a signal transmitted from component  608  via trace pad  622  flows to component  610  via trace pad  620 . Thus, the flexible packaging provided in accordance with the present invention operates to route signals between multiple components. It is therefore possible to mount multiple components on a flexible interconnect package and route signals between those components to perform specific functions. For example, it is possible to mount a microphone component and it associated pre-amp circuitry onto flexible interconnect packaging constructed in accordance with the present invention. Thus, the flexible microphone package may be easily coupled or uncoupled from a main circuit board, for example, within a cellular telephone housing. The flexible packaging allows the microphone to be located anywhere in the housing without regard to the orientation of the main circuit board. 
     FIG. 8  shows three devices that use a flexible interconnect packaging system in accordance with the present invention. For example, a packaging system as described in any of the above embodiments may be used to couple a fingerprint sensor to a main circuit board within a cell phone, a PDA, and a smart card. In all these devices, the flexible interconnect packaging allows the sensor to be orientated independently from the main circuit board so that it is possible to achieve a desired presentation to the user at the outside surface of the device. 
   In one embodiment, a pre-molded package is included with a flexible packaging system to mount a fingerprint sensor on a cell phone housing. The pre-molded package operates to support a flexible substrate during the wire bonding process that bonds the fingerprint sensor to the flexible substrate. The pre-molded package includes an open top cavity that allows the fingerprint sensor to be mounted to the flexible substrate while maintaining user access to a sensor surface of the fingerprint sensor. Thus, the flexible packaging system allows the fingerprint sensor to be mounted at virtually any location on the cell phone housing and have its sensor surface exposed for access by a user. The flexible substrate allows the fingerprint sensor to be mounted independent of its orientation with respect to a main internal circuit board to which it is connected. 
   The present invention includes a flexible interconnect packaging system. The embodiments described above are illustrative of the present invention and are not intended to limit the scope of the invention to the particular embodiments described. Accordingly, while one or more embodiments of the invention have been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit or essential characteristics thereof. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.