Abstract:
A packaged integrated circuit (IC) device includes a flexible substrate having contact pads, an IC die mounted on the substrate and electrically connected to the contact pads, and conductive threads sewn into the substrate. The conductive threads have proximal ends electrically connected to corresponding ones of the contact pads with conductive bumps. The conductive threads eliminate the need for a complicated multi-layer substrate structure for interconnect fan-out so the substrate may be formed of a variety of materials such as cloth or paper.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to integrated circuit (IC) device assembly and, more particularly, to the use of conductive threads for interconnections within a packaged IC device. 
     Typical integrated circuit devices, where devices refers to packaged IC devices ready for attachment to a printed circuit board (PCB) or similar item, comprise integrated circuit dies encapsulated in plastic together with at least a portion of a corresponding and electrically connected lead frame or substrate. These typical devices are well suited for conventional applications, such as mounting on conventional PCBs. 
     Subsequent developments in assembly technologies have enabled the manufacture of relatively thin and flexible IC devices. Conventional flexible IC devices are assembled using a complicated process involving the attachment of a thin IC die to a thin polyimide substrate and the formation of additional layers, copper vias, plated through-holes, and/or copper traces in multiple lithographic steps. The complexity of conventional assembly processes makes the assembly of conventional flexible IC devices relatively expensive. Accordingly, it would be advantageous to have a simpler and less expensive method of assembling flexible IC devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects, features, and advantages of the invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings in which like reference numerals identify similar or identical elements. Note that elements in the figures are not drawn to scale. 
         FIG. 1  is a simplified top view of an exemplary substrate in accordance with one embodiment of the invention; 
         FIG. 2  is a simplified top view of the substrate of  FIG. 1  with an IC die mounted thereon; 
         FIG. 3  is a simplified top view of the assembly of  FIG. 2  with thread interconnects; 
         FIG. 4  is a simplified cross-sectional side view of the assembly of  FIG. 3 ; 
         FIG. 5  is a simplified top view of the assembly of  FIGS. 3 and 4  with intermediate and distal conductive bumps; 
         FIG. 6  is a simplified cross-sectional side view of the assembly of  FIG. 5 ; 
         FIG. 7  is a simplified top view of an exemplary substrate in accordance with an alternative embodiment of the invention; 
         FIG. 8  is a simplified top view of the substrate of  FIG. 7  after the attachment of an IC die, thread connections, and the attachment of (1) intermediate conductive bumps and (2) distal conductive bumps; 
         FIG. 9  is a simplified top view of an exemplary assembly in accordance with an alternative embodiment of the invention where the IC die of the assembly of  FIG. 2  is covered with an encapsulant prior to making thread connections; 
         FIG. 10  is a side cross-sectional view of the assembly of  FIG. 9 ; 
         FIG. 11  is a simplified top view of an exemplary assembly in accordance with an alternate embodiment of the invention where the entire top side of the assembly of  FIG. 2  is covered with an encapsulant prior to adding the thread connections; 
         FIG. 12  is a side cross-sectional view of the assembly of  FIG. 11 ; 
         FIG. 13  is a simplified top view of an exemplary assembly in accordance with an alternate embodiment of the invention where the substrate includes traces and vias; and 
         FIG. 14  is a side cross-sectional view of the assembly of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     Detailed illustrative embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. Embodiments of the present invention may be embodied in many alternative forms and should not be construed as limited to only the embodiments set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. 
     As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It further will be understood that the terms “comprises,” “comprising,” “has,” “having,” “includes,” and/or “including” specify the presence of stated features, steps, or components, and do not preclude the presence or addition of one or more other features, steps, or components. It also should be noted that, in some alternative implementations, the functions/acts noted may occur out of the order shown in the figures. 
     Novel methods of assembling novel packaged IC devices may allow for the manufacture of IC devices at a lower cost relative to conventional packaged IC devices having similar functionality. Note that, as used herein, a packaged IC device refers to a device containing one or more IC dies and one or more interconnections, which device is singulated (if assembled as one of an array or strip) and ready for connection to one or more other devices. The packaged device may be encapsulated or may be without any encapsulant if an encapsulant is not necessary to protect any sensitive components or connections. 
     In one embodiment of the present invention, carbon nanotube (CNT) thread is used to electrically connect components of a flexible IC device. The CNT thread is sewn into a substrate of the flexible IC device much as a conventional fiber thread would be sewn into a fabric using a sewing machine. 
     Carbon nanotubes are cylindrical nano-scale structures composed of carbon atoms. One typical form of CNT is a tube whose wall is a one-atom thick sheet of carbon in a regular repeating pattern. The particular properties of a particular CNT structure depend on the form of the structure—such as, for example, its diameter and the interconnection pattern of the constituent carbon atoms. A typical CNT tube has a diameter of less than 10 μm. CNTs may be manufactured to have an electrical and thermal conductivity on par with—or better than—comparably sized metal structures. CNTs may be formed into a flexible CNT thread that may be worked in ways similar to conventional fabric threads. As noted above, in one embodiment, CNT thread is sewn into the substrate of a flexible IC device. Flexible IC devices are relatively thin and their substrates may be pierced by the needle of a sewing machine. 
     A conventional sewing machine reciprocates a thread-carrying needle in such a way as to sew the thread—which is carried by an eye near the tip of the needle—into a substrate—typically a fabric—by the creation of stitching using the thread. One conventional single-thread stitch is a chain stitch in which the thread is sewn to form a repeating series of interconnected loops. The chain stitch may be relatively easily unraveled from the substrate. 
     A second, more common, machine stitch is a lock stitch, which uses two threads that may be referred to as (i) a needle thread and a bobbin thread or (ii) a top thread and a bottom thread. The needle thread is carried near the tip of the needle, which pierces the substrate (e.g., fabric) from above and forms a loop below the substrate, with which the bobbin thread is crossed before the needle thread is pulled up, thereby locking the needle and bobbin threads together. If the thread tensions are correctly set, then the two threads are interlocked inside of the substrate and, assuming an opaque substrate, (i) only the needle thread is visible from above the substrate and (ii) only the bobbin thread is visible from below the substrate. If the tensions of the threads are not correctly set, then both threads would be visible from either the top or bottom of the substrate, depending on which of the two threads has the higher tension. 
       FIGS. 1-6  illustrate steps in the assembly of an exemplary IC device  500 , shown in  FIGS. 5 and 6 . It should be noted that not every instance of plural elements, such as, for example, contact pads, piercings, and threads, is labeled in the figures; rather, exemplary instances are labeled. 
     Referring now to  FIG. 1 , a simplified top view of an exemplary substrate  100  in accordance with one embodiment of the invention is shown. The substrate  100  comprises a substrate medium  101 , which may include, for example, ultra thin FR4. FR4 is a material typically used for PCBs and comprises a woven fiberglass cloth with an epoxy resin binder and a flame retardant (the “FR” of FR4 is derived from the initials for “flame retardant”). Typically, FR4 is manufactured at a thickness making the resultant PCB substantially rigid. However, ultra-thin FR4 is both thin and relatively flexible. It should be noted that the substrate medium  101  may further include additional materials (not shown), such as, for example, paper, fabric, solder mask or solder resist material, and polyimide tape. 
     The substrate  100  further comprises a three-by-four array of twelve under-die contact pads  102  for attachment and electrical connection to an IC die (not shown in  FIG. 1 ). The under-die contact pads  102  connect to twelve corresponding intermediate contact pads  103  by way of corresponding conductive traces  104 . The intermediate contact pads  103  may be referred to as dog-ear pads or round connective pads. The under-die contact pads  102 , intermediate contact pads  103 , and traces  104  may all be formed from a conductive material such as copper. The under-die contact pads  102 , intermediate contact pads  103 , and traces  104  may be plated on top of the substrate medium  101  or may be formed within or on the substrate medium  101  using, for example, lithography. 
       FIG. 2  is a simplified top view of an assembly  200  formed by the mounting of an exemplary IC die  205  on the substrate  100  of  FIG. 1 . In a presently preferred embodiment, the IC die  205  comprises a flip-chip die having contact pads (not shown) on its bottom surface that correspond to the under-die contact pads  102  of  FIG. 1 . The die contact pads may be electrically connected to the corresponding under-die contact pads  102  with conductive balls (not shown in  FIG. 2 ). An underfill (not shown in  FIG. 2 ) may be used to improve the physical adhesion of the IC die  205  to the substrate  100 . While the under-die contact pads are covered by the IC die  205 , the intermediate contact pads  103  are not covered by the IC die  205 . 
       FIG. 3  is a simplified top view of an assembly  300  formed by attaching electrically conductive threads  306  to the substrate  100 . The threads  306  have proximal ends electrically connected to the intermediate contact pads  103  and distal ends spaced from the intermediate contact pads  103  and away from the IC die  205 . In one embodiment, the threads  306  comprise sewing needle threads, where there are corresponding bobbin threads (not shown in  FIG. 3 ) also sewn into the substrate  100  of the assembly  200  of  FIG. 2  to provide extended and/or varied connection contacts and pathways to the under-die contact pads  102 . The needle threads  306  may be Carbon Nanotube (CNT) threads as described above. The bobbin threads, which may be considered dummy threads as it is preferred that they are formed of a non-conductive material, may be, for example, conventional fabric, carbon fiber, or glass fiber threads. The needle threads  306  are sewn so as to contact corresponding intermediate contact pads  103 . The needle (not shown) used to sew the needle threads  306  into the substrate  100  punches through the substrate  100  at piercings  307 . Note that, while  FIG. 3  shows six needle threads  306  sewn to six corresponding intermediate contact pads  103 , the other six intermediate contact pads  103  may also have corresponding needle threads  306  sewn to them. 
       FIG. 4  is a simplified cross-sectional side view of the assemblage  3   y  of  FIG. 3  along cut line Y-Y.  FIG. 4  shows the bobbin thread  408  interlocking with the needle thread  306  in the piercings  307 .  FIG. 4  further shows (i) conductive balls  409  used to connect the bonding pads of the IC die  205  to the corresponding under-die contact pads  102  of the substrate  100  and (ii) underfill  412  that adheres the IC die  205  to the substrate  100 . Note that, while  FIG. 4  shows the proximal ends of the needle threads  306  trimmed to reach just to the corresponding intermediate contact pad  103 , the proximal end of the needle thread  306  may extend beyond the corresponding intermediate contact pad  103 . Furthermore, in some implementations, the needle may pierce through the corresponding intermediate contact pad  103  so that the intermediate contact pad  103  corresponds with one of the piercings  307 . 
       FIG. 5  is a simplified top view of an assembly  500  formed by adding intermediate and distal conductive bumps  510  and  511  to the assemblage  300  of  FIGS. 3 and 4 . In particular, the intermediate conductive bumps  510  electrically connect the proximal ends of the needle threads  306  to the intermediate contact pads  103 . In addition, the distal ends of the needle threads  306  are secured to the substrate  100  with the distal conductive bumps  511 . The conductive bumps  510  and  511  may comprise, for example, solder and may be formed by, for example, soldering or stud-bump forming. 
       FIG. 6  is a simplified cross-sectional side view of the assembly  500  of  FIG. 5  along cut line Y-Y. Note that the distal conductive bumps  511  may be flatter and larger than the intermediate conductive bumps  510  in order to allow for easier connections to external components. External components may include, for example, power supplies, batteries, light-emitting diodes (LEDs), sensors, connectors, and/or other IC devices. 
       FIG. 7  is a simplified top view of an exemplary substrate  700  in accordance with an alternative embodiment of the invention. Elements of the substrate  700  that are substantially similar to corresponding elements of the substrate  100  of  FIG. 1  are similarly labeled, but with a different prefix. Notably, the substrate  700  comprises a substrate medium  701 , under-die contact pads  702 , corresponding intermediate contact pads  703 , and corresponding conductive traces  704 . 
     In addition, the substrate  700  comprises distal contact pads  713  and corresponding electrically conductive distal traces  714  that are connected to the distal contact pads  713 . The distal contact pads  713  are for connecting to the distal ends of the needle threads (not shown in  FIG. 7 ). The distal traces  714  are for easier connection to external devices. The distal traces  714  are shown as linear traces, but they may be in any suitable shape or pattern to complement a corresponding attachment mechanism on an external device. The distal traces  714  may, for example, include leads extending out past the edges of the substrate medium  701 . The distal traces  714  may, for example, include holes or other receptacles for connecting to external devices. 
       FIG. 8  is a simplified top view of an assembly  800  that comprises the substrate  700  after the attachment of an IC die  805 , the sewing of needle threads  806  into the substrate  700 , and the attachment of (1) intermediate conductive bumps  810  and (2) distal conductive bumps  811 . Elements of the assembly  800  that are substantially similar to corresponding elements of the assembly  500  ( FIG. 5 ) are similarly labeled, but with a different prefix. Note that, during sewing, the needle (not shown) may pierce through the distal contact pads  713  so that the distal contact pads  713  correspond to piercings (not shown) where the needle threads  806  interlock with the bobbin threads (not shown). 
       FIG. 9  is a simplified top view of an exemplary assembly  900  in accordance with another alternative embodiment of the invention where the IC die  205  of the assembly  200  of  FIG. 2  is covered with an encapsulant  915  prior to sewing connections with the needle thread  306 . Note that  FIG. 1  is also illustrative of this alternative embodiment.  FIG. 10  is a side cross-sectional view of the assembly  900  of  FIG. 9 . 
     The encapsulant  915  may be an epoxy molding compound as is known in the art. The underfill  412  may be a mold underfill, where the underfill  412  and the encapsulant  915  comprise the same material. 
       FIG. 11  is a simplified top view of an exemplary assembly  1100  in accordance with an alternative embodiment of the invention where the entire top side of the assembly  200  of  FIG. 2  is covered with an encapsulant  1115  prior to sewing connections with the needle thread  306 . Note that  FIG. 1  is also illustrative of this alternative embodiment.  FIG. 12  is a side cross-sectional view of the assembly  1100  of  FIG. 11 . 
     The encapsulant  1115  may be an epoxy molding compound. The encapsulant  1115  has several holes  1216  to allow access to the intermediate contact pads  103 . The holes  1216  may be filled with a conductor to serve as conductive vias to the surface of the substrate  100 . Alternatively, metal pillars may be formed in the locations of the holes  1216  prior to encapsulation with the encapsulant  1115 . If the encapsulant  1115  is too hard for a sewing needle to pierce through, then piercings  1207  may be pre-formed prior to sewing by, for example, mechanical or laser drilling. After sewing with the needle threads  306 , the proximal ends of the needle threads  306  may be inserted into the holes  1216  and then soldered to the corresponding intermediate contact pads  103  for a more secure connection. The underfill  412  may be a mold underfill, where the underfill  412  and the encapsulant  1115  comprise the same material. 
       FIG. 13  is a simplified top view of an exemplary assembly  1320  in accordance with an alternative embodiment of the invention where the traces of the substrate  1300  are buried inside the substrate  1300  and connect to the surface using conductive vias.  FIG. 14  is a side cross-sectional view of the assembly  1320  along cut line Y-Y. Elements of the assembly  1320  that are substantially similar to corresponding elements of the assembly  500  of  FIGS. 5 and 6  are similarly labeled, but with a different prefix. 
     Notably, the assembly  1320  comprises a substrate  1300 , a sewn needle thread  1306 , a sewn bobbin thread  1408 , a mounted IC die  1305 , and underfill  1412  and conductive balls  1409  that attach and electrically connect the IC die  1305  to the substrate  1300 . The substrate  1300  comprises a substrate medium  1301 , several buried traces  1421 , corresponding intermediate contact pads  1303 , corresponding under-die contact pads  1402 , and corresponding vias  1422  that connect the contact pads  1303  and  1402  to the corresponding buried traces  1421 . The needle threads  1306  and the bobbin threads  1408  interlock inside the piercings  1307  formed by the needle (not shown) in the substrate  1300  during sewing. 
     Several illustrative embodiments of the invention have been described as having various feature combinations. It should be noted that, unless otherwise indicated, features of different inventions may be recombined in ways not described above, unless doing so would render the combination inoperable. 
     It should be noted that the sewing may also be used to attach additional elements to the substrate including, for example, another substrate layer. 
     Embodiments of the invention have been described where the sewing of the needle and bobbin threads into the substrate is performed after the mounting of the IC die onto the substrate. The invention is not, however, so limited. In alternative embodiments, the needle threads may be sewn into the substrate prior to the mounting of the IC die. 
     Embodiments of the invention have been described where the bobbin threads are used on the underside of the substrate. It should be noted that the loose ends of a bobbin thread may, for example, (i) be left loose, (ii) be trimmed, (iii) be solder bumped to the substrate, or (iv) be otherwise attached to the substrate. 
     Embodiments of the invention have been described where the substrate medium may be ultra-thin FR4. The invention is not, however, so limited. Any suitable substrate medium that is sufficiently non-conductive may be used. The substrate may also be relatively rigid. A particularly rigid substrate may have piercings pre-formed prior to sewing, as described elsewhere herein. Suitable substrate mediums include, for example, polyimide tape, paper, glass, leather, polyvinyl chloride (PVC), polyethylene terephthalate (PET), sheets, fabric, and cloth. Sheet, fabric, and cloth materials may include, for example, cotton, linen, silk, wool, nylon, bamboo, barkcloth, polyester, polypropylene, polyolefin, and cross-linked polyolefin (“polycryo”). 
     Embodiments of the invention have been described where the IC die is a flip chip conductively connected to the substrate with conductive balls. The invention is not, however, so limited. In alternative embodiments, other suitable types of IC dies—such as, for example, through-silicon via (TSV) dies—and/or other types of conductive connections may be used instead. 
     In some alternative embodiments, the IC die is inside an IC-die carrier such as, for example, a ball-grid array (BGA) package, where the IC die may be wire-bonded to a carrier substrate and encapsulated in an encapsulant. In these embodiments, the carrier substrate has contact pads on its underside that correspond to the under-die contact pads of the IC-device substrate. In these embodiments, the IC-die carrier functions as the above-described IC die. Consequently, the above-described embodiments that use a flip-chip die or TSV die may be considered to have IC-die carriers that include only an IC die. 
     In some alternative embodiments, the IC die has bond pads on its top surface that are electrically connected—via, for example, wire bonds—to the intermediate contact pads. As a result, the substrate would not need under-die contact pads or connected traces, which may be absent from the substrate. In these alternative embodiments, the IC die and wire bonds are encapsulated in an encapsulant. 
     Embodiments of the invention have been described wherein the packaged IC device comprises one IC die. It should be noted that a single packaged IC device in accordance with the present invention may comprise a plurality of IC dies. 
     Embodiments of the invention have been described where the needle thread is sewn with a sewing machine. The invention is not, however, so limited. In some alternative embodiments, the thread may be manually sewn through the substrate, either piercing the substrate or using pre-formed piercings in the substrate. 
     Embodiments of the invention have been described where the needle thread may be a CNT thread and the bobbin thread may be a conventional non-conductive fabric thread. The invention is not, however, so limited. In alternative embodiments, either or both of the needle threads and the bobbin threads may be CNT thread or other conductive thread, such as, for example, metallic thread. In addition, in some alternative embodiments, the needle thread may be a non-conductive thread with the bobbin thread being a CNT or other conductive thread. Note that, in embodiments where the bobbin thread is conductive, the intermediate and distal conductive bumps may be placed on the underside of the substrate. 
     Embodiments of the invention have been described where the sewing needle punches holes through the substrate during the stitching process to form the piercings where the needle and bobbin threads interlock. The invention is not, however, so limited. In some alternative embodiments, the piercings are pre-formed by, for example, laser drilling or any other suitable means. In some alternative embodiments an auxiliary thread other then a bobbin thread is sewn together with the needle thread to form suitable stitching. 
     Embodiments of the invention have been described where a needle thread and a bobbin thread are sewn together to form a lock stitch. The invention is not, however, so limited. In some alternative embodiments, the needle and bobbin threads are sewn together to form a different suitable kind of stitch. In some other alternative embodiments, only a needle thread is used and no bobbin thread is used. One such alternative embodiment may use the chain stitch. 
     Embodiments of the invention have been described where the needle thread is sewn as a straight-line conductive path from an intermediate contact pad to a distal location. The invention is not, however, so limited. In alternative embodiments the needle thread is sewn in a conductive path that is not a straight line, where the conductive path may comprise a plurality of connected straight-line segments, curves, loops, decorative segments, and/or backstitches. 
     It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims. 
     Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.” 
     Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range. As used in this application, unless otherwise explicitly indicated, the term “connected” is intended to cover both direct and indirect connections between elements. 
     The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims. 
     In this specification including any claims, the term “each” may be used to refer to one or more specified characteristics of a plurality of previously recited elements or steps. When used with the open-ended term “comprising,” the recitation of the term “each” does not exclude additional, unrecited elements or steps. Thus, it will be understood that an apparatus may have additional, unrecited elements and a method may have additional, unrecited steps, where the additional, unrecited elements or steps do not have the one or more specified characteristics. 
     Although the steps in the following method claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those steps, those steps are not necessarily intended to be limited to being implemented in that particular sequence.