Abstract:
A tape automated bonding (TAB) structure which includes a flex tape having a conductive lead pattern formed thereon. The conductive lead pattern includes a plurality of leads configured to form an inner lead bond (ILB) portion of the TAB structure. At least one of the plurality of leads is internally routed and has a contact exposed interior to the ILB portion of the TAB structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a division of U.S. application Ser. No. 09/970,145, filed on Oct. 2, 2001, now U.S. Pat. No. 7,190,069, which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention relates to the field of integrated circuit packaging and more specifically to a method and system of tape automated bonding for an integrated circuit for an implantable medical device such as a defibrillator, pacemaker, or cardioverter. 
   BACKGROUND 
   Patients prone to irregular and sometimes life threatening heart rhythms sometimes have miniature defibrillators, cardioverters, and pacemakers implanted in their bodies, typically in the upper chest area above their hearts. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current, to hearts. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives. 
   The devices include a set of electrical leads, which extend from a housing into a heart after implantation. Within the housing, among other components, is electronic circuitry for detecting abnormal heart rhythms and for controlling the bursts of electric current through the leads to the heart. The electronic circuitry includes integrated circuits (ICs) which are mounted to a circuit board and connected to various other discrete electrical components by electrically conductive conduits between input/outputs (I/O&#39;s) of the IC and the various discrete electrical components. 
   One method of mounting the IC to the circuit board and providing the interconnections between the IC and the discrete components includes tape automated bonding (TAB). In TAB, interconnection leads are patterned on a flex tape. The tape is positioned above the bare IC chip so that the metal tracks on the tape correspond to I/O bonding sites on the perimeter of the chip. An outer portion of the TAB leads are then connected to contacts on the circuit board. The circuit board includes leads running from the contacts to the discrete electrical components. Since the implantable devices are typically implanted in the left region of the chest or in the abdomen, a smaller size device, which is still capable of performing complex cardiac rhythm management schemes, is desirable. 
   Accordingly, there is a need to provide a compact implantable device which is capable of performing complex cardiac rhythm management schemes. Furthermore, there is a need to provide methods of manufacturing devices and assembling structures such as the ICs within the implantable devices that provide more efficient and thus less expensive manufacturing. 
   SUMMARY 
   To address these and other needs, methods and systems for tape automated bonding have been devised. One aspect of the present system includes a TAB structure. In one embodiment, a TAB structure includes a tape having a conductive lead pattern formed thereon, wherein the conductive lead pattern includes a plurality of leads configured to form an inner lead bond (ILB) portion of the TAB structure. At least one of the plurality of leads is internally routed relative to the ILB portion and has a contact exposed interior to the ILB portion of the TAB structure. 
   One aspect of the present system includes an electrical device. In one embodiment, an electrical device includes a circuit board, an IC chip mounted to the circuit board, and an electrical component mounted above the IC chip and electrically connected to the IC chip via a lead extending from the electrical component to an I/O of the IC chip. 
   One aspect includes a method of interconnecting an IC chip to an electronic component. In one embodiment, a method includes connecting the IC to a TAB tape at an ILB portion of the TAB tape and connecting discrete components to one or more leads of the TAB tape at internal portions of the TAB tape within the ILB portion and above the IC chip. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a top view of a TAB structure according to one embodiment. 
       FIG. 2  shows a sectional side view of the TAB structure of  FIG. 1 . 
       FIG. 3  is an isometric view of the TAB structure of  FIG. 1  having electrical components mounted thereto. 
       FIG. 4  shows a top view of a TAB structure according to one embodiment. 
       FIG. 5  shows an isometric view of the TAB structure of  FIG. 4  having electrical components mounted thereto. 
       FIG. 6  shows a block diagram of a generic implantable device including an electrical circuit in accordance with one embodiment. 
   

   DETAILED DESCRIPTION 
   In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
   The increases in density that have occurred within ICs have made it possible to provide more functions in each IC, such as more logic gates or more memory bits. This increase in function has made it necessary in many cases to provide more interconnections per IC chip. IC chips have also grown in size to accommodate the larger number of individual circuits, gates or bits required for the expanded functions. The present system and method offers a technique of redistributing the I/O interconnections of an integrated circuit. In one example, a TAB leadframe is utilized to embody the technique. 
     FIGS. 1-3  show a TAB structure  100  according to one embodiment.  FIG. 1  shows a top view of TAB structure  100 . TAB structure  100  is one of a plurality of similar TAB lead-frame structures that are located in a series along a sprocketed tape  110 . Each TAB structure  100  includes tape  110 , such as polyimide or other flex tape, having a conductive lead pattern  120  formed thereon. The TAB structure  100  provides the necessary connections for the perimeter bonded I/Os of an unpackaged or bare IC chip  126 . 
   IC  126  includes a plurality of IO contact pads  202  (See  FIG. 2 ) for providing coupling of the IC to outside components. The I/O contact pads can be located all around the perimeter circumference of a surface of the IC. By way of example, there can be anywhere from approximately 16 to 500 I/O contact pads or more on the chip. IC  126  can be a square or non-square rectangular chip. 
   In one embodiment, the conductive lead pattern  120  includes a copper etched and gold plated metallization on tape  110 . In one example, in forming TAB structure  100 , a conductor layer composed of Cu or the like is formed on a tape  110  composed of a material such as a polyimide tape or other flex tape. Thereafter, the conductor layer is etched out and thereby a conductive lead pattern is formed. 
   Conductive lead pattern  120  includes a plurality of leads  123 . The leads  123  of conductive lead pattern  120  include an inner lead bond (ILB) portion  122  and an outer lead bond (OLB) portion  124 . One or more of the IC chip I/O contact pads  202  connect to the one or more of leads  123  at the ILB portion  122  when the IC chip is mounted within an inner frame section  128  of TAB  100 . The inner frame section  128  is dimensioned to hold IC  126  chip therein. OLB portion  124  is for connecting the IC chip to a circuit board, for example. Accordingly, a conductive path is formed from the ILB portion  122  at the I/O of the IC to the OLB portion  124  which is connected to a circuit board. 
   One or more of the plurality of leads  123  of TAB structure  100  includes internally located contacts  132 . Contacts  132  are located within frame section  128  and are connected interiorly relative to ILB portion  122 . Among other advantages, this allows one or more components to be mounted on or above the surface of the IC and thus within the perimeter of the IC, thus not using up any more footprint area upon a circuit board. In one example, the internally running leads are formed in the same manner along with the rest of lead pattern  120 . Since TAB leadframe cost is relatively constant even with added complexity, the present system does not cause any significant incremental cost to manufacturing or assembly of the TAB. 
   In one embodiment, a plurality of test contact pads  127  are located on the TAB structure and are connected to one or more of leads  123 . For example,  FIG. 1  shows example leads  123   b  connected to test contact pads  127 . In some embodiments, each of the plurality of leads  123  are connected to test contact pads. Other embodiments only connect one or more of leads  123  to contact test pads. The present example is shown for sake of clarity. The present TAB structure having test contact pads  127  allows for “known-good-die” testing. Known-good-die testing is electrical testing or bum-in of the integrated circuit prior to committing the expensive discrete components to the overall electrical assembly. Accordingly, in one example use of the present TAB system, once the ILB TAB bonds are completed, the IC  126  can be electrically tested using test contact pads  127  to verify that the circuit is stable and capable of meeting the rigors and high quality standards needed of an implantable defibrillator or pacemaker or other implantable device. The present embodiment accommodates known-good-die testing while still optimizing the surface area utilization above the IC in the form of active circuitry. This results in a smaller, more comfortable, and more reliable implantable device. Moreover, the present structure allows the packaging designer to optimize the circuit board or hybrid surface area which helps to minimize overall device volume while still allowing for complex electronic functions. 
   One advantage of the present structure is that it allows for reductions in electrical impedance between the IC and the associated discrete electrical components due to the very short and direct connections between the IC and the components mounted above the IC. The structure also reduces the number of electrically redundant interconnects between the IC, the components above the chip, and the hybrid (motherboard) by utilizing a continuous stitch TAB inner lead bond approach to make the necessary electrical connections. In the past, the IC was connected to the hybrid, such as a circuit board, and then a lead went from the hybrid to the component. Now a component can utilize the TAB lead itself as the component&#39;s direct interconnect. 
   Moreover, the present internal contacts  132  allow for lower cost and less complex manufacturing. This is because the internal contacts  132  allow a component to be mounted with a one-step manufacturing process to the IC. A typical two-step process of first mounting the component to the circuit board and then connecting the component to the IC is reduced to mounting the component directly within the frame of the TAB structure with its built-in connection. 
     FIG. 2  shows a schematic representation of a cross-section of portions of TAB structure  100 . In this embodiment, example lead  123 D extends from a test contact pad  127  to OLB portion  124  to ILB portion  122  and to inner contact  132  located above the major surface of chip  126 . In this example, a conductive filler material  133  is used to make the connection between lead  123 D and inner contact  132 . 
   Chip  126  includes I/O contact  202  for making the connection to the lead. In other examples a lead such as lead  123 D can extend only inward, for example, from ILB  122  to contact  132 . Other leads extend only outward, for example, from ILB  122  to OLB  124 . 
     FIG. 3  is an isometric view of TAB structure  100  having electrical components, such as components  302 ,  304 ,  306 , and  307 , mounted thereto. In this example, ILB portions  122  are connected to the I/Os of chip  126  and OLD portions  124  have been bent into a gull-wing configuration in preparation for mounting onto a circuit board. An example lead  123 C runs from IC I/O  202  to inner contact  132 . Components  302 ,  304 ,  306 , and  307  can be soldered to contacts  132 . Alternatively they can be connected by an electrically conductive epoxy. Other equivalent connection techniques are within the scope of the present system. 
     FIGS. 4 and 5  show a TAB structure  400  according to one embodiment.  FIG. 4  shows an isometric view of TAB structure  400 . Tab structure  400  includes similar features to TAB structure  100  and certain details will be omitted for sake of clarity. TAB structure  400  generally includes a tape  410  having a conductive lead pattern  420  formed thereon. Conductive lead pattern  420  includes a plurality of leads  423 . The leads  423  of conductive lead pattern  420  include an ILB portion  422  and an OLB portion  424 . 
   One or more of the plurality of leads  423  of TAB structure  400  includes internally located contacts  432 . Contacts  432  are located within frame section  438  and are connected interiorly relative to ILB portion  422 . This allows one or more components to be mounted above the surface of an IC and thus within the perimeter of the IC, thus not using up any more footprint area upon a circuit board. 
   In one embodiment, TAB structure  400  includes internally located contacts  425 . In this example, inner contacts  425  do not include contact pads such as provided for inner contacts  432 . Inner contacts  425  include a bare portion of portions of each of one or more of leads  423  and are internally located relative to ILB portion  422 . Again, inner contacts  425  allow one or more components to be mounted above the surface of the IC and within the perimeter of the IC, thus not using up any more footprint area upon a circuit board. 
     FIG. 5  is an isometric view of TAB structure  400  having an IC chip  526  mounted thereto and having electrical components, such as components  502 ,  504 ,  506  and so on, mounted thereto. ILB portions  422  are connected to the I/Os  528  of chip  526  and OLB portions  424  have been bent into a gull-wing configuration in preparation for mounting onto a circuit board  532 . In this example, lead  423 D is attached to an I/O  528  of IC  526 . One end of lead  423 D extends to OLB portion  424  and a second end extends to an inner contact  432  (see  FIG. 4 ), which in  FIG. 5  has a component  504  mounted thereon. Again, the present TAB structure provides that components such as component  504  do not take up any space on the surface of the circuit board. 
   This example also shows a lead  423 E connected to an I/O  528  of the IC. Lead  423 E includes a first end extending to OLB portion  424  and a second end extending internally to inner contact  425 , where inner contact  425  is attached to the I/Os of component  506 . In this example, component  506  is an IC chip having similar I/Os as shown for IC chip  526 . Thus, the present embodiment allows the back-to-back, internally located mounting of a second IC chip  506  relative to a first IC chip  526 . 
     FIG. 6  shows one of the many applications for circuit boards incorporating one or more teachings of the present TAB system: a generic implantable device  600 . As used herein, implantable device includes an implantable device for providing therapeutic stimulus to a heart muscle. Thus, for example, the term includes pacemakers, defibrillators, cardioverters, congestive heart failure devices, and combinations of these devices. 
   Device  600  includes a lead system  603 , which after implantation electrically contacts strategic portions of a patient&#39;s heart. Shown schematically are portions of device  600  including electrical circuitry such as a monitoring circuit  602  for monitoring heart activity and for detecting abnormal heart rhythms through one or more of the leads of lead system  603 , and a therapy circuit  601  for controlling and delivering bursts of electrical energy through one or more of the leads to a heart. Device  600  also includes an energy storage component, which includes a battery  604  and a capacitor  605 . Therapy circuit  601  and monitoring circuit  602  can both include circuit boards or hybrids having electrical devices which include one or more of the TAB features described above. In one example, the electrical circuitry of device  600  includes application-specific integrated circuits (ASICs) to monitor, regulate, and control the delivery of electrical impulses to the heart. The present TAB structure allows a packaging designer to increase hybrid efficiency by turning the otherwise passive IC surface into an electrically active design element and therefore offering a significant reduction in the size of implantable device  600 . 
   It is understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.