The present invention is directed to integrated circuit devices and approaches and, more particularly, to coupling applications involving integrated circuit devices and external circuit components.

The integrated circuit industry has experienced technological advances that have permitted dramatic increases in circuit density and complexity, and equally dramatic decreases in the size of circuit components and circuit arrangements. These technology advances have promulgated equally dramatic growth in the industry and corresponding demand for products employing high-density, complex and compact integrated circuit devices.

To meet the needs of such high-density and high functionality, increased numbers of external electrical connections are implemented with circuit chips, on the exterior of the chips and on the exterior of the semiconductor packages which receive the chips and for connecting packaged devices to external components such as a printed circuit board. The electrical conductivity (and any associated losses or delays) of connections with the circuit chips have become increasingly important as higher demands for speed and efficiency are promulgated with many applications.

Externally-implemented connectors have been used to electrically connect different circuit components such as bonded chips, flip chips, package substrates, ball grid array (BGA) substrates and pin grid array (PGA) substrates. These electrical connections facilitate the transfer of signals between the circuit components for a variety of purposes.

Each of these applications benefit from various circuit connector characteristics such as strength, electrical conductivity (and resistivity), size, stiffness and thermal conductivity. Other factors such as cost, manufacturability and reliability are also important for these applications. Achieving desirable circuit connector characteristics has been challenging, however, while meeting such other factors. In addition, many connection approaches involve liquefying connector material such as solder, which makes a bond to a connector upon solidification; however, this liquefying can result in undesirable flow of the connector material and corresponding short circuiting, particularly in high density applications. Moreover, many liquefying approaches involve heating nearby circuitry, which may be undesirable for a variety of applications.

These and other difficulties present challenges to the implementation of circuit substrates for a variety of applications.

Various aspects of the present invention involve circuit connection approaches implemented with integrated circuits and other devices. The present invention is exemplified in a number of implementations and applications, some of which are summarized below. According to an example embodiment, carbon nanotubes are used to electrically couple integrated circuit dies to external circuits such as package substrates or leadframes.

In another example embodiment of the present invention, carbon nanotubes grown from a metal connector at a surface of an integrated circuit chip are pressed into an opposing metal connector on an external circuit, as facilitated by the relative stiffness of the carbon nanotubes. The carbon nanotubes are thus bonded to both connectors and form a low-resistance electrical connection therebetween.

In some applications, metal at the opposing metal connector is softened, prior to coupling with the carbon nanotubes, to facilitate the insertion of the carbon nanotubes into the metal. In this (and other) applications, this carbon nanotube connection can be made without necessarily liquefying metal at either connector, inhibiting the possibility of metal from undesirably flowing and/or causing shorts between connectors.

In another example embodiment of the present invention, surface connectors on an integrated circuit device are placed at a relatively small pitch as facilitated by the use of carbon nanotubes to connect the connectors to external circuits. As discussed above, the ability to press the carbon nanotubes into the external circuit connector makes possible the connection without necessarily liquefying metal at the connector. In this regard, flow of liquefied metal is not necessarily a concern, facilitating smaller spacing between the connectors.

Various devices and approaches are manufactured and/or implemented in other example embodiments, with flip chip devices, conventional devices and others, and with various connector approaches including direct connection to surface contacts of devices and indirect connection via connectors such as those implemented with a leadframe.

The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments.

The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

FIG. 1 shows a cross-sectional view of a flip chip integrated circuit package arrangement, according to an example embodiment of the present invention;

FIG. 2 shows a cross-sectional view of a connection between a flip chip integrated circuit die and a package substrate, according to another example embodiment of the present invention;

FIG. 3 shows a cross-sectional view of a connection between a flip chip integrated circuit die and a package substrate, according to another example embodiment of the present invention;

FIG. 4 shows a cross-sectional view of an integrated circuit chip coupled to a substrate, according to another example embodiment of the present invention;

FIG. 5 shows a cross-sectional view of a connection between an integrated circuit chip and a substrate, according to another example embodiment of the present invention; and

FIG. 6 shows a flow diagram for an approach to coupling carbon nanotubes between an integrated circuit device and another circuit, according to another example embodiment of the present invention.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

The present invention is believed to be applicable to a variety of circuits and approaches involving and/or benefiting from connection to external circuit components. While the present invention is not necessarily limited to such applications, an appreciation of various aspects of the invention is best gained through a discussion of examples in such an environment.

According to an example embodiment of the present invention, carbon nanotubes electrically couple an integrated circuit chip to an external circuit component such as a leadframe or package. The carbon nanotubes extend in a generally straight direction from a conductive circuit connector at a surface of a first component. The nanotubes are coupled to an opposing connector at a surface of another component and form a low-resistance electrical path between the connectors. In some applications, the first component is the

integrated circuit chip, with the carbon nanotubes extending from the chip and subsequently coupled to an external circuit, such as a leadframe or a package substrate (e.g., for a flip chip package). In other applications, the first component is a substrate from which the carbon nanotubes extend, with the integrated circuit chip being subsequently coupled to the extending carbon nanotubes.

In one implementation, the carbon nanotubes are mechanically engaged with the opposing connector. For example, nanotubes extending from a connector at an integrated circuit surface can be forced into an opposing connector using a pressing force without necessarily liquefying connector material. Stiffness characteristics of the carbon nanotubes facilitate the coupling, while characteristics of the opposing connector such as ductility facilitate the coupling of the carbon nanotubes thereto while maintaining the integrity (i.e., general shape and conductivity characteristics) of the carbon nanotubes.

In some implementations, the opposing connector is softened to facilitate the coupling of the nanotubes thereto. Heat is applied to the opposing connector in an amount sufficient to soften the connector to a condition where the nanotubes can be pushed into the connector while reliably maintaining the shape and arrangement of the carbon nanotubes. This heating approach does not necessarily involve heating the integrated circuit chip and/or the connection between the carbon nanotubes and the connector at the integrated circuit chip surface. > The carbon nanotube connection approach discussed herein is applicable to a variety of circuit types and arrangements, as well as to a variety of connection approaches and materials. In some instances, the carbon nanotubes are used to couple integrated circuit connectors to a connector such as a leadframe that is brought in close proximity to a surface of the integrated circuit at the connector. Other instances involve the coupling of an integrated circuit chip to a substrate from which carbon nanotubes extend by coating an underside of the chip with a conductive metal and forcing the carbon nanotubes into the metal to make a connection. In other instances, integrated circuit dies in a flip chip type arrangement are coupled to a package substrate using a plurality of carbon nanotubes as discussed herein. In such a flip chip arrangement, the circuit side of the integrated circuit die is placed face-down (flipped, relative to conventional packaging approaches) onto a package substrate to reduce the length of external circuit connections. In this regard, carbon nanotubes are formed extending from connectors on the circuit side of the integrated circuit

die and, when the die is flipped, brought into contact to couple to connectors on the package substrate.

According to another example embodiment of the present invention, an integrated circuit device is manufactured with carbon nanotubes electrically coupling an integrated circuit device with an external circuit. Carbon nanotubes are formed at select locations on a surface connector of the integrated circuit chip by placing and/or growing the nanotubes at the select locations. The carbon nanotubes are coupled to the surface connector, extending generally away from the connector in a rigid arrangement. The carbon nanotubes are coupled to a conductive connector on an external circuit such as a leadframe or package substrate, making an electrical connection between the integrated circuit device and the external circuit.

The coupling of the carbon nanotubes to the external circuit involves one or more of a variety of approaches. In one implementation, the carbon nanotubes are pressed into a ductile metal such as gold in the conductive connector on the external circuit. The carbon nanotubes can be pressed by forcing the integrated circuit device together with the external circuit, holding the integrated circuit device stable while pressing the external circuit thereto or a combination of moving both the integrated circuit device and the external circuit. In another implementation, the conductive connector on the external circuit is softened by heating, prior to coupling with the carbon nanotubes, to facilitate the insertion of the carbon nanotubes into the conductive connector. The conductive connector on the external circuit can be heated separately from or together with the external circuit itself. Further, the integrated circuit device does not necessarily require heating for this approach, inhibiting undesirable heating of the circuit components in the integrated circuit device. With these approaches, the carbon nanotubes are bonded to the conductive connector on the external circuit. Furthermore, the bonding can be accomplished without necessarily liquefying metal in the conductive connector on the external circuit, inhibiting the flow of the metal and, correspondingly, inhibiting the opportunity for shorts to occur as a result of such flow (e.g., as potentially associated with solder connections).

In an implementation involving the growth of carbon nanotubes from a metal connector on the integrated circuit chip, catalyst material is arranged on the metal connector at locations where the carbon nanotubes are desirably located. Common carbon nanotube growth approaches involving, e.g., chemical vapor deposition (CVD) with the introduction of a carbon-containing gas such as methane to the catalyst material are used in the carbon

nanotube growth. For general information on carbon nanotubes and for specific information regarding carbon nanotube growth approaches that can be implemented in connection with this and other example embodiments of the present invention, reference may be made to M. S. Dresselhaus, G. Dresselhaus, and P. C. Eklund, "Science of Fullerenes and Carbon Nanotubes" (Academic Press, San Diego, 1996), which is fully incorporated herein by reference.

Turning now to the figures, FIG. 1 shows a cross-sectional view of a flip chip integrated circuit package arrangement 100 with carbon nanotube connectors, according to another example embodiment of the present invention. The arrangement 100 includes a flip chip integrated circuit die 120 coupled to a package substrate 110 using carbon nanotube connectors.

The flip chip die 120 has a circuit side 122 (e.g., epitaxial silicon) opposite a back side 124 (e.g., bulk silicon), with the circuitry of the flip chip die located in the circuit side, near the package substrate 110. Connectors (e.g., conductive interconnects or pads) at a lower surface 221 of the circuit side 122 of the flip chip die 120 are coupled to connectors (e.g., conductive pads) on an upper surface 111 of the package substrate 110 via carbon nanotubes. A representative carbon nanotube connector region 130 is shown, with a multitude of carbon nanotube connectors making electrical connection between circuitry in the flip chip 120 and the package substrate 110. The package substrate 110 includes a network of interconnects (lateral connector circuits) and vias (vertical connector circuits) within the package (and, in some instances, at surfaces thereof). The network of interconnects and vias electrically couple connectors at the upper surface 111 of the package substrate 110 to solder balls on a lower surface of the package substrate. A representative solder ball is labeled 105, with this and other solder balls readily coupled to circuit components for operation with the flip chip die 120.

FIG. 2 shows a cross sectional view of a flip chip integrated circuit package 200 with carbon nanotube connectors between a flip chip die 220 and a package substrate 210, according to another example embodiment of the present invention. The approach shown and described with the flip chip integrated circuit package 200 may be implemented, for example, in connection with the flip chip integrated circuit package 100 shown in FIG. 1 at carbon nanotube connector region 130.

The flip chip die 220 includes a metal interconnect 222 at a lower surface 221 in the circuit side of the flip chip die. The metal interconnect is coupled to circuitry in the flip

chip die 220 and also to carbon nanotubes, including representative carbon nanotube 232. The carbon nanotubes extend in a direction generally perpendicular to the lower surface 221 of the flip chip die 220, away from the surface and towards the package substrate 210. The package substrate 210 has an interconnect 212 extending laterally along an upper surface 211 and a metal pad 234 coupled to the interconnect and adapted for coupling with the carbon nanotubes. The nanotubes, including carbon nanotube 232, together with the metal pad 234 and the interconnect 222 make up a connector region 230 via which the flip chip 220 and the package substrate 210 are electrically coupled.

The nanotubes are coupled to the interconnect 222 and to the metal pad 234 in one or more of a variety of manners, depending upon the application and desirable characteristics of the connection between the flip chip die 220 and the package substrate 210. In one implementation, the nanotubes are grown from the interconnect 222 using an approach such as CVD, with carbon growth locations (i.e., seed locations) with the interconnect 222 facilitating the growth. The nanotubes grow in a direction that is generally away from and/or perpendicular to the lower surface 221. The length of the grown nanotubes is generally short, providing desirable stiffness but long enough to facilitate contact with the metal pad 234.

After the nanotubes have been grown, connection is made to the metal pad 234 using a forcible approach. That is, the nanotubes and the metal pad 234 are pressed together, with opposing ends of the nanotubes embedding in the metal pad and forming a bond (e.g., mechanical) therewith. In some applications, the package substrate 210 is held fixed while the flip chip die 220 is pressed towards the package substrate to embed the carbon nanotubes in the metal pad 234. In other applications, the flip chip die 220 is held fixed while the package substrate 210 is pressed towards the flip chip die to press the metal pad 234 onto the carbon nanotubes. hi some implementations, the metal pad 234 is softened, prior to the embedding the opposing ends of the nanotubes. For example, when the ductility of the metal pad 234 is such that softening of the metal would improve the connection approach, heat can be applied to the metal pad to soften it. Gold is one type of metal that can be implemented with the metal pad 234, and in some implementations, is heated using this approach. The heating, while facilitating the embedding of the carbon nanotubes, can be accomplished without necessarily flowing the metal in the metal pad 234. In this regard, adjacent metal

pads do not suffer the risk of flowing metal inadvertently shorting a connection between the pads as, e.g., conventional solder connections are susceptible.

In another example embodiment, the above-discussed softening approach can also be used to remove the flip chip die 120 from the package substrate 210. The metal pad 234 is heated to soften it, and pressure is applied to the flip chip die 220 and/or to the package substrate 210 to push the carbon nanotubes away from the metal pad 234. Once removed, the connection is re-made for certain applications. This softening and removal of the carbon nanotubes is carried out while maintaining the integrity of the carbon nanotubes such that, e.g., the length and general shape of the carbon nanotubes are substantially unchanged.

FIG. 3 shows a cross sectional view of two carbon nanotube connectors implemented with a flip chip integrated circuit package 300, according to another example embodiment of the present invention. The flip chip integrated circuit package 300 is similar to the package 200 in FIG. 2, with components including a flip chip die 320 and a package substrate 320 labeled with similar numbers. The flip chip die 320 includes two interconnects 322 and 323. The package substrate 310 includes two interconnects 312 and 313, respectively coupled to metal pads 334 and 335.

Two connector regions 330 and 331 are shown adjacent to one another and spaced at a relatively small pitch (distance "p"). This relatively small pitch is facilitated by the ability of the carbon nanotubes 332 and 333 to connect to their corresponding metal pads 334 and 335 without necessarily flowing any metal, such as used in solder type connections. In some applications, such as with coupling integrated circuit dies or other components manufactured using small-scale approaches such as lithography, the pitch is less than about 1 micron and, where connectors are very close, less than about 10 nanometers. This approach may be useful in connection with, e.g., flip-chipping dies on dies. In other applications with somewhat larger scale features such as those often associated with BGA substrates, the pitch is less than about 100 microns.

FIG. 4 shows a cross-sectional view of an integrated circuit package arrangement 400, according to another example embodiment of the present invention. An integrated circuit die 420 is coupled to a substrate 410 using a plurality of carbon nanotubes at an interface region 430. The carbon nanotubes facilitate thermal and electrical connection between the integrated circuit die 420 and the substrate 410.

The substrate 410 includes conductive interconnects 412 and 414, and a conductive die pad 416. Circuits in the integrated circuit die 420 are electrically coupled to the interconnects 412 and 414 (and others, where applicable) respectively with wirebonds 440 and 442. Distal ends of carbon nanotubes extending from the conductive die pad 416 are embedded in a metal layer 422 on an underside of the integrated circuit die 420.

FIG. 5 shows a close-up cross-sectional view of an interface 500 of an integrated circuit package arrangement, according to another example embodiment of the present invention. The interface 500 has a substrate (or leadframe) 510 coupled to an integrated circuit die 520 via a carbon nanotube connector region 530. The interface 500 can be implemented, for example, with the integrated circuit package arrangement 400 shown in FIG. 4.

The substrate (or leadframe) 510 has a metal contact region 516 (e.g., gold or aluminum) with a plurality of carbon nanotubes extending therefrom, a representative one of the carbon nanotubes labeled 532. These carbon nanotubes are coupled to the metal contact region 516 in a variety of manners, depending upon the implementation. For example, the carbon nanotubes can be grown from catalyst material at the metal contact region 516, extending as shown. Distal ends of the carbon nanotubes are embedded into a metal layer 522 on an underside of the integrated circuit die 520, via pressure and, in some instances, softening of the metal layer to facilitate the embedding of the carbon nanotubes. The approach shown in FIGs. 4 and 5 is implemented with a leadframe to support the integrated circuit die 420 in connection with other example embodiments. For instance, referring to FIG. 4, the substrate 410 can be implemented (e.g., replaced) with a leadframe having interconnects 412 and 414 as well as die pad 416 for making electrical connection with the integrated circuit die 420. FIG. 6 shows a flow diagram for an approach to coupling carbon nanotubes between an integrated circuit device and another device, according to another example embodiment of the present invention. At block 610, catalyst growth locations are arranged at connection points on a conductive integrated circuit connector. In some applications, the connector is located on or part of an interconnect or surface pad at an integrated circuit chip or package substrate. In other applications, the connector is part of a leadframe.

A carbon-containing gas such as methane is introduced to the catalyst at block 620, and carbon from the gas is used (e.g., via CVD) to grow carbon nanotubes from the catalyst at block 630. If the length of the carbon nanotubes is desirably shortened at block 640, such

as where a particular connection length is desired or where multiple nanotubes are desirably formed at a consistent length, the carbon nanotubes are shortened at block 645. With this approach, the length of the carbon nanotubes can be selected to achieve desirable stiffness for connection to the external circuit. After shortening (or if no shortening is desired), the carbon nanotubes are ready for coupling with an opposing metal connector of the other device. If softening of metal at the opposing connector is desired at block 650, the metal is softened at block 655. After softening (or if no softening is desired at block 640), the opposing connector and the carbon nanotubes are pressed together to form a mechanical bond and conductive (e.g., electrical and/or thermal) connection. The pressing may involve pressing the carbon nanotubes into the connector, pressing the connector onto the carbon nanotubes, or a combination of pressing both the carbon nanotubes and the connector. The resulting structure has carbon nanotubes extending from metal at catalyst growth locations of a first integrated circuit package component, with distal ends of the carbon nanotubes embedded in an opposing connector of another integrated circuit package component.

The various embodiments described above and shown in the figures are provided by way of illustration only and should not be construed to limit the invention. Based on the above discussion and illustrations, those skilled in the art will readily recognize that various modifications and changes may be made to the present invention without strictly following the exemplary embodiments and applications illustrated and described herein. For example, the carbon nanotubes may be implemented with material different from, or in addition, to, carbon, such as Boron. In addition, the interface arrangements discussed by way of example may be implemented with a multitude of different types of materials, arrangements and orientations. Such modifications and changes do not depart from the true spirit and scope of the present invention.