The present invention is directed, in general, to integrated circuits and, more specifically, to a circuit and method for providing interconnections among individual integrated circuit (xe2x80x9cICxe2x80x9d) chips in a multi-chip module (xe2x80x9cMCMxe2x80x9d).
Integrated circuits (xe2x80x9cICxe2x80x9d) are the tiny xe2x80x9cchips,xe2x80x9d usually less than 0.5xe2x80x3 on a side, of silicon (or other similar material) on which is patterned the transistors and interconnections that make modern electronic systems do what they do; compute, amplify, etc. Many advances in IC fabrication processes have brought about dramatic increases in the number of transistors that can be fabricated on each chip, thereby increasing the capabilities, as well as decreasing the size of ICs and, thus, the size of devices using ICs. Whereas the actual size of a typical IC is much less than the size of a conventional IC package, novel IC packaging designs that can significantly reduce the size of electronic devices are being explored. Moreover, as ICs become faster and more powerful, device packaging becomes a major limitation on system speed.
Conventional IC packages consist of the same basic elements: the IC, a lead frame, wire bonds, and an encapsulant. The lead frame is connected to the IC using a very thin wire bonded to both the chip and the lead frame. The encapsulant or molding, usually made from plastic, forms a package that encloses the IC, wire bonds, and part of the lead frame, thereby protecting the IC from the ambient environment. An electronic system is typically constructed from multiple packaged IC devices, which are electrically-and physically-coupled to a printing circuit board (xe2x80x9cPCBxe2x80x9d) by leads that form a portion of the lead frame and which extend from the IC package; the PCB including metallic traces for interconnecting the multiple ICs. A relatively new approach to packaging is to place more than one IC in the same package; the multiple IC package is called a Multi-Chip Module (xe2x80x9cMCMxe2x80x9d), or a xe2x80x9chybridxe2x80x9d package.
MCM packages are similar to conventional single-chip package designs. MCM packages, however, house more than one IC by mounting conventional chips on a common substrate, which has metallic paths formed thereon that interconnect the individual chips. A conventional lead frame is connected to terminals on the substrate using a very thin wire, and the substrate and lead frame are then enclosed by an encapsulant to form a protective package.
The current objective in electronic systems is toward smaller, lighter, faster, portable systems; e.g., cellular telephones, pagers, notebook computers. The development of MCMs may play an important role in furthering that objective by eliminating a level of packaging for many components, facilitating the integration of multiple analog and digital technologies in a single module, reducing electromagnetic interference (xe2x80x9cEMIxe2x80x9d) problems, and increasing the input/output (xe2x80x9cI/Oxe2x80x9d) capabilities per chip. Furthermore, chip-to-chip wiring within a MCM is cheaper and faster than PCB wiring and reduces the board area needed for a device.
In some cases, the capabilities of ICs designed for conventional single chip packages is reduced due to a desire to reduce the package size, which necessarily requires reducing the number of package leads. For example, although an IC may process data internally using a plural-conductor (i.e., xe2x80x9cparallelxe2x80x9d) bus, the data may be serialized such that it can be communicated to another IC through only one lead. In an MCM, however, there are no leads associated with individual ICs; i.e., the ICs are coupled internally via very small metallic paths formed on a common substrate that is coupled to a lead frame. Thus, although a principle advantage of MCMs is the capability to integrate many ICs in one package, that advantage is partially diminished if it is necessary to design ICs specifically for use in MCMs, rather than using ICs designed for conventional single-chip packages.
Therefore, what is needed in the art are circuits and methods for employing conventional ICs in MCMs. There is a further need in the art for techniques of integrating conventional ICs in MCMs such that the performance of the conventional ICs is enhanced when employed in an MCM.
To address the above-discussed deficiencies of the prior art, the present invention provides an MCM and methods of operation and manufacture thereof. The MCM includes: (1) a substrate for supporting a plurality of separate integrated circuit (IC) chips thereon, (2) first and second separate IC chips mounted on the substrate, the first separate IC chip including first and second circuit portions coupled together by at least one signal conductor, and (3) interconnecting means that directly couples at least one signal conductor of the first separate IC chip to the second separate IC chip, the interconnecting means bypassing the second circuit portion of the first separate IC chip.
The present invention therefore introduces the broad concept of bypassing circuit portions associated with existing IC chips, when used in an MCM, by providing an interconnecting means that directly couples signal conductors within one IC to another IC within the MCM, rather than using the conventional bonding pads used when an IC is separately-packaged. By directly coupling to signal conductors within an IC, circuit portions of the IC can be selectively-bypassed, which may advantageously increase the overall signal processing speed and/or efficiency of the MCM.
In one embodiment of the present invention, the interconnecting means directly couples at least one signal conductor of one IC to a conventional bonding pad of a second IC. In an alternate embodiment, the second IC chip also includes first and second circuit portions coupled together by at least one signal conductor, and the interconnecting means directly couples at least one signal conductor of the first IC chip to at least one signal conductor of the second IC chip, thereby completely bypassing the conventional bonding pads of both the first and second IC chips. In effect, the internal signal conductors of the ICs are directly coupled together to form a trans-IC bus that spans the MCM. The interconnecting means, therefore, may selectively-bypass conventional bonding pads and/or circuit portions associated with conventional and existing IC chips. In this manner, conventional and existing IC chips may be suitably employed in conventional single-IC packages, as well as MCMs, without modification thereto.
In one embodiment of the present invention, the circuit portions of one or both ICs which are bypassed may be decoupled from a source of electrical power. While not necessary to the broad scope of the present invention, disabling the power to one or more of the circuit portions decreases overall power consumption by the MCM.
In one embodiment of the present invention, a first circuit portion of each of the IC chips is a clock driver circuit for providing a clock signal to a second circuit portion of each of the IC chips, the interconnecting means bypassing the clock driver of one of the IC chips whereby the second circuit portion of that IC chip receives the clock signal from the clock driver of the other IC chip. The operation of multiple IC chips within an MCM from a single clock source helps to ensure the accurate transmission of signals therebetween.
In one embodiment, described in detail hereinafter, a first IC chip includes a plural-conductor bus and a circuit portion that includes a multiplexing circuit and an output buffer, the interconnecting means directly coupling to the plural-conductor bus to thereby bypass the multiplexing circuit and output buffer of the first IC chip. In a related embodiment, a second IC chip includes a plural-conductor bus and a circuit portion that includes an input buffer and a demultiplexing circuit, the interconnecting means directly coupling to the plural-conductor bus to thereby bypass the input buffer and the demultiplexing circuit of the second IC chip. In combination, the related embodiments provide a means of bypassing the circuits necessary to serialize data communications between the ICs when the ICs are separately-packaged; the interconnecting means providing a trans-IC plural-conductor bus that spans the MCM, whereby the transmission efficiency of data between the separate ICs may be improved when employed in an MCM.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.