PLUGGABLE INTEGRATED CIRCUIT PACKAGE

Abstract: A pluggable, high density, reliable integrated circuit package is disclosed. The package has a plurality of integrated circuit chips mounted on a multilayer ceramic substrate. Input-output signals are provided to the module (10) by means of mating male female input-output pins (12) which are located on the bottom of the module (10). Power is provided to the module (10) from a multilayer ceramic frame (20) through an edge connector (27) that is an integral part of the multilayer ceramic substrate. Matching circuit vias (41) located on the edge of the multilayer ceramic substrate (10) and on the edge of the multilayer ceramic frame (20) are cut and tinned with tin-lead (42) to provide power input connections. When the module is plugged into the circuit board (30) the edge connectors (17) on the module (10) mate with the edge connectors (27) in the ceramic frame (20). Since the frame (20) is made of the same material as the module substrate, the power connectors (17, 27) have excellent thermal match and they are highly reliable.

Description: This invention relates to a pluggable high density package for integrated circuits, see e.g. IBM technical disclosure bulletin, Vol. 27, No 10A, March 1985, "Pluggable-Module Power-connection Mechanism", pages 5599-5600. High speed computers require densely packaged integrated circuits. Such packages must be highly reliable and they must provide for physically supporting, interconnecting, and for cooling the integrated circuits. Factors that must be considered in the design of high density packages for integrated circuits include: (a) the number of circuits per chip, (b) the number of chip to module interconnections, (c) the chip power requirements and (d) the number of input-output connections provided by the package. Modern digital computers require a packaging technology that provides a relatively large number of integrated circuit chips in a single package and which provides for literally thousands of I-O connections to the package. Furthermore, the I-O pins must be pluggable so that the package can be removed from a circuit board on which the package is mounted. One modern packaging system used in commercially available high speed digital computers is shown in several articles published during 1981 and 1982 in the IBM Journal of Research and Development , Volume 25 Number 5, Volume 26 Number 1, and Volume 26 Number 3. In particular see: (a) An article entitled "Electronic Packaging Evolution in IBM", IBM Journal of Research and Development , Volume 25, pages 617-629, 1981 by D.P. Seraphim and I. Feinberg, (b) An article entitled "Advanced Printed Circuit Board Design for High Performance Computer Applications", IBM Journal of Research and Development , Volume 26, Pages 302-317, 1982, by R.F. Bonner, J.A. Asselta, and F.W. Haining, and (c) An article entitled "Thermal Conduction Module: A high Performance Multilayer Ceramic Package", IBM Journal of Research and Development , Volume 26, Number 1, Pages 30-37 by A.J. Blodgett and D.R. Barbour. In the module shown in the above articles, power is supplied to the module through the same type of pins that carry signals to the module. This has at least two disadvantages. First, the design of the pins and the pin connectors must take into account both the requirements of signal connections and the requirements of power connections, thereby limiting the design choices available. Second, any pins used for power connections reduces the number of pins available for signal connections. A large variety of other packages for integrated circuits are known in the art. For example, U.S. Patent 3,846,734 (Pauza) shows an example of a dual in-line circuit package. U. S. Patent 3,808,506 (Lang) shows a package with contact pads on both sides of a block. U.S. Patent 3,614,541 (Farrand) shows a board with connectors on multiple sides. U.S. Patent 4,137,559 (Reuting) shows a package with connectors on multiple sides of the package. Other references of general interest which show the state of the art include U.S. Patents 3,634,602 (Bruck), 3,934,959 (Gilissen), 3,795,037 (Luttmer), 3,496,283 (Andrasfay), 3,107,414 (Sterling), 3,105,868 (Feigin), 3,029,495 (Doctor), and 3,643,135 (Devore). There are known circuit packaging technologies where the power connections are separated from the signal connections. Furthermore, as shown in the previously referenced articles in the IBM Journal of Research and Development the use of multilayer ceramic (generally termed MLC) substrates in electronic packages is well known. However, none of the art shows or suggests a structure which has a frame made of MLC and where the power connectors are separated from the signal connectors as with the present invention. Furthermore, none of the known circuit packaging technologies provide the density, reliability and number of I-O connections provided by the present invention. The present invention also provides an improved edge connector for a multilayer ceramic substrate which is not shown or suggested by the prior art. It is the object of the invention to provide a pluggable integrated circuit package having additional input-output pins on a standard TCM module and having the signal input-output pins separated from the power pins thereby allowing the signal pins to be designed to optimize the signal pin requirements and the power connections to be designed to optimize the requirements for power connections. The advantages of the invention are achieved by a pluggable, high density, reliable integrated circuit package. The package has a plurality of integrated circuit chips mounted on a multilayer ceramic substrate. Input-output signals are provided to the module by means of mating male female input-output pins. Power is provided to the module by a separate set of connectors. Male signal input-output pins are brazed to the bottom layer of MLC circuitry in a conventional manner. These pins plug into female connectors which are located on a circuit board. Power is provided to the module from a multilayer ceramic frame through an edge connector that is an integral part of the multilayer ceramic substrate. Matching circuit vias located on the edge of the multilayer ceramic substrate and on the edge of the multilayer ceramic frame are cut and tinned with tin-lead to provide power input connections. When the module is plugged into the circuit board the edge connectors on the module mate with the edge connectors in the ceramic frame. Input-output signals are provided to the module by means of the input-output pins located on the bottom of the module and power is provided to the module by means of the mating connectors on the sides of the module. Since the frame is made of the same material as the module substrate, the power connectors have excellent thermal match and they are highly reliable. In the following the invention is described in detail with reference to the drawings of which Figure 1 is an exploded perspective view of an integrated circuit package built in accordance with the present invention. Figure 2 is a perspective view of an edge connector on a module built in accordance with the present invention. Figure 3 is a top view of an edge connector on a module built in accordance with the present invention. An overall exploded perspective view of a circuit package built in accordance with the present invention is shown in Figure 1. The package includes a circuit module 10, a retainer frame 20 and a multilayer circuit board 30. The structure of module 10 is not shown or explained in detail herein since the module 10 is a modification of the integrated circuit module shown in an article by A.J. Blodgett and D.R. Barbour in the January 1982 issue of the IBM Journal of Research and Development , Volume 26 November 1, pages 30 to 37. The details of how the module is constructed other than as described herein are not particularly relevant to the present invention; however, for completeness the description of the module in the above cited article is hereby incorporated herein by reference. The package shown in the above article is termed a Thermal Conduction Module (abbreviated TCM). It utilizes a 99 × 90 mm multilayer ceramic substrate to interconnect up to 100 logic chips each of which have up to 704 circuits per chip. The module has 1800 pins brazed to the back side of the substrate and it connects to a circuit board through a connector assembly. The 90 mm substrate consists of up to 33 layers of molybdenum metalized alumina. These layers provide for power distribution, impedance controlled interconnection of up to 12000 chip pads, and for wiring to the 1800 module pins. A typical substrate contains 350,000 vias for layer to layer connections and 130 meters of x-y wiring. The total substrate thickness is approximately 5.5 mm. Module 10 includes a plurality of input output pins 12 which are brazed to circuitry at points 15. This is conventional and is as shown in the above cited article in the IBM Journal of Research and Development . It is noted that the pins 12 cover the entire under surface of the module 10 as shown in the above cited reference. Figure 1 only shows a few of the pins for ease of illustration. Module 10 also has a plurality of power connectors 17 on three sides of module 10. These connectors are not part of the module shown in the above referenced article and there structure will be explained in detail later with reference to Figures 2 and 3. Multilayer ceramic frame 20 has power connectors 27 on three sides thereof corresponding to the sides of module 10 which have connectors 17. The structure of multilayer ceramic frame 20 and of connectors 27 will be described in detail later with respect to Figures 2 and 3. A metal support frame 14 which has bolt holes 15 is adapted to hold the entire assembly together. Module 10 includes a plurality of integrated circuit chips (not shown) mounted on a multilayer ceramic substrate. A portion of the multilayer ceramic substrate in module 10 is shown in Figures 2 and 3 and it will be described in detail later. The retainer 20 is made of multilayer ceramic and it has three rows of connectors 27 which are positioned to mate with connectors 17 on module 10. Three rows of circuitry 23, 24 and 25 in frame 20 interconnect the three rows of connectors 27. Circuit lines 21 connect the rows of circuitry 23, 24 and 25 to the connectors 27. It is noted that in Figure 1, the top layers of frame 20 are shown cut away so that the circuitry 21, 23, 24, and 25 can be shown. Pins 29 are connected to circuit lines 23, 24 and 25 using the same technique that is used to braze pins 12 to the circuitry on module 10. Pins 29 plug into a standard connector 29A which supplies power to the frame. Multilayer circuit board 30, only a portion of which is shown, includes a plurality of male connectors 31 which are positioned to mate with pins 12 on module 10. Multilayer circuit board 30 is conventional and is similar to the board shown in the previously referenced IBM Journal of Research and Development . The multilayer ceramic module 10 and the multilayer ceramic frame 20 are built using the same technology used to build conventional multilayer ceramic circuitry. The basic building block used in the multilayer ceramic process is ceramic "green sheets". These sheets consist of a mixture of ceramic and glass powder suspended in an organic binder. They are nominally 0.2 mm or 0.28 mm thick prior to being fired. The green sheets are metalized in the desired patterns by screen printing with a molybdenum powder which is dispersed in a resin and solvent mixture. Following the screening operation the sheets are dried and stacked. The stacked sheets are laminated and sheared to the desired shape and then sintered. This process is conventional and is described in the literature. The details of the connectors 17 on module 10 are shown in Figures 2 and 3. Figure 2 shows one circuit line 40 in the multilayer circuit board in module 10. Circuit line 40 extends to the edge of the circuit board and a through hole via 41 is located at the edge of the board. The via 41 is positioned such that it is cut in half when the stacked sheets are sheared to the final desired shape. With the present invention the process of building multilayer ceramic module 10 and multilayer ceramic frame 20 is identical to the conventional multilayer ceramic process except that a conductive via is located at the edge of the board at each point where one desires a connector 17 or 27. These vias are positioned such that they are cut in half when the board is cut to the required size. As shown in Figure 3, the exposed edge of the conductive via is "tinned" with a tin-lead composition to form the connector 17. This tinning can be done by dipping the edge of the substrate in a molten tin-lead bath. The tin-lead will only adhere to the exposed conductive via. The connectors 27 on frame 20 are formed in the same way. That is, frame 20 is a multilayer ceramic structure with at least three circuit layers. Lines on these circuits are brought out to form connectors 27 in the same way that connectors 17 are formed on module 10 as shown in Figures 2 and 3. It is noted that the lines 23, 24, 25 and 26 shown in Figure 1 are shown schematically in Figure 1 for ease of drawing and clarity of explanation. In fact lines 23, 24, 25 and 26 are circuit lines in a multilayer ceramic circuit structure.

Claims: A pluggable integrated circuit package including a module (10) which has a multilayer ceramic substrate with integrated circuit chips mounted thereon, characterized in that the module (10) has only signal line pins (12) that are connected to the bottom of said substrate, and in that connectors (17) for power input to said module are positioned on at least one side of said module, and in that the package further comprises a multilayer ceramic frame (20) having connectors (27) adapted to mate with the connectors on the sides of said module. The package according to claim 1, characterized in that the connectors (17, 27) are formed by cut conductive vias (41) exposed at the edges of the module and frame respectively, the cut conductive vias of the module being adapted to mate with those of the frame, all cut conductive vias being tinned on the cut surface and connected to a conductor (40) on a ceramic layer.

Inventors: WERBIZKY, GEORGE GREGORY
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1988
Main classification: H05K7
IPC codes: H01L23, H05K7