LIQUID IMMERSION COOLING ASSEMBLY FOR INTEGRATED CIRCUITS

Abstract: Integrated circuit packaging assembly (10) in which a plurality of electrical pins (46) of an integrated circuit package (40, 42) is removably mounted to a corresponding plurality of mating pins (50) each having a receptacle (52) filled with liquid mercury (60), and the temperature is reduced such that the liquid mercury (60) solidifies thereby firmly bonding the electrical pins (46 and 50) together. The mating pins (50) are mounted inside a Dewar type vessel (12) and the assembly is covered with a low temperature liquified gas (20) for the dual purpose of solidifying the liquid mercury (60) and cooling the integrated circuit package (40, 42).

Description: Liquid immersion cooling assembly for integrated circuits. Technical Field This invention relates generally to an integrated circuit packaging assembly. More specifically, this invention provides a means and a method of mounting an integrated circuit package which may have at least 100 pins, and which in some instances may have upwards of 200 pins, within a cryogenic vessel filled with a liquified gas for cooling purposes and/or performance enhancement. It also provides a means and a method for plugging and unplugging the integrated circuit package with ease at room temperatures, yet provides for a sound, reliable electrical and mechanical connection at cryogenic temperatures. A means is provided to thermally isolate the immersed circuit from the outside temperature by using a vacuum insulation vessel with carbon leads that thermally isolate the interconnections. The unique features of the present invention are that it (1) provides for a method of interconnecting an integrated circuit package which is immersed in a liquid, to a printed circuit board assembly that is not immersed, (2) provides for a means of plugging-in and unplugging a multi-pin, "Pin Grid Array (PGA) Package" into a socket with zero force at room temperature that will provide solid reliable electrical and mechanical interconnection at cryogenic temperatures below minus 38.80C using mercury (Hg) as a solder materials, (3) provides for a means of interconnection from an integrated circuit package located in a cold cryogenic temperature to a room temperature printed circuit board assembly using a high electrical conductivity yet low thermal conductivity medium such as carbon, as a buffer medium to minimize thermal conduction out of the cryogenic chamber through the electrical interconnection, and (4) provides for a protective enclosure for the cryogenic, package to meet safety requirements. Disclosure of the Invention It is an object of the present invention to provide a cryogenic packaging assembly which permits easy insertion and removal of an integrated circuit package to and from a circuit board. Thus, according to the invention, there is provided an integrated circuit packaging assembly including an integrated circuit package having a plurality of electrical pins, characterized by a thermally insulating vessel containing an electrically non-conductive liquified gas having a temperature lower than the solidification temperature of mercury; a plurality of mating pins fixed relative to said vessel and each having a cup portion at one end disposed inside said vessel for receiving a respective one of said plurality of electrical pins, said pins being held in said cup portions by mercury solidified at the low temperature of said liquified gas; and connecting means for electrically coupling and thermally insulating each of said plurality of mating pins with respect to circuitry external of said vessel. Brief Description of the Drawings One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a full sectioned view of the -integrated circuit packaging assembly according to the invention. Fig. 2 is an enlarged view of a portion of the assembly of Fig. 1. Best Mode for Carrying out the Invention Referring to Figs. 1 and 2, the integrated circuit packaging assembly is shown generally as item 10 and includes a vessel 12 which may be a Dewar vessel having a closed but removable top 14 into which vessel is placed a low temperature liquified gas 20 such as nitrogen, Freon, argon or helium to form a cryogenic chamber. Within the vessel 12 is positioned an IC chip 40 mounted on a carrier 42 to form a package having electrical conductors 44 and a plurality of electrical connecting pins 46. A corresponding plurality of openings 58 are formed through the wall of the vessel 12. A corresponding number of pins 50, each having an open receiver portion 52 shaped as a cup, are embedded in an electrically conductive and thermally insulating material 54 which fills the openings 58.. The open cup portions 52 are partially filled with mercury 60. The material 54 may be carbon which functions as a buffer medium to minimize thermal conduction out of the cryogenic chamber through the electrical interconnections. A corresponding plurality of electrical connector pins 56 are inserted into the carbon material and extend outwards from the vessel 12. These connector pins are configured and positioned so as to mate with the connector pins 72 mounted in a receiving socket 70. Each of the pins 72 has a projecting portion 74 designed to mate with conductors on a PC board 80 and to be soldered to a conductor at 82. To insert the electrical pins 46 of the integrated circuit package into the open cup portions 52 with a zero force, the temperature of the mercury 60 is raised to a temperature above minus 38.80C since the mercury in the cup portions 52 of the pins 50 is in a liquid state at these temperatures. The integrated circuit package 40 can then either be inserted and/or removed and a new integrated circuit package inserted without the necessity of unsoldering all of the conductors. Once the integrated cif ' cuit package 40 is in place, the temperature is lowered causing the mercury to solidify, thus forming an electrical and mechanical connection similar to that of tin/lead eutectic solder. The tube 18 extending through the top of 14 of the vessel 12 is used to take off the liquified gas commonly call the boil-off so that the gas can be reprocessed to form it back into a liquid and to reinject it, via the tube 16, back into the vessel 12.

Claims: CLAIMS : 1. An integrated circuit packaging assembly (10) including an integrated circuit package (40, 42, 44) having a plurality of electrical pins (46), characterized by a thermally insulating vessel (12) containing an electrically non-conductive liquified gas (20) having a temperature lower that the solidification temperature of mercury; a plurality of • mating pins (50) fixed relative to said vessel (12) and each having a cup portion (52) at one end disposed inside said vessel for receiving a respective one of said plurality of electrical pins (46), said pins (46) being held in said cup portions (52) by mercury solidified at the low temperature of said liquified gas (20); and connecting means (54, 56) for electrically coupling and thermally insulating each of said plurality of mating pins (50) with respect to circuitry (80) external of said vessel. 2. An assembly according to claim 1, charaterized in that said connecting means (54, 56) includes a low thermal conductivity, electrically conductive, material (54) filling each one of a plurality of openings (58) extending through said vessel (12) and corresponding in number with- the number of electrical pins (46) of said integrated circuit package (40, 42, 44), wherein the other end of each of said mating pins (50) is embedded in said low thermal conductivity, eletrically conductive, materials (54) contained in a respective opening (58). 3. An assembly according to claim 2, characterized in that said low thermal conductivity, electrically conductive, material (54) is carbon. 4. An assembly according to claim 2, characterized in that said connecting means (54, 56) further includes a plurality of electrically conductive connector pins (56) each embedded at one end in said low thermal conductivity, electrically conductive, material (54) and projecting outwardly from said vessel (12); and in that said circuitry (80) external to said vessel (12) includes a pin grid array socket (70, 72, 74) for receiving said connector pins (56) to facilitate the electrical connection of said integrated circuit assembly to a printed circuit board. 5. An assembly according to claim 4, characterized in that said pin grid array socket (70, 72, 74) includes a plurality of receiving pins each having a portion (72) for receiving a corresponding connector pin (56) and a projecting portion (74) arranged to be connected and soldered (82) to respective conductors on said printed circuit board (80). 6. An assembly according to claim 1, characterized in that said vessel is a Dewar vessel (12) having a emovable-top (14) and in which said liquified gas (20) covers said integrated circuit package (40, 42, 44, 46) and the mercury (60) contained in said cup portions (52). 7. An assembly according to claim 1, characterized in that the number of electrical pins (46) of said integrated circuit package is at least 100. 8. An assembly according to claim 7, characterized in that the number of electrical pins (46) of said integrated circuit package is at least 200. 9. An assembly according to claim 1, characterized in that said liquified gas selected from nitrogen, Freon, argon and helium. 10. A method of mounting an integrated circuit package (40, 42, 44, 46) in an integrated circuit packaging assembly (10) according to any one of claims 1 to 9, characterized by inserting each pin (46) of said integrated circuit package (40, 42, 44, 46) into liquid mercury (60) contained in the cup portion (52) of a respective mating pin (50), and solidifying the liquid mercury (60) by immersing said integrated circuit package (40, 42, 44, 46) and the mercury-containing cup portions (52) in said liquified gas (20) so as to bond rigidly each pin (46) of said integrated circuit package (40, 42, 44, 46) to a respective mating pin (50). 11. A method of removing an integrated circuit package (40, 42, 44, 46) from an integrated circuit packaging assembly (10) according to any one of claims 1 to 9, characterized by increasing the temperature within said -vessel (12) so as to liquify the mercury (60) contained in each cup portion (52) to permit removal of each pin (46) of said integrated circuit package (40, 42, 44, 46) from the cup portion (52) of a respective mating pin (50).

Inventors: LAUFFER DONALD KEITH, SANWO IKUO JIMMY, TIPON DONALD GREATHOUSE, LAUFFER, DONALD, KEITH, SANWO, IKUO, JIMMY, TIPON, DONALD, GREATHOUSE
Applicants: NCR CO, NCR CORPORATION
Application year: 1988
Main classification: H01L23
IPC codes: H01L23, H01R12, H05K7