Method and Apparatus for Cooling an Integrated Circuit Chip During Testing

1. Field of the Invention

The present invention relates to a method and apparatus for cooling an integrated circuit device which is mounted in a socket for testing. More particularly, the present invention relates to a cooling chuck system which thermally engages an integrated circuit device during testing to maintain it at a stable temperature.

2. Description of the Prior Art

In high speed super computers of the type produced by Cray Research, Inc., the assignee of this application, banks of printed circuit boards containing integrated circuit devices are used to complete the circuitry which enables high speed calculations to be performed. As computer design evolves toward circuitry of ever increasing density, the operating temperature thereof becomes higher and cooling systems must be integrated into the physical packing which is provided for the circuitry. By using various different methods, the actual operating temperature of any particular integrated circuit within the computer can be estimated.

Prior to beginning actual production of an expensive, complicate super computer, it is essential that each individual integrated circuit device be tested at its estimated operating temperature to ensure against temperature caused failure. From a cost standpoint, it is important that such testing be conducted quickly and efficiently. It is clear that there has existed a long and unfilled need in the prior art for an integrated circuit cooling apparatus and method to determine the actual performance of an integrated circuit device at a predetermined temperature.

Accordingly, it is an object of the present invention to provide an integrated circuit cooling apparatus and method to determine the actual performance of an integrated circuit device at a predetermined temperature.

In order to achieve the foregoing object, an apparatus according to the instant invention is for dissipating thermal energy produced by a board mounted electronic device or the like during testing, comprising a chuck holder body having a board defined therein; a cooling chuck for conducting heat from the electronic device to the chuck holder body, the cooling chuck being slidably received within the chuck holder bore; structure adapted for mounting the chuck holder body to the board; and structure for extending the cooling chuck within the chuck holder bore toward the electronic device, whereby the temperature of the electronic device is controlled during testing.

According to the instant invention, a method for testing an integrated circuit device includes providing a testing assembly including a test board adapted for receiving the integrated circuit device, a chuck holder body having a board defined therein, cooling chuck structure slidably received in the chuck holder bore, structure for mounting the chuck holder body to the board and structure for extending the cooling chuck structure within the chuck holder bore toward the test board; using the mounting structure to mount the chuck holder body to the test board; presetting the cooling chuck structure to a predetermined temperature; inserting the integrated circuit device into the test board; extending the cooling chuck structure with the extending structure to establish thermal contact between the cooling chuck structure and the integrated circuit device; and maintaining the cooling chuck structure at the predetermined temperature while testing, whereby operation of the integrated circuit device may be tested at the predetermined temperature.

These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.

FIG. 1 is a schematic view of an apparatus constructed according to the preferred embodiment of the invention;

FIG. 2 is a cross-sectional view of the chuck holder body illustrated in FIG. 1;

FIG. 3 is a top view of a cooling chuck according to the instant invention, taken in cross-section along lines 3--3 in FIG. 4;

FIG. 4 is a side cross-sectional view of the cooling chuck shown in FIG. 3, taken along lines 4--4 in FIG. 3;

FIG. 5 is a top view of the cooling chuck body illustrated in FIG. 2;

FIG. 6 is a cross-sectional view of the alignment screws of the invention; and

FIG. 7 is a cross-sectional view of a thermally conductive pad constructed according to the invention.

Referring now to the drawings, wherein like reference numerals designate corresponding elements throughout the views, and particularly referring to FIG. 1, an improved device for regulating the temperature of an integrated circuit device during testing is shown. Integrated circuit testing and cooling chuck system 10 includes a test board 12 having a test socket 14 in which an integrated circuit device 16 may be mounted. Testing and cooling chuck system 10 includes a chuck holder body 18 which is supported and aligned with respect to test socket 14 by a plurality of alignment screws 20, as will be further described below. A corresponding number of locking nuts 22 are provided to axially fix alignment screws 20 with respect to chuck body 18. Alignment screws 20 are secured to test socket 14 and test board 12 by means of a corresponding number of bolts or studs 24 which extend into an internal threaded portion of the alignment screws 20.

Referring again to FIG. 1, testing system 10 includes a cooling chuck ram 26 which is disposed for sliding movement within a cylindrical bore 46 defined in chuck body 18, as may be seen in FIG. 2. Chuck holder body 18 further has a coolant inlet 30 defined in a lower portion thereof having an inlet port 44 which is in communication with a lower portion of the cylindrical bore 46. A coolant outlet 32 is defined in a side wall portion of chuck holder body 18 and is also in communication with cylindrical bore 46, as may be seen in FIG. 1. A coolant circuit 34 is provided to circulate a cooling fluid between the coolant inlet 30 and coolant outlet 32 of the chuck holder body 18. Coolant circuit 34 includes a chiller unit 36 which is of conventional design and capable of regulating the temperature of a coolant flowing through coolant circuit 34. A pump 38 is provided to circulate coolant within the coolant circuit 34, and a fluid control valve 40 which is preferably solenoid actuated. Valve 40 is shiftable between a first position in which fluid is directed through an operative path 43 into the chuck body or a second position in which the coolant is directed through a bypass path 41, as is shown in FIG. 1. Valve 40 may be conveniently controlled through a remote switch 42, which, in the preferred embodiment, is actuatable by the foot of an operator In operation, the coolant fluid may be circulated through bypass path 41 until it reaches a predetermined temperature, at which time it may be shifted to flow through path 43 and chuck holder body 18.

As also shown in FIG. 2, chuck holder body 18 includes a plurality of tapped holes 50 about an upper peripheral surface thereof, which extend in a direction parallel to the axis of cylindrical bore 46. As is best seen in FIG. 5, cooling chuck ram 26 is held within chuck body 18 by a retaining ring 78. Retaining ring 78 is secured with respect to chuck body 18 by a plurality of bolts which extend into a corresponding number of mounting holes 52. In the preferred embodiment, there are four such mounting holes, and four tapped holes 50.

Referring to FIG. 4, the cooling chuck ram 26 will now be described in detail. Ram 26 includes a longitudinally extending body portion 54 having an upper enlarged portion 56 and a lower enlarged portion 58. Upper and lower enlarged portions 56, 58 are both formed to have a radial cross-section and to sealingly engage the wall defining cylindrical chuck holder bore 46. To that end, a number of annular recesses 60 are formed circumferentially about each of the upper and lower enlarged portions 56, 58 for receiving a corresponding number of 0-rings 62 therein in order to provide a tight seal with the surface defining bore 46. As may be seen in FIG. 1, a space 64 is defined by the surface which defines cylindrical bore 46, the upper enlarged portion 56 and the lower enlarged portion 58. Chuck body 18 and ram 26 are so formed so that space 64 is always in communication with the outlet port 48 formed in the side of chuck body 18.

Referring again to FIG. 4, a longitudinal bore 66 is defined in ram 26 so as to communicate with the portion of bore 46 beneath the ram. Ram 26 further includes a thermally conductive top cap member 68 which is preferably formed of copper or another material having high thermal conductivity. A chamber 70 is defined between top cap 68 and the remainder of ram 26, which is in communication with the longitudinal bore 66. A plurality of return passages, of which there are four in the illustrated embodiment, communicate with chamber 70 and the portion of the longitudinally extending body section of ram 26 which is between enlarged portions 56 and 58. Return passages 72 open out into space 64 through a corresponding number of orifices 74 which are defined in the wall of elongate body portion 54. Top cap 68 preferably has a flat upper surface 76 that is adapted to bear against an integrated circuit device or a heat transfer facilitation medium 28 which is placed between top cap 68 and the integrated circuit device.

Referring to FIGS. 1 and 6, alignment screws 20 each preferably have a first end portion with external threads 84 formed thereon for threaded insertion into a corresponding tapped hole 50. Alignment screws 20 further have a second end portion 82 with a bore formed therein having internal threads 86. The bores bearing internal threads 86 are sized to receive the bolts or studs 24 which are used to secure alignment screws 20 to the test socket 14 and test board 12.

According to the preferred method of the present invention, cooling chuck body 18 is first secured to the underside of test board 12, as is shown in FIG. 1. Preferably, only three alignment screws 20 are used to effect such mounting, so that a planar stability which is characteristic of three point connections is achieved At approximately the same time, the chiller unit 36 is turned on and coolant is allowed to flow in a circuitous path through passage 43 and chuck body 18 to set the coolant and cooling chuck ram 26 at a predetermined temperature. Due to the piston-cylinder action between cooling chuck ram 26 and chuck body 18, the cooling chuck ram 26 will be at its upper most position during this period. The chiller must run for approximately five minutes before any testing is done to allow the fluid temperature to stabilize.

Once the temperature of the coolant and cooling chuck ram 26 reaches its predetermined value, foot switch 42 may be actuated to cause fluid control valve 40 to direct flow of the coolant through bypass passage 41 rather than through the operative path 43, so that flow of the coolant bypasses cooling chuck body 18. In this way, the pressurization of the lower portion of cylindrical bore 46 is relieved, allowing cooling chuck ram 26 to drop into its lowermost position. At this time, the heat transfer facilitation mechanism 28, which, for example, may be a thermally conductive oil, may be placed upon the top surface 76 of the thermally conductive top cap 68. The foot switch 42 may then be actuated to cause fluid control valve 40 to return fluid flow through cooling chuck body 18, whereby cooling chuck ram 26 again rises and bears against the integrated circuit device 16 so as to establish a thermal connection therewith. Operation of integrated circuit 16 may then be tested at a controlled operating temperature as desired. When tests have been completed, foot switch 42 may be actuated to cause valve 40 to go into its bypass mode, so that coolant ceases to flow through chuck body 18 and cooling chuck ram 26 again drops to its lower position. At this time, the integrated circuit device 16 may be removed from test socket 14 and the process can be repeated if desired

In order to adjust the rate of cooling which is provided at cooling chuck ram 26, the capacity of chiller unit 36 may be adjusted In addition, the rate of coolant flow through circuit 34 may be controlled, as may be the fluid pressure within coolant circuit 34. By varying these factors singularly or in combination, the present invention makes it possible to test a large number of integrated circuit devices at various operating temperatures which correspond to their predicted operating temperature in their proposed environment. As a result, a great deal of time and effort is eliminated from the testing process that is necessary for the development of sophisticated electronic devices such as the next generation of super computers.

According to a second embodiment of the invention, heat transfer facilitation mechanism 28 is formed as a thermally conductive pad 100. Pad 100 preferably has a thin outer layer 102 which is formed of polyethylene or an equivalent polymer, and an inner core of thermally conductive grease 104 sealed within outer layer 102. Use of pad 100 in lieu of a thermally conductive oil obviates the need to clean the integrated circuit device after testing, which further enhances the efficiency of the testing process. Preferably, outer layer 102 should have sufficient resiliency to prevent leakage or bursting of the pad 100 when pressure is applied to the pad 100 during testing. The grease 104 is preferably a commercially available silicone based grease such as Castell 802.RTM..

It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.