Abstract:
A mechanical assembly for regulating the temperature of an IC-chip in an IC-module includes: a) a heat-exchanger having a first face for contacting a second face on the IC-module; and b) a gimbal, coupled to the heat-exchanger, for tilting and pressing the first face flatly against the second face, as the first and second faces are moved from a spaced-apart position to an engaged position at which the IC-chip temperature is regulated. In addition, the mechanical assembly further includes an output tube, coupled to an output port on the heat-exchanger, which has two ends that move relative to each other as the first and second faces move from the spaced-apart position to the engaged position; and, this output tube is coiled into a weak spring which is characterized by a stiffness matrix that is limited by a predetermined acceptance criterion.

Description:
RELATED CASES 
   The present invention is related to another invention, by the current inventors, which is entitled “Dual Feedback Control System For Maintaining The Temperature Of An IC-Chip Near A Set-Point”. A patent application on this related invention was filed in the USPTO, on Feb. 16, 2004, and it is assigned Ser. No. 10/780,417. This related patent application is herein referred to as the &#39;417 application. 
   BACKGROUND OF THE INVENTION 
   The present invention is a mechanical assembly, for regulating the temperature of an integrated circuit chip (IC-chip), having a gimbaled heat-exchanger with coiled spring conduits. This mechanical assembly has use in electromechanical systems that test IC-chips. 
   Today, a single state-of-the-art IC-chip can contain more than one-hundred-million transistors, and those transistors must be tested before the IC-chip is sold to a customer. Usually, each IC-chip is incorporated into an integrated circuit module (IC-module), and then the IC-chip in the IC-module is tested with a “burn-in” test, a “class” test, and a “system level” test. In one type of IC-module, the IC-chip is attached to a substrate and covered with a lid. In another type of IC-module, the IC-chip is attached to the substrate, but the IC-chip is not covered with any lid. In either case, electrical terminals are provided on the substrate which are connected by microscopic conductors in the substrate to the IC-chip. 
   The “burn-in” test thermally and electrically stresses the IC-chips to accelerate “infant mortality” failures. The stressing causes immediate failures that otherwise would occur during the first 10% of the IC-chips&#39; life in the field, thereby insuring a more reliable product for the customer. The burn-in test can take many hours to perform, and the temperature of the IC-chip typically is held in the 90° C. to 140° C. range. Because the IC-chips are also subjected to higher than normal voltages, the power dissipation in the IC-chip can be significantly higher than in normal operation. This extra power dissipation makes the task of controlling the temperature of the IC-chip very difficult. Further, in order to minimize the time required for burn-in, it is also desirable to keep the temperature of the IC-chip as high as possible without damaging the IC-chip. 
   The “class” test usually follows the burn-in test. Here, the IC-chips are speed sorted and the basic function of each IC-chip is verified. During this test, power dissipation in the IC-chip can vary wildly as the IC-chip is sent a stream of test signals. Because the operation of an IC-chip slows down as the temperature of the IC-chip increases, very tight temperature control of the IC-chip is required throughout the class test. This insures that the speed at which the IC-chip operates is measured precisely at a specified temperature. If the IC-chip temperature is too high, the operation of the IC-chip will get a slower speed rating. Then the IC-chip will be sold as a lower priced part. 
   The “system level” test is the final test. Here, the IC-chips are exercised using software applications which are typical for a product that incorporates the IC-chips. In the system level test, the IC-chips are tested over a temperature range that can occur under normal operating conditions, i.e. approximately 20°-80° C. 
   In the &#39;417 application, FIG. 1 shows an entire control system for maintaining the temperature of an IC-chip near a set-point while the above tests are performed. That FIG. 1 system includes an electric heater, an evaporator, an input conduit, and an output conduit, all of which are connected together to form one heat-exchanger. The present invention is a mechanical assembly which constitutes a novel physical implementation of the heat-exchanger. 
   For ease of reference, FIG. 1 of the &#39;417 application is reproduced here as  FIG. 1 . Also, TABLE 1 from the &#39;417 application, which identifies all of the components in FIG. 1, is reproduced below. 
   
     
       
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Component 
               Description 
             
             
                 
             
           
           
             
               20 
               Component 20 is a thin, 
             
             
                 
               flat electric heater. The 
             
             
                 
               heater 20 has one flat face 
             
             
                 
               which contacts the IC-chip 
             
             
                 
               10, and it has an opposite 
             
             
                 
               flat face which is 
             
             
                 
               connected directly to 
             
             
                 
               component 21. Electrical 
             
             
                 
               power P H  is sent to the 
             
             
                 
               heater 20 on conductors 
             
             
                 
               20a. The temperature of 
             
             
                 
               the heater 20 is detected 
             
             
                 
               by a sensor 20b in the 
             
             
                 
               heater 20. This 
             
             
                 
               temperature is indicated by 
             
             
                 
               a signal ST H  on conductors 
             
             
                 
               20c. 
             
             
               21 
               Component 21 is an 
             
             
                 
               evaporator for a 
             
             
                 
               refrigerant. The 
             
             
                 
               refrigerant enters the 
             
             
                 
               evaporator 21 in a liquid 
             
             
                 
               state through a conduit 
             
             
                 
               21a, and the refrigerant 
             
             
                 
               exits the evaporator 21 in 
             
             
                 
               a gas state through a 
             
             
                 
               conduit 21b. The 
             
             
                 
               temperature of the 
             
             
                 
               evaporator 21 is detected 
             
             
                 
               by a sensor 21c on the 
             
             
                 
               exterior of the evaporator. 
             
             
                 
               This temperature is 
             
             
                 
               indicated by a signal ST E  on 
             
             
                 
               conductors 21d. 
             
             
               22 
               Component 22 is a valve 
             
             
                 
               which receives the 
             
             
                 
               refrigerant in a liquid 
             
             
                 
               state from a conduit 22a, 
             
             
                 
               and which passes that 
             
             
                 
               refrigerant at a selectable 
             
             
                 
               flow rate to the conduit 
             
             
                 
               21a. The flow rate through 
             
             
                 
               the valve 22 is selected by 
             
             
                 
               a control signal SF V  on 
             
             
                 
               conductors 22b. In one 
             
             
                 
               embodiment, the signal SF V   
             
             
                 
               is a pulse modulated 
             
             
                 
               signal, and the valve 22 
             
             
                 
               opens for the duration of 
             
             
                 
               each pulse. In another 
             
             
                 
               embodiment, the signal SF V   
             
             
                 
               is an amplitude modulated 
             
             
                 
               analog signal, and the 
             
             
                 
               valve 22 opens to a degree 
             
             
                 
               that is proportional to the 
             
             
                 
               amplitude of the signal. 
             
             
               23 
               Component 23 is a 
             
             
                 
               compressor-condenser which 
             
             
                 
               has an input that is 
             
             
                 
               connected to conduit 21b, 
             
             
                 
               and an output that is 
             
             
                 
               connected to conduit 22a. 
             
             
                 
               The compressor-condenser 23 
             
             
                 
               receives the refrigerant in 
             
             
                 
               the gas state, and then 
             
             
                 
               compresses and condenses 
             
             
                 
               that refrigerant to the 
             
             
                 
               liquid state. 
             
             
               24 
               Component 24 is a socket 
             
             
                 
               which holds the substrate 
             
             
                 
               11. Electrical conductors 
             
             
                 
               24a, 24b and 24c pass 
             
             
                 
               through the socket to the 
             
             
                 
               IC-chip 10. The conductors 
             
             
                 
               24a carry test signals to 
             
             
                 
               and from the IC-chip 10. 
             
             
                 
               The conductors 24b carry 
             
             
                 
               electrical power P C  to the 
             
             
                 
               IC-chip 10. The conductors 
             
             
                 
               24c carry signals ST C  which 
             
             
                 
               indicate the temperature of 
             
             
                 
               the IC-chip 10. These 
             
             
                 
               signals ST C  are generated by 
             
             
                 
               a temperature sensor 10a 
             
             
                 
               that is integrated into the 
             
             
                 
               IC-chip 10. 
             
             
               25 
               Component 25 is a power 
             
             
                 
               supply which sends the 
             
             
                 
               power P H  to the electric 
             
             
                 
               heater 20 with a selectable 
             
             
                 
               magnitude. The amount of 
             
             
                 
               power that is sent at any 
             
             
                 
               instant is selected by a 
             
             
                 
               signal SP H  on conductors 
             
             
                 
               25a. 
             
             
               26 
               Component 26 is a control 
             
             
                 
               circuit for the heater 
             
             
                 
               power supply 25. This 
             
             
                 
               control circuit 26 
             
             
                 
               generates the signal SP H  on 
             
             
                 
               the conductors 25a in 
             
             
                 
               response to the signals ST E , 
             
             
                 
               ST H  , ST C , and SP which it 
             
             
                 
               receives on the conductors 
             
             
                 
               21d, 20c, 24c and 26a. The 
             
             
                 
               signal SP indicates a set- 
             
             
                 
               point temperature at which 
             
             
                 
               the IC-chip 10 is to be 
             
             
                 
               maintained. The control 
             
             
                 
               circuit 26, together with 
             
             
                 
               the power supply 25 and the 
             
             
                 
               electric heater 20, form a 
             
             
                 
               first feedback loop in the 
             
             
                 
               FIG. 1 control system. 
             
             
                 
               This first feedback loop 
             
             
                 
               quickly compensates for 
             
             
                 
               changes in power 
             
             
                 
               dissipation in the IC-chip 
             
             
                 
               10 and thereby maintains 
             
             
                 
               the temperature of the IC- 
             
             
                 
               chip 10 near the set-point. 
             
             
               27 
               Component 27 is a control 
             
             
                 
               circuit for the valve 22. 
             
             
                 
               This control circuit 27 
             
             
                 
               generates the signal SF V  on 
             
             
                 
               the conductors 22b in 
             
             
                 
               response to the signals SP H , 
             
             
                 
               ST E , and SP which it 
             
             
                 
               receives on the conductors 
             
             
                 
               25a, 21d, and 26a. The 
             
             
                 
               control circuit 27, 
             
             
                 
               together with the valve 22 
             
             
                 
               and the evaporator 21, form 
             
             
                 
               a second feedback loop in 
             
             
                 
               the FIG. 1 control system. 
             
             
                 
               This second feedback loop 
             
             
                 
               passes the liquid 
             
             
                 
               refrigerant through the 
             
             
                 
               evaporator with a variable 
             
             
                 
               flow rate that reduces the 
             
             
                 
               overall usage of electrical 
             
             
                 
               power in the FIG. 1 system. 
             
             
                 
             
           
        
       
     
   
   In the &#39;417 application, the invention focuses on the first and second feedback loops which are identified in TABLE 1 under components 26 and 27. With those two feedback loops, the temperature of the IC-chip is maintained near the set-point, and the overall power usage in the FIG. 1 system is greatly reduced. This is achieved independently of any particular physical implementation of the heat-exchanger components 20, 21, 21a, and 21b. 
   By comparison, the present invention focuses entirely on a physical implementation for the heat-exchanger components 20, 21, 21a, and 21b. With this physical implementation, certain interface problems are avoided which can occur at the pressed joint between the electric heater  20  and the IC-chip  10 . These interface problems are described herein in the BRIEF SUMMARY OF THE INVENTION and the DETAILED DESCRIPTION. 
   Accordingly, a primary object of the present invention is to provide a mechanical assembly, which is a heat-exchanger for controlling the temperature of an IC-chip, having a novel physical structure which overcomes the above interface problems. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is a mechanical assembly for regulating the temperature of an IC-chip in an IC-module. This mechanical assembly is of the type that includes: a) a heat-exchanger having a first face for contacting a second face on the IC-module; and b) a gimbal coupled to the heat-exchanger, for tilting and pressing the first face flatly against the second face, as the first and second faces are moved from a spaced-apart position to an engaged position. 
   In one preferred embodiment, this mechanical assembly also includes a coiled input tube and a coiled output tube. The coiled input tube has one end coupled to an input port on the heat-exchanger and has another end coupled to a source for a coolant. The coiled output tube has one end coupled to an output port on the heat-exchanger and has another end coupled to return the coolant to the source. In this preferred embodiment, the coiled input tube and the coiled output tube are springs which are so weak that their one end can move relative to their other end without exerting any significant force or torque on the heat-exchanger as the first and second faces move from the spaced-apart position to the engaged position. To achieve this, each spring has a respective stiffness matrix that is limited by a pre-determined acceptance criterion. 
   If the input tube and/or the output tube are not coiled, those tubes can be so stiff that they will prevent the first face of the heat-exchanger from always lying flatly against the second face of the IC-chip. When those two faces do not lie flatly against each other the thermal resistance between those two faces will increase. But as that thermal resistance increases, the ability of the heat-exchanger to regulate the temperature of the IC-chip is degraded. 
   The above interface problem is most severe when the heat-exchanger includes an evaporator for the coolant, and the coolant in the input tube is in a liquid state whereas the coolant in the output tube is in a gas state. In that case, the tubes must be strong enough to withstand coolant pressures which occur in refrigeration systems. The coolant pressure in the input tube is typically at least 100 psi more than the coolant pressure in the output tube when the system is operating, and the coolant pressure in both tubes is typically at least 50 psi when the system is off. One candidate for handling such pressures is tubes which have metal walls, but such metal-walled tubing is stiff. 
   In addition, to ensure that the gas in the output tube is at low pressure, the output tube needs to have a large diameter. In one embodiment, the diameter of the output tube is one-quarter of an inch, whereas the diameter of the input tube is only one-sixteenth of an inch. Preferably, the diameter of the output tube is at least twice the diameter of the input tube, but this large diameter also tends to make the output tube stiff. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a control system, for maintaining the temperature of an IC-chip near a set-point, which includes a heat-exchanger that is the subject of the present invention. 
       FIG. 2  shows a three-dimensional view of one preferred physical implementation for the heat-exchanger in the  FIG. 2  control system. 
       FIG. 3A  shows a side view of certain parts in the heat-exchanger of  FIG. 2 , when that heat-exchanger is spaced-apart from (and not pressing against) an IC-chip. 
       FIG. 3B  shows a side view of certain parts in the heat-exchanger of  FIG. 2 , when that heat-exchanger is pressing against an IC-chip. 
       FIG. 4  illustrates various movements which are made by the ends of two coiled tubes in the heat-exchanger of  FIG. 2 . 
       FIG. 5  is a set of equations which define certain limits for the movements of the ends of the coiled spiral tube in the heat-exchanger of  FIG. 2 . 
       FIG. 6  is a set of equations which define certain limits for the movements of the ends of the coiled cylindrical tube in the heat-exchanger of  FIG. 2 . 
       FIG. 7A  shows the first three steps of an eight step process by which physical parameters are determined for the two coiled tubes in the heat-exchanger of  FIG. 2 . 
       FIG. 7B  shows the next two steps of an eight step process by which physical parameters are determined for the two coiled tubes in the heat-exchanger of  FIG. 2 . 
       FIG. 7C  shows the remaining three steps of an eight step process by which physical parameters are determined for the two coiled tubes in the heat-exchanger of  FIG. 2 . 
   

   DETAILED DESCRIPTION 
   To begin this Detailed Description, reference should now be made to  FIG. 2 . There, a mechanical assembly is shown which is one preferred embodiment of the present invention. 
   In  FIG. 2 , item  20  is a physical implementation of the electric heater  20  that is shown schematically in  FIG. 1 . Also, item  21  in  FIG. 2  is a physical implementation of the evaporator  21  that is shown schematically in  FIG. 1 . Further, item  22  in  FIG. 2  is a physical implementation of the control valve  22  that is shown schematically in  FIG. 1 . 
   Items  21   a - 1 ,  21   a - 2 , and  21   a - 3  in  FIG. 2  together constitute a physical implementation of the input conduit  21   a  that is shown schematically in  FIG. 1 . Item  21   a - 1  is the central portion of the conduit  21   a . This central portion  21   a - 1  is a tube which is coiled into a cylindrical spring. One end  21   a - 2  of this cylindrically coiled tube  21   a - 1  connects to an input port on the evaporator  21 , and the opposite end  21   a - 3  connects to an output port on the control valve  22 . 
   Similarly, items  21   b - 1 ,  21   b - 2 , and  21   b - 3  in  FIG. 2  together constitute a physical implementation of the output conduit  21   b  that is shown schematically in  FIG. 1 . Item  21   b - 1  is the central portion of the conduit  21   b . This central portion  21   b - 1  is a tube which is coiled into a spiral spring. One end  21   b - 2  of this spiral coiled tube  21   b - 1  connects to an output port on the evaporator  21 , and the opposite end  21   b - 3  connects to the compressor/condenser  23  (shown in  FIG. 1  but not shown in  FIG. 2 ). 
   Further in  FIG. 2 , items  30 ,  31 , and  32  together constitute a portion of a gimbal. Other parts of this gimbal are hidden from view in  FIG. 2 , but they are shown in  FIGS. 3A and 3B . Note that in  FIGS. 3A and 3B , the springy central section  21   a - 1  of the input conduit  21   a  and the springy central section  21   b - 1  of the output conduit  21   b  are not shown because they would hide the gimbal. 
   Item  30  is a base plate in the gimbal. Four support legs  31  are connected to the upward facing surface of the base plate  30 . The open ends of these support legs  31  can be connected to a stationary frame if a mechanism is provided which moves the socket  24  for the IC-chip  10  up and down. Alternatively, the open ends of the support legs  31  can be connected to a mechanism which moves those legs up and down if the socket  24  for the IC-chip  10  is held stationary. 
   The output port on the evaporator  21  passes loosely through a central hole (not shown) in the base plate  30  and connects to end  21   b - 2  of the spiral coiled tube  21   b - 1 . Also, three guides  32  respectively pass through three additional holes (not shown) in the base plate  30  which are spaced around the central hole. These guides  32  are best seen in  FIGS. 3A and 3B . 
   Each guide  32  slides loosely in its corresponding hole. One end of each guide is attached to the evaporator  21 . The opposite end of each guide  32  is open and has a flange which tapers outward. This tapered flange stops the guide from passing through its hole and centers the guide in its hole. 
   Item  33  is a cylindrically coiled spring which is hidden in  FIG. 2 , but which is seen in  FIGS. 3A  and  3 B. The output port of the evaporator  21  passes loosely through the coils of the spring  33 . One end of the spring  33  presses against the base plate  30 , and the opposite end of the spring  33  presses against the evaporator  21 . 
   Consider now how all of the components in the  FIG. 2  mechanical assembly move, as that assembly is used to regulate the temperature of IC-chips in the system of  FIG. 1 . When any one IC-chip  10  is being tested, the heater  20  must lie flat against that chip. If the heater  20  and the IC-chip  10  are at a slight angle with respect to each other, then the thermal resistance between the heater  20  and the IC-chip  10  will be so large that the first and second feedback loops in the  FIG. 1  system (which were identified in the Background) will not work properly. 
   After the testing of any one IC-chip  10  is completed, the heater  20  and the IC-chip  10  must then be separated. This enables the IC-chip  10  which was just tested to be removed, on its substrate  11 , from the socket  24 . Then the next IC-chip  10  that is to be tested can be inserted, on its substrate  11 , into the socket  24 . 
   Each time another IC-chip  10  on its substrate  11  is inserted into the socket  24 , the surface of the IC-chip  10  which needs to lie flat against the heater  20  will have a slightly different orientation due to various tolerances. For example, variation in height across the IC-chip  10  can occur. Also, variation in height in the attachment of the IC-chip  10  to its substrate  11  can occur. 
   To accommodate the different orientations of the IC-chip  10 , the heater  20  in  FIG. 2  is attached to the evaporator  21  which in turn is attached to the gimbal  30 - 33 . However, the evaporator  21  is also attached to the input conduit  21   a  and the output conduit  21   b , and those conduits will impede the movement of the gimbal  30 - 33  if they are too stiff. But this stiffness problem is completely avoided by the springy cylindrical coil  21   a - 1  and the spring spiral coil  21   b - 1 . 
   When the heater  20  and the IC-chip  10  are spaced apart, the components in the  FIG. 2  assembly are positioned as shown in  FIG. 3A . There, spring  33  in the gimbal pushes the evaporator  21  away from the base plate  30  until the tapered ends of the guides  32  hit the base plate. In  FIG. 3A , the two ends  21   a - 2  and  21   a - 3  of the input conduit  21   a  are separated by a maximum distance. Likewise in  FIG. 3A , the two ends  21   b - 2  and  21   b - 3  of the output conduit  21   b  are separated by a maximum distance. 
   By comparison, when the heater  20  is pressed flatly against the IC-chip  10 , the components in the  FIG. 2  assembly are positioned as shown in  FIG. 3B . There, spring  33  in the gimbal is compressed by the IC-chip  10  (not shown) which is being pressed against the heater  20 . It is this spring  33  that provides the nominal contact force for the thermal interface between the IC-chip  10  and the heater  20 . This force by the spring  33  must be large enough to ensure a low thermal resistance, but small enough to not damage the IC-chip. It is because this force cannot be arbitrarily large that any forces or torques exerted by the input and output conduits  21   a  and  21   b  must be limited. 
   As the spring  33  is compressed, the tapered ends of the guides  32  move above the base plate  30 . That allows the evaporator  21  and the attached heater  20  to tip and thereby lie flat against the IC-chip  10 . In  FIG. 3B , the two ends  21   a - 2  and  21   a - 3  of the input conduit  21   a  are closer together than they are in  FIG. 3A . Also in  FIG. 3B , the two ends  21   b - 2  and  21   b - 3  of the output conduit  21   b  are closer together than they are in  FIG. 3A . 
   To analyze the movement of the conduit ends  21   a - 2  and  21   b - 2  in more detail, reference should now be made to  FIG. 4 . There, the evaporator  21  and the heater  20  are shown at the instant where the heater  20  makes initial contact with the IC-chip  10 . This initial contact occurs at one point “P” because, due to tolerances, the top surface of the IC-chip  10  is at a slight angle Δθ with respect to the contact surface of the heater  20 . 
   As the IC-chip  10  and the heater  20  are pressed together, the previously described gimbal  30 - 33  enables the heater  20  and the evaporator  21  to tip until the contact surface of the heater  20  lies flat against the top surface of the IC-chip  10 . Thus, the heater  20  and the evaporator  21  rotates on point P by the angle Δθ. 
   During the above rotation, point A 1  on end  21   a - 2  of the input conduit  21   a  moves to point A 2 . This movement occurs relative to the opposite end  21   a - 3  of the input conduit  21   a . Similarly during the above rotation, point B 1  on end  21   b - 2  of the output conduit  21   b  moves to point B 2 . This movement occurs relative to the opposite end  21   b - 3  of the output conduit  21   b.    
   Thereafter, as the IC-chip  10  and the heater  20  are pressed together with additional force, the spring  33  in the previously described gimbal  30 - 33  gets compressed. Thus the conduit ends  21   a - 2  and  21   b - 2  move upward relative to their opposite ends  21   a - 3  and  21   b - 3 . In  FIG. 4 , point A 2  on the conduit end  21   a - 2  moves vertically to point A 3 , and point B 2  on the conduit end  21   b - 2  moves vertically to point B 3 . 
   Equation 1 of  FIG. 5  gives a practical numerical value for the maximum angle between the top of the IC-chip  10  and the contact face of the heater  20 , when the heater  20  initially touches the IC-chip  10  at point P as shown in  FIG. 4 . This angle “Δθ MAX” is set by equation 1 to 2.5°. 
   After the heater  20  has rotated on point P by 2.5° in order to lie flat against the IC-chip  10 , end  21   b - 2  of the output conduit  21   b  will tilt 2.5° from the vertical axis Z. This is stated by equation 2 in  FIG. 5 . This tilt can be visualized in  FIG. 4  as point B 1  moves to point B 2 . 
   Equation 3 of  FIG. 5  gives a practical numerical value for the distance from point P in  FIG. 4  to point B 1 . This distance is set by equation 3 to three inches. 
   Based on equations 2 and 3, the straight line distance from point B 1  to point B 2  can be approximated, as shown by equation 4. In equation 4, the product of “3 inches” times “2.5° in radians” equals the length of an arc from point B 1  to point B 2 . The length of that arc approximately equals the straight line distance from point B 1  to point B 2  because the angle of 2.5° is so small. 
   In equation 5, the term ΔXB is the distance from point B 1  to point B 2  in the horizontal plane X-Y. This distance ΔXB is slightly smaller than the straight line distance from point B 1  to point B 2  because a straight line from point B 1  to point B 2  is at small angle with the horizontal plane. Thus equation 5 says ΔXB is less than the 130 mils that was calculated by equation 4. 
   Equation 6 of  FIG. 5  gives a practical numerical value for distance from point B 2  in  FIG. 4  to point B 3 . This distance ΔZB is set by equation 6 to three tenths of one inch, or three-hundred mils. 
   The three values of 2.5° in equation 2, 130 mils in equation 5, and 300 mils in equation 6 together define three limits for how far end  21   b - 2  might move, relative to the opposite end  21   b - 3  of the output conduit  21   b . However, due to symmetry in  FIG. 4 , the rotation of 2.5° might occur around the X-axis and the Y-axis. A smaller rotation of 0.5° might occur around the Z-axis. Also in  FIG. 4 , the horizontal movement ΔXB might occur on both the X-axis and the Y-axis. Thus, end  21   b - 2  of the output conduit  21   b  has a total of six degrees of freedom (three translational in directions X, Y and Z and three rotational about any of these three axes). 
   Next, in  FIG. 6 , equation 11 says that end  21   a - 2  of the input conduit  21  tilts from the horizontal plane (X-Y plane) by a maximum angle of 2.5°. This is deduced from equations 1 and 2 of  FIG. 5 , and from the geometries of  FIG. 4 . 
   Equation 12 of  FIG. 6  gives a practical numerical value for the distance from point P in  FIG. 4  to point A 1 . This distance is set by equation 12 to three inches. 
   In  FIG. 4 , point A 1  on end  21   a - 2  moves to point A 2  when point B 1  on end  21 B- 2  moves to point B 2 . But end  21   b - 2  moves further in the X-Y plane than end  21   a - 2 . This is stated by the left side of equation 13. Further, a limit for ΔXB was previously calculated by equation 5 to be less than 130 mils, and this value is given on the right side of equation 13. 
   Equation 14 of  FIG. 6  gives an approximate numerical value for the distance from point A 2  in  FIG. 4  to point A 3 . This distance ΔZA is approximately equal to ΔZB that is given by equation 6. 
   The three values of 2.5° in equation 11, 130 mils in equation 13, and 300 mils in equation 14 together define three limits for how far end  21   a - 2  might move, relative to the opposite end  21   a - 3  of the output conduit  21   a . But again, due to symmetry in  FIG. 4 , the rotation of 2.5° might occur around the X-axis and the Y-axis. The smaller rotation of 0.5° might again occur around the Z-axis. Also in  FIG. 4 , the horizontal movement ΔXA might occur on both the X-axis and the Y-axis. So end  21   a - 2  of the input conduit  21   a  also has six degrees of freedom. 
   When the two conduit ends  21   a - 2  and  21   b - 2  move as described above, those conduit ends must not exert any significant interfering force or torque on the evaporator  21 .  FIGS. 7A-7B  illustrate an eight step process for designing the coiled central portion  21   a - 1  of the input conduit  21   a , and the coiled central portion  21   b - 1  of the output conduit  21   b , such that this criterion is met. The details of that process will now be described. 
   In step  1 , a set of parameters are selected which define the physical structure of the coils in one of the tube portions  21   a - 1  or  21   b - 1 . This step is illustrated in  FIG. 7A . There, the parameters which are selected are: 1) the total number of coils, 2) a radius for each coil (in the case of a cylindrical coil) or a minimum radius plus a rate of change for the radius. (in the case of a spiral coil), 3) an outside diameter for the tube which makes up the coils, 4) a thickness for the tube sidewalls, and 5) the material of which the tube is made. 
   Next, in step  2 , a three-dimensional model is generated in a computer of the coiled section  21   a - 1  (or  21   b - 1 ) that was defined by step  1 . To generate this model, a computer-aided-design program is used. One such program, called “ProEngineer”, is commercially available from Parametric Technology Corporation. 
   Next, in step  3 , a “stiffness matrix” S M  is produced for the coiled section  21   a - 1  (or  21   b - 1 ) that is being modeled. This stiffness matrix S M , which is illustrated in  FIG. 7A , has a total of six rows and six columns. 
   In the stiffness matrix S M , a separate column is provided for each degree of freedom with which end  21   a - 2  (or  21   b - 2 ) can move in  FIG. 4 . Columns  1 ,  2 , and  3  are provided for linear movement which respectively occurs parallel to the X, Y, and Z axis in  FIG. 4 . Columns  4 ,  5 , and  6  are provided for rotational movement which respectively occurs around the X, Y, and Z axis in  FIG. 4 . 
   To determine all of the entries in column  1  of the stiffness matrix, end  21   a - 2  (or end  21   b - 2 ) of the coiled tube that is modeled is deflected in the “X” direction by one unit (e.g. —by one inch) while holding all other displacements and rotations fixed at zero. For that deflection to occur, three forces (F x , F y , and F z ) and three moments (M x , M y , and M z ) must be applied to the deflected end. The forces F x , F y , and F z  respectively occur parallel to the X, Y, and Z axis in  FIG. 4 , and those forces are entered into the stiffness matrix in rows  1 ,  2 , and  3  of column  1 . The moments M x , M y , and M z  respectively occur around the X, Y, and Z axis in  FIG. 4 , and they are entered into the stiffness matrix in rows  4 ,  5 , and  6  of column  1 . 
   All of the entries in any other column of the stiffness matrix are generated in a similar fashion. For example, to generate the entries for column  4 , end  21   a - 2  (or end  21   b - 2 ) of the modeled coiled tube is rotated by one unit (e.g. —one degree) around the X-axis in  FIG. 4  while holding all other displacements and rotations fixed at zero. Then, the forces (F x , F y , and F z ) and moments (M x , M y , and M z ) which must be applied to the rotated end to cause the rotation are entered into rows  1 - 6  of column  4 . 
   To calculate the numerical values of all of the forces and moments which get entered into the stiffness matrix, a computer program for performing finite element stress analysis is used. One such program, called “Pro/Mechanica”, is available from Parametric Technology Corporation. The input to Pro/Mechanica is the 3D model from ProEngineer. 
   Next, in step  4 , a “displacement vector” D v  is generated which defines the maximum displacements that occur in all six degrees of freedom for end  21   a - 2  (or  21   b - 2 ) in  FIG. 4 . This displacement vector, which is illustrated in  FIG. 7B , has six rows and one column. Rows  1 ,  2 , and  3  respectively are the maximum movements for end  21   a - 2  (or  21   b - 2 ) in  FIG. 4  which can occur in the X, Y, and Z directions. Rows  4 ,  5 , and  6  respectively are the maximum angular movements for end  21   a - 2  (or end  21   b - 2 ) in  FIG. 4  which can occur around the X, Y, and Z axis. These entries in rows  1 - 6  were previously determined by equations 1-6 of  FIG. 5  and equations 11-14 of  FIG. 6 . 
   Next, in step  5 , the displacement vector D v  and the stiffness matrix S M  are multiplied together. This produces a force/moment vector FM v , as shown in  FIG. 7B , which has six rows and one column. The entries in rows  1 ,  2 , and  3  respectively are the maximum forces in the X, Y, and Z directions which are asserted by end  21   a - 2  (or end  21   b - 2 ) on the input port (or output port) of the evaporator  21  in  FIG. 4 . The entries in rows  4 ,  5 , and  6  respectively are the maximum moments around the X, Y, and Z axis which are asserted by end  21   a - 2  (or end  21   b - 2 ) on the input port (or output port) of the evaporator  21  in  FIG. 4 . 
   If one of the coiled tube sections  21   a - 1  or  21   b - 1  is much stiffer than the other, then as a simplification, the above described steps  1 - 5  need only be performed on the stiffer section. Otherwise, the above described steps  1 - 5  need to be performed separately on each of the coiled tube sections  21   a - 1  and  21   b - 1 . Then the forces and moments which each of the coiled tubes sections exert on the evaporator  21 , as determined by step  5 , are added together. 
   Next, in step  6 , one moment “M” and five forces “F a ”, “F b ”, “F c ”, “F d ”, and “F e ” are calculated which the evaporator  21  exerts on the IC-chip  10 . The moment M occurs around an axis which is perpendicular to the contact surface of the IC-chip  10 . Each of the forces F a , F b , F c , and F d  occur perpendicular to the contact surface of the IC-chip  10 . The force F e  occurs parallel to the contact surface of the IC-chip  10 . 
   To make the above calculation, the IC-chip  10  is assumed to have four hypothetical bumps on its contact surface at points “a”, “b”, “c”, and “d”. These bumps are located at the midpoint on each side of the contact surface, as shown in  FIG. 7C . 
   Also to make the above calculation, the coiled tube sections  21   a - 1  and  21   b - 1  are assumed to exert the forces and moments on the evaporator  21  which were determined by their respective force/moment vector FM v  from step  5 . Further to make the above calculation, the gimbal spring  33  is assumed to exert a force on the evaporator  21  which is perpendicular to the contact surface of the IC-chip  10 . That force is opposed equally by the four bumps at points a, b, c, and d. 
   All of the forces “F a ”, “F b ”, “F c ”, “F d ”, and “F e ”, and the moment “M”, are calculated by applying the following equations to the evaporator  21  and heater  20  of  FIG. 4 : ΣF x =0, ΣF y =0, ΣF z =0, ΣM x =0, ΣM y =0, ΣM z , =0. In these equations, F x , F y , and F z  respectively are all of the forces that occur parallel to the X, Y, and Z axis, and M x , M y , and M z  respectively are all of the moments that occur around the X, Y, and Z axis. 
   After numerical values are calculated in step  6  for the moment M and the forces F a , F b , F c , and F d  and F e , those values are compared to an acceptance criterion. This occurs in  FIG. 7C  as step  7 . 
   Preferably, one part of the acceptance criterion is not met if any one of the forces F a , F b , F c , and F d  is negative. A calculated negative force indicates that at least part of the heater  20  has lifted off of the IC-chip  10 . 
   Also preferably, a second part of the acceptance criterion is not met if the forces F a , F b , F c , and F d  are too far out of balance, since that would tend to increase the thermal resistance between the IC-chip  10  and the heater  20  in the area where the weaker forces occur. Preferably, each force F a , F b , F c , and F d  is at least one-fifth of the average value of F a , F b , F c , and F d . In more general terms, the force per unit area at any particular point between the heater  20  and the IC-chip  10  preferably is at least one-fifth of the average force per unit area between those two components. 
   Also preferably, a third part of the acceptance criterion is not met if F e  is greater than μ(F a +F b +F c +F d ), where “μ” is the coefficient of friction between the IC-chip  10  and the heater  20 . This ensures that the IC-chip  10  will not slip in the lateral direction on the heater  20 . 
   Also preferably, a fourth part of the acceptance criterion is not met if M is greater than μL(F a +F b +F c +F d )/3. Here, “μ” is the above coefficient of friction, and “L” is the length of the IC-chip  10  along its smaller side. This ensures that the IC-chip  10  will not slip in a rotational manner on the heater  20 . 
   If all four parts of the above preferred acceptance criterion are not met, the physical parameters for the coiled tube sections  21   a - 1  and/or coiled tube section  21   b - 1 , that were previously selected in step  1 , need to be modified. Then, after the modified parameters are selected, all of the steps  2 - 6  are repeated to thereby determine new values for the moment M and forces F a , F b , F c , F d  and F e . If these new values meet all four parts of the preferred acceptance criterion, the process of  FIGS. 7A-7C  ends. Otherwise, steps  1 - 7  are repeated over and over until all four parts of the preferred acceptance criterion are met. This is indicated in  FIG. 7C  as step  8 . 
   One preferred embodiment of the present invention has now been described in detail. Next, various changes and modifications which can be made to this preferred embodiment, without departing from the gist of the invention, will be described. 
   As a first modification in  FIG. 2 , the central portion  21   a - 1  of the input conduit  21   a  and the central portion of  21   b - 1  of the output conduit  21   b , can each be coiled into a cylindrical spring. Similarly, in  FIG. 2 , the central portion  21   a - 1  of the input conduit  21   a  and the central portion  21   b - 1  of the output conduit  21   b  can each be coiled into a spiral spring. 
   When the first modification is incorporated into  FIG. 1 , then as a second modification, the two tubes  21   a  and  21   b  can have different diameters with one tube being inside of the other tube. Preferably, the output tube  21   b  has the larger diameter since it needs to carry a gas at low pressure. Each end of the larger diameter tube can be covered with a cap that has two holes. The smaller diameter tube should extend in an airtight manner through one of the holes, and the other hole is a port to the larger diameter tube. 
   As a third modification, the central section  21   a - 1  and  21   b - 1  of each coiled tube can have any number of turns. Preferably however, the central sections  21   a - 1  and  21   b - 1  each have at least two complete turns, since the forces and torques which the coiled tubes exert on the input port and output port of the heat-exchanger  21  decrease as the total number of turns increase. 
   As a fourth modification, it may be possible to design around the preferred embodiment of  FIG. 2  by not putting any coils in one of the two tubes  21   a  or  21   b . For example, one of those tubes could possibly have a very long length and a very small diameter so that it will easily flex. But when the output tube  21   b  needs to pass the coolant as a gas at low pressure, the tube diameter needs to be large in order to keep the gas pressure low. However, the stiffness of a tube increases as its diameter increases, so the large diameter output tube will need to be coiled to prevent it from being too stiff. 
   As a fifth modification, in  FIG. 2 , the electric heater  20  can be deleted from the evaporator  21 . With this modification, the evaporator  21  makes direct contact with the IC-chip  10 . 
   As a sixth modification, in  FIG. 2 , the evaporator  21  can be replaced with a hollow heat-sink which passes a coolant in just the liquid state. With this modification, the liquid coolant flows into the heat-sink through the coiled input tube  21   a , and the liquid coolant flows out of the heat-sink into the coiled output tube  21   b.    
   Also, when the above sixth modification is incorporated, then as a seventh modification the electric heater  20  can be deleted from the heat-sink. In that case, the heat-sink will make direct contact with the IC-chip. 
   As an eighth modification, the mechanical assembly in  FIG. 2  can be used to regulate the temperature of an IC-chip in an IC-module of the type where the IC-chip is covered with a lid. For that type of IC-module, the heater  20  simply presses against the lid instead of the IC-chip. The ends of the coiled tubes  21   a  and  21   b  again move as shown in  FIGS. 3A and 3B . 
   Also, as a ninth modification, the acceptance criterion which is used in steps  7  and  8  of  FIG. 7C  can be modified to be any desired AND/OR combination of the four parts that are in the preferred acceptance criterion. For example, this modified acceptance criterion can be that just the second part AND the third part of the preferred acceptance criterion is met. As another example, this modified acceptance criterion can be that just one particular part of the preferred acceptance criterion is met. 
   Accordingly, it is to be understood that the present invention is not limited to just the details of the illustrated preferred embodiment, but is defined by the appended claim.