Patent Publication Number: US-7224586-B2

Title: Method of maintaining an IC-module near a set-point

Description:
The present patent application is a Division of a prior patent application Ser. No. 10/647,090, that was filed on Aug. 21, 2003, and is entitled “TEMPERATURE CONTROL SYSTEM WHICH SPRAYS LIQUID COOLANT DROPLETS AGAINST AN IC-MODULE AT A SUB-ATMOSPHERIC PRESSURE. 
    
    
     RELATED CASES 
     The above-identified invention is related to one other invention which is described herein with a single Detailed Description. The other related invention has U.S. Ser. No. 10/647,091 and is entitled “TEMPERATURE CONTROL SYSTEM WHICH SPRAYS LIQUID COOLANT DROPLETS AGAINST AN IC-MODULE AND DIRECTS RADIATION AGAINST THE IC-MODULE”. U.S. patent applications on both inventions were concurrently filed on Aug. 21, 2003. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to temperature control systems for maintaining the temperature of an integrated circuit chip (IC-chip) near a constant set point temperature while the IC-chip is being tested. Also the present invention relates to subassemblies which comprise key portions of the above temperature control systems. 
     The IC-chip whose temperature is being regulated typically is part of an integrated circuit module. In the IC-module, the IC-chip usually is mounted on a substrate and covered with a lid. Alternatively, an uncovered IC-chip can be mounted on the substrate. Any type of circuitry can be integrated into the IC-chip, such as digital logic circuitry, or memory circuitry, or analog circuitry. Further, the circuitry in the IC-chip can be comprised of any type of transistors, such as field effect transistors or bipolar transistors. 
     One reason for trying to keep the temperature of an IC-chip constant, while the IC-chip is tested, is that the speed with which the IC-chip operates may be temperature dependent. For example, an IC-chip which is comprised of complementary field effect transistors (CMOS transistors) typically operates faster as the temperature of the IC-chip is decreased. 
     A common practice in the IC-chip industry is to mass produce a particular type of IC-chip, and thereafter speed sort them and sell the faster operating IC-chips at a higher price. CMOS memory chips and CMOS microprocessor chips are processed in this fashion. However, in order to properly determine the speed of such IC-chips, the temperature of each IC-chip must be kept nearly constant while the speed test is performed. 
     Maintaining the IC-chip temperature near a constant set point is relatively easy if the instantaneous power dissipation of the IC-chip is constant, or varies in a small range, while the speed test is being performed. In that case, it is only necessary to couple the IC-chip through a fixed thermal resistance to a thermal mass which is at a fixed temperature. For example, if the maximum IC-chip power variation is only ten watts, and the thermal resistance between the IC-chip and the thermal mass is 0.2 degrees centigrade per watt, then the maximum variation in the IC-chip temperature will only be two degrees centigrade. 
     But, if the instantaneous power dissipation of the chip varies up and down in a wide range while the speed test is being performed, then maintaining the IC-chip temperature near a constant set point is very difficult. Each time the power dissipation in the IC-chip makes a big change, its temperature and its speed will also make a big change. 
     The instantaneous power dissipation of a present day microprocessor chip typically varies from zero to over one-hundred watts. Also, the trend in the IC-chip industry is to continually increase the total number of transistors on an IC-chip, and that increases the maximum power dissipation of the IC-chip. Further, in one type of test that is called “burn-in”, the power dissipation in the IC-chip is larger than normal because the voltage to the IC-chip is increased in order to accelerate the occurrence of failure. 
     In the prior art, one control system for maintaining the temperature of a high power IC-chip near a set point while the IC-chip is tested is disclosed in U.S. Pat. No. 5,821,505 (entitled “TEMPERATURE CONTROL SYSTEM FOR AN ELECTRONIC DEVICE WHICH ACHIEVES A QUICK RESPONSE BY INTERPOSING A HEATER BETWEEN THE DEVICE AND A HEAT SINK”). The &#39;505 temperature control system includes a thin flat electric heater which has one surface that gets pressed against a corresponding surface on the IC-module, and has an opposite surface which is rigidly connected to a cooling jacket that carries a liquid coolant. The corresponding surface of the IC-module can be the lid which covers the IC-chip, or the IC-chip itself if there is no lid. 
     To cool the IC-chip at a maximum rate in the &#39;505 temperature control system, the electric heater is turned off. Then heat quickly travels from the IC-chip through the electric heater to the cooling jacket. To reduce the rate at which heat travels from the IC-chip through the electric heater to the cooling jacket, the electric heater is turned on at a low level. To add heat to the IC-chip, the electric heater is turned on at a high level. 
     However, in the &#39;505 temperature control system, a thermal resistance exists between the surfaces of the electric heater and the corresponding surface of the IC-module that get pressed together. This thermal resistance occurs due to microscopic mismatches between the two contacting surfaces. 
     The above thermal resistance times the power dissipation in the IC-chip equals a rise in temperature which occurs from the electric heater to the IC-chip when the electric heater is turned off to cool the IC-chip. This temperature rise limits the maximum power dissipation which can occur in the IC-chip without causing the IC-chip to overheat and destroy itself. Thus, the maximum power dissipation which can be tolerated without destroying the IC-chip is limited by the magnitude of the thermal resistance. 
     Further in the &#39;505 temperature control system, the electrical heater inherently has a thermal mass. The larger that thermal mass is, the longer it takes to change the temperature of the electrical heater. Consequently, the thermal mass of the electrical heater limits the speed at which the temperature of the IC-chip can be regulated. 
     Accordingly, a primary object of the inventions which are disclosed herein is to provide a totally different structure for a temperature control systems, which completely avoids the above limitation of the &#39;505 temperature control system. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a system for maintaining an IC-chip near a set-point temperature while electrical power dissipation in the IC-chip is varied includes an open container having a bottom and surrounding sides with a seal ring. Located in the bottom of the container is at least one nozzle for spraying liquid coolant droplets on a portion of an IC-module which holds the IC-chip. This spraying of the liquid coolant occurs while the seal ring is pressed against the IC-module. Also, a pressure reducing means is coupled to the container for producing a sub-atmospheric pressure in the space between the container and the IC-module while the seal ring is pressed against the IC-module. 
     When each droplet of coolant hits the IC-module, heat is transferred from the IC-module directly to the coolant droplet. The thermal resistance from the IC-module to the coolant droplet is very small. Thus the thermal resistance limitation, which occurs in the &#39;505 temperature regulating system, is completely avoided. 
     The heat transfer from the IC-module to each coolant droplet occurs in a time period Δt which decreases as the difference between the temperature of the IC-chip (T IC ), and the vaporization temperature of the droplet (T V ) increases. By maintaining the inside of the container at a sub-atmospheric pressure, the vaporization temperature T V  is reduced. Thus the difference between T IC  and T V  is increased, and so the speed at which each droplet vaporizes and cools the IC-package is increased from that which would otherwise occur if the pressure in the container is at, or above, atmospheric pressure. 
     When the total number of droplets that are vaporized per second, times the heat of vaporization per droplet, exceeds the power which the IC-chip is dissipating, then the temperature of the IC-chip gets reduced. However, the minimum temperature to which the IC-chip can be reduced is just slightly above the vaporization temperature of the droplets. Thus, with the present invention, the lowest temperature to which the IC-chip can be maintained is lower than that which would otherwise occur if the pressure in the container is at, or above, atmospheric pressure. 
     Also, the sub-atmospheric pressure within the container makes the seal ring leak tolerant. If a leak occurs between the seal ring and the IC-module, only air will get sucked into the container. No liquid coolant will leak out of the container onto the IC-module where it could cause electrical shorts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an overview of a first embodiment of a temperature regulating system which incorporates the present invention. 
         FIG. 2  shows additional details of an array of nozzles which sprays droplets of liquid coolant, and IR-windows which pass radiation, in the  FIG. 1  system. 
         FIGS. 3A–3D  show several patterns of coolant droplets and radiation which are sent by the  FIG. 2  array. 
         FIG. 4  shows a set of equations which contain numerical details of one specific implementation of the  FIG. 2  array. 
         FIG. 5A  illustrates one particular benefit which is obtained with the  FIG. 1  temperature regulating system. 
         FIG. 5B  illustrates another particular benefit which is obtained with the  FIG. 1  temperature regulating system. 
         FIG. 6  shows one alternative array of nozzles and IR-windows which can replace the  FIG. 2  array in the  FIG. 1  temperature control system. 
         FIG. 7A  shows a second alternative array of nozzles and IR-windows which can replace the  FIG. 2  array in the  FIG. 1  temperature control system. 
         FIG. 7B  shows additional details of the array in  FIG. 7A . 
         FIG. 7C  shows further details of the array in  FIG. 7A . 
         FIG. 8A  shows a third alternative array of nozzles and IR-windows which can replace the  FIG. 2  array in the  FIG. 1  temperature control system. 
         FIG. 8B  shows additional details of the array in  FIG. 5A . 
         FIG. 9  shows the temperature control system of  FIG. 1  incorporating the alternative array of  FIGS. 8A–8B  and operating on a bare IC-chip which is mounted on a substrate. 
     
    
    
     DETAILED DESCRIPTION 
     One preferred temperature regulating system, which incorporates the present invention, will now be described with reference to  FIGS. 1 ,  2 ,  3 A– 3 D,  4  and  5 A– 5 B. An overview of this temperature regulating system is shown in  FIG. 1 . 
     In  FIG. 1 , the temperature regulating system is comprised of everything that is shown except item  10 . Item  10  is an IC-module (integrated circuit module) on which the temperature regulating system operates. This IC-module  10  includes components  10   a – 10   g , each of which is described in TABLE 1 below. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Component 
                 Description 
               
               
                   
               
             
            
               
                 10a 
                 Component 10a is an IC-chip 
               
               
                   
                 (integrated circuit chip) which is 
               
               
                   
                 enclosed within the IC-module 10. 
               
               
                 10b 
                 Component 10b is a substrate which 
               
               
                   
                 holds the IC-chip 10a. 
               
               
                 10c 
                 Component 10c is one or more 
               
               
                   
                 conductors, in the substrate 10b, 
               
               
                   
                 which carry electrical power PWR to 
               
               
                   
                 the IC-chip 10a. 
               
               
                 10d 
                 Component 10d is one or more 
               
               
                   
                 conductors, in the substrate 10b, 
               
               
                   
                 which carry TEST signals to and 
               
               
                   
                 from the IC-chip 10a. 
               
               
                 10e 
                 Component 10e is one or more 
               
               
                   
                 conductors, in the substrate 10b, 
               
               
                   
                 which carry TEMP signals from the 
               
               
                   
                 IC-chip 10a. 
               
               
                 10f 
                 Component 10f is a lid which is 
               
               
                   
                 attached to the substrate 10b and 
               
               
                   
                 which encloses the IC-chip 10a. 
               
               
                 10g 
                 Component 10g is a thermal 
               
               
                   
                 interface_material which fills a 
               
               
                   
                 gap between the IC-chip 10a and the 
               
               
                   
                 lid 10f. 
               
               
                   
               
            
           
         
       
     
     In operation, the  FIG. 1  temperature regulating system maintains the temperature of the IC-chip  10   a  near a set-point temperature, while the power which the IC-chip  10   a  dissipates is varied in response to the TEST signals. To accomplish this operation, the  FIG. 1  temperature regulating system includes components  20 – 34 , each of which is described in TABLE 2 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Component 
                 Description 
               
               
                   
                   
               
             
            
               
                   
                 20 
                 Component 20 is a container which 
               
               
                   
                   
                 has one open end that faces the IC- 
               
               
                   
                   
                 package 10. The bottom of the 
               
               
                   
                   
                 container 20 is identified by 
               
               
                   
                   
                 reference numeral 20a, and the 
               
               
                   
                   
                 sidewall of the container is 
               
               
                   
                   
                 identified by reference numeral 
               
               
                   
                   
                 20b. Two vacuum ports P are in the 
               
               
                   
                   
                 sidewall 20b. 
               
               
                   
                 21 
                 Component 21 is a seal ring, on the 
               
               
                   
                   
                 sidewall 20b. This seal ring 21 
               
               
                   
                   
                 surrounds the open end of the 
               
               
                   
                   
                 container 20 and forms a seal with 
               
               
                   
                   
                 the lid 10f of the IC-package. 
               
               
                   
                 22 
                 Component 22 is a conduit which has 
               
               
                   
                   
                 two inputs that are connected to 
               
               
                   
                   
                 the vacuum ports P in the container 
               
               
                   
                   
                 20, and which has one output. 
               
               
                   
                 22a 
                 Component 22a is a pressure relief 
               
               
                   
                   
                 valve, in the conduit 22, which can 
               
               
                   
                   
                 be manually opened to put the 
               
               
                   
                   
                 inside of the conduit at 
               
               
                   
                   
                 atmospheric pressure. 
               
               
                   
                 22b 
                 Component 22b is an isolation 
               
               
                   
                   
                 valve, in the conduit 22, which can 
               
               
                   
                   
                 be manually closed to block any 
               
               
                   
                   
                 flow through the conduit. 
               
               
                   
                 22c 
                 Component 22c is a vacuum control 
               
               
                   
                   
                 valve, in the conduit 22, which 
               
               
                   
                   
                 opens by a selectable amount in 
               
               
                   
                   
                 response to a control signal VSET. 
               
               
                   
                 23 
                 Component 23 is a condenser/heat- 
               
               
                   
                   
                 exchanger which has an input port 
               
               
                   
                   
                 23a that is coupled to the output 
               
               
                   
                   
                 of the conduit 22. 
               
               
                   
                 24 
                 Component 24 is a vacuum pump which 
               
               
                   
                   
                 has an input 24a that is coupled to 
               
               
                   
                   
                 the output of the condenser/heat 
               
               
                   
                   
                 exchanger 23. 
               
               
                   
                 25 
                 Component 25 is a control input by 
               
               
                   
                   
                 which an operator manually_selects 
               
               
                   
                   
                 a particular sub-atmospheric 
               
               
                   
                   
                 pressure for the vacuum pump 24 to 
               
               
                   
                   
                 generate in the container 20. A 
               
               
                   
                   
                 signal VSET, from this control 
               
               
                   
                   
                 input, indicates the selected 
               
               
                   
                   
                 pressure and is sent to the vacuum 
               
               
                   
                   
                 control valve 22c. 
               
               
                   
                 25a 
                 Component 25a is a vacuum gauge 
               
               
                   
                   
                 which displays the actual sub- 
               
               
                   
                   
                 atmospheric pressure that is 
               
               
                   
                   
                 generated in the container 20. 
               
               
                   
                 26 
                 Component 26 is a reservoir which 
               
               
                   
                   
                 has an input port 26a that is 
               
               
                   
                   
                 coupled to an output port on the 
               
               
                   
                   
                 vacuum pump 24. 
               
               
                   
                 26b 
                 Component 26b is an air vent, on 
               
               
                   
                   
                 the top of the reservoir 26, which 
               
               
                   
                   
                 enables air to escape from the 
               
               
                   
                   
                 reservoir and which places the 
               
               
                   
                   
                 liquid coolant in the reservoir at 
               
               
                   
                   
                 atmospheric pressure. 
               
               
                   
                 27 
                 Component 27 is a liquid pump which 
               
               
                   
                   
                 has an input port 27a that is 
               
               
                   
                   
                 coupled to an output port on the 
               
               
                   
                   
                 reservoir 26. 
               
               
                   
                 28 
                 Component 28 is a pressure 
               
               
                   
                   
                 regulator, for a liquid, which has 
               
               
                   
                   
                 an input port 28a that is coupled 
               
               
                   
                   
                 to an output port on the liquid 
               
               
                   
                   
                 pump 27. 
               
               
                   
                 29 
                 Component 29 is a conduit which 
               
               
                   
                   
                 couples an output port 28b on the 
               
               
                   
                   
                 pressure regulator 28 to an 
               
               
                   
                   
                 internal channel in the bottom 20a 
               
               
                   
                   
                 of the container 20. This internal 
               
               
                   
                   
                 channel is hidden in FIG. 1, but is 
               
               
                   
                   
                 shown in FIG. 2. 
               
               
                   
                 30 
                 Component 30 is replicated multiple 
               
               
                   
                   
                 times (eg —twenty to two-thousand 
               
               
                   
                   
                 times) on the bottom 20a of the 
               
               
                   
                   
                 container 20. Each component 30 is 
               
               
                   
                   
                 a bubble jet nozzle, like those 
               
               
                   
                   
                 which are in a printer for a 
               
               
                   
                   
                 computer. A liquid coolant is sent 
               
               
                   
                   
                 to each nozzle 30 from the conduit 
               
               
                   
                   
                 29 and the internal channel in the 
               
               
                   
                   
                 bottom 20a of the container 20. 
               
               
                   
                 31 
                 Component 31 is replicated multiple 
               
               
                   
                   
                 times, between the nozzles 30, on 
               
               
                   
                   
                 the bottom 20a of the container 20. 
               
               
                   
                   
                 Each component 31 is a window which 
               
               
                   
                   
                 passes IR-radiation (infrared 
               
               
                   
                   
                 radiation) but does not pass any 
               
               
                   
                   
                 liquid and vapor that is in the 
               
               
                   
                   
                 container 20. 
               
               
                   
                 32 
                 Component 32 is a source of IR 
               
               
                   
                   
                 radiation which is coupled to the 
               
               
                   
                   
                 bottom 20a of the container 20. 
               
               
                   
                 33 
                 Component 33 is a control signal 
               
               
                   
                   
                 generator for the nozzles 30 and 
               
               
                   
                   
                 the IR source 32. This control 
               
               
                   
                   
                 signal generator 33 receives the 
               
               
                   
                   
                 TEMP signal on a conductor 33a, and 
               
               
                   
                   
                 it receives set-point signals SP 
               
               
                   
                   
                 on a conductor 33b. In response to 
               
               
                   
                   
                 the TEMP and SP signals, the 
               
               
                   
                   
                 control signal generator produces 
               
               
                   
                   
                 two control signals CS1 and CS2. 
               
               
                   
                   
                 The control signals CS1 are sent on 
               
               
                   
                   
                 conductors 33c to the nozzles 30, 
               
               
                   
                   
                 and the control signals CS2 are 
               
               
                   
                   
                 sent on conductors 33d to the IR 
               
               
                   
                   
                 source 32. 
               
               
                   
                 34 
                 Component 34 is a manual control 
               
               
                   
                   
                 input by which an operator selects 
               
               
                   
                   
                 a particular set-point temperature. 
               
               
                   
                   
                 The signal SP from the control 
               
               
                   
                   
                 input 34 indicates the selected 
               
               
                   
                   
                 set-point temperature. 
               
               
                   
                   
               
            
           
         
       
     
     Now, the manner in which all of the components in TABLE 2 interact with an IC-package  10  will be described. Initially, one particular IC-package  10  which is to be tested is pressed against the seal ring  21 , as shown in  FIG. 1 . Then an operator manually selects a particular set-point temperature via the control input  34 , and selects a particular sub-atmospheric pressure via the control input  25 . Thereafter, the valve  22   b  is opened. Then, after the selected sub-atmospheric pressure is reached inside of the container  20 , electrical power PWR and electrical test signals TEST are applied to the conductors  10   c  and  10   d  from an external source (not shown). However, if the gauge  25   a  indicates that the selected sub-atmospheric pressure cannot be reached inside of the container  20  due to a leak past the seal ring  21 , then the  FIG. 1  system is shut down and corrective action is taken. This avoids any damage to the IC-module  10 . 
     Whenever the TEST signals change from one state to another, the amount of electrical power which is dissipated by the IC-chip  10   a  also changes. Consequently, the temperature of the IC-chip  10   a  tends to vary. However, the temperature at the IC-chip  10   a  is monitored by the control signal generator  33  via the TEMP signals. And, by properly generating the control signals CS 1  and CS 2 , the control signal generator  33  is able to keep the temperature of the IC-chip  10   a  near the set-point temperature. 
     To remove heat from the IC-chip  10   a , the control signal generator  33  sends the control signals CS 1  to a selectable subset of the nozzles  30 . Each nozzle that receives the control signal CS 1  ejects one droplet of liquid against the cover  10   f  of the IC-package  10 . Four ejected liquid droplets are indicated by the letter “L” in  FIG. 1 . 
     When an ejected liquid droplet L hits the cover  10   f  of the IC-package  10 , heat is quickly transferred from the cover  10   f  to the liquid droplet L and that causes the droplet to vaporize. In  FIG. 1 , vaporized droplets are indicated by the letter “V”. 
     All of the vaporized droplets are removed from the container  20  through the vacuum ports P. From those ports, the vaporized droplets travel through the conduit  22  to the condenser/heat-exchanger  23 . 
     In the condenser/heat-exchanger  23 , heat is removed from the vaporized droplets which converts them back to a liquid. Then the liquid from the condenser/heat-exchanger  23  travels through the vacuum pump  24  to the_reservoir  26 . From the reservoir  26 , the liquid travels through the liquid pump  27 , the pressure regulator  28 , and the conduit  29  to the internal channel in the bottom  20   a  of the container  20 . 
     To add heat to the IC-chip  10   a , the control signal generator  33  sends the control signals CS 2  to the IR-source  32 . In response, the IR-source  32  emits infrared radiation as long as it receives the CS 2  signal. That infrared radiation passes through the IR-windows  31  and hits the cover  10   f  of the IC-package  10 . In  FIG. 1 , the infrared radiation is indicated by the dashed lines from the IR-windows  31 . 
     Next, with reference to  FIG. 2 , additional details will be described regarding the nozzles  30  and IR-windows  31  which are on the bottom  20   a  of the container  20 .  FIG. 2  shows that the nozzles  30  and IR-windows  31  are interleaved in an array of rows and columns. In  FIG. 2 , there is room to illustrate only three rows and four columns; however, the actual array can have any number of rows and columns. 
     Each nozzle  30  in  FIG. 2  receives liquid coolant from an internal channel which lies within the bottom  20   a  of the container  20 . That internal channel is coupled to the conduit  29  in  FIG. 1 . 
     Each nozzle  30  in  FIG. 2  also receives a separate control signal RiCj from the control signal generator  33  in  FIG. 1 . Here, “i” and “j” are indices  1 ,  2 ,  3 , etc. Control signal RiCj is sent to the nozzle  30  in the i-th row and j-th column of the  FIG. 2  array. All of the control signals RiCj together constitute the control signals CS 1  in  FIG. 1 . 
     Each control signal RiCj is a voltage pulse (or a current pulse) of a predetermined width. When this pulse is received by a nozzle  30 , the nozzle ejects a single droplet of the liquid coolant from its orifice  30   a . The total amount of liquid coolant which is ejected against the lid  10   f  of the IC-package  10  is increased by increasing the number of control signals RiCj which are sent concurrently, and/or by increasing the repetition rate of the control signals. 
     All of the nozzles  30  in the  FIG. 2  array, as well as all of the conductors that carry the control signals RiCj and all channels that carry the liquid coolant, are integrated onto one surface of a planar substrate (not shown). The IR-source  32  is attached to the opposite surface of the planar substrate. That substrate is made of a material such as glass which is essentially transparent to radiation from the IR-source  32 . The IR-windows  31  are defined by portions of the substrate that lie between the nozzles  30 , through which none of the conductors for the control signals RiCj, and none of the internal channels for the liquid coolant, are routed. 
     Referring now to  FIGS. 3A–3D , an example will be described which illustrates how the signal generator  33  uses the nozzles  30  and IR-windows  31  of  FIG. 2  to maintain the temperature of the IC-chip  10   a  near the set point while the power dissipation by the IC-chip varies. In each of the  FIGS. 3A–3D , one complete array of nozzles  30  and IR-windows  31  shown. Also, each particular nozzle  30  which is ejecting coolant droplets is shown by the letter “C” in a circle, whereas each nozzle  30  which is not ejecting coolant droplets is shown by the letter C without a circle. Similarly, each particular IR-window  31  which is passing energy as infrared radiation is shown by the letter “H” in a circle, whereas each IR-window  31  which is not passing energy is shown by the letter H without a circle. 
     Assume now that the IC-chip  10   a , in the  FIG. 1  temperature regulating system, is dissipating 100 watts of power. In that case, to keep the temperature of the IC-chip  10   a  constant, the amount of liquid coolant which is ejected from the nozzles  30  must remove 100 joules of heat per second from the IC-chip  10   a . This is shown in  FIG. 3A  as being achieved by ejecting coolant droplets, at a predetermined rate, from the subsets of nozzles  30  which are shown by “C” in a circle. 
     Next, assume that the power which the IC-chip  10   a  is dissipating increases from 100 watts to 200 watts. Then, to keep the temperature of the IC-chip  10   a  constant, the amount of liquid coolant which is ejected from the nozzles  30  must remove 200 joules of heat per second from the IC-chip  10   a . This is shown in  FIG. 3B  as being achieved by doubling the number of nozzles  30  which are ejecting coolant droplets over that which is shown in  FIG. 3A , and keeping the ejection rate constant. 
     Next, assume that the power which the IC-chip  10   a  is dissipating decreases to zero watts. Then, to keep the temperature of the IC-chip  10   a  constant, the ejection of liquid coolant from each nozzle  30  must be stopped, and all heat which the IC-chip  10   a  looses (such as by conduction cooling to the substrate  10   b ) must be replaced by infrared radiation through the IR-windows  31 . This is shown as being achieved in  FIG. 3C . There, the amount of heat which is added to the IC-chip  10   a  is increased (or decreased) by increasing (or decreasing) the ON to OFF ratio of the control signal CS 2  to the IR-source  32 . 
     The ON/OFF ratio of the control signal CS 2  can be varied by generating the CS 2  signal as a series of pulses at a fixed frequency and varying the width of each pulse. Alternatively, the width of each pulse can be fixed and the pulse frequency can be varied. Also, the IR-source  32  can have any internal structure which enables it to emit radiation in response to the pulses in the CS 2  signal. For example, the IR-source  32  can include a quartz lamp which is always on, and further include a shutter which only opens while a CS 2  pulse is present. 
     Next, assume that the power which the IC-chip  10   a  is dissipating increases to 300 watts. In that case, to keep the temperature of the IC-chip  10   a  constant, the amount of liquid coolant which is ejected from the nozzles  30  must remove 300 joules of heat per second from the IC-chip  10   a . This is shown in  FIG. 3D  as being achieved by ejecting coolant droplets from a number of nozzles  30  that equals those which eject coolant in  FIG. 3A  and  FIG. 3B  combined, while keeping the ejection rate constant. 
     Now, with reference to  FIG. 4 , some additional details will be provided regarding the structure of the array of nozzles  30  and IR-windows  31  in  FIG. 2 . In  FIG. 4 , equation 1 indicates that the volume of a single drop of liquid coolant which is ejected from one of the nozzles  30  in  FIG. 2  is ten picoliters, as one practical example. This volume has a weight of ten nanograms when the liquid coolant is water. 
     Equation 2 in  FIG. 4  calculates the amount of heat ΔQ which can be removed from the IC-chip  10   a  in  FIG. 1  by the single drop of water in equation 1. The result of that calculation is ΔQ approximately equals twenty micro joules per drop. In equation 2, ΔT is the difference between the temperature at which the water droplet vaporizes and its initial temperature when it is ejected from the nozzle  30 , and Cp is the specific heat of water. Also in equation 2, the term of 2260 joules per gram is the heat of vaporization for water. The heat of vaporization_is significantly larger than the term (ΔT) (Cp), and so as a rough approximation, the term (ΔT)(Cp) can be ignored. 
     Suppose now that the maximum rate at which heat needs to be removed from an IC-chip  10   a  is 400 joules per second. Then, equation 3 in  FIG. 4  expresses that requirement in terms of the heat per drop from equation 2, the total number of nozzles  31  in the  FIG. 2  array, and the frequency with which pulses are sent to any one nozzle  30  via the control signals RiCj. 
     One particular frequency for the pulses in the control signals RiCj is 10 KHz This is stated by equation 4. Then, substituting 10 KHz into equation 3 and solving for the total number of nozzles  30  in the array yields a result of 2000. 
     Assume now that the lid  10   f  on the IC-package  10  has a square area that is available for heat transfer which is one inch on a side. For such a lid, 2000 of the nozzles  30  may be fabricated in a square array which has forty-five rows and forty-five nozzles per row. This is stated by equation 5. 
     When forty-five of the nozzles  30  are equally spaced in each row, then the center-to-center spacing of those nozzles  30  is 560 micrometers. This is derived by equation 6. 
     A single nozzle in a present day inkjet printer occupies an area of less then fifty by one-hundred micrometers. This area is stated in equation 7. Such nozzles would easily fit in the array of  FIG. 2  where there spacing is 560 micrometers. 
     Also in the array of  FIG. 2 , there must be room for one of the IR-windows  31  between any two consecutive nozzles  30  in a row. Each IR-window  31  only needs to be larger then the wavelength of infrared radiation in order to pass that radiation, and the wavelength of infrared radiation ranges from one to ten micrometers. Thus a large IR-window  31  of twenty-by-twenty micrometers, as indicated by equation 7, will easily fit between the nozzles  30  which are spaced by 560 micrometers. 
     Turning next to  FIGS. 5A–5B , three particular benefits which are obtained by the  FIG. 1  system, will be described. In  FIG. 5A , reference numeral  40  identifies a single droplet which has been ejected by one of the nozzles  30  against a portion of the lid  10   f.    
     While the droplet  40  is against the lid  10   f , the heat of vaporization is transferred from the lid  10   f  to the droplet  40 . That heat transfer occurs while the droplet is_at a temperature T V , and it occurs in a time period Δt which decreases as the difference between T IC  and T V  increases. Here, T IC  is the surface temperature of the lid  10   f  of the IC-package  10 , and T V  is the temperature at which the droplet  40  changes from a liquid to a vapor. 
     By maintaining the inside of the container  20  at a sub-atmospheric pressure, the temperature T V  is reduced. This increases the difference T IC −T V , and so the heat flux ΔQ/Δt which flows into each droplet is increased from that which would otherwise occur if the pressure in the container  20  were at, or above, atmospheric pressure. 
     In  FIG. 5B , reference numeral 40* identifies the droplet  40  from  FIG. 5A  after it has vaporized. When the total number of droplets that are vaporized per second, times the heat of vaporization per droplet, is more than the power which the IC-chip  10   a  is dissipating, then the temperature of the IC-chip  10   a  gets reduced. However, the minimum temperature to which the IC-chip boa can be reduced is just slightly above the temperature where the droplet  40  vaporized. Thus, in the  FIG. 1  system, the lowest temperature at which the IC-chip  10   c  can be maintained is lower than that which would otherwise occur if the pressure in the container  20  were at, or above, atmospheric pressure. 
     Preferably, the sub-atmospheric pressure inside of the container  20  is kept at a point where essentially each liquid coolant droplet that is ejected from each nozzle rapidly vaporizes as soon as it hits the IC-module. Also preferably, the sub-atmospheric pressure inside of the container  20  is kept at a point where the boiling point of the liquid coolant is lowered by at least 10° C. from its boiling point at atmospheric pressure. 
     Further in the  FIG. 1  system, the sub-atmospheric pressure which is created by the vacuum pump  24  makes the seal ring  21  (as well as the container  20  and the conduit  22 ) leak tolerant. If a leak occurs between the seal ring  21  and the lid  10   f  of the IC-module  10 , air will get sucked into the container  20 , but that air can get purged from the system. By comparison, if the vacuum pump  24  was eliminated and the pressure inside of the container  20  was positive, liquid coolant would squirt out from any leak between the seal ring  21  and the lid  10   f , and that could cause an electrical short between the conductors  10   c ,  10   d , and  10   e  on the substrate  10   b.    
     After one particular IC-module  10  has been tested in the system of  FIGS. 1–5B , that IC-module is removed and replaced with another IC-module, which is then tested. This sequence is repeated over and over as desired. To aid in the removal of each IC-module, the isolation valve  22   b  is closed, and then the pressure relief valve  22   a  is opened. This enables the inside of the container  20  to be quickly returned back to atmospheric pressure before the IC-module  10  is separated from the seal ring  21 . 
     One preferred embodiment of a temperature regulating system which incorporates the present invention has now been described in detail. Next, with reference to  FIG. 6 , a second embodiment will be described. This second embodiment is the same as the embodiment of  FIGS. 1–5B  except that the array of nozzles  30  and IR-windows  31 , as shown in  FIG. 6 , replaces the previously described array of  FIG. 2 . 
     The difference between the arrays of  FIG. 6  and  FIG. 2  is that in  FIG. 6 , a single control signal ALLRC is sent to all of the nozzles  30 , whereas in  FIG. 2 , a separate control signal RiCj was sent to each nozzle. Thus in  FIG. 6 , the conductors that carry the signal ALLRC occupy substantially less space than the conductors in  FIG. 2  that carry the signals RiCj. 
     With the modified array of  FIG. 6 , all of the nozzles  30  eject one coolant droplet in response to each pulse in the control signal ALLRC. To increase (or decrease) the amount of heat that is removed per second from the IC-chip  10   a , the frequency of the pulses in the control signal ALLRC is increased (or decreased). The particular frequency at any time instant is selected by the control signal generator  33  in  FIG. 1  which generates the control signal CS 1  as signal ALLRC. 
     When the temperature of the IC-chip  10   a , as indicated by the TEMP signal, equals the set-point temperature, then the control signal generator  33  holds the frequency of the pulses in the ALLRC signal constant at its current rate. If the temperature of the IC-chip  10   a  starts to increase above the set point, then the control signal generator  33  increases the frequency of the pulses in the ALLRC signal. Conversely, if the temperature of the IC-chip  10   a  starts to decrease below the set point, then the control signal generator  33  decreases the frequency of the pulses in the ALLRC signal. When the frequency of the pulses in the ALLRC signal is decreased to zero, then the control signal generator  33  adds heat to the IC-chip  10   a  by sending control signal CS 2  to the IR-source  32 , as was previously described in conjunction with  FIG. 3C . 
     Next, with reference to  FIGS. 7A–7C , a third embodiment of a temperature regulating system which incorporates the present invention will be described. This third embodiment is the same as the embodiment of  FIGS. 1–5B  except that the array of nozzles  30  and IR-windows  31 ′, as shown in  FIGS. 7A–7C , replaces the previously described array of  FIG. 2 . 
     One difference between the arrays of  FIG. 2  and  FIGS. 7A–7C  is that in  FIGS. 7A–7C , the nozzles  30  are clustered together and are surrounded by four enlarged IR-windows  31 ′, whereas in  FIG. 2 , the nozzles  30  and IR-windows  31  are interleaved. Also in the array of  FIGS. 7A–7C , the single control signal ALLRC is sent to all of the nozzles  30 , just like the ALLRC control signal in  FIG. 6 . 
     By separating the IR-windows  31 ′ from the nozzles  30 , as shown in  FIGS. 7A–7C , all radiation from the IR-source  32  can be directed by optical components away from the cluster of nozzles  30  and through the IR-windows  31 ′. Thus in the array of  FIGS. 7A–7C , the maximum power level which can be radiated by the IR-source  32 , without.cndot.3damaging the nozzles  30  or their operation, is increased over the array of  FIG. 2 . 
       FIG. 7C  shows one particular structure for the bottom  20   a  of the container  20  which includes optical components that direct radiation, emitted by the IR-source  32 , around the nozzles  30 . Component  51  in  FIG. 7C  is a pyramid-shaped mirror. Radiation from the IR-source  32  is deflected by the mirror  51  into four beams which are perpendicular to each other. Two of those beams are shown in  FIG. 7C  as dashed lines, and the other two beams (not shown) are perpendicular to the plane of  FIG. 7C . 
     Components  52  and  53  in  FIG. 7C  together form four hollow passageways  54  in which the radiation from the mirror  51  travels. Each passageway  54  has reflective sidewalls which direct the radiation to the open ends  54   a  of the passageway. 
     Component  55  in  FIG. 7C  is a planar substrate. The array of nozzles  30  as shown in  FIG. 7B  is fabricated on the top surface of the substrate  55 , and components  52  and  53  are subsequently attached with an adhesive to the bottom surface of the substrate  55 . Four holes  55   a  extend through the substrate  55  in alignment with the open ends  54   a  of the passageways  54 . 
     All of the holes  55   a  in the substrate  55  are covered by a respective lens  56 . Each lens  56  is shaped to spread the radiation that it receives into the region over the array of nozzles  30  where the IC-chip  10   a  is held. Alternatively, all of the holes  55   a  can be plugged with a material which passes the radiation, and a mirror can be located near each hole to direct the radiation into the region where the IC-chip  10   a  is held. 
     Next, with reference to  FIGS. 8A and 8B , a fourth embodiment of a temperature regulating system which incorporates the present invention will be described. This fourth embodiment is the same as the embodiment of  FIGS. 1–5B  except that a single aerosol spray nozzle  61  which is surrounded by four enlarged IR-windows  31 ′, as shown in  FIG. 8A , replaces the array of nozzles  30  and IR-window  31  that are shown in  FIG. 2 . 
     The aerosol spray nozzle  61  receives liquid coolant from the conduit  29  in  FIG. 1 , and it continuously ejects multiple droplets of the liquid coolant as long as the control signal CS 1  is in an “ON” state. Those coolant droplets are ejected in a cone-shaped pattern onto the IC-package  10 , which in  FIG. 1  is pressed against the seal ring  21 . 
     Preferably, the control signal generator  33  generates the control signal CS 1  as a series of pulses which occur at a fixed frequency. To increase (or decrease) the amount of heat that is removed per second from the IC-chip  10   a , the width of the pulses in the control signal CS 1  is increased (or decreased). The particular pulse width at any time instant is selected by the control signal generator  33 . 
     Alternatively, the control signal generator  33  generates the control signal CS 1  as a series of pulses which have a fixed pulse width. To increase (or decrease) the amount of heat that is removed per second from the IC-chip  10   a , the frequency of the pulses in the control signal CS 1  is increased (or decreased). The particular frequency at any time instant is selected by the control signal generator  33 . 
     To direct the radiation which is emitted by IR-source  33  away from the aerosol spray nozzle  61 , the previously described structure of  FIG. 7C  may be used with one modification wherein the array of nozzles  30  is replaced with the aerosol nozzle  61 . Alternatively, the structure which is shown in  FIG. 8B  may be used. 
     In  FIG. 8B , the substrate  55  and four lenses  56  from  FIG. 7C  are retained. Also, a separate IR-source  32  is provided in each of the four holes  55   a  in the substrate  55  that are aligned with the lens  56 . Control signal CS 2  is sent to all four of the IR-sources  32 . 
     Next, a modification w ill be described which can be made to any one of the embodiments of  FIGS. 1–5B ,  FIG. 6 ,  FIGS. 7A–7C , and  FIGS. 8A–8B . For all of those embodiments,  FIG. 1  shows that the sidewall  20   b  of the container  20  squeezes the seal ring  21  against the lid  10   f  of the IC-package  10 . However, as a modification, the sidewall  20   b  can squeeze the seal ring  21  directly against the IC-chip  10   a.    
     One example of the above modification is shown in  FIG. 9 . There, the IC-package  10 ′ is the same as the IC-package  10  in  FIG. 1  except that the lid  10   f  and thermal interface material  10   g  are eliminated. Also in  FIG. 9 , the bottom  20   a  of the container  20  is shown as having the structure that was previously described in conjunction with  FIGS. 8A–8B . Alternatively, the bottom  20   a  of the container  20  can have the structure that was previously described in conjunction with  FIG. 2 , or  FIG. 6 , or  FIGS. 7A–7B . 
     Next, a modification will be described which can be made to the embodiment of  FIGS. 7A–7C . For that embodiment,  FIG. 7B , shows that all of the nozzles  30  eject one droplet of liquid coolant in response to a single control signal ALLRC. However as a modification, each of the nozzles  30  in  FIG. 7B  can be sent a separate control signal RiCj, as is shown in  FIG. 2 . 
     Next, a modification will be described which can be made to the embodiment of  FIGS. 8A–8B . In each of the  FIGS. 8A and 8B , only a single aerosol spray nozzle  61  is shown. However as a modification, two (or more) aerosol spray nozzles  61  can be held by the substrate  55  between the lenses  56 . Also, the same control signal can be sent to all of the aerosol spray nozzles  61  to turn all of them on, or the aerosol spray nozzles  61  can be sent separate control signals. 
     Next, a modification will be described which can be made to any one of the embodiments of  FIGS. 1–5B ,  FIG. 6 , or  FIGS. 7A–7C . For all of those embodiments, each nozzle  30  was described as a bubble-jet nozzle, like those which are in a printer for a computer. A bubble-jet nozzle ejects a liquid droplet by heating it with an electric resistor. However as a modification, each nozzle  30  can be a piezoelectric device which ejects a droplet by squeezing the droplet out of an orifice. Such a piezoelectric device is currently used in Epson printers for digital computers. 
     Next, a modification will be described which can be made to any one of the embodiments of  FIGS. 1–5B ,  FIG. 6 ,  FIGS. 7A–7C , and  FIGS. 8A–8B . For all of those embodiments,  FIG. 1  includes an IR-source  32  on the bottom  20   a  of the container  20 . However, when some particular types of the IC-chips  10   a  are tested, the electrical power dissipation in the IC-chip never reaches zero. Consequently, to test those types of IC-chips  10   a , the IR-source  32  and the IR-windows  31 – 31 ′ can be eliminated from the embodiments of  FIGS. 1–5B ,  FIG. 6 ,  FIGS. 7A–7C , and  FIGS. 8A–8B . 
     Next, another modification will be described which also can be made to any one of the embodiments of  FIGS. 1–5B ,  FIG. 6 ,  FIGS. 7A–7C , and  FIGS. 8A–8B . For all of those embodiments,  FIG. 1  includes a vacuum pump  23  which keeps the inside of the container  20  at a sub-atmospheric pressure. That in turn reduces the minimum temperature at which the IC-chip  10   a  can be maintained, and increases the speed at which each liquid droplet vaporizes, as was previously described in conjunction with  FIGS. 5A–5B . 
     However, when some particular types of tests are performed on the IC-chips  10   a , the set-point temperature is so high that a sub-atmospheric pressure inside of the container  20  is not needed. Consequently, to perform those tests, the vacuum pump  24  can be eliminated from the embodiments of  FIGS. 1–5B ,  FIG. 6 ,  FIGS. 7A–7C , and  FIGS. 8A–8B . Then, the vaporized droplets in the container  20  pass through the conduit  22  and the condenser/heat-exchanger  23  under a positive pressure which is created by the liquid pump  27  and the vapor itself. 
     Next, a modification will be described which can be made to the calculations that are shown by equations 1–7 in  FIG. 4 . There, the pulses in the control signals RiCj are set by equation 4 and occur with a frequency of ten-thousand pulses per second. However, that is just one specific example. A practical range for the frequency that can be set by equation 4 is 500 Hz to 500 KHz. 
     Next, a modification will be described which can be made to the IR-windows  31  and  31 ′ that are shown in  FIGS. 1 ,  2 ,  3 A– 3 D,  6 ,  7 A,  7 C,  8 A,  8 C, and  9 . Those windows pass infrared radiation from the IR-source  32  into the container  20  and onto the IC-module  10 . But as a modification, the IR-source  32  can be replaced by a substitute source (such as a laser) which radiates electromagnetic energy in a frequency band other than the infrared band. In that case, the IR-windows  31  and  31 ′ would be modified to pass the energy which the substitute source radiates. 
     Next, a modification will be described which can be made to any one of the embodiments of  FIGS. 1–5B ,  FIG. 6 ,  FIGS. 7A–7C , and  FIGS. 8A–8B . For all of those embodiments,  FIG. 1  shows that only a single container  20  is connected by the conduit  22  to the condenser/heat-exchanger  23 . However, as a modification, multiple copies of the container  20  can have their vacuum ports P connected by one conduit to the condenser/heat-exchanger  22 . In that case, the output of the pressure regulator  28  would be connected by another conduit to the internal channel for the liquid coolant in the bottom  20   c  of each container  20 . 
     When the above modification is made, each container  20  will hold a separate IC-module  10  as shown in either  FIG. 1  or  FIG. 8 . Also, the control signal generator  33  will concurrently generate separate control signals CS 1  and CS 2  for each IC-module  10  in response to a separate TEMP signal from each IC-module. 
     Next, another modification will be described which also can be made to any one of the embodiments of  FIGS. 1–5B ,  FIG. 6 ,  FIGS. 7A–7C , and  FIGS. 8A–8B . For all of those embodiments, the description of  FIG. 1  indicated that the set-point temperature is selected when the testing of an IC-chip begins and remains constant throughout the test. However, as a modification, the set-point temperature can be changed by the control input  34  at any time while an IC-chip is tested. 
     If the set-point temperature is changed while an IC-chip is being tested, each of the above embodiments of the temperature control system will respond very quickly to change the temperature of the IC-chip to the new set point. This quick response occurs because the amount of heat which is removed from the IC-chip by the coolant droplets, and the amount of heat which is added to the IC-chip through the IR-windows, can be quickly increased or decreased as was previously described in conjunction with  FIGS. 3A–3D  and  FIGS. 5A–5B . 
     Next, a modification which can be made to the temperature regulating system of  FIGS. 8A–8B  will be described. In that embodiment, the control signal CS 1  is sent to the aerosol spray nozzle  61  to thereby increase or decrease the amount of liquid coolant that is sprayed onto the IC-module  10 . However, as a modification, the control signal CS 1  can be sent to the pressure regulator  28  in  FIG. 1 . In that case, the pressure regulator  28  would be structured to increase or decrease the pressure at which it sends the liquid coolant to the aerosol spray nozzle, in response to the control signal CS 1 . 
     Multiple embodiments of the present invention and multiple modifications thereto have now been described in detail. Accordingly, it is to be understood that the present invention is not limited to just the details of any one particular embodiment, but is defined by the appended claims.