Abstract:
An evaporator ( 102 ) provides a compact design in which thermal energy can be removed from a DUT ( 108 ) in an efficient manner. The evaporator ( 102 ) can include a cover ( 306 ) which includes both input and output apertures for providing refrigerant into and out of the evaporator ( 102 ). An orifice plate ( 304 ) is located between the cover ( 306 ) and a heat exchanger ( 302 ). The heat exchanger ( 302 ) includes a plurality of pillars which help increase the surface area of the heat exchanger ( 302 ). The orifice plate ( 304 ) includes an aperture ( 310 ) which forms a nozzle which sprays refrigerant onto the heat exchanger in order to remove the heat away from the heat exchanger ( 302 ).

Description:
FIELD OF THE INVENTION 
   The invention relates in general to heat dissipation devices and more particularly to an evaporator for use in dissipating heat from electronic devices that are undergoing testing. 
   BACKGROUND 
   Modern electronic devices such as high-speed microprocessors, power amplifiers and laser diodes generate large amounts of thermal energy in the form of heat when in operation. Designing a test system to test a large volume of electronic devices that dissipate a large amount of heat in a timely fashion is not an easy task since the heat generated by the electronic device-under-test (DUT) has to be removed or minimized in a timely fashion in order to properly test the DUT, while at the same time minimizing the size of the test/cooling system in order to conserve floor space. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention may best be understood by reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which: 
       FIG. 1  shows a portion of a test assembly including a DUT and evaporator for removing the heat from the DUT in accordance with an embodiment of the invention. 
       FIG. 2  shows a cross-sectional view of the test assembly shown in  FIG. 1  in accordance with an embodiment of the invention. 
       FIG. 3  shows an exploded of an evaporator in accordance with an embodiment of the invention. 
       FIG. 4  shows a top view of the evaporator shown in  FIG. 3  in accordance with an embodiment of the invention. 
       FIG. 5  shows an isometric view of a heat exchanger in accordance with an embodiment of the invention. 
       FIG. 6  shows a top view of the heat exchanger in  FIG. 5  in accordance with an embodiment of the invention. 
       FIG. 7  shows a side view of the heat exchanger in  FIG. 5  in accordance with an embodiment of the invention. 
       FIG. 8  shows a block diagram of a test system with DUT cooling capability in accordance with an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures. 
   Referring now to  FIG. 1  there is shown a portion of a test assembly  100  including a test socket  106  for receiving a Device-Under-Test (DUT)  108  such as an integrated circuit (IC) semiconductor or other electronic device that requires testing. Although not shown, the DUT  108  is placed in the test socket  106  using conventional pick-and-place equipment which is well known in the art. The test assembly further includes an evaporator  102  coupled to a refrigerant distribution manifold  104 . The evaporator  102  may be attached to the manifold using conventional fasteners such as screws. A gasket (not shown) is placed between the evaporator  102  and distribution manifold  104  in order to seal the refrigerant inputted into the evaporator  102 . In one embodiment of the invention, the refrigerant provided to the evaporator  102  is liquid R-134a Freon, although other refrigerants may be used. 
   In operation, once a DUT  108  is placed in the test socket  106  the evaporator  102  is lowered and placed in thermal contact with the evaporator  102 . In one embodiment, a compressible material having a high thermal conductivity coefficient which can transfer heat readily attached to the bottom of the evaporator  102  so that a tight fit is achieved between the DUT  108  and evaporator  102  in order for heat to flow easily from the DUT  108  to the heat exchanger  302 . Once testing of the DUT  108  begins and the DUT starts generating heat, the liquid Freon being passed through the evaporator absorbs the heat and causes the liquid Freon to convert instantly into a gas which is outputted from the evaporator  102 . By transferring heat away from the DUT  108  allows proper testing of the DUT  108  since the DUT  108  is allowed to stay within its operational thermal limits which prevent damaging the DUT  108  while it is undergoing testing. 
   In  FIG. 2 , there is shown a cross-sectional view of the evaporator  102  in thermal contact with the DUT  108 . Once the testing of the DUT  108  is completed, the evaporator  102  is raised and the DUT  108  is removed from the testing socket  106 . A new DUT  108  is then placed in the testing socket  106  and the entire testing process is repeated. 
   An exploded view of the evaporator  102  is shown in  FIG. 3 . The evaporator  102  is comprised of a cover  306 , an orifice plate  304  and a heat exchanger  302 . In one embodiment, each of the pieces of the evaporator  102  is formed from copper or other material having high thermal conductivity. The orifice plate  304  is brazed to the heat exchanger  302  and the cover  306  is then brazed to the heat exchanger  302  in order to form a sealed evaporator. Other attachment techniques such as welding can also be used to attach the individual pieces together. 
   The orifice place  304  has a nozzle aperture  310  which in one embodiment has a precision double bevel which causes the liquid refrigerant sent via an input aperture  308  to form a controlled spray or misting pattern onto the heat exchanger  302 . Since the heat exchanger  302  is very hot while the DUT  108  is undergoing testing, once the refrigerant mist hits the heat exchanger  302  the liquid refrigerant is immediately turned into gas allowing for the transfer of heat away from the heat exchanger  102  and thus away from the DUT  108 . The refrigerant in the gaseous state leaves the evaporator  102  via the side edges of the orifice place and then via an output aperture located on cover  306  (shown in  FIG. 4 ) and the process is repeated as needed. Although not shown, pressure and temperature sensors are located on the refrigerant manifold  104  in order to monitor the operating conditions of the evaporator  102  and make necessary adjustments to the amount and frequency of refrigerant provided to the evaporator  102 . 
   Located in the underside of the cover  306  is a curved channel groove  312  which causes liquid refrigerant entering the evaporator via refrigerant input  308  to form a swirling pattern before it enters nozzle  310 . In one embodiment, the refrigerant entering the nozzle  310  is at a pressure of about 90 PSI (pounds-per-square inch), although the pressure the refrigerant is provided will depend on the particular system requirements; pump size found in the cooling system, etc. A refrigerant swirl chamber is formed between the cover  306  and orifice plate  304 , with refrigerant entering input  308  being spun into a high RPM before being sheared off by nozzle  310  and forming a fine spray or mist pattern onto the heat exchanger  302 . The heat exchanger  302  includes in one embodiment a plurality of vertical pillars which helps form a heat exchanger having excellent thermal capacity for its compact size. The sprayed liquid refrigerant from nozzle  310  is immediately flashed into a gaseous state upon making contact with the hot heat exchanger  302  given that the heat exchanger  302  is in thermal contact with a DUT that is undergoing testing. This also creates a very short thermal path making very fast thermal responses possible. 
   In  FIG. 4 , there is shown a top view of the cover  306 . The smallest aperture shown is used for aligning the cover  306  to its proper attachment location in the refrigerant distribution manifold  104 . Of the remaining four apertures one is the refrigerant input aperture  308 , one is the refrigerant output aperture and the remaining two are preferably threaded and are used to fasten the evaporator to the distribution manifold  104 . O-rings are preferably used in the input and output apertures in order to firmly seal the refrigerant entering and leaving the evaporator  102 . 
   Referring now to  FIG. 5 , there is shown an isometric view of the heat exchanger  302  having first and second major sides. The first major side of the heat exchanger  302  is relatively flat and is the side that is thermally coupled to the DUT  108 . In order to maximize the surface area for the liquid refrigerant to remove heat away from the heat exchanger  302 , a plurality of pillars are formed extending away from the base of the heat exchanger on the second side. The greater surface area provided by the plurality of pillars helps to quickly remove heat away from the heat exchanger  302  and thus away from the DUT in a very compact area. At the center of the heat exchanger  302  is a circular cavity which is aligned with the nozzle  310  found in the orifice plate. The cavity helps evenly distribute the refrigerant spray that is being presented to the heat exchanger  302  second side via nozzle  310  and allows the sprayed refrigerant to contact as much surface area of possible. By distributing the liquid refrigerant as evenly as possible to all of the pillars and the rest of the heat exchanger&#39;s surface enclosed by cover  306 , the quicker the heat is removed from the heat exchanger&#39;s surface using a very compact space. 
   In  FIG. 6  there is shown a top view of the pillar side of the heat exchanger  302 . In the embodiment shown, the pillars except for the pillars along the edge have a square shape and the edge pillars have a triangular shape. The cavity or recess at the center of the heat exchanger which is preferably in alignment or in registration with nozzle  310  further improves the distribution of the sprayed refrigerant amongst all of the pillars and the rest of the heat exchanger on that side. Dimensions for one embodiment of the heat exchanger are highlighted in  FIGS. 6 and 7 . Different shapes and sizes for the heat exchanger and the pillars can also be used with the present invention. The pillars for example can take different exotic shapes in order to further maximize the surface area presented to the sprayed refrigerant to further maximize the heat removal from the heat exchanger  302 . In the embodiment shown in  FIG. 6 , the plurality of pillars are evenly spaced and oriented in such a fashion that they form channels extending away from the central cavity and which are at right angles. 
   The heat exchanger  302  can be milled in order to form the pillars or in an alternative embodiment can be formed from a mold. The orifice plate  304  is brazed, welded or otherwise fastened to the top of the pillars. The edge margin around the entire second side of the heat exchanger that does not have pillars allows the gaseous refrigerant to exit towards the output refrigerant aperture located on cover  306  since the orifice plate  304  does not extend into the edge margin areas when fastened to the heat exchanger  302 . 
   In  FIG. 8 , there is shown a block diagram of a test system incorporating the evaporator of the present invention. Coupled to the evaporator is a cooling system that provides the liquid refrigerant to the evaporator and collects the refrigerant in a gas form from the evaporator. The cooling system also includes a test system and pick-and-place equipment that automatically places the DUT in the proper test socket and performs the needed tests on the DUT. The test system will also include a controller for controlling the cooling system and controlling the amount of refrigerant presented to the evaporator using conventional metering valves, etc. 
   Evaporator  302  provides for a very compact way of removing heat away from a DUT. Having a heat exchanger  302  that includes a plurality of pillars helps to increase the surface area in which the refrigerant can extract heat from the heat exchanger and away from the DUT. Although the heat exchanger  302  has been shown with pillars that extend perpendicular from the base since this helps increase the ability of the sprayed refrigerant to contact most if not all of the pillars in a fairly even fashion, the pillars can extend away from the base at other angles. 
   While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.