Abstract:
A thermal chamber and system for influencing the temperature of an IC chip under test including a thermal block that receives a chip socket, the thermal block adapted to be disposed between a docking interface plate and a workpress. The thermal block receives a flow of heated or cooled gas, and causes an IC chip to become heated or cooled prior to and during a test of the chip. The thermal chamber and system allows an IC chip to be testing under specific temperature conditions without using an expensive handler costing hundreds of thousands of dollars.

Description:
BACKGROUND 
     The present invention is related generally to testing apparatus for integrated circuit chips (“IC chip” or “chip”), and more particularly to an assembly for regulating the temperature of an IC chip while the chip is mounted on a testing board so that it can be tested under predetermined temperature conditions. 
     Current IC chips can be designed to include hundreds of thousands of transistors, and those transistors require testing before the IC chip is delivered to a customer. Typically, 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. 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 ten percent of the 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 degree C. to 140 degree 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 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, resulting in the IC-chip being sold as a lower priced part. 
     The “system level” test is the final test. In the system level test, the IC chips are exercised using software applications that 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 degree −80 degree C. 
     During each of these tests, it is important to control and be able to test the chips under a variety of temperature ranges. Currently, to control the temperature of the chips during testing, large and expensive machines have been constructed such as those available from Delta Designs of Poway California, for example the ETC handlers (see www.deltad.com). These machines can cost up to four hundred thousand dollars or more. The temperature control of such machines requires larger volumes to be heated or cooled, and require large allocations of space and capital to operate. The present chip testing technology is in need of a low cost, efficient method of controlling the temperature of an IC chip under test. 
     SUMMARY OF THE INVENTION 
     The present invention is a small, lightweight cooling/heating chamber that can be used to test IC chips at a controlled temperature on a bench for device characterization and evaluation. This chamber can be retrofitted for use with existing test equipment and be incorporated into current test protocols without significant modification of the test equipment. The thermal chamber of the present invention is a block that has at least one inlet for a hot or cold fluid to circulate through a closed channel to heat or cool the chip, thereby reducing preheating/precooling, or “soak” time. There is also a second flow path that directly cools or heats the chip while testing. The cooling/heating chamber is designed to mate with a workpress (also referred to as a device nest or device plunger) and a docking interface plate to enclose the IC chip for testing purposes. The chamber can be designed with a ball valve or similar mechanism that controls the input of fluid into the chamber. 
     A clamp is also disclosed for use in securing the chip to the workpress, having a lever and pair of linkages that drive the workpress through the docking interface plate and against the chip/socket arrangement. The clamp includes spring mounted inside a block that connects to the workpress that yields a compliance for connecting to the chip. This compliance allows the downward force of the chip with the socket to be lessened, thereby reducing PCB wear and socket wear. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is perspective view of a first embodiment of the chamber of the present invention; 
         FIG. 2  is a cross-section of the chamber of  FIG. 1 ; 
         FIG. 3  is a view of the chamber of  FIG. 1  mounted on a docking interface plate; 
         FIG. 4  is a reverse view of the docking interface plate of  FIG. 3  showing the workpress; 
         FIG. 5  is a cross-sectional view of the chamber showing the ball valve; 
         FIG. 6  is a view perspective view of a clamp for use with the thermal chamber in testing an IC chip; 
         FIG. 7  is another perspective view of the clamp of  FIG. 6  showing the thermal chamber and IC chip mounted thereto; and 
         FIG. 8  is a perspective view, partially cut away, of the clamp assembly and the cooling chamber. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is a thermal chamber that can be used to control the temperature of an IC chip under test. The temperature control uses a flow of fluid, which is preferably a cooled or heated gas such as air, nitrogen, or the like. The thermal chamber is designed to hold a chip socket, that itself contains an IC chip to be tested. The thermal chamber is mounted to a docking interface plate that includes a thermal insulator surrounding the thermal chamber. A work press engages a valve actuator on the thermal chamber to introduce fluid across the socket/chip surface. 
       FIG. 1  is a perspective view of the thermal block  10  that defines the thermal chamber. The thermal block  10  has a top side  12  and a bottom side  14 , and front  16  and rear  18  walls along with first and second side walls  20 , 22 . An aperture  24  in the interior of the block  10  allows a chip socket  26  to be inserted and held therein. The front wall  16  of the block  10  includes first and second nozzles  28 ,  30  that serve as ports for the introduction and exit of a fluid such as a heated or cooled gas. Nozzle  28  serves as the port for the temperature controlled fluid to enter the block  10 , and nozzle  30  is the exhaust port where the temperature controlled fluid exits the block  10 . The rear wall  18  also includes two nozzles  32   a,b  that connect to two channels  33  that are fed from a opening  31  in the block at the aperture  24 , the two channels  33  leading to the rear wall  18  and the nozzles  32   a,b,  and can channel the fluid out of the block  10  from the aperture  24 . There are two fluid flow paths that are defined in the thermal block  10 , a first channel  34  that internally extends around the block  10 , entering at the first nozzle  28  and exiting through the second nozzle  30  on the front wall  16 . A second path flows the fluid through the first nozzle  28  and into a first pathway (not shown) that leads to the aperture  24 , where the fluid flows across the aperture  24 , into the opening  31  and through the two channels  33  that lead out to the two nozzles  32   a,b  on the rear wall  18 . A ball valve  36  is disposed on the first nozzle&#39;s  28  entrance to govern the flow of the fluid either through the first path or the second, as set forth more fully below. 
       FIG. 2  shows a cross-section of the block  10  illustrating the two paths of the fluid flow. When the ball valve  36  is in a first position, the flow of the fluid entering through the nozzle  28  is directed entirely through the channel  34 , around the block  10 , until the fluid exits the exhaust nozzle  30  after having completed a path around the entire block (depicted as arrows  42 ). The fluid flowing through the channel  34  will heat or cool the entire block, thereby shortening any pre-heating or pre-cooling, also referred to as “soak.” A chip and socket disposed in the aperture  24  can be brought to the desired temperature during the soak period as the fluid circulates through the block  10 . 
     During the actual testing, the ball valve can be moved to a second position by depressing the actuator  38 , which blocks or partially blocks the flow path into the channel  34  while opening a flow path through the channel that leads to the aperture  24 . With the socket and chip disposed in the aperture  24 , the fluid can flow directly over the chip (depicted as arrows  48 ) to maintain even greater control on the temperature of the chip during the testing procedure. The relatively small mass of the chip will predominantly assume the temperature of the flowing gas over its surface during the test, ensuring a more accurate temperature response. The fluid flowing over the gas exits the aperture area through the opening  31  and through the channels  33  and out the nozzles  32   a,b.    
     The gas or temperature controlled fluid can also be directed to flow in both paths by letting the ball valve occupy a position that blocks neither the channel  34  nor the path across the socket/chip. In some embodiments, this will be the mode for normal testing, with both flow paths employed. To control the amount of flow between the two flow paths, a flow control valve  40  may be located at the end of the channel  34  that controls the area of the exit exhaust nozzle. By reducing the area, more flow will be directed in the second flow path across the chip (indicated by arrows  48 ) and less flow will be directed around the channel  34  (indicated by arrows  42 ). 
       FIGS. 3 and 4  illustrate how the thermal chamber can be incorporated into a testing set-up. In  FIG. 3 , a docking interface plate  44  has mounted on it a thermal insulating material  46  on a first surface to prevent heat loss or heat gain into the system during the testing. The insulating material has a depth that is approximate to the thickness of the block  10 , and surrounds the block  10  while providing a pathway  47  for conduits that couple to the nozzles  28 ,  30  to extend therefrom. Inside the block  10  is a socket  26  that mounts in the aperture  24 , and an IC chip  50  is mounted in the socket  26 . With the socket  26  and chip  50  in the block  10 , heating or cooling fluid such as air can be passed directly over the face of the chip while it is being tested, thereby providing an efficient method of testing the chip under a variety of different temperature conditions without using large, expensive equipment for this purpose. 
       FIG. 4  illustrates the reverse view of  FIG. 3 , showing the underside of the docking interface plate  44  with the nozzles  32   a,b,  exposed. A workpress  52  is mounted to the underside of the docking interface plate  44 , as is well known in the industry. As  FIG. 4  illustrates, the thermal chamber is incorporated directly into the workpress/docking interface plate assembly without inhibiting the testing function of the chip or the testing set-up. Hot or cold air, nitrogen, or other gas can be introduced through nozzle  28  and allowed to flow over the chip  50  while the chip is being tested, and while the block  10  is temperature controlled by the same fluid. 
     The workpress, which can be for example a TCWP Titan Compliant workpress, can be installed in a handler or other automation equipment. The workpress picks up the chip from a tray and delivers it to the socket and thermal chamber assembly. The socket/thermal chamber may then be installed on a printed circuit board (PCB) fixture, which is mounted on a tester equipment or plugged into testing equipment. In the present set-up, the chip is seated in the socket and engaged for electrical testing before the ball valve is fully depressed for full airflow. An important feature is that the airflow will not blow the chip off of the workpress as it is being presented to the socket. That is, as the chip is being removed from the socket, the ball valve closes the airflow, preventing airflow from separating the chip from the workpress. This is important because, if the chip falls off the workpress vacuum, the machine stops and an operator must remove the chip and reset the machine, causing downtime. This feature is unique to the present set-up. 
       FIG. 5  illustrates the ball valve  36  at the entrance to the channel  34 , and also the flow control valve  40  at the exit of the channel  34 . The flow control valve can be a screw member  40  that blocks or partially blocks the exit  54  of the channel  34 , such that rotation of the screw member  40  in a first direction entirely blocks the exit, forcing the fluid to flow entirely through the second path  48  across the block. Conversely, rotation of the control valve  40  in the opposite direction opens the path out of the channel  34  through exit  54  (which leads to nozzle  30 ), such that more of the fluid will follow the first path through channel  34  since there is less resistance along this path. The ball valve  36  includes an occluding member  58  that blocks the path across the aperture  24  in the unbiased condition due to the force of the spring member  56 . However, when the pin  38  is depressed, the occluding member  58  compresses the spring as it lowers, exposing a channel through the block leading to the aperture  24  and across the block  10 . 
       FIGS. 6-8  illustrate a clamp  70  that may be used in conjunction with the thermal chamber in a manual mode. The clamp  70  works with the workpress  52  to allow for manual operation without using a large automated handler or other expensive equipment. The clamp  70  mounts on the docking interface plate  44  as shown in  FIG. 6 . The clamp  70  has a manual lever  72  that pivots to open and close a pair of linkages  74 ,  76  in a scissor motion, which in turn drives a base  78  that secures the workpress  52 . The workpress  52  moves vertically down through the hole in the docking interface plate  44  and against the socket  26  and chip  50 , secured on the underside of the docking interface plate  44 . The lower surface of the workpress  52  depresses the ball valve actuator  38  to direct the flow across the chip  50  as discussed above, and when the lever  72  is rotated back, the workpress  52  disengages the docking interface plate  44  and the ball valve actuator  38  springs back to the original position. 
     Traditional workpresses have no compliance or spring; rather, the traditional workpress includes a plunger gap of approximately one millimeter and then bottoms out. The lower portion of the workpress, (referred to sometimes as a “bladepak”), pushes directly on the chip mounted in the workpress.  FIG. 8  illustrates a new workpress  52  that has compliance due to an internal spring  82  that allows resilient pressure on the chip  50 . The workpress  52  is mounted to the base  78  at a lower platform. A plunger  98  is coupled to the spring  82 , decoupling the plunger&#39;s vertical motion from the cover of the workpress. The spring may have a force of between seven and twenty seven pounds in a preferred embodiment, although the spring may be chosen to meet the needs of the particular application. The compliance can be in the range of about one millimeter, depending upon the selected spring and the tolerances desired, which provides for a chip thickness variation of up to 0.5 mm. The lower platform preferably rides on guides that allow the workpress to slide vertically, but allow some play in the vertical position to prevent damage to the chip. 
     The spring provides some tolerance with respect to the force of the workpress, which helps to prevent wear on the PCB and the socket by reducing the force on the socket and load boards. The compliance also has an important feature with respect to the thermal chamber. As a chip  50  is seated in the socket  26  and engaged for electrical testing before the workpress  52  engages the ball valve actuator  38 , air will be flowing around the block  10  but not across the chip  50 . It is important that the airflow does flow across the chip until the workpress is fully seated against the socket. Otherwise, the airflow can blow the chip  50  off of the workpress  52  as it is being presented to the socket  26 . As a result of the compliance in the clamp  70 , as the chip  50  is being removed from the socket  26 , the ball valve  36  closes the airflow, preventing blowoff. 
     The cooling/heating block  10  can take other configurations and the illustrated embodiment is meant to be exemplary only. For example, the number and placement of the nozzles can vary depending upon the requirements of the system without departing from the spirit of the invention. Similarly, the shape of the block is not critical and can take other shapes that make it convenient for the workpress and docking interface plate if necessary. Therefore, the preceding descriptions and embodiments should not be interpreted to limit the invention in any manner other than where expressly stated herein, and that the invention&#39;s scope should properly be interpreted based on the appended claims, in view of the foregoing but wherein the words of the claims are given their ordinary meaning.