Patent Publication Number: US-8981802-B2

Title: Systems and methods for conforming device testers to integrated circuit device profiles

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part and claims benefit of U.S. application Ser. No. 13/081,439 filed on Apr. 6, 2011, entitled “Systems and Methods for Thermal Control of Integrated Circuits during Testing”, which is a continuation-in-part and claims benefit of U.S. application Ser. No. 12/957,306 filed on Nov. 30, 2010, entitled “Improved Thermal Control Unit Used to Maintain the Temperature of IC Devices Under Test”, which claims benefit of U.S. Provisional Patent Application No. 61/265,285 filed Nov. 30, 2009, all applications are hereby fully incorporated by reference. 
    
    
     BACKGROUND 
     The present invention generally relates to the testing of IC devices such as packaged semiconductor chips (also referred to as packaged dies), and more particularly relates to device testers configured to conform to the shape of integrated circuit (IC) devices under test (DUTs). 
     Conventional integrated circuit devices include a die, incorporating the IC, attached a substrate. The die is bonded electrically (e.g. solder) and physically (e.g. epoxy) to the top of the substrate, at an elevated temperature sufficient to melt solder and to cure the epoxy. 
     Initially, before they are bonded to each other, both the substrate and the die are flat. However as illustrated by the simplified and exaggerated cross-sectional view (not to scale) of  FIG. 12A , during the cooling process after heated bonding process, device  1280 A becomes slightly curved (slightly bowed like the top of a mushroom) because of a mismatch of expansion and contraction coefficients of the die and the substrate. 
     The curvature of the device at room temperature (after cooling) should not be a problem because during the assembly of the device to a motherboard, at the elevated reflow temperature (sufficient to melt solder paste) inside a surface mount technology (SMT) reflow oven, the reheated device should become substantially flat again, thereby ensuring satisfactory electrical bonds between the device pads and the motherboard contacts. 
     Ideally, the curvature of the device should be preserved prior to assembly to the motherboard. However, these devices need to be tested for proper functionality at different temperatures prior to assembly to the motherboard. Typical device testers are designed with the assumption that the devices under test (DUTs) are flat. As a consequence, the flat profiles of the pedestal, the substrate pusher and the test socket result in undue pressure being exerted on the curved DUT, especially on the die, during testing. 
     This undue pressure problem is exacerbated by the existence of other components, in addition to the die, on the same substrate. So in a typical tester, the pedestal and the substrate pusher only contact the die and the perimeter of the substrate, respectively, leaving the remaining surface of the substrate, where the other components reside, unsupported. 
     As a result, after testing the surface of the device is somewhat flattened due to the undue pressure from the pedestal and the pusher, and often uneven, due to the uneven pressure between the supported and unsupported surfaces of the DUT.  FIG. 12B  is a simplified and exaggerated cross-section view (not to scale) of one such exemplary post-testing uneven, e.g., wavy, device  1280 B. 
     Hence there is an urgent need for improved device tester designs that do not unduly deform the DUTs, especially for devices with thinner substrates needed for manufacturing compact portable electronic devices such as smart phones and tablets. 
     SUMMARY 
     To achieve the foregoing and in accordance with the present invention, systems and methods for testing of IC devices such as packaged semiconductor chips, while conforming to the shape of the IC device under test (DUT). 
     In one embodiment, an IC device tester configured to maintain a set point temperature on the DUT having a substrate having a die attached to an upper surface thereof, and also configured to conform to the profile of the DUT. The device tester includes a thermal control unit and a test socket assembly. 
     The thermal control unit includes a pedestal assembly with a heat-conductive pedestal having a bottom end configured to contact the die of the DUT, a temperature-control fluid circulation block, a thermally-conductive heater having a fuse coupled to a heating element, a substrate pusher configured to contact the substrate of the DUT, and a controllable force distributor for receiving a z-axis force and controllably distribute such z-axis force between the pedestal assembly and the substrate pusher. The test socket assembly includes a test socket operatively coupled to a socket insert for supporting the DUT. The socket insert has a shaped profile substantially conforming to a corresponding profile of the DUT. 
     In some embodiments, the test socket assembly has an elevator mechanism that includes a plurality of spring-loaded suspension support pins for supporting the socket insert. The test socket assembly may also include a plurality of spring-loaded test pins. The support pins enable the test pins to be withdrawn while in a rest condition and further enable the test pins to protrude during a test condition. 
     Note that the various features of the present invention described above may be practiced alone or in combination. These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the present invention may be more clearly ascertained, some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a side view of an exemplary thermal control unit that includes a z-axis force balancing mechanism in accordance with one aspect of the invention; 
         FIG. 2  is a cross-sectional view thereof taken along section lines  2 - 2  in  FIG. 1 ; 
         FIG. 3  is another cross-sectional view thereof taken along section lines  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a bottom perspective view of the z-axis load distributor actuator block of the z-axis force distribution system of the TCU shown in  FIGS. 1-4 ; 
         FIG. 5  is a cross-sectional view of the load distributor actuator block shown in  FIG. 4  along the line  5 - 5 , in combination with a spring loaded gimbal; 
         FIG. 6  is a side view of another exemplary embodiment of a thermal control unit in accordance with the present invention; 
         FIG. 7A  is cross-sectional view thereof taken along section lines  7 A- 7 A in  FIG. 6 , while  FIG. 7B  is an exploded view of  FIG. 7A ; 
         FIG. 8  is another cross-sectional view thereof taken along section lines  8 - 8  in  FIG. 7A ; 
         FIG. 9  is another cross-sectional view thereof taken along section lines  9 - 9  in  FIG. 7A ; 
         FIG. 10A  is a bottom perspective view of an exemplary z-axis load distributor actuator block for the z-axis force distribution system of the TCU  600  shown in  FIGS. 6-9 ; 
         FIG. 10B  is a bottom perspective view of an alternative embodiment of the z-axis load distributor actuator block of  FIG. 10A ; 
         FIG. 11  is a cross-sectional view of the load distributor actuator block shown in  FIG. 10A  along the line  11 - 11 , in combination with a spring loaded gimbal; 
         FIG. 12A  is a cross-sectional view of a slightly curved IC device prior to testing; 
         FIG. 12B  is a cross-sectional view of an IC device deformed by testing; 
         FIGS. 13A and 13B  are cross-sectional views illustrating embodiments of a pedestal, a substrate pusher and the test socket in accordance with the present invention; 
         FIGS. 13C and 13D  are cross-sectional views of additional embodiments of the test socket inserts; 
         FIG. 13E  is a perspective view of the test socket and test socket insert for the embodiment of  FIG. 13A ; 
         FIGS. 13F and 13G  are cross-sectional views illustrating a suspension pin and a test pin for the embodiment of  FIG. 13A , in rest condition and test condition, respectively; and 
         FIGS. 14A-14D  are a front view, a top view, a perspective view and a blown-up view illustrating an exemplary fused heater in accordance with some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described in detail with reference to several embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, to one skilled in the art, that embodiments may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. The features and advantages of embodiments may be better understood with reference to the drawings and discussions that follow. 
     Before describing the present invention in detail, it is to be understood that the invention is not limited to the TCU illustrated herein. It is also to be understood that the terminology used herein is for describing particular embodiments only, and is not intended to be limiting. 
     In addition, as used in this specification and the appended claims, the singular article forms “a,” “an,” and “the” include both singular and plural referents unless the context of their usage clearly dictates otherwise. Thus, for example, reference to “a piston” includes a plurality of springs as well as a single piston, reference to “an outlet” includes a single outlet as well as a collection of outlets, and the like. 
     In general, the invention relates to thermal control units (TCUs) that may be used to maintain a set point temperature on an IC device under test (DUT). The TCU can suitably include features common to those described in U.S. Pat. No. 7,663,388, which is incorporated herein by reference. Such features would include, in a z-axis stacked arrangement, a heat-conductive pedestal for contacting the DUT and containing a thermal sensor, a fluid circulation block, and a thermoelectric module (a Peltier device) or heater between the heat-conductive pedestal and the fluid circulation block for pumping heat away from the DUT and into the fluid circulating block (or for pumping heat into DUT). The common features would also include in the z-stack arrangement a spring loaded pusher mechanism for exerting a z-axis force compliant force that holds the fluid block, thermoelectric module (or heater) and heat conducting pedestal tightly together. 
     The present invention also relates to systems and methods for testing of IC devices such as packaged semiconductor chips (also referred to as packaged dies) while preserving the devices&#39; original specifications, especially with respect to the IC devices physical characteristic. 
     The TCUs in accordance with the invention may be used on DUTs of different constructions. For example, the TCU may be used with IC devices having a lidded package that employs an integrated heat spreader (IHS) or with IC devices having a bare die chip package. 
     One aspect of the invention is directed to TCUs having different pushers used to push against different parts of a chip package. In this aspect of the invention, a z-axis load distribution system is provided for controllably distributing the total z-axis force applied to from the top of the TCU between different pushers so that a desired balance can be achieved for the exerted by the different pushers. For example, when a die pusher/pedestal and a substrate pusher are used in conjunction with bare die chip packages, the z-axis forces applied the die pusher/pedestal can be adjusted relative to with the pushing force applied by the substrate pusher to balance the loads on the die and substrate of the bare die package. 
     In another and separate aspect of the invention, at least one and preferably both the fluid inlet and/or fluid outlet for the fluid circulation block are swivelable, preferably about a swivel axis that is substantially perpendicular to the z-axis of the TCU. The swivel capability of the fluid inlet and outlet acts to reduce instability of the thermal control unit in response to z-axis movement of the temperature-control fluid block. 
     In a further and separate aspect of the invention, a means for abating condensation is provided. Such means includes a condensation-abating gas inlet and condensation-abating gas transporting passageways in the thermal control unit near surfaces of the thermal control unit on which condensation may occur. 
     An exemplary embodiment of a TCU in accordance with the invention is illustrated by  FIGS. 1-5 . 
     The thermal control unit  1  includes the following basic sections arranged in stacked relationship along the z-axis of the TCU: a force transmitting section  10  for transmitted a z-axis force denoted by the arrow F in  FIG. 1  to the TCU&#39;s DUT contacting pushers as hereinafter described; an inner spring loaded pusher block section  40 ; a fluid circulation block section  50 ; a thermoelectric module (hereinafter Peltier device) section  60 ; and a heat conductive pedestal section  72  having a pusher end  76 , which contains a temperature sensor  78 , for contacting and pushing against a thermally active central portion of an IC chip, such as the die  104  of a bare die chip package  100 . An outer pusher structure is also provided. This pusher structure, denoted by the numeral  80 , includes a rigid bottom pusher plate  81  and is suitably fabricated of a metal material, such as aluminum, for rigidity. The bottom pusher plate has a center opening to allow the pusher end of the heat conducting pedestal to project through the pusher plate. A second DUT contacting pusher  82  extends from the bottom of the pusher plate around this center opening. This second pusher extends in the z-axis direction in parallel with the pusher end of the pedestal and contacts and pushes against another part of the IC chip, such as the substrate  102  of the bare die chip package. 
     The outer pusher structure additional includes a skirt  90  secured around the outer perimeter of the bottom pusher plate  81  and that extends upward in the z-axis direction. 
     Referring to  FIG. 3 , the fluid circulation block section  50  is seen to have a lower contact plate  58  at the bottom of block&#39;s main body  56 . This lower contact plate is made of a good heat conductor such as copper and is suitable provided to achieve efficient heat conduction between the fluid circulation block section and the thermoelectric module  60 . The upper section  56  of the may be formed from material that does not conduct heat as well as copper or other metals. 
     The force transmitting section  10  of the TCU includes a force distribution block  12  and can additionally include a gimbal adapter  30  above the force distribution block to form a gimbal. The gimbal adapter  30  includes a top coupler part  32  having upper and lower surfaces  32  and  34 , with the upper surface of the coupler part being positioned to receive the indicated z-axis force F. The gimbal adaptor further includes springs  36  positioned beneath the lower surface of the top coupler part of the gimbal adaptor at the corners of the coupler part. Springs  36  are held in compression between the adaptor&#39;s coupler part and the upper surface  16  of the force distribution block  12  for preload gimbal stability. 
     As best seen in  FIG. 2 , the outer pusher structure is secured to the force distribution block  12  by force transfer shafts  110 . These shafts freely pass through suitably sized holes in the inner spring loaded pusher block and fluid circulation block sections  40 ,  50 . The bottom ends  113  of shafts  110  are suitably anchored to the pusher plate  81  near the outer perimeter of the plate, such as by threaded engagement, while the top ends  112  of the shafts extend through openings  20  (shown in  FIG. 4 ) in the corners of the force distribution block and are topped by cap nuts  115 , or any other captive mechanism that allows z-movement to retain the force distribution block on the shafts. As shown in  FIG. 2 , the force distribution block is compliantly supported on springs  117  provided around the recessed portion of the shaft beneath the force distribution block and which set on shoulders  119  presented by the recessed portion of the shaft. A z-axis force F applied to the force transmitting section  10  will thus be compliantly transmitted to pusher  82  of the outer pusher structure, and thus to the substrate  102  of bare die chip package  100 . The springs can be used to pre-load the force distribution block to the inner pusher spring loaded block  40 . 
     It is noted that bottom shoulders  121  are provided near the bottom end  113  of each of the force transfer shafts  110 . These shoulders rest against the rigid pusher plate  81  to maintain the perpendicularity of the shafts. 
     The z-axis force F is transmitted to the die  104  of bare die chip package  100  through the stacked thermal control sections of the TCU, namely, the inner spring loaded pusher block section  40 , the fluid circulation block section  50 , the Peltier device  60 , and the heat conductive pedestal section  72 , all of which must be secured together. As best seen in  FIG. 2 , the fluid circulation block section  50  can be pre-attached to the inner pusher block section by suitable fasteners such as screw fasteners  41 . A pedestal retainer ring  43  can be provided at the bottom of the stacked thermal control sections, and retaining fasteners, such as screw fasteners  45 , can be used in conjunction with this retainer ring to tie the pedestal  72  and the other thermal control sections  40 ,  50  and  60  together. As generally described in U.S. Pat. No. 7,663,388, this creates a stacked assemblage of thermal control sections held in tight thermal contact with one another by the compliant z-axis force exerted by springs (such as the spring  47  shown in  FIG. 3 ) captured in the inner pusher block  40  behind the block&#39;s pusher plate  49 . As shown in  FIG. 3 , the pedestal  72  sets into retainer ring  43  on top of insulation ring  73 . This insulation ring can have notches or passages that allow a condensation abatement gas to flow through the insulation ring as hereinafter described. 
     The force transmitted to the pusher end of pedestal  72  is uniquely controlled by means in the force distribution block  12 , which can be actuated to change the force transmitted to the thermally active part of the DUT through the pedestal relative to the force transmitted to another part of the DUT through the outer pusher structure parts  80 ,  82 . 
     Referring to  FIGS. 4 and 5 , the force changing actuation means for the force distribution block can be provided in the form of at least one and preferably a plurality of pistons  18  nested in bottom surface  14  of the z-axis force distribution block  12 . Pistons  18 , which are preferably evenly spaced in a grouping centered in the bottom to the force distribution block  12 , protrude from piston holes  17  in the bottom of block and can be actuated in the z-axis direction by altering fluid pressure behind the pistons. Fluid pressure is provided to the pistons from inlet  22  which protrudes from a side wall  24  of the force distribution block  12 . 
     As shown in  FIG. 5 , the inlet  22  fluidly communicates with the pistons  18  via fluid passageways  25  within the force distribution block  12 . The inlet may be connected to a source of pressured gas or fluid to effect pneumatic actuation of the pistons. Although pressured air is typically used, the pressured fluid may be nongaseous as well. For example, oils, water, or aqueous solutions may be used to actuate the piston. The result is pistons that produce a z-axis force that can be adjusted on the fly. By adjusting the pressures behind the pistons, the force transferred to the heat conducting pedestal  72  relative to the force transmitted to the outer pusher  82  can be modified during testing of the DUT without unloading or disassembling the thermal control unit. Alternatively, the adjustable pistons may be preset before use. 
     The z-axis force distribution block  12  can be constructed for ease of loading the pistons  18  in the block by providing a top cover plate  13  that fits in a recess  15  in the top surface  16  of the block. The top cover plate  16  can be secured in this recess by any suitable means such as by screw fasteners. The fluid passageways that are in communication with the piston holes  17  can be formed on the underside of the block. The fluid inlet  22  can be a fluid line coupler attached, such as by a threaded attachment, to a fluid inlet extension  19  of top cover plate  13 . 
     The fluid circulation block  50  constructed fluid passages that enable fluids to be circulated through the block and carry heat away from the pedestal that contacts the thermally active part of the DUT, such as described in U.S. Pat. No. 7,663,388. In accordance with one aspect of the invention, fluid is introduced into and is evacuated from the fluid circulation block by fluid inlet and outlet arms  52 ,  54  swivelably attached to the sides of the TCU generally at or near the position of the fluid circulation block. Swivel attachments to the fluid inlet and outlet arms, in conjunction with compliant mounting of force distribution block  12  and the corner shafts  110 , reduce instability of the thermal control unit due to external forces exerted on the TCU, and particularly due to biasing forces exerted by external hoses connected to the fluid inlet and outlet of the fluid circulation block.  FIG. 1  depicts the exemplary range of motion for the swivel attachment of fluid outlet  54 . The inlet and outlet arms preferably swivel about a common swivel axis S (shown in  FIG. 2 ), and suitably have a swivel axis that is perpendicular to the z-axis of the TCU. While the fluid inlet arm  52  and fluid outlet arm  54  are shown attached opposite each other on opposite sides of the TCU, it is not intended that this swivel arm attachment aspect of the invention be limited to opposed swivel arms. 
     Thus, in accordance with this aspect of the invention, should any uncontrolled forces arise from hoses connected to the fluid inlet and outlet arms  52 ,  54  of the TCU, during a test cycle, the swivel action of the fluid inlet and outlet arms  52 ,  54  relative to the TCU will relieve these forces and cause z-axis alignment of the parts of the TCU to be maintained. 
     Any of a number of fluids may be circulated through fluid circulation block  50 . Preferably, the fluids are provided in liquid form, but gaseous fluids may be used on occasion. Liquids having a relatively high heat capacity are particularly useful in certain application. In addition, the temperature-control fluids may be chosen according to desired conditions. For example, for testing of DUTs at ambient or elevated temperatures, e.g. 20° C. to about 65° C., water may serve as a temperature-control fluid. In contrast, cold testing of DUTs at −20° C., −5° C., 0° C., or temperatures therebetween may involve the use of aqueous solutions containing, methanol, ethylene glycol, or propylene glycol or nonaqueous liquids. 
     In still another aspect of the invention the thermal control unit  1  includes a condensation-abating system. The condensation-abating system includes a condensation-abating gas inlet  42 , which can suitably be located at one edge of the inner spring loaded pusher block section  40  of the TCU. As shown in  FIG. 3 , gas inlet  42  connects to gas transporting passageways that extend around the pedestal  72 , between the pedestal and the pedestal retaining ring  43 , and between the pedestal retaining ring, pedestal and the outer pusher structure  80 . The gas transporting passageways are denoted by the numerals  44 A,  44 B,  44 C,  44 D,  46 A,  46 B and  47 . The condensation-abating system in further described below. 
     In use, the illustrated thermal control unit  1  may be placed over a test socket (not shown) containing a bare die chip package  100 . A z-axis force is applied to the gimbal adapter  30 , such as by a pneumatic press of an automated chip tester. The z-axis force is transferred by the force distribution block  12  of the self-centering gimbal  10  to pedestal  72  through the stack of thermal control blocks  40 ,  50  and  60  to the heat conducting pedestal  72 , and to the outer pusher structure  80  through the force transfer shafts  110 . The two pushers to which this z-axis force is transferred are the pusher end  76  of the pedestal which contacts the die  104  of the bare die chip package and the substrate pusher  72  of the outer pusher structure. The exerted z-axis force is controllably distributed between these pushers by the force distribution block  12 . The force exerted on the die relative to the force exerted on the substrate can be adjusted by adjusting the pressure behind the pistons  18  of the force distribution block, which acts a z-axis force actuation means. The force distribution may be preset or adjusted on the fly such that the die force does not exceed a desired or predetermined upper limit to ensure that the die force does not damage the die. 
     It is noted that the z-axis distance between the pedestal pusher end  76  and the bottom substrate pusher end  82  should be calibrated to ensure the substrate force does not fall below a desire or predetermined lower limit to ensure proper engagement between electrical pads of the DUT and the probes of the test socket. For example, a manufacturer of a particular IC device in bare-die packaging may specify that the particular IC device be cold tested with the application of at least a 55 pound load to the substrate. However, the specification may also prohibit the die from experiencing a load of 15 pounds or greater. In such a case, a total load of 70 pounds may be applied to the DUT with the die pusher adjusted to limit the load applied to the die not to exceed 15 pounds. 
     When so engaged, testing may begin. The thermal measurement and control elements of the thermal control unit act to monitor and maintain the DUT&#39;s set point temperature. The DUT temperature may be monitored by the sensor  78  in the pedestal pusher end  76 . A desired electrical signal is supplied to the Peltier device  60  from an external power source to generate the heat flow needed to maintain a desired set point temperature for the DUT in the test socket. Heat transfer between the pedestal and fluid circulating block  50  can be regulated in accordance with the temperature of the DUT as detected by the sensor  78 , with heat being removed from the pedestal to the temperature-control fluid being circulated through the fluid block  50  when it is desired to lower the DUT temperature, and with heat being added to the pedestal  72  from the circulating fluid if the DUT temperature needs to be raised. In short, the heat is either carried away or supplied by the temperature-control fluid which is passed through the fluid passage within the fluid circulating block  50 . 
     To help achieve an efficient interface, a thermal interface material, such as a thermal grease or foil, is optionally provided between the pedestal&#39;s top surface  74  and the Peltier device  60 , and between the Peltier device and the fluid circulating block  50 . 
     Regarding the condensation-abatement aspect of the invention, the DUTs of the invention may be used to carry out cold testing of DUTs. During such cold testing, temperature-control fluid may be chilled to temperatures of 0° C. or below. If such testing is carried out under uncontrolled ambient conditions, water or ice may accumulate on surface of the TCUs, DUTs, and test sockets. Such condensation is may short or otherwise interfere with the proper functioning the electronic components of TCUs, DUTs and test sockets. 
     A number of techniques known in the art have been used to address the condensation problems associated with cold testing. For example, high-volume cold testing of IC devices have been carried out in controlled environments, e.g., within rooms having a low level of atmospheric humidity. In some low-volume cold testing facilities, IC devices may be tested within an enclosure that maintains a low-humidity. In addition or in the alternative, plastic form of other material having a low thermal conductivity may be applied to surfaces of TCUs to address condensation problems associated with the chilling of components of TCUs engaged in cold testing. 
     In accordance with the condensation abatement aspect of the invention, provides a new and efficient approach to abatement of condensation on TCU and chip surfaces, which is integrated into the TCU. A condensation-abating gas is introduced under pressure into the TCU through gas inlet  42 . The abating gas flushes through the TCU so as to pass over surfaces on which condensation is likely to occur. In particular, in illustrated embodiment and as shown in  FIG. 3  the gas introduced at inlet  42  flows into horizontal passageway  44 A and down through vertical passageway  44 B and from there flushes through passageways  44 C and  44 D around the pedestal (including openings in the pedestal insulating ring  73 ), and exiting the TCU through two exit routes: through passageways  46 A,  46 B between parts of the outer pusher structure  80  and the pedestal retainer  43 , which is preferably stainless steel, and through passageway  47  between the pusher end  76  of the pedestal  72  and the substrate pusher  82  of the outer pusher structure. 
     It will be appreciated that gas passageways may be provided in ways other than as shown. For example, passageway  44 A extends generally horizontally through inner spring loaded pusher block  40  until it joins with passageway  44 B in a fluid-communicating manner. Passageway  44 B extends in a z-axis direction through a portion of block  40 , as well as both the upper section  56  and lower section  58  of the fluid circulation block  50 . Passageways  44 C,  44 D,  46 A,  46 B, and  47  are shown downstream from passageway  44 B and located between the skirt  90  and the pedestal  72 . Optionally, one or more additional passageways may be formed by placing a first surface having one or more channels formed therein against a second surface, the surfaces in combination defining the one or more additional passageways. For example, condensation abating gas transporting passageways may be integrated within or interposed between the modules of the inventive TCU. 
     In operation, a condensation-abating gas source (not shown) may be connected with inlet  42 . Condensation-abating gas is introduced through the inlet  42 , and flushed through the gas passageways as above-described, and flows over surfaces on which condensation may occur. As the pedestal  72  is necessarily cold during cold testing, skirt  90  may help direct condensation-abating gas over exposed surfaces of the pedestal prone to collect moisture or ice. 
     Any of a number of gases may be used. For example, any dry inert gas, e.g., nitrogen, helium, argon, etc. may be used. In particular, commercially available, dry, oil-free air has been demonstrated to abate condensation on the inventive TCU. TCUs having the above-described integrated means for abating condensation do not experience condensation-related problems during cold testing in uncontrolled atmospheric conditions, whereas the same TCU may suffer from condensation-related problems during cold testing when no condensation-abating gas is used. 
     In addition to the use of condensation-abating gas, appropriate measures should be taken to address heat conduction issues. For example, different components of the temperature control unit should be thermally isolated from one another whenever possible to inhibit chilling of water sensitive components of TCUs. In addition, material of low thermal conductivity should be used whenever possible. For example, metals should generally be avoided for components that do not have to conduct heat. As discussed above, portions of the temperature-control fluid block may be made from a metal such as copper for efficient heat conduction. However, other portions of the temperature-control fluid-block, e.g., those exposed to the surrounding ambient environment, may be formed from a material that does not conduct heat, e.g., plastic, to deter the formation of condensation thereon. 
     To facilitate discussion,  FIGS. 6-11  illustrate another exemplary embodiment of a thermal control unit (TCU)  600  in accordance with the present invention. Advantages of this embodiment include a fast thermal response of 40° C./second for an IC device under test (DUT) have a test surface area of approximately 16 mm×16 mm, with a resulting watt density of approaching 1000 watts per square inch. In addition, TCU  600  has an operating range of −60° C. to 160° C. 
     The superior thermal performance of TCU  600  is made possible by several key design features such as choices of thermal conductive materials, fluid and electrical pathways and thermal sensor locations, these design features described in greater detail below. Briefly,  FIG. 6  is a side view of thermal control unit  600 .  FIG. 7A  is cross-sectional view thereof taken along section lines  7 A- 7 A in  FIG. 6 , while  FIG. 7B  is an exploded view of  FIG. 7B  illustrating the components of TCU  600 , including force transmitting assembly  610 , fluid circulation block (heat exchanger with thermally-conductive plate)  650 , heater  660 , pedestal  772 , and substrate pusher  690 .  FIGS. 8 and 9  cross-sectional views thereof taken along section lines  8 - 8  and  9 - 9 , respectively, in  FIG. 7A .  FIGS. 10A and 10B  are bottom perspective views of two exemplary z-axis load distributor actuator blocks for the z-axis force distribution system of the TCU  600 , while  FIG. 11  is a cross-sectional view along the line  11 - 11  in  FIG. 10A . 
     As shown in  FIGS. 6-9 , the thermal control unit (TCU)  600  includes the following basic sections arranged in stacked relationship along the z-axis of the TCU  600 : a force transmitting assembly  610  for transmitted a z-axis force denoted by the arrow F (see  FIG. 6 ) to the TCU&#39;s IC device under test (DUT) contacting pushers as hereinafter described; a fluid circulation block  650 ; a heater  660 ; and a heat conductive pedestal  772  having a pusher end  776 , which includes at least one pedestal temperature sensor, for contacting and pushing against a thermally active central portion of an IC chip, such as the die  799  of a bare die chip package  797 . 
     An outer pusher structure  780  is also provided. Pusher  780  includes a rigid bottom pusher plate  781  and is suitably fabricated of a metal material, such as aluminum, for rigidity. The bottom pusher plate  781  has a center opening to allow the pusher end of the heat conducting pedestal to project through the pusher plate. A second DUT contacting pusher  682  extends from the bottom of the pusher plate around this center opening. This second pusher  682  extends in the z-axis direction in parallel with the pusher end of the pedestal and contacts and pushes against another part of the IC chip, such as the substrate  798  of the bare die chip package  797 . 
     Referring to  FIG. 7A , the fluid circulation block (also known as the chiller block)  650  is seen to have a lower contact plate  758  at the bottom of block&#39;s main body  656 . This lower contact plate  758  is made of a good heat conductor such as copper and is suitable provided to achieve efficient heat conduction between the fluid circulation block  650  and the heater  660 . Hence the block&#39;s main body  656  of the may be formed from material that does not conduct heat as well as copper or other metals. Suitable materials for main body  656  include thermoplastics such as Peek™, Ultem™ or Torbn™, capable of withstanding repeated rapid thermal shock cycles and also reducing condensation abatement needs, during multiple rapid heating/cooling cycles of TCU  600 . 
     To prevent thermal runaway and resulting damage to TCU  600 , fluid circulation block  650  preferably includes at least one chiller temperature sensor, enabling TCU  600  to sense when permitted operating range has been exceeded and triggering an appropriate thermal cut off. 
     Referring also to  FIG. 6 , the force transmitting assembly  610  of the TCU  600  includes a force distribution block  612  and can additionally include a gimbal adapter  630  above the force distribution block  612  to form the force transmitting assembly  610 . The gimbal adapter  630  includes upper and lower surfaces  632  and  634 , with the upper surface  632  being positioned to receive the indicated z-axis force F. The gimbal adaptor  630  further includes springs  636  positioned beneath the lower surface  634 . Springs  636  are held in compression between the gimbal adaptor  630  and the upper surface  616  of the force distribution block  612  for preload gimbal stability. 
     As shown in  FIGS. 7A ,  7 B,  9  and  10 A, the outer pusher structure  780  is secured to the force distribution block  612  by force transfer shafts  710 . These shafts freely pass through suitably sized holes in the fluid circulation block  650 . The bottom ends  713  of shafts  710  are suitably anchored to the pusher plate  781  near the outer perimeter of the plate, such as by threaded engagement, while the top ends  712  of the shafts extend through openings  1020  (shown in  FIG. 10A ) in the corners of the force distribution block and are topped by cap nuts  715  to retain the force distribution block on the shafts  710 . 
     In addition, gimbal block  612  also includes suitably sized holes  1077  for coupling with a corresponding set of alignment pins  757  protruding vertically from the top surface of fluid circulation block  650 . 
       FIGS. 7A and 9  both show the force distribution block  612  compliantly supported on springs  717  provided around the recessed portion of the shaft  710  beneath the force distribution block and which set on shoulders  719  presented by the recessed portion of the shaft  710 . A z-axis force F applied to the force transmitting assembly  610  will thus be compliantly transmitted to pusher  682  of the outer pusher structure, and thus to the substrate  798  of bare die chip package  797 . The springs  717  can be used to preload the force distribution block (gimbal block)  612  to the main body  656  of fluid circulation block  650 . 
     It is noted that bottom shoulders  721  are provided near the bottom end  713  of each of the force transfer shafts  710 . These shoulders rest against the rigid pusher plate  781  to maintain the perpendicularity of the shafts. 
     The z-axis force F is transmitted to the die  799  of bare die chip package  797  through the stacked thermal control sections of the TCU  600 , namely, the fluid circulation block  650 , heater  660 , and the heat conductive pedestal  772 , all of which must be secured together. The force transmitted to the pusher end of pedestal  772  is uniquely controlled by means in the force distribution block  612 , which can be actuated to change the force transmitted to the thermally active part of the DUT through the pedestal relative to the force transmitted to another part of the DUT through the outer pusher structure parts  780 ,  682 . 
     Referring to  FIGS. 10A and 11 , the force changing actuator for the force distribution block  612  (also known as the gimbal block), can be provided in the form of at least one and preferably a plurality of pistons  1018  nested in bottom surface  1014  of a gimbal block  612  for distributing the z-axis force. Pistons  1018 , which are preferably evenly spaced in a grouping centered in the bottom to the force distribution block  612 , protrude from piston holes  1117  in the bottom of gimbal block  612  and can be actuated in the z-axis direction by altering fluid pressure behind the pistons  1018 . Fluid pressure is provided to the pistons from fluid inlet  622  which protrudes from a side wall  1024  of gimbal block  612 . 
     As shown in  FIG. 11 , the inlet  622  fluidly communicates with the pistons  1018  via fluid passageway  1125  within the gimbal block  612 . The inlet  622  may be connected to a source of pressured gas or fluid to effect pneumatic actuation of the pistons  1018 . Although pressured air is typically used, the pressured fluid may be nongaseous as well. For example, oils, water, or aqueous solutions may be used to actuate the pistons  1018 . The result is pistons that produce a z-axis force that can be adjusted on the fly. By adjusting the pressures behind the pistons  1018 , the force transferred to the heat conducting pedestal  772  relative to the force transmitted to the outer pusher  682  can be modified during testing of the DUT without unloading or disassembling the thermal control unit. Alternatively, the adjustable pistons may be preset before use. 
     The gimbal block  612  can be constructed for ease of loading the pistons  1018  in the block by providing a top cover plate  1113  that fits in a recess  1115  in the top surface  1116  of the block  612 . The top cover plate  1113  can be secured in this recess  1115  by any suitable means such as by screw fasteners. The fluid passageways that are in communication with the piston holes  1117  can be formed on the underside of the block  612 . The fluid inlet  622  can be a fluid line coupler attached, such as by a threaded attachment, to a fluid inlet extension  1119  of top cover plate  1113 . 
       FIG. 10   b  shows an alternate embodiment of the gimbal block  1012 , wherein instead of machine screws, pivoted latches  1090  are used to secure the stacked components of TCU  600  to each other without the need for tools. 
     Referring to both  FIGS. 6 and 7A , the fluid circulation block  650  constructed fluid passages that enable fluids to be circulated through the block and carry heat away from the pedestal that contacts the thermally active part of the DUT, such as described in U.S. Pat. No. 7,663,388. In accordance with one aspect of the invention, fluid is introduced into and is evacuated from the fluid circulation block by fluid inlet and outlet arms  752 ,  654  swivelably attached to the sides of the TCU  600  generally at or near the position of the fluid circulation block. Swivel attachments to the fluid inlet and outlet arms, in conjunction with compliant mounting of force distribution block  612  and the corner shafts  710 , reduce instability of the thermal control unit due to external forces exerted on the TCU  600 , and particularly due to biasing forces exerted by external hoses connected to the fluid inlet and outlet of the fluid circulation block.  FIG. 6  depicts the exemplary range of motion for the swivel attachment of fluid outlet arm  654 . The inlet and outlet arms  752 ,  654  preferably swivel about a common swivel axis S (shown in  FIG. 7A ), and suitably have a swivel axis that is perpendicular to the z-axis of the TCU  600 . While the fluid inlet arm  752  and fluid outlet arm  654  are shown attached opposite each other on opposite sides of the TCU  600 , it is not intended that this swivel arm attachment aspect of the invention be limited to opposed swivel arms. 
     Thus, in accordance with this aspect of the invention, should any uncontrolled forces arise from hoses connected to the fluid inlet and outlet arms  752 ,  654  of the TCU  600 , during a test cycle, the swivel action of the fluid inlet and outlet arms  752 ,  654  relative to the TCU  600  will relieve these forces and cause z-axis alignment of the parts of the TCU to be maintained. 
     Any of a number of fluids may be circulated through fluid circulation block  650 . Preferably, the fluids are provided in liquid form, but gaseous fluids may be used on occasion. Liquids having a relatively high heat capacity are particularly useful in certain application. In addition, the temperature-control fluids may be chosen according to desired conditions. For example, for testing of DUTs at ambient or elevated temperatures, e.g. 20° C. to about 65° C., water may serve as a temperature-control fluid. In contrast, cold testing of DUTs at −20° C., −5° C., 0° C., or temperatures therebetween may involve the use of aqueous solutions containing, methanol, ethylene glycol, or propylene glycol or nonaqueous liquids. 
     In still another aspect of the invention the thermal control unit (TCU)  600  includes a condensation-abating system. During cold testing, temperature-control fluid may be chilled to temperatures of 0° C. or below. If such testing is carried out under uncontrolled ambient conditions, water or ice may accumulate on surface of the TCUs, DUTs, and test sockets. Such condensation may short or otherwise interfere with the proper functioning the electronic components of TCUs, DUTs and test sockets. 
     Accordingly, the condensation-abating system includes a condensation-abating gas inlet  668 , which can suitably be located at one edge of the fluid circulation block  650 . As shown in  FIGS. 6 and 7A , gas inlet  668  connects to gas transporting passageways that extend around the pedestal  772 , in a manner similar to that of the other embodiment of TCU 1 described above, thereby enabling the approach to abatement of condensation on TCU and chip surfaces, described above for TCU 1 to be integrated into the TCU  600 . 
     In addition to the use of condensation-abating gas, appropriate measures should be taken to address heat conduction issues. For example, different components of the temperature control unit should be thermally isolated from one another whenever possible to inhibit chilling of water sensitive components of TCUs. In addition, material of low thermal conductivity should be used whenever possible. For example, metals should generally be avoided for components that do not have to conduct heat. As discussed above, portions of the temperature-control fluid block may be made from a metal such as copper for efficient heat conduction. However, other portions of the temperature-control fluid-block, e.g., those exposed to the surrounding ambient environment, may be formed from a material that does not conduct heat, e.g., plastic, to deter the formation of condensation thereon. 
     In use, the illustrated thermal control unit  600  may be placed over a test socket (not shown) containing a bare die chip package  797 . A z-axis force is applied to the gimbal adapter  630 , such as by a pneumatic press of an automated chip tester. The z-axis force is transferred by the force distribution block  612  of the self-centering gimbal  610  to pedestal  772  through the stack of thermal control subassemblies  650  and  660  to the heat conducting pedestal  772 , and to the outer pusher structure  780  through the force transfer shafts  710 . The two pushers to which this z-axis force is transferred are the pusher end  776  of the pedestal which contacts the die  798  of the bare die chip package  799  and the substrate pusher  690  of the outer pusher structure. 
     The exerted z-axis force is controllably distributed between these pushers by the force distribution block  612 . The force exerted on the die  799  relative to the force exerted on the substrate  798  can be adjusted by adjusting the pressure behind the pistons  1018  of the force distribution block, which acts a z-axis force actuation means. The force distribution may be preset or adjusted on the fly such that the die force does not exceed a desired or predetermined upper limit to ensure that the die force does not damage the die  799 . In other words, the total z-axis force exerted by force distribution block  612  is equal to a sum of the force exerted on the substrate  798  and the force exerted on the die  799 . This force distribution between the substrate  798  and the die  799  is carefully controlled so that no undue internal structural stress, caused by harmful bending forces, is transmitted by the TCU  600  to the DUT, while maintaining efficient thermal conductivity between the TCU  600  and the DUT during the test. 
     It is noted that the z-axis distance between the pedestal pusher end  776  and the bottom substrate pusher end  682  should be calibrated to ensure the substrate force does not fall below a desire or predetermined lower limit to ensure proper engagement between electrical pads of the DUT and the probes of the test socket. For example, a manufacturer of a particular IC device in bare-die packaging may specify that the particular IC device be cold tested with the application of at least a 55 pound load to the substrate  798 . However, the specification may also prohibit the die  799  from experiencing a load of 15 pounds or greater. In such a case, a total load of 70 pounds may be applied to the DUT with the die pusher  776  adjusted to limit the load applied to the die not to exceed 15 pounds. 
     When so engaged, testing may begin. The thermal measurement and control elements of the thermal control unit act to monitor and maintain the DUT&#39;s set point temperature. The DUT temperature may be monitored by the pedestal thermal sensor in the pedestal pusher end  776 . 
     A desired electrical current is supplied to the heater  660  from an external power source to generate the heat flow needed to maintain a desired set point temperature for the DUT in the test socket. Heat transfer between the pedestal  772  and fluid circulating block  650  can be regulated in accordance with the temperature of the DUT as detected by the thermal sensor, with heat being removed from the pedestal  772  to the temperature-control fluid being circulated through the fluid block  650  when it is desired to lower the DUT temperature. It is also possible to add supplement heat generated by the heater  660  to the pedestal  772  with additional heat from the circulating fluid if the DUT temperature needs to be raised rapidly. In short, the heat is either carried away or supplied by the temperature-control fluid which is passed through the fluid passage within the fluid circulating block  650 . 
     As discussed above, although fluid circulating block  650  can be made from a suitable thermo-plastic to reduce condensation, while the thermally-conductive plate  758  is made from a relatively-thin (low-mass) and highly-conductive material, such as nickel-plated copper, for superior thermal transfer performance. Similarly, the electrically-resistive heater  660  can be made from suitable materials, including ceramic materials such as AlN (aluminum nitride), which is has suitable thermally-conductive properties. 
     To further improve the efficiency of the various thermal interfaces, a suitable thermal interface material, such as a thermal grease or foil, e.g., “Artic-Silver™ thermal compound, can be provided between the pedestal&#39;s top surface  774  the heater  660 , and between the heater  660  and the thermally-conductive plate  758  located at the bottom of fluid circulating block  650 . This thermal interface material, typically about one mil in thickness, fills out minor imperfections and voids, thereby enhancing thermal conductivity and efficiency of the respective interfaces. In addition, the thermal interface material also accommodates the different expansion coefficients of the corresponding components made from different materials, namely, the plate  758 , the heater  660  and the pedestal  772  during rapid heating and cooling cycles. 
     In some embodiments, in order to improve the thermal efficiency of interface between the pedestal pusher end  776  and the die  799 , a suitable liquid thermal interface material (LTIM), for example water and glycerin, is injected under pressure into the pedestal/die interface from one or more perforations located at the bottom of pedestal pusher end  776 . Subsequently, after the testing of the DUT, residual LTIM is removed under suction from the same bottom perforations of the pedestal pusher end  776 . The LTIM is supplied to and removed from pedestal pusher end  776  via a corresponding set of LTIM input and output  669  shown in  FIGS. 6 and 9 . 
     As discussed above, typical device testers are designed with the assumption that the devices under test (DUTs) are flat. As a consequence, the flat profiles of the pedestal, the substrate pusher and the test socket result in undue pressure being exerted on curved DUTs, especially by the pedestal on the die, during testing. In addition, the pedestal and the substrate pusher exert pressure on the selected surface areas of the substrate. Hence, after testing, the surface of the device is somewhat flattened due to the undue pressure from the pedestal and the pusher, and often uneven, due to the uneven pressure between the supported and unsupported surfaces of the DUT. 
     The uneven pressure problem on the DUTs can be partially mitigated by introducing adjustable touchdown coverage that attempts to increase the supported top surface area of the DUTs. This is accomplished by providing additional surface support between the pedestal and the substrate pusher, i.e., on the surrounding components surrounding the die on the substrate, such as resistors, capacitors and I/O drivers. However, the adjustable touchdown coverage does not solve the more serious, undesirable and unintended device flattening problem. 
     The device flattening problem becomes more pronounced as the substrate thickness decreases. With today&#39;s portable devices, device substrate thicknesses have steadily decreased from about 800 microns to about 100-200 microns. Unlike thicker, e.g., 800 microns, devices, capable of resuming its original curvature after being flattened by the device tester, today thinner devices are much more likely to become permanently deformed as exemplified by device  1280 B of  FIG. 12B . 
     To minimize this undesirable flattening problem, in some embodiments of the device testers, as illustrated by  FIG. 13A  (not to scale), the pedestal  1360 , the substrate pusher  1370  and the socket insert  1392  of test socket  1390  are configured to accommodate the curved device  1380 . Accordingly, the pusher end  1366  of pedestal  1360  is slighted concave in order to substantially match the curvature of the surface of die  1384  of device  1380 . Similarly, the top surface of socket insert  1392  is slightly convex in order to substantial match the curvature of the bottom of substrate  1380  of device  1380 . 
     For illustrative purposes,  FIG. 13B  is a simplified and exaggerated (not to scale) cross-sectional view showing in greater detail the respective curved profiles of pedestal pusher end  1366 , die  1384 , substrate pusher ends  1372 ,  1374 , substrate  1382 , and socket insert  1392 . 
     Hence, depending on the sizes and thicknesses of the DUTs, wide variations of curved shapes for the socket inserts and/or pusher ends, alone and in combination, are contemplated, including circular, elliptical, spherical, faceted (like a cut jewel) and compound shapes and combinations thereof. It should also be appreciated that irregularities, such as depressions and/or bumps, may also be intentionally introduced into selected portion(s) of the socket inserts and/or pusher ends depending on the particular DUT profile and construction. 
       FIG. 13E  is a perspective view of test socket  1390  and test socket insert  1392  showing a plurality of suspension support pins  1396 , while  FIGS. 13F and 13G  are cross-sectional views illustrating a rest condition and a test condition, respectively. In this embodiment, there are four support pins  1396  along each of the four sides of insert  1392  (totaling sixteen support pins) supporting and stabilizing socket insert  1396 . 
     Suspension support pins  1396  support socket insert  1392  in an elevated position (see  FIG. 13F ) above the recess surface of test socket  1390  and ensures that the one or more spring-loaded test pins  1398  do not protrude above the top surface of socket insert  1392  during the rest condition. As a result, the top surface of the socket insert  1392  is substantially smooth and free of any obstructive protrusions, thereby facilitating the proper alignment and placement of the device  1380  with respect to the test socket  1390  and the socket insert  1392 . 
     Subsequently, as illustrated by  FIG. 13G , during the test condition, after the device  1380  has been properly seated with respect to the socket insert  1392  and the test socket  1390 , the test pin(s)  1398  are exposed to and come into contact with the corresponding pad(s) located at the substrate bottom device  1380 . 
     Note that typical DUTs include square DUTs ranging from approximately 14 mm square to 50 mm square, and rectangular DUTs ranging from approximately 22 mm×25 mm to 24 mm×42 mm. Curvature of a typical DUT depends on factors such as the size, thicknesses, and/or aspect ratio of the substrate and the die. For example, a 50 mm square substrate has a profile that is about 250 mils higher in the middle of the substrate than the sides of the substrate. In this example, the corresponding socket insert should have a profile that is about 120 mils higher in the middle than the sides, thereby substantially reducing the flattening problem while allowing the test pins to function within their operational compression and expansion range during testing. 
     Many modifications and additions to the device testers described above are also possible. For example, the thickness and/or profile of different portions of the test socket insert may be varied enabling the socket insert to flex and conform in a manner (e.g., differentially across the socket insert) thereby generating substantially less overall stress, i.e., less flattening effect, on the DUTs (see the exaggerated cross-sectional view of  FIGS. 13C and 13D ). Test socket inserts may also be made from materials with a variety of stiffness and/or flexibility depending on the DUTs. 
     It may also possible to fabricate the socket inserts using two or more bonded materials that substantially match the temperature-related profile changes of the DUTs, in a manner similar to a bi-metallic strip, thereby reducing overall stress on the DUTs. Further, test sockets may also be heated and/or cooled to minimize temperature differences. 
     Referring now to  FIGS. 14A-14D , are a front view, a top view, a perspective view and a blown-up view illustrating an exemplary heater  1460  for some embodiments of the device testers described above. Heater  1460  is configured to be operatively coupled to the pedestal of the device tester. Heater  1460  may be fused, thermally and/or electrically. For example, as shown in  FIG. 14B , heater elements  1464 ,  1466  are linked by a fuse  1468 , thereby completing a fuse circuit comprising of conductive lead  1461 , heater element  1466 , fuse  1468 , heater element  1464 , and conductive lead  1462 . Fuse  1468  is located along an open edge of heater body  1469  and hence can be readily accessed during assembly, reconfiguration and/or maintenance. Exemplary fuse  1468  can be made from a material with a suitable melting point, approximately 300 degrees Celsius, thereby substantially reducing the risk of tester damage and/or fire hazards, such as spontaneous combustion. 
     In sum, the present invention provides systems and methods for testing of IC devices such as packaged semiconductor chips while preserving the devices&#39; original specifications. The advantages include minimizing deformation of IC devices under test (DUTs) thereby reducing losses due to physical damage and/or poor contact alignment during subsequent assembly with motherboards. 
     It will be apparent to those of ordinary skill in the art that the invention may be embodied in various forms and that the invention. For example, the materials used for fabricating the components of the thermal control unit would be readily apparent to persons skilled in the art upon review of the disclosure contained herein to ensure that the proper component functioning under the forces and temperatures required for IC device testing. Similarly, those of ordinary skill in the art, upon review of the disclosure contained herein and through routine experimentation, will be able to distinguish optional versus critical elements of the invention for different contexts. For example, those of ordinary skill in the art will recognize that the invention may require only one pusher in some instances, but may require a plurality of pushers in other. 
     It is to be understood that while the invention has been described in conjunction with the preferred specific embodiments thereof, that the foregoing description is intended to illustrate and not limit the scope of the invention. For example, while the above description has focused on a TCU for IC devices with bare die packaging, the invention is not limited to such packaging. Accordingly, the above-described pistons, swivelable inlet and outlet arms, and condensation abating means as described above may be used for TCUs constructed for testing lidded die packages as well as bare die packages. In addition, the invention is not limited to force-providing means having a construction as shown in the drawing. Those of ordinary skill in the art, upon review of the disclosure contained herein may devise various differ force-providing means for receiving a total z-axis force and controllably distributing the total z-axis force on different parts of IC packages. In any case, aspects of different embodiments of the invention may be included or excluded from other embodiments. Other aspects, advantages and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains. 
     Hence, while this invention has been described in terms of several embodiments, there are alterations, modifications, permutations, and substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and substitute equivalents as fall within the true spirit and scope of the present invention.