Patent Abstract:
One embodiment of the present invention is a method for aligning a first workpiece to a second work piece that includes: (a) placing the first workpiece on an alignment apparatus including: (i) two or more fluid chambers disposed in fixed relation to each other, the chambers having a movable wall and one or more apertures for admitting or releasing fluid; (ii) fluid channels coupled to the one or more apertures that enable fluid to flow between at least two of the fluid chambers; and (iii) one or more valves disposed to enable or to stop the flow of fluid through one or more of the one or more fluid channels; (b) pumping incompressible fluid into the fluid chambers; (c) opening the one or more valves; (d) bringing the first and second workpieces into contact; (e) waiting a predetermined time for fluid flow in the fluid channels; (f) determining whether the first and second workpieces are aligned; (g) if they are aligned, shutting the valves; and (h) if they are not aligned, moving the second workpiece a predetermined amount in a predetermined direction, and returning to waiting.

Full Description:
[0001]    This patent application is a divisional of a U.S. patent application having Ser. No. 11/708,517 that was filed on Feb. 20, 2007, which U.S. patent application is incorporated herein in its entirety. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    One or more embodiments of the present invention relate to method and apparatus for aligning and leveling a test head. 
       BACKGROUND OF THE INVENTION 
       [0003]    Semiconductor components are used in the fabrication of electronic items such as multichip modules. For example, bare semiconductor dice can be mounted to substrates such as printed circuit boards, and ceramic interposers. Flip chip mounting of bumped dice is one method for electrically connecting the dice to the substrates. With flip chip mounting, solder bumps on the device bond pads are reflowed into electrical contact with contacts on the substrate. Chip on board (COB) mounting of dice to substrates can also be employed. With chip on board mounting, wire bonds are formed between the device bond pads and contacts on the substrate. 
         [0004]    Chip scale packages are sometimes used in place of bare dice for fabricating electronic items. Typically, a chip scale package includes a substrate bonded to the face of a bare die. The substrate includes external contacts for making outside electrical connections to the chip scale package. The external contacts for one type of chip scale package include solder balls arranged in a dense array such as a ball grid array (BGA) or a fine ball grid array (FBGA). In general, chip scale packages can be mounted to substrates using the same mounting methods employed with bare dice. 
         [0005]    Besides making permanent electrical connections between semiconductor components and substrates for fabricating multichip modules or other packaging applications, electrical connections are necessary for testing applications. For example, bare dice are tested in the manufacture of known good dice (KGD). Chip scale packages must also be tested prior to use in electronic items. In these cases, electrical connections with device bond pads for bare dice, or with the external contacts for chip scale packages, are typically non-bonded, temporary electrical connections. 
         [0006]    In either packaging or testing applications, a substrate includes contacts that must be physically aligned with, and then electrically connected to, corresponding contacts on a component. As semiconductor components become smaller, and contacts become denser, aligning and electrically connecting components to substrates become more difficult. Accordingly, a design consideration in packaging and testing of semiconductor components is a method for aligning and connecting components to mating substrates. 
         [0007]    As such, one such problem facing the semiconductor industry is how to planarize a probe card to a wafer during testing of individual die on that wafer. During probe testing a probe card must be aligned and placed in electrical contact with a wafer. When the wafer and probe card are moved together in a vertical direction, contacts on the wafer may not always engage contacts on the probe card along the same plane. Such misalignment can cause pivoting of the wafer or the probe card. Also, the potential of misalignment can require overdriving the wafer or the probe card in the vertical direction to make reliable electrically connections. This overdrive can damage contacts. In addition, if planarization is not achieved, then some probes may apply more pressure to corresponding lead pads on a die, while others may apply less. This could result in incomplete electrical interfacing with the die so that the die tests bad, or that the lead pads to which more pressure is applied are physically damaged—thereby making it impossible to use the die in a finished product. Further, as the number of probes is increased in probe apparatus, tilting becomes more of a problem. 
         [0008]    Besides the above examples, alignment problems can occur in other semiconductor packaging or assembly processes such as wire bonding and adhesive bonding of dice to leadframes. Another manufacturing process involving alignment occurs during fabrication of flat panel field emission displays (FEDs). An individual field emission display pixel includes emitter sites formed on a baseplate. Electrons emitted by the emitter sites strike phosphors contained on a display screen to form an image. During fabrication of the field emission display it is necessary to align the baseplate with the display screen. However, field emission displays are typically constructed as a sealed package with a vacuum space between the baseplate and the display screen. This space complicates the alignment procedure because most alignment devices, such as aligner bonder tools, are constructed to bring the mating components into physical contact. 
         [0009]    A need for alignment of a platen also arises in industries unrelated to semiconductor testing; most importantly, in metal stamping and in printing. The forces involved in these applications are relatively large in comparison to the forces involved in testing a semiconductor wafer, for example. Hydraulic cylinders have been used in various configurations to support and level a platen involved in metal stamping and printing. Generally, the one or more hydraulic cylinders supporting a platen are relatively long, with a stroke that is comparable to or larger than the bore. At the high forces and hydraulic pressures involved in these applications, compressibility of the hydraulic fluid is a significant factor in determining the position and movement of the platen as the press is actuated. Compression of the hydraulic fluid in supporting hydraulic cylinders is used as a cushion in high force presses that helps to level the loading of the press. As the influence of compressibility of the hydraulic fluid increases with length of the cylinder, a long hydraulic cylinder is used to provide cushioning that acts to level the platen under force. In certain configurations of the prior art, fluid is allowed to flow between hydraulic cylinders in a press in order to level the load. However, because of the length of the hydraulic cylinders used in presses, the cylinders are not an accurate method of setting the height of the platen. More accurate means are needed to set and maintain alignment that are not sensitive to pressure, temperature, and loading. 
         [0010]    In light of the above, there is a need in the art for method and apparatus that can align and level a substrate and a test head or electronic components. 
       SUMMARY OF THE INVENTION 
       [0011]    One or more embodiments of the present invention satisfy one or more of the above-identified needs. In particular, one embodiment of the present invention is a method for aligning a first workpiece to a second work piece that comprises: (a) placing the first workpiece on an alignment apparatus comprising: (i) two or more fluid chambers disposed in fixed relation to each other, the chambers having a movable wall and one or more apertures for admitting or releasing fluid; (ii) fluid channels coupled to the one or more apertures that enable fluid to flow between at least two of the fluid chambers; and (iii) one or more valves disposed to enable or to stop the flow of fluid through one or more of the one or more fluid channels; (b) pumping incompressible fluid into the fluid chambers; (c) opening the one or more valves; (d) bringing the first and second workpieces into contact; (e) waiting a predetermined time for fluid flow in the fluid channels; (f) determining whether the first and second workpieces are aligned; (g) if they are aligned, shutting the valves; and (h) if they are not aligned, moving the second workpiece a predetermined amount in a predetermined direction, and returning to waiting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0012]      FIG. 1A  shows a cross-sectional view of an alignment apparatus that is fabricated in accordance with one or more embodiments of the present invention, the alignment apparatus is shown prior to alignment of a test head with a wafer; 
           [0013]      FIG. 1B  shows a cross-sectional view of the alignment apparatus shown in  FIG. 1A  in use after alignment of the test head with the wafer; 
           [0014]      FIG. 1C  shows a top sectional view of the alignment apparatus shown in  FIG. 1A , which section is taken in a plane indicated by arrows A and A′ of  FIG. 1B ; 
           [0015]      FIGS. 2A-2C  show top views of alignment apparatus that are fabricated in accordance with one or more embodiments of the present invention; 
           [0016]      FIG. 3  shows a flow chart of a method for aligning a test head in accordance with one or more embodiments of the present invention; 
           [0017]      FIGS. 4A-4C  show partial cross-sectional views of alternative embodiments of fluid chambers that may be used to fabricate one or more embodiments of the present invention; 
           [0018]      FIGS. 5A-5B  show a cross-sectional view and a top sectional view, respectively, of an alignment and leveling apparatus that is fabricated in accordance with one or more embodiments of the present invention in which pneumatic actuators are used to level a test head; 
           [0019]      FIG. 6A  shows a sectional perspective view of the alignment and leveling apparatus shown in  FIG. 5A ; 
           [0020]      FIG. 6B  shows an exploded assembly view, in perspective, of the alignment and leveling apparatus shown in  FIG. 5A ; 
           [0021]      FIG. 7  shows a schematic drawing of the alignment and leveling apparatus shown in  FIG. 5A , which drawing is used to help describe its operation; 
           [0022]      FIG. 8  shows a flow chart of a method for aligning and leveling a test head in accordance with one or more embodiments of the present invention using the alignment and leveling apparatus shown in  FIG. 5A ; 
           [0023]      FIG. 9A  is a cross-sectional view of an alignment and leveling apparatus that is fabricated in accordance with one or more embodiments of the present invention for aligning and leveling a test head comprising of multiple segments; 
           [0024]      FIG. 9B  is a top sectional view of the alignment and leveling apparatus shown in  9 A; 
           [0025]      FIG. 9C  is a cross-sectional view of the alignment and leveling apparatus shown in  FIG. 9A  in a locked configuration; and 
           [0026]      FIG. 9D  is a top sectional view of the alignment and leveling apparatus shown in  9 C. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIG. 1A  shows a cross-sectional view of alignment apparatus  1000  that is fabricated in accordance with one or more embodiments of the present invention. In accordance with one or more such embodiments, alignment apparatus  1000  may be utilized, for example and without limitation, as an apparatus for aligning a test head such as, for example and without limitation, a wafer probe test head, a thermal contactor test head, a mechanical measurement test head, an optical test head, an array of electrical contacts test head, and a multiplicity of any of such test heads. 
         [0028]    As shown in  FIG. 1 , alignment apparatus  1000  comprises support plate  1010  in which a multiplicity of reservoirs or chambers, for example and without limitation, four reservoirs  1020   1 - 1020   4  are arrayed (reservoirs  1020   1 - 1020   4  are seen in  FIG. 1C , and a cross-section of reservoirs  1020   1 - 1020   2  is seen in  FIGS. 1A and 1B ). As shown in  FIG. 1C , and in accordance with one or more embodiments of the present invention, reservoirs  1020   1 - 1020   4  are arrayed in a fixed relationship with respect to each other. In particular, reservoirs  1020   1 - 1020   4  are disposed symmetrically about vertical central axis  1300  of support plate  1010 . In addition, and in accordance with one or more such embodiments of the present invention, reservoirs  1020   1 - 1020   4  are arrayed in a plane on support plate  1010 . 
         [0029]    In accordance with one or more embodiments of the present invention, each of reservoirs  1020   1 - 1020   4  includes a bottom surface and a top surface (top surfaces  1030   1 - 1030   2  are shown in  FIG. 1A ) that includes a movable portion. In accordance with one or more such embodiments, top surfaces  1030   1 - 1030   2  are movable and include diaphragms made, for example and without limitation, of thin embossed sheets of type 316L stainless steel. Further, in accordance with one or more such embodiments, one or more pillars are mechanically connected (for example and without limitation, rigidly connected) to top surfaces  1030   1 - 1030   2  of reservoirs  1020   1 - 1020   2  (as shown in  FIG. 1A , pillars  1040   1 - 1040   2  are mechanically connected to top surfaces  1030   1 - 1030   2 ). In accordance with one or more such embodiments, pillars  1040   1 - 1040   2  may be any suitable material such as, for example and without limitation, a metal such as type 304 stainless steel, hardened tool steel, titanium, and the like. Pillars  1040   1 - 1040   2  support test head  3000 , and thereby, determine its orientation with respect to support plate  1010 . In accordance with one or more embodiments of the present invention, pillars  1040   1 - 1040   2  may be attached to top surfaces  1030   1 - 1030   2  by means of, for example and without limitation, mechanical fasteners, posts, magnetic force, adhesives, or vacuum. 
         [0030]      FIG. 1C  shows a top sectional view of alignment apparatus  1000 , which section is taken in a plane indicated by arrows A and A′ of  FIG. 1B . As shown in  FIG. 1C , and in accordance with one or more embodiments of the present invention, each of reservoirs  1020   1 - 1020   4  has an aperture that admits and releases fluid, which apertures are connected to fluid channels that are interconnected at junction  1400 . Thus, in accordance with one or more such embodiments, as shown in  FIG. 1A , fluid may flow: (a) from reservoir  1020   2 , through the aperture therein; (b) through fluid channel  1050   2 ; (c) past junction  1400 ; (d) through fluid channel  1050   1 ; and (e) into reservoir  1020   1 , through the aperture therein. In addition, as shown in  FIGS. 1A and 1B , and in accordance with one or more embodiments of the present invention, alignment apparatus  1000  includes valve mechanism  1600  (for example and without limitation, a solenoid-operated, spring-return valve) that is adapted to stop the flow of fluid in alignment apparatus  1000 . In particular, as shown in  FIGS. 1A and 1B , valve mechanism  1600  is affixed to support plate  1010  by screws (not shown), and sealed against fluid leaks by O-rings  1601  and  1602 . Valve mechanism  1600  includes plug  1620  which is urged upward in a vertical direction by spring  1630 , and may be urged in a downward vertical direction by activation of electromagnet  1610  by a controller (not shown). Such a controller may be fabricated readily by one of ordinary skill in the art utilizing, for example and without limitation, any one of a number of commercially available programmable microprocessors, which microprocessors may be programmed routinely and without undue experimentation utilizing any one of a number of methods that are also well known to those of ordinary skill in the art. In accordance with one or more such embodiments, plug  1620  may be one or more of a metal, a plastic-coated ferromagnetic metal impregnated plastic, a glass-filled PTFE polymer, a PEEK polymer, a PFA-coated alnico magnet, and so forth. In accordance with one or more embodiments of the present invention, plug  1620  may have a relief hole along an axis through the plug which is designed to allow fluid flow from a top cavity to a bottom cavity in which plug  1620  moves in an upward and downward motion. 
         [0031]    In accordance with one or more embodiments of the present invention, the fluid used in alignment apparatus  1000  may be a gas or a liquid such as, for example and without limitation, a hydraulic fluid. More preferably, the fluid is a relatively incompressible liquid such as, for example and without limitation, silicone vacuum pump oil, aliphatic oil, and various hydraulic fluids. 
         [0032]    In addition, in accordance with one or more embodiments of the present invention, alignment apparatus  1000  includes a pump (not shown) to pump fluid into reservoirs  1020   1 - 1020   4  from a fluid reservoir (not shown). Such a fluid replenishment system may further include a pressure relief valve and a check valve. The pressure relief valve ensures that any excess fluid pressure is returned to the system fluid reservoir. In accordance with one or more embodiments of the present invention, the pump may be any suitable pump such as, for example and without limitation, a piezoelectric pump, a peristaltic pump, or a contraction of a bladder. In accordance with one or more such embodiments, the pump may pump fluid into a fluid channel at common junction  1400  or into any of the fluid channels individually. Alternatively, each of chambers  1020   1 - 1020   4  may be connected to a fluid reservoir. 
         [0033]    In accordance with one or more embodiments of the present invention, a volume, including a cross sectional area and height of a reservoir may be determined routinely and without undue experimentation by one of ordinary skill in the art in light of a particular application taking into account one or more of the following: a force needed to be applied (for example to engage a test head with a wafer); a predetermined time for fluid to flow among the reservoirs; and a viscosity of the fluid utilized. 
         [0034]      FIGS. 2A-2C  show top sectional views of alignment apparatus that are fabricated in accordance with one or more embodiments of the present invention.  FIG. 2A  shows a top sectional view of an embodiment of the present invention which comprises three reservoirs  2000   1 - 2000   3  wherein: fluid channel  2010   1  having valve  2020   1  is connected between reservoirs  2000   1  and  2000   2 ; fluid channel  2010   2  having valve  2020   2  is connected between reservoirs  2000   2  and  2000   3 ; and fluid channel  2010   3  having valve  2020   3  is connected between reservoirs  2000   3  and  2000   1 . In accordance with such an embodiment, closure of all valves  2020   1 - 2020   3  is required to stop the flow of fluid in the alignment apparatus.  FIG. 2B  shows a top sectional view of an embodiment of the present invention which comprises four reservoirs  2100   1 - 2100   4  wherein: fluid channel  2110   1  having valve  2120   1  is connected between reservoirs  2100   1  and  2100   3 ; and fluid channel  2110   2  having valve  2120   2  is connected between reservoirs  2100   2  and  2100   4 . In accordance with such an embodiment, closure of all valves  2120   1 - 2120   2  is required to stop the flow of fluid in the alignment apparatus. Lastly,  FIG. 2C  shows a top sectional view of an embodiment of the present invention which comprises five reservoirs  2200   1 - 2200   5  wherein: fluid channels  2210   1 - 2210   5  having valves  2220   1 - 2220   5 , respectively, all meet at a common junction. In accordance with such an embodiment, closure of all valves  2220   1 - 2220   5  is required to stop the flow of fluid in the alignment apparatus. Thus, as one can readily appreciate from this, embodiments of the present invention exist in many variations, for example and without limitation, an embodiment having four reservoirs where each of the four reservoirs may have fluid channels connecting each of the four reservoirs with an opposite chamber so that fluid may fluid therebetween. In addition, and in accordance with one or more such embodiments, each reservoir may connect to a fluid channel that connects each reservoir to a common point or junction. Further, in accordance with one or more such embodiments, each fluid channel may have a fluid valve that is capable of stopping a flow of liquid to or from each reservoir, and there may be a fluid valve at a common point or junction of all the fluid channels. 
         [0035]    Referring back to  FIGS. 1A-1C , in accordance with one or more further embodiments of the present invention, pillars  1040   1 - 1040   4  are not utilized, and reservoirs  1020   1 - 1020   4  may include bellows that protrude above the surface of support plate  1010 . Further, in accordance with one or more further embodiments of the present invention, reservoirs  1020   1 - 1020   4  may include pistons that may be activated to provide an initialization state wherein each reservoir has the same volume of fluid therein, which pistons would operate under the control of a controller (not shown). Such a controller may be fabricated readily by one of ordinary skill in the art utilizing, for example and without limitation, any one of a number of commercially available programmable microprocessors, which microprocessors may be programmed routinely and without undue experimentation utilizing any one of a number of methods that are also well known to those of ordinary skill in the art. 
         [0036]      FIG. 3  shows a flow chart of a method for aligning a test head in accordance with one or more embodiments of the present invention. As shown in  FIG. 3 , at step  5000 , alignment apparatus  1000  is initialized by a controller which causes fluid to be pumped from a reservoir (not shown) into reservoirs  1020   1 - 1020   4 . Such a controller may be fabricated readily by one of ordinary skill in the art utilizing, for example and without limitation, any one of a number of commercially available programmable microprocessors, which microprocessors may be programmed routinely and without undue experimentation utilizing any one of a number of methods that are also well known to those of ordinary skill in the art. Then, control is transfer to step  5010 . 
         [0037]    At step  5010  shown in  FIG. 3 , the controller sends a signal that causes valve mechanism  1600  to open to enable fluid flow in fluid channels  1050   1 - 1050   4 . Then, control is transferred to step  5020 . 
         [0038]    At step  5020  shown in  FIG. 3 , wafer  4000  is mounted in a conventional, movable chuck (not shown) that is capable of moving in a vertical direction in response to control signals sent by the controller. Next, the controller sends a signal that causes wafer  4000  to be moved downward to touch test head  3000 , as detected, for example and without limitation, by electrical contact between probes on test head  3000  and wafer  4000 . The controller also delays, by a predetermined amount, to allow fluid flow in fluid channels  1050   1 - 1050   4 . Then, control is transferred to step  5030 . 
         [0039]    At step  5030  shown in  FIG. 3 , the controller carries out a test to determine whether wafer  4000  and test head  3000  are aligned in an orientation in which a bottom surface of wafer  4000  is parallel to a top surface of probe head  3000 , such alignment test being carried out, for example and without limitation, by the controller&#39;s examining a map of electrical contacts made between an array of probes on test head  3000  and wafer  4000 . Then, control is transferred to decision step  5040 . 
         [0040]    At decision step  5040 , the controller determines whether wafer  4000  and test head  3000  are aligned. If they are aligned, control is transferred to step  5070 , otherwise; control is transferred to step  5050 . 
         [0041]    At step  5050  shown in  FIG. 3 , the controller sends a signal that causes wafer  4000  to be moved downward by a predetermined amount. Then, control is transferred to step  5060 . 
         [0042]    At step  5060  shown in  FIG. 3 , the controller delays by a predetermined amount to allow fluid to flow in fluid channels  1050   1 - 1050   4 . Then, control is transferred to step  5030 . 
         [0043]    At step  5070 , the controller sends a signal that causes valve mechanism  1600  to stop fluid flow in fluid channels  1050   1 - 1050   4 . Then, control is transferred to step  5080  where the process ends. 
         [0044]    As one of ordinary skill in the art will readily appreciate from the above, test head  3000  may be a planar test head or test head  3000  may comprise test pins that are projected up and in a plane. In general, test head  3000  may be a first workpiece and wafer  4000  may be a second workpiece. Further, as wafer  4000  and test head  3000  are urged into contact, test head  3000  generates forces on each of reservoirs  1020   1 - 1020   4 . These forces cause fluid to flow in fluid channels  1050   1 - 1050   4  between reservoirs  1020   1 - 1020   4  and junction  1400 . If more force is applied to one of reservoirs  1020   1 - 1020   4  than others of reservoirs  1020   1 - 1020   4 , then fluid will flow from the one chamber to other chambers. As this occurs, the top surface of the one chamber will subside and the top surface of the other chambers will rise. The speed at which this occurs will be determined by the rate of fluid flow in fluid channels  1050   1 - 1050   4  and the surface area of reservoir tops  1030   1 - 1030   4 . In this manner, reservoirs  1020   1 - 1020   4  will enable test head  3000  to adjust for aplanarity of wafer  4000  or for alignment of test head  3000  with wafer  4000 . When alignment has been achieved, fluid flow in the fluid channels is halted by closing the valves, thereby locking test head  3000  in a fixed orientation with respect to wafer  4000 . 
         [0045]    In accordance with one or more alternative embodiments of the present invention, test head  3000  may be leveled or aligned by applying a force to change the amount of fluid contained in one or more of reservoirs  1020   1 - 1020   4 , wherein the force may be applied using one or more of a magnetic mechanism, a pneumatic mechanism, and a spring mechanism. 
         [0046]    In accordance with one or more embodiments of the present invention, a fluidic chamber may be configured to have a movable side that depends upon the specific requirements of the application. By way of example,  FIGS. 4A-C  are partial cross-sectional views of fluidic chambers that may be used to fabricate one or more embodiments of the present invention, the fluidic chambers having different configurations. In particular,  FIG. 4A  shows a cross-sectional view of fluidic chamber  100  having movable pillar  200  attached to test head  3000  by means of threaded bolt  300 . As shown in  FIG. 4A , movable pillar  200  comprises two pillars having a bridge connecting them. As further shown in  FIG. 4A , bolt  300  is attached from a bottom side of movable pillar  200  to enable easy dismounting of test head  3000  (i.e., an attachment mechanism is formed by bolt  300  being threaded through movable pillar  200  and test head  3000 ). As still further indicated by  FIG. 4A , diaphragm  400  is an annulus attached to movable pillar  200  at an inner diameter edge and at an outer diameter edge. In addition, as shown in  FIG. 4A , movable pillar  200  is attached to a top surface of diaphragm  400  on an area between undulation  410  proximal to an inner diameter of diaphragm  400  and undulation  420  proximal to an outer diameter of diaphragm  400 . Fluid pressure in chamber  100  of  FIG. 4A  bows diaphragm  400  upward, thereby urging movable pillar  200  and attached test head  3000  in upward direction. As further shown in  FIG. 4A , fluid chamber  100  is connected to shut-off valve  500  by fluid channel  450 . Whenever valve  500  in fluid channel  450  is open, fluid is able to flow from annular chamber  100  to other similar fluid chambers (not shown). Whenever valve  500  is closed, as shown in  FIG. 4A , fluid in annular chamber  100  is fixed, thereby holding movable pillar  200  and attached portion of test head  3000  in a fixed vertical position. 
         [0047]    In order that the attached portion of test head  3000  be held in a fixed position that is substantially unchanged by downward pressure on test head  3000 , in accordance with one or more embodiments of the present invention, fluid chamber  100  is preferably filled with a relatively incompressible fluid such as, for example and without limitation, silicone vacuum pump oil, aliphatic oil, and the like. In accordance with one or more further such embodiments, fluid chamber  100  has a height in a vertical direction that is less than a maximum diameter of fluid chamber  100  in a horizontal direction. In particular, in accordance with one or more such embodiments, fluid chamber  100  has a height in the vertical direction that is less than 10% of a maximum diameter of fluid chamber  100  in a horizontal direction, thereby reducing vertical deflection of test head  3000  due to compressibility of fluid in fluid chamber  100 . Alternatively, in accordance with one or more such embodiments, fluid chamber  100  encloses a volume of fluid that is less than 1/10 times an area of moveable wall  400  raised to a power 3/2. 
         [0048]    In accordance with one or more embodiments of the present invention, test head  3000  may be supported on two or more posts that are attached directly to fluid chambers of the type (i.e., fluid chamber  100 ) shown in  FIG. 4A . In addition, in accordance with one or more embodiments, a post supporting test head  3000  may be rigidly attached to movable pillar  200 , wherein mechanical means exist for adjusting a height of the post. By way of example, and as has been described above, test head  3000  may be supported on posts including one post that has a height that is adjustable by a screw mechanism; and two or more posts (comprising legs of movable pillar  200  shown in  FIG. 4A ) that are each attached to a movable wall (wall  400  shown in  FIG. 4A ) of a fluid chamber (for example, fluid chamber  100  shown in  FIG. 4A ). 
         [0049]      FIG. 4B  shows a cross-sectional view of a fluidic chamber that may be used to fabricate one or more embodiments of the present invention, which fluidic chamber enables positioning of a test head in a horizontal plane as well as leveling in a vertical direction. As shown in  FIG. 4B , fluid chamber  650  is formed by horizontal support plate  600 , expandable bellows structure  610 , plate  620 , and movable plate  615  which is affixed to test head  3000 . In accordance with one or more such embodiments of the present invention, expandable bellows structure  610  enables movable plate  615  to have a limited amount of movement in a horizontal direction as well as in a vertical direction. As further shown in  FIG. 4B , test head  3000  is urged upwardly by a force generator comprising Belleville spring  630  that thrusts ball  640  against a center portion of test head  3000 . In operation, Belleville spring  630  is initially put in a tensioned state by introducing fluid under pressure from an external source (not shown) into the fluid chambers, including fluid chamber  650  shown in  FIG. 4B , that support test head  3000 , thereby urging movable plate  615  and attached test head  3000  in a downward direction. After the initial tensioning of Belleville spring  630 , the external source of fluid pressure is sealed off from a network of fluid channels connecting the fluid chambers, i.e., the network is thereby made closed. Then, test head  3000  shown in  FIG. 4B  is aligned as described above in conjunction with  FIG. 1A . In particular, the fluid valve or valves in channels connecting the chambers is opened (for example, valve  660  shown in  FIG. 4B ), and a test piece is urged downwardly against test head  3000 , thereby causing fluid to flow in channels interconnecting the fluid chambers to enable test head  3000  to come into parallel registration with respect to the test piece. The valve or valves in the fluid channels (for example, valve  660  shown in  FIG. 4B ) are closed when test head  3000  is in registration with the test piece, as determined, for example and without limitation, by electrical contact patterns, by interferometer measurements, by optical measurements, or by use of any other means that are well known by one of ordinary skill in the art. After the valves are closed, an upward force of Belleville spring  630  on test head  3000  urges movable plate  615  upward in a vertical direction, thereby maintaining a positive fluid pressure in the chambers. It will be understood by one of ordinary skill in the art that a negative fluid pressure in the fluid chambers may also be used, wherein a spring or other mechanical force generator is employed to urge test head  3000  downward toward support plate  620 , thereby urging movable plate  615  downward and bellows structure  610  to expand downwardly. 
         [0050]    In accordance with one or more embodiments of the present invention, and as indicated in  FIG. 4B , test head  3000  is aligned in a first horizontal direction by alignment screw  670  that urges test head  3000  horizontally toward the right. Other alignment screws (not visible in  FIG. 4B ) urge test head  3000  in a second horizontal direction, preferably orthogonal to the first direction, and thereby may be used to urge test head  3000  in a rotational direction around a vertical axis. In accordance with one or more such embodiments, bellows structure  610  of each fluid chamber is sufficiently flexible to allow horizontal movement necessary to align test head  3000  in a desired horizontal direction. 
         [0051]      FIG. 4C  shows a cross-sectional view of fluidic chamber  700  that may be used to fabricate one or more embodiments of the present invention. As shown in  FIG. 4C , chamber  700  includes movable piston  710  that is sealed at a perimeter of chamber  700  by O-ring  720 . Further, piston  710  includes post  715  which supports test head  3000 . In accordance with one or more embodiments of the present invention, test head  3000  may rest on post  715  or it may be connected thereto, for example and without limitation, by adhesives. As further shown in  FIG. 4C , fluid channel  730  passes through solenoid-operated, spring-return valve  740  (shown in a closed position in  FIG. 4C ), where solenoid-operated, spring-return valve  740  is sealed to support plate  705  by O-rings  735  using, for example and without limitation, screws (not shown). 
         [0052]    One or more embodiments of the present invention are capable of aligning a test head to be parallel to a test piece without the need for contact therebetween. In order to do this, a test head is connected to movable walls of fluid chambers while fluid is able to flow in channels interconnecting the fluid chambers. Then, a force is applied to the test head using, for example and without limitation, pneumatic actuators, springs, electromagnetic actuators, magnets, and hydraulic actuators. In accordance with one or more such embodiments, the force acts to change an orientation of the test head.  FIG. 5A  shows a cross-sectional view of alignment and leveling apparatus  1500  that is fabricated in accordance with one or more embodiments of the present invention wherein pneumatic actuators are used to align a test head. In accordance with one or more such embodiments, alignment and leveling apparatus  1500  may be utilized to level a test head and to align it to a horizontal orientation. 
         [0053]      FIG. 5A  shows a cross-sectional view of alignment and leveling apparatus  1500 ;  FIG. 5B  shows a top sectional view of alignment and leveling apparatus  1500  where the section is taken in a plane indicated by arrows B and B′ of  FIG. 5B ;  FIG. 6A  shows a sectional perspective view of alignment and leveling apparatus  1500 ; and  FIG. 6B  shows an exploded assembly view in perspective of alignment and leveling apparatus  1500 . 
         [0054]    In accordance with one or more embodiments of the invention, test head  3000  is supported on four studs  1530   1 - 1530   4  that are aligned in predetermined directions along an x-axis and a y-axis (studs  1530   1 - 1530   2  are shown in  FIG. 5A ). Each of four studs  1530   1 - 1530   4  is held in a corresponding post (posts  1540   1 - 1540   2  are shown in  FIG. 5A , and posts  1540   1 - 1540   4  are shown in  FIG. 6B ) attached to spider plate  1510  that spans the distance between posts  1540   1 - 1540   4  and links posts  1540   1 - 1540   4  together. In accordance with one or more such embodiments, each of studs  1530   1 - 1530   4  is held fast within a hole in a corresponding post and is fastened to the post by a set screw (not shown); other means such as a magnetic clamp, an electromagnetic clamp, a shape memory alloy clamp, a vacuum clamp, a press fit, and the like may be used to fasten the stud to the post. In addition, and in accordance with one or more such embodiments, each of posts  1540   1 - 1540   4  is connected or attached to movable walls  1550   1 - 1550   4  (movable walls  1550   1 - 1550   2  are shown in  FIG. 5A ) of a corresponding one of fluid chambers  1560   1 - 1560   4  (fluid chambers  1560   1 - 1560   2  are shown in  FIG. 5A ). In further addition, and in accordance with one or more such embodiments, each of fluid chambers  1560   1 - 1560   2  contains silicone vacuum pump oil; alternatively the chambers may be filled with a fluid including mineral oil, hydraulic fluid, and the like which will remain fluid over a range of temperatures experienced by test head  3000 . In still further addition, and in accordance with one or more such embodiments, each of fluid chambers  1560   1 - 1560   4  is connected by fluid channels  1570   1 - 1570   4  (fluid channels  1570   1 - 1570   2  are shown in  FIG. 5A ) to common junction  1580  which may be closed by solenoid-operated, spring-return valve  1700 . As shown in  FIG. 5A , valve  1700  is sealed to support plate  1730  using O-rings  1710 - 1720 . 
         [0055]    In accordance with one or more embodiments of the present invention, during a leveling and aligning process, fluid is free to flow in fluid channels  1570   1 - 1570   4  that interconnect fluid chambers  1560   1 - 1560   4 —-central valve  1700  is shown in an open position in  FIG. 5A  to allow fluid to flow therethrough. In accordance with one or more such embodiments, fluid flows in the network of fluid channels  1570   1 - 1570   4  to bring pressure within fluid chambers  1560   1 - 1560   4  into equilibrium. In particular, a downward force applied to one post causes fluid to from the fluid chamber attached to the one post, through channels to the other chambers, thereby acting to tilt test head  3000  downward on a side attached to the one post. Likewise, an upward force on one post acts to tilt test head  3000  upward on a side attached to the one post. After test head  3000  is brought into alignment, shut-off valve  1700  is closed by releasing a magnetic force applied by solenoid  1750  on poppet  1740 , thereby trapping fluid within each of fluid chambers  1560   1 - 1560   4  and fixing the vertical position of each of movable walls  1550   1 - 1550   4  of each of fluid chambers  1560   1 - 1560   4  and locking the orientation of test head  3000  attached thereto. 
         [0056]    As shown in  FIG. 6A , and in accordance with one or more embodiments of the present invention, a force generator applies a downward force to spider plate  1510  and to attached posts  1540   1 - 1540   4 , thereby urging each of movable walls  1550   1 - 1550   4  attached thereto downward so as to maintain a fluid pressure within each of fluid chambers  1560   1 - 1560   4 . In accordance with one or more embodiments of the present invention, the force generator comprises: Belleville spring  1810  which is held in compression by central screw attachment  1820  (central screw attachment  1820  is screwed into support plate  1835 ) so as to apply downward force to spider plate  1510  and to attached posts  1540   1 - 1540   4 , thereby urging each of movable walls  1550   1 - 1550   4  attached thereto downward. In accordance with one or more such embodiments, a baseline of fluid pressure is set by adjustment of screw  1820  so as to reduce the occurrence of bubbles in the fluid, for example and without limitation, silicone oil, due to evolution of dissolved gas. Advantageously, Belleville spring  1810  applies a downward pressure to spider plate  1510  without hindering the tilting motion necessary for alignment of test head  3000 . 
         [0057]    As shown in  FIG. 5A , and in accordance with one or more embodiments of the present invention, alignment and leveling apparatus  1500  comprises four force generators that are upwardly movable so as to engage a bottom surface of test head  3000 . In accordance with one or more embodiments of the present invention, the four force generators comprise four pneumatically activated bosses  1830   1 - 1830   4  (bosses  1830   1 - 1830   2  are shown in  FIG. 5A , and bosses  1830   1 - 1830   4  are shown in  FIG. 6B ) that are upwardly movable so as to engage a bottom surface of test head  3000 . Air pressures P X2 , P X1 , P Y1  and P Y2  are supplied to four air pockets  1840   1 - 1840   4 , respectively, in support plate  1835 , the top of each pocket being sealed by an expandable diaphragm (i.e., diaphragms  1850   1 - 1850   4  where diaphragms  1850   1 - 1850   2  are shown in  FIG. 5A , and diaphragms  1850   1 - 1850   4  are shown in  FIG. 6B ) upon which a boss is mounted (air pockets  1840   1 - 1840   4  and diaphragms  1850   1 - 1850   4  may be referred to below as pressure actuators  1890   1 - 1890   4 ). As shown in  FIG. 5B , and in accordance with one or more such embodiments, air at pressures P X2 , P X1 , P Y1  and P Y2  are applied as input to nozzles  1870   1 - 1870   4 , respectively, from sources of pressurized air (not shown), and channels  1880   1 - 1880   4  connect nozzles  1870   1 - 1870   4  to air pockets  1840   1 - 1840   4 . 
         [0058]    In accordance with one or more such embodiments of the present invention, each boss may be moved independently by control of air pressure in a corresponding pocket under the boss. For example, a boss may be moved vertically by air pressure so as to contact a back side of test head  3000  and to urge test head  3000  to tilt upward on a side proximal to the boss. After the alignment process is complete, air pressure in each pocket may be released, thereby allowing each boss to retract downward, and out of contact with test head  3000 . 
         [0059]    A process of aligning and leveling a test head in accordance with one or more embodiments of the present invention may be better understood by reference to  FIG. 7  (which is a schematic drawing of alignment and leveling apparatus  1500  shown in  FIG. 5A ) and to  FIG. 8  (which is a flow chart of a method for aligning and leveling test head  3000  in accordance with one or more embodiments of the present invention using alignment and leveling apparatus  1500 ). For simplicity of exposition in  FIG. 7 , test head  6000  is represented as having arms X 1  and X 2  disposed along an x-axis and arms Y 1  and Y 2  disposed along a y-axis, the remainder of test head  6000  being cut away to show the pneumatic actuators and the fluidic chambers of alignment and leveling apparatus  1500  (wherein the pneumatic actuators and the fluidic chambers are each being represented as a fluidic cylinder for of ease of understanding the following). 
         [0060]    As shown in  FIG. 8 , at step  7000 , the process of leveling test head  6000  begins by having controller  6010  cause an equal pressure to be applied to each of pneumatic actuators  1890   1 - 1890   4  (i.e., this initializes the force in the force generators) To do this, pneumatic switches  1910   1 - 1910   4  are activated by having controller  6010  apply a voltage to each of the solenoids that control pneumatic switches  1910   1 - 1910   4 , and by having controller  6010  apply equal control voltages V X1 , V Y1 , V X2 , and V Y2  to each of electronically-controlled, pressure regulators  1920   1 - 1920   4 . As a result, air pressures of P X1 =P Y1 =P X2 =P Y2  are applied to pneumatic actuators  1890   1 - 1890   4 , thereby moving bosses  1830   1 - 1830   4  connected to pneumatic actuators  1890   1 - 1890   4 , respectively, upward into contact with test head  6000 . Next, an electronic counter associated with controller  6010  is reset to i=0. Then, control is transferred to step  7010 . Such a controller may be fabricated readily by one of ordinary skill in the art utilizing, for example and without limitation, any one of a number of commercially available programmable microprocessors, which microprocessors may be programmed routinely and without undue experimentation utilizing any one of a number of methods that are also well known to those of ordinary skill in the art. 
         [0061]    At step  7010  shown in  FIG. 8 , a position of test head  6000  is unlocked by causing controller  6010  to send signals to shut-off valves  1930   1 - 1930   4  disposed in fluid channels  1570   1 - 1570   4  interconnecting fluid chambers  1560   1 - 1560   4 , thereby allowing fluid to flow therebetween (in accordance with the embodiments described here, each fluid channel has a valve). Shut-off valves  1930   1 - 1930   4  are opened by having controller  6010  apply a voltage to solenoids operating shut-off valves  1930   1 - 1930   4 . For clarity of exposition, shut-off valves  1930   1 - 1930   4  shown in  FIG. 7  are shown as being operated by separate solenoids, whereas in further embodiments, the solenoids may be consolidated into a single solenoid. Whenever shut-off valves  1930   1 - 1930   4  are held open, an upward force on one side of test head  6000  near arm Y 1  will cause fluid to flow into the chamber disposed thereunder and the side proximal to arm Y 1  to move upward. Then, control is transferred to step  7020 . 
         [0062]    At step  7020  shown in  FIG. 8 , i.e., after unlocking the position of test head  6000 , an X-level is sensed by, for example and without limitation, a pattern of electrical contacts arrayed between a surface of test head  6000  and a surface of a work piece (not shown). Then, control is transferred to decision step  7030 . 
         [0063]    At decision step  7030  shown in  FIG. 8 , electronic decision-making circuitry in controller  6010  branches depending on whether the sensed X-level indicates that a position of arm X 1  is higher than, lower than, or equal to a position of arm X 2  (i.e., equal to within a predetermined tolerance). If the sensed X-level indicates that the position of arm X 1  is higher than the position of arm X 2 , control is transferred to step  7040 ; if the sensed X-level indicates that the position of arm X 1  is lower than the position of arm X 2 , control is transferred to step  7050 ; and if the sensed X-level indicates that the position of arm X 1  is equal to the position of arm X 2 , control is transferred to step  7060 . 
         [0064]    At step  7040  shown in  FIG. 8 , the electronic decision-making circuitry causes controller  6010  to decrease voltage V X1  applied to electronically-controlled, pressure regulator  1920   4 , thereby decreasing pneumatic pressure to pneumatic actuator  1890   4  and relaxing test head  6000  downward on the side of test head  6000  proximal to arm X 1 . Electronic decision-making circuitry suitable for this purpose can be fabricated in accordance with any one of a number of methods that are well known to those of ordinary skill in the art. For example and without limitation, such electronic decision-making circuitry may be fabricated utilizing logic circuitry, software controlled circuitry, or a combination thereof. Then, control is transferred to step  7070 . 
         [0065]    At step  7050  shown in  FIG. 8 , the electronic decision-making circuitry causes controller  6010  to increase voltage V X1 , thereby increasing pneumatic pressure to pneumatic actuator  1890   4  and urging test head  6000  upward on the side of test head  6000  proximal to arm X 1 . Then, control is transferred to step  7070 . 
         [0066]    At step  7060  shown in  FIG. 8 , the electronic decision-making circuitry causes controller  6010  to set indicator i to i=1. Then, control is transferred to step  7070 . 
         [0067]    At step  7070  shown in  FIG. 8 , a Y-level is sensed by, for example and without limitation, a pattern of electrical contacts arrayed between a surface of test head  6000  and a work piece (not shown). Then, control is transferred to decision step  7080 . 
         [0068]    At decision step  7080  shown in  FIG. 8 , electronic decision-making circuitry in controller  6010  branches depending on whether the sensed Y-level indicates that a position of arm Y 1  is higher than, lower than, or equal to a position of arm Y 2  (i.e., equal to within a predetermined tolerance). If the sensed Y-level indicates that the position of arm Y 1  is higher than the position of arm Y 2 , control is transferred to step  7090 ; if the sensed Y-level indicates that the position of arm Y 1  is lower than the position of arm Y 2 , control is transferred to step  7110 ; and if the sensed Y-level indicates that the position of arm Y 1  is equal to the position of arm Y 2 , control is transferred to step  7100 . 
         [0069]    At step  7090  shown in  FIG. 8 , the electronic decision-making circuitry causes controller  6010  to decrease voltage V Y1  applied to electronically-controlled, pressure regulator  1920   3 , thereby decreasing pneumatic pressure to pneumatic actuator  1890   3  and relaxing test head  6000  downward on the side of test head  6000  proximal to arm Y 1 . Then, control is transferred to decision step  7120 . 
         [0070]    At step  7110  shown in  FIG. 8 , the electronic decision-making circuitry causes controller  6010  to increase voltage V Y1 , thereby increasing pneumatic pressure to pneumatic actuator  1890   3  and urging test head  6000  upward on the side of test head  6000  proximal to arm Y 1 . Then, control is transferred to decision step  7120 . 
         [0071]    At step  7100  shown in  FIG. 8 , the electronic decision-making circuitry causes controller  6010  to set indicator i to i=i+1. Then, control is transferred to decision step  7120 . 
         [0072]    At decision step  7120  shown in  FIG. 8 , decision making circuitry in controller  6010  transfers control depending on the value of indicator i. In particular, if i=2 (indicating that test head  6000  is level in the X-direction and in the Y-direction), control is transferred to step  7130 ; if i=1, control is transferred to step  7150 ; and if i=0, control is transferred to step  7160 . 
         [0073]    At step  7130  shown in  FIG. 8 , controller  6010  sends signals to cause shut-off valves  1930   1 - 1930   4  in fluid channels  1570   1 - 1570   4  to be closed, thereby locking test head  6000  in a leveled position. Then, control is transferred to step  7140 . 
         [0074]    At step  7140  shown in  FIG. 8 , the leveling process is finished. 
         [0075]    At step  7150  shown in  FIG. 8 , the electronic decision-making circuitry causes controller  6010  to set indicator i to i=0. Then, control is transferred to step  7020  to sense the X-level. 
         [0076]    At step  7160  shown in  FIG. 8 , the electronic decision-making circuitry causes controller  6010  to delay to allow more time for fluid to flow in fluid channels  1570   1 - 1570   4 . Then, control is transferred to step  7020  to sense the X-level. 
         [0077]    In accordance with one or more embodiments of the present invention, a multiplicity of test heads may be leveled, and the test heads may be aligned, one to another. In particular,  FIGS. 9A-9D  show alignment and leveling apparatus  8000  which is fabricated in accordance with one or more embodiments of the present invention for leveling and aligning four independent segments of test head  8010 , the four segments  8010   1 - 8010   4  being best illustrated in a top sectional view of alignment and leveling apparatus  8000  shown in  FIG. 9D , which section is taken in a plane indicated by arrows G and G′ of  FIG. 9C . 
         [0078]    As indicated in  FIGS. 9A-9D , each of segments  8010   1 - 8010   4  of test head  8010  is supported on four balls (balls  8020   1 - 8020   4  are shown in  FIGS. 9A and 9C ) wherein each of the balls rests on a movable wall (movable walls  8030   1 - 8030   4  are shown in  FIGS. 9A and 9C ) of a corresponding fluid chamber (fluid chambers  8050   1 - 8050   4  are shown in  FIGS. 9A and 9C ). In addition, in accordance with one or more embodiments of the present invention, each of segments  8010   1 - 8010   4  is secured in place by a bolt which is: (a) inserted through support plate  8100 ; (b) threaded into the segment; and (c) held in tension by a Belleville spring (bolts  8060   1 - 8060   2  and Belleville springs  8070   1 - 8070   2  are shown in  FIGS. 9A and 9C ). In further addition, in accordance with one or more such embodiments, the Belleville springs are designed to have a large dynamic range such that the spring exerts a downward force on a test head segment that is relatively constant over a typical range of vertical motion of the test head segment. By way of example, a stack of two (2) Belleville springs may be used to provide a force that is within 10% of the maximum force over a range of motion of 500 microns. While Belleville springs may have desirable properties in that they may be designed to have a nearly constant force vs. displacement, other attachment methods may be used including without limitation helical springs, cone springs, leaf springs, wave springs, magnetic holders, electromagnetic catches, and the like. In accordance with one or more alternative embodiments of the present invention, the ball supports disposed under each segment of test head  8010  may be replaced by any one of a number of other suitable mechanisms such as, for example and without limitation, solid posts, wherein the posts are the means of attachment of the segment to the array of movable walls of the fluid chambers, thereby eliminating a need for the bolt and the Belleville spring as an attachment means. 
         [0079]    As further shown in  FIGS. 9A-9C , alignment and leveling apparatus  8000  further comprises fluid chambers  8050   1 - 8050   16 , each with a movable top wall, that are disposed in a surface of support plate  8100 . As further shown in  FIGS. 9A and 9C , attachment bolts (attachment bolts  8060   1 - 8060   2  are shown in  FIGS. 9A and 9C ) are disposed in holes through support plate  8100 , wherein each bolt is preferably located under an area centroid of a test head segment attached thereto. Further, as has been described above, each of segments  8010   1 - 8010   4  of test head  8010  is supported on four balls (balls  8020   1 - 8020   4  are shown in  FIGS. 9A and 9C ), wherein each of the balls rests on a movable wall (movable walls  8030   1 - 8030   4  are shown in  FIGS. 9A and 9C ) of a corresponding fluid chamber (fluid chambers  8050   1 - 8050   4  are shown in  FIGS. 9A and 9C ). In addition, and in accordance with one or more such embodiments, the balls supporting a segment of test head  8010  are arrayed around an attachment bolt attaching the segment to support plate  8100 . Thus, in accordance with one or more such embodiments, each of the four segments  8010   1 - 8010   4  of test head  8010  are supported by interposition of four balls on four movable walls of four fluid chambers. In further addition, each of sixteen fluid chambers fluid chambers  8050   1 - 8050   16  are each connected by a fluid channel to central shut-off valve  8110 . Whenever shut-off valve  8110  is open (as shown  FIG. 9A ), fluid in each chamber is free to flow to other chambers. 
         [0080]    A method for leveling each of segments  8010   1 - 8010   4  of test head  8010  and aligning the segments, one to another, is best understood by reference to the cross-sectional view of alignment and leveling apparatus  8000  shown in  FIG. 9A , and the top sectional view of alignment and leveling apparatus  8000  shown in  FIG. 9B , which section is taken in a plane indicated by arrows E and E′ of  FIG. 9A . In accordance with one or more embodiments of the present invention, during the leveling and aligning process, a controller (not shown) sends a signal to electromagnetic mechanism  8130  (for example and without limitation, a solenoid) of shut-off valve  8110  is cause plug  8120  to be drawn downward, thereby opening fluid channels from each chamber to common manifold  8140  and enabling fluid in each chamber to flow to other chambers via manifold  8140 . Such a controller may be fabricated readily by one of ordinary skill in the art utilizing, for example and without limitation, any one of a number of commercially available programmable microprocessors, which microprocessors may be programmed routinely and without undue experimentation utilizing any one of a number of methods that are also well known to those of ordinary skill in the art. In accordance with one or more such embodiments, plug  8120  may have a through-hole, from top to bottom, that allows fluid trapped in manifold  8140  to relieve through plug  8120  as plug  8120  is drawn downward. Next, test piece  9000  is urged downward against electrical probes arrayed on a top surface of each of segments  8010   1 - 8010   4  of test head  8010  by a distribution of forces F. In accordance with one or more embodiments of the present invention, fluid flows in the fluid channels to equalize pressure in the fluid chambers. When the fluid pressure within all of the fluid chambers is equal, and the forces on each of segments  8010   1 - 8010   4  of test head  8010  are equal, segments  8010   1 - 8010   4  are in alignment. Then, shut-off valve  8110  is closed by having the controller send a signal to release electromagnetic mechanism  8130 , thereby allowing spring  8150  to move plug  8120  upward into manifold  8140 , thereby closing off each of the channels leading from manifold  8140  to a corresponding fluid chamber. As the volume of fluid in each chamber is fixed when shut-off valve  8110  is closed, each of segments  8010   1 - 8010   4  of test head  8010  supported by each chamber is locked in a level position by closing shut-off valve  8110 . 
         [0081]    Preferably, the fluid in the fluid chambers is relatively incompressible so as to maintain the position of test head segments, notwithstanding a variable force transmitted to the test head segments by a test piece. More preferably, the fluid is a low vapor pressure liquid such as silicone vacuum pump oil supplied by Dow Corning. Alternatively, the fluid is selected from a group, for example and without limitation, of hydraulic fluid, mineral oil, aliphatic oil, chlorinated hydrocarbon oils, Galden (available from Solvay Chemical), Fluorinert (available from 3M Corporation), and the like. 
         [0082]    As will be appreciated by one of ordinary skill in the art, the principles described above pertaining to various embodiments of the present invention may be used to design leveling and aligning apparatus that disposes fluid chambers in various combinations. By way of example, each segment of a test head may be supported on movable walls of a first set of fluid chambers in a first support plate. In turn, each of a group of first support plates may be supported on movable walls of a second set of fluid chambers in a second support plate. In addition, during a process of leveling and aligning segments of a test head, fluid may be allowed to flow between fluid chambers of a first set of fluid chambers by means of a first set of fluid channels; and fluid may be allowed to flow between fluid chambers of a second set of fluid chambers by means of a second set of fluid channels. Further, when segments of a test head are level and aligned, fluid flow in the first set of channels may be shut off by one or more valves, and fluid flow in the second set of channels may be shut off by one or more valves, thereby locking segments of the test head in alignment. 
         [0083]    Embodiments of the present invention described above are exemplary. As such, many changes and modifications may be made to the disclosure set forth above while remaining within the scope of the invention. In addition, materials, methods, and mechanisms suitable for fabricating embodiments of the present invention have been described above by providing specific, non-limiting examples and/or by relying on the knowledge of one of ordinary skill in the art. Materials, methods, and mechanisms suitable for fabricating various embodiments or portions of various embodiments of the present invention described above have not been repeated, for sake of brevity, wherever it should be well understood by those of ordinary skill in the art that the various embodiments or portions of the various embodiments could be fabricated utilizing the same or similar previously described materials, methods or mechanisms. Further, as is apparent to one skilled in the art, the embodiments may be used for making connections to semiconductor devices, electronic devices, electronic subsystems, cables, and circuit boards and assemblies. 
         [0084]    As one or ordinary skill in the art will readily appreciate, sockets fabricated in accordance with one or more embodiments of the present invention may include any number of fluid seals, gaskets, adhesives, washers, or other elements that function to seal the assembly and to prevent thermal transfer fluid from leaking (internally or externally). 
         [0085]    The scope of the invention should be determined with reference to the appended claims along with their full scope of equivalents.

Technology Classification (CPC): 8