Abstract:
A compliance assembly is disclosed for use in a semiconductor tester testhead stand. The compliance assembly includes an airspring having compliance along a plurality of axes and a containment vessel adapted for receiving the airspring. The containment vessel includes walls that, when the airspring is loaded, control the compliance along the plurality of axes.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to automatic test equipment, and more particularly to a reduced-cost manipulator apparatus employed for use with automatic test equipment. 
     BACKGROUND OF THE INVENTION 
     Automatic test equipment provides semiconductor device manufacturers the ability to test each and every device fabricated. By testing each device, the manufacturer can sort devices having like speeds, and/or separate failed devices from passing devices. In this manner, the manufacturer is able to confidently put fully functioning devices into the marketplace. 
     Automatic test equipment, often referred to as a tester, typically employs a mainframe or computer workstation and a testhead. The testhead houses sophisticated electronics and includes interface circuitry for coupling the electronics close to the devices-under-test (DUTs). This is done in order to minimize propagation delays on the test signals transmitted between the testhead and the DUTs. The DUTs are typically positioned on a prober (if at the wafer level) or handler (if at the packaged-device level). 
     Due to the size and weight of a conventional testhead, coupling the tester electronics to the DUTs involves carefully docking the testhead to the handler or prober (hereafter generically referred to as a handling device). The device employed to carry and position the testhead for docking is a manipulator. FIG. 1 illustrates a conventional manipulator  10  adapted for carrying and positioning a testhead  12 . 
     Further referring to FIG. 1, the conventional manipulator includes a base  14  and a cradle  15  for engaging and carrying the testhead  12 . A positioning mechanism  16  provides the ability to displace the two-thousand pound testhead along a plurality of compliance axes with manual control. Conventionally, one example of the mechanism includes high-precision linear bearings  18  that cooperate with telescopically sliding members to provide compliance needed to carefully position the testhead. Generally, compliance refers to the force applied by the manipulator to offset the force of gravity acting on the testhead. Once leveraged out, the compliance allows the testhead to be moved around in any direction. The mechanism is actuated by a pneumatic or hydraulic piston  20 . Alignment pins (not shown), help to guide the testhead onto the handling apparatus. 
     While this example of a conventional manipulator works well for its intended applications, the mechanical construction for establishing compliance employs parts and assemblies built to a high degree of precision with very tight tolerances. This translates into a high cost of fabrication. 
     What is needed and currently unavailable is a manipulator solution that provides multiple axes of compliance with low-cost components. The low-cost manipulator of the present invention satisfies this need. 
     SUMMARY OF THE INVENTION 
     The manipulator of the present invention employs low-cost components to effect reliable and accurate multi-axial compliance without sacrificing performance. This correspondingly reduces test costs for semiconductor device manufacturers. 
     To realize the foregoing advantages, the invention in one form comprises a compliance assembly for use in a semiconductor tester testhead stand. The compliance assembly includes an airspring having compliance along a plurality of axes and a containment vessel adapted for receiving the airspring. The containment vessel includes walls that, when the airspring is loaded, control the compliance along the plurality of axes. 
     In another form, the invention comprises a testhead stand for compliantly docking a semiconductor tester testhead to a handling apparatus. The testhead stand includes a base having oppositely disposed side members and a pair of spaced-apart extension members. The extension members are disposed on the side members and project upwardly therefrom. A pair of compliance assemblies disposed on the pair of extension members are adapted to receive the testhead. Each compliance assembly includes an airspring having compliance along a plurality of axes and a containment vessel. The containment vessel is adapted for receiving the airspring and has walls that, when the airspring is loaded, control the compliance along the plurality of axes. 
     In a further form, the invention comprises a linkage-based manipulator for automatic test equipment. The linkage-based manipulator includes a base and a cradle having a testhead end adapted for coupling to a testhead. The manipulator further includes a linkage means for vertically displacing the cradle between a lower position and an upper position while maintaining the cradle parallel to the base and while avoiding any horizontal displacement. A load element pivotally mounted at one end to the base and at the other end to the linkage means provides a force to the linkage means opposite the force of gravity acting on the testhead. 
     Other features and advantages of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood by reference to the following more detailed description and accompanying drawings in which 
     FIG. 1 is a high-level block diagram of a conventional manipulator; 
     FIG. 2 is a perspective view of a testhead stand according to one form of the present invention; 
     FIG. 3 is a partial lateral view of the compliance assembly along line  3 — 3  of FIG. 2; 
     FIG. 4 is a plan view of the airspring along line  4 — 4  of FIG. 3; 
     FIG. 5 is a cross-sectional view of the airspring along line  5 — 5  of FIG. 3; 
     FIG. 6 is a side view block diagram of an alternative manipulator according to the present invention; and 
     FIG. 7 is a rear perspective view of the manipulator of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The manipulator of the present invention provides a low-cost way to position semiconductor tester testheads without sacrificing the necesssary compliance to carefully dock to a handling apparatus. This is done by employing a low-cost airspring-based compliance assembly in the manipulator rather than expensive high-tolerance linear bearings and the like. 
     FIG. 2 illustrates a low-cost manipulator, or testhead stand, generally designated  30 , for holding a semiconductor tester testhead  32  in a given orientation, while providing multiple compliant degrees-of-freedom. This compliance is often necessary to dock the testhead to a handler (for packaged devices, not shown) or a prober (for wafer-level devices, not shown). Bulk motion is often provided by a dedicated service manipulator, such as the conventional manipulator  10  described previously and shown in FIG.  1 . 
     Further referring to FIG. 2, the testhead stand  30  includes a rectangular base formed with a plurality of slidable tubular elements  34   a - 34   d . The base is carried by a plurality of corner-disposed casters  36   a - 36   d  to provide mobility for the stand. Leveling feet  38   a - 38   c  (fourth caster not shown) are provided to establish a level platform once the stand is situated in a static position. 
     Mounted on opposite sides of the base are upwardly projecting extendable support beams  40  and  42 . The support beams form a pair of support structures suitable for mounting respective compliant assemblies  44  (only one assembly shown in FIG.  2 ). 
     With particular reference to FIGS. 3,  4  and  5 , each compliance assembly  44  includes an airspring  46  constrained within a containment vessel  60 . The airspring comprises a resilient hollow body  48  (FIG. 5) having respective spaced-apart axial sides  50  and  52 . A pair of circular metallic disks  54  and  56  are mounted to the axial sides to seal the inside of the hollow body. A valve (not shown) provides for pressurization of the airspring to a suitable compliant level. Preferred airsprings are available as model #s W01-358-7731, 7751, AND 7451, available from Firestone Corporation. 
     Further referring to FIG. 3, the containment vessel  60  includes a base plate  62  formed with upwardly projecting side walls  64  and  66 . The side walls are formed respectively with upwardly opening threaded bores  68 . With the airspring  46  situated on the base plate  62 , a floating load plate  70  is disposed on the airspring. In this manner, the airspring is effectively sandwiched between the base plate and the load plate. A pair of stabilizer assemblies are positioned on each end of the load plate and include respective threaded bolts  72  and  74  biased by stabilizer springs  76  and  78 . The bolts include threaded shanks  80  and  82  that mate to the base plate threaded bores, and place the springs in compression to minimize lateral load imbalances on the airspring. C-shaped overtravel stops  84  and  86  are also mounted to the base plate  62  and extend over and above the load plate  70  a predetermined height to prevent the plates from vertically separating beyond the stop height. 
     In a preferred embodiment, a pair of horizontally and oppositely disposed open-ended bolt tubes  88  (second tube not shown) are secured to the load plate  70  and are adapted to receive correspondingly formed cylindrical bolts (often referred to as “Frankenstein” bolts)  90  (FIG. 2) that carry the testhead  32 . 
     Prior to operation, the testhead  32  is first installed onto the stand  30  through use of a service manipulator, as alluded to previously. Once installed in the stand, the testhead may be moved to the docking interface of a handler or prober (not shown). The service manipulator is then free to install another testhead on another stand. Once positioned near the docking interface, the testhead may be finely manipulated, as required, to effect a final docking. The multiple compliant degrees of freedom provided by the compliance assemblies allow for the fine positioning. 
     One of the key cost advantages realized through the use of low-cost manipulator stands lies in the ability to leverage the cost of a single expensive service manipulator across several test systems while providing the individual inexpensive stands to each test system for support and final compliant positioning of the testhead. 
     Referring now to FIGS. 6 and 7, a manipulator according to a second embodiment of the present invention, generally designated  126 , includes a support frame  130  having a base  132  with respective vertically upstanding struts  131 ,  133  and  135 ,  137 . A pair of upstanding bars project vertically from the front end of the base. As can be seen more clearly from FIG. 7, much of the linkage construction comprises two parallel structures disposed on each side of the base. Consequently, because FIG. 6 illustrates a side view, only one of the structures is clearly visible. 
     Further referring to FIGS. 6 and 7, a pair of rear-disposed lower support members  138 ,  140  are pivotally coupled to the base at respective joints  142 ,  144 . The opposite ends of the support members terminate at the respective rear ends of a pair of lower arms  146 ,  148  at pivots  150 ,  152 . A pair of stabilizer arms  154 ,  156  are pivotally disposed between the vertically upstanding bars  134 ,  136  at pivots  158 ,  160  and the lower arms  146 ,  148  at joints  158 ,  160 . The resulting construction defines a pair of side-by-side lower parallelograms. 
     Cooperating with the lower parallelograms are a pair of upper side-by-side parallelogram links as more fully described below. Coupled to the pair of lower support members  138 ,  140  at joints  150 ,  152  are a pair of upper support members  162 ,  164 . The upper support members each include respective horizontally projecting struts  166 ,  168 . Pivotally disposed between the horizontal struts and the base vertical struts  135 ,  137  are a pair of parallel front upright support members  170 ,  172 . 
     With continuing reference to FIGS. 6 and 7, disposed in parallel relationship to the lower arms  146 ,  148  is a moment arm beam  180 . The moment arm beam comprises an elongated bar and a pair of forks  183 ,  185  mounted at the testhead end. The beam couples to the upper support members  162 ,  164  at pivots  182 ,  184 . A cantilevered support  186  is pivotally disposed between the ends of the moment arm beam forks  183 ,  185  and the lower arms  146 ,  148  at joints  192 ,  194 , and  196 ,  198 . The support includes a pair of cantilevered arms  187 ,  189  and a pair of vertical beams  188 ,  190 . The beams are of a length matching the length of the upper support members  162 ,  164 . This ensures that the moment arm beam  180  and the lower arms maintain a parallel relationship. The cantilever arms define a cradle for carrying a semiconductor tester testhead  202 . 
     To effect vertical displacement of the cantilevered support without any horizontal displacement, a load element is pivotally coupled between the moment arm beam strut  181  and a base strut  131   a . The load element preferably comprises the airspring-based construction previously described with respect to the first embodiment of the present invention, and illustrated in FIGS. 1 through 5. Control over the load element operation is provided through a control system (not shown) that monitors the load acting on the load element, and generates enough counter-load to effect compliance over the testhead. The construction additionally employs a braking system (not shown) to lock the linkages into a predetermined position once docking has occurred. 
     Optionally, to effect additional rotational bulk motion, or twist, with the cradle, a twist bearing (not shown) may be employed proximate the cradle. Similarly, a twist bearing (not shown) may also be implemented on the base to provide rotational bulk motion along a base rotational axis. 
     Operation of the linkage-based manipulator is different to that of the stand manipulator in that the linkages provide bulk compliance for the testhead in addition to fine compliance that the stand offers. Specifically, the load element is pressurized to effect actuation of the linkages as desired by the user. Positive pressurization will force the structure to raise the platform, albeit in a vertical plane, while depressurizing the load element causes a lowering of the platform. Once a coarse position is set, the operator may manually place the testhead into its final docking position with the handler/prober. 
     Those skilled in the art will appreciate the many benefits and advantages afforded by the present invention. Of significant importance is the implementation of a low-cost airspring to achieve compliance in a testhead manipulator without sacrificing manipulator performance. 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.