Abstract:
A modular offset Automated Testing Equipment (ATE) test head with split backplane is presented. The ATE test head is modularized into a card cage module having a first backplane for accommodating general purpose instrument cards and a cassette module having a second backplane that is offset relative to the first backplane for accommodating personality (specific purpose) instrument cards. The general purpose instrument cards and the personality instrument cards communicates with each other by cables connecting them. The general purpose instrument cards and personality instrument cards can be quickly disengaged from and engaged to the respective backplanes individually or concurrently. Because of this latter feature, a cassette module can be easily and rapidly disengaged from the card cage module and a different cassette module can be easily and rapidly engaged to the card cage module. In so doing, the test head can be easily and rapidly reconfigured to perform different test functions without any ATE down time. When attached to the card cage, the cassette module extends beyond the card cage&#39;s boundary along one direction to form a platform. This platform provides the interface to a Device Under Test (DUT) board. As a result of the modularity of the three major elements: card cage, cassette module, and split backplanes that together form a ATE test head, rapid and accurate attachment to and removal from a variety of IC handlers and probers are facilitated.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to automatic test equipments, and more particularly to the structural design of remote test heads. 
     BACKGROUND OF THE INVENTION 
     To provide quality assurance, semiconductor device makers systematically perform tests on their products to ensure that they meet or exceed all of their design parameters. Some of the types of tests routinely performed include device parametric testing (a.k.a. DC testing), device logic function testing, and device timing testing (a.k.a. AC testing). The semiconductor device being tested is commonly known as the Device Under Test (DUT) and the test system used in conducting the above tests on the DUT is commonly known as Automatic Test Equipment (ATE). In carrying out the aforementioned tests on very sensitive DUTs, the ATE is necessarily very precise. In general, the ATE hardware is controlled by a computer which executes a test program to present the correct voltages, currents, timings, and functional states to the DUT and monitor the response from the device for each test. The result of each test is then compared to pre-defined limits and a pass/fail decision is made. As such, the ATE hardware normally includes a collection of power-supplies, meters, signal generators, pattern generators, etc. The Pin Electronics (PE) circuitry provides the interface between the ATE and the DUT. 
     U.S. Pat. No. 4,517,512 to Petrich et al. (hereinafter the &#39;512 patent) shows an example of a prior art rack-and-stack ATE. As shown in FIG. 1 of the &#39;512 patent, a control computer including display, power supplies, I/O peripherals (e.g., data storage drives, printers) are stacked on top of each other in a rack console which may be 19 inches wide. The ATE has a remote test head module which carries the instrument cards designed to provide voltages, currents, timings, and functional states to the DUT and to monitor the responses. A cable links the remote test head module to the equipments in the rack console to supply power from the rack console to the remote test head module as well as to allow the transfer of data and control/command signals between the rack console and the remote test head module. During testing, the remote test head module is attached to a test fixture underneath a prober/handler also attached to the test fixture. The prober/handler is used to hold the DUT and to position the DUT relative to the remote test head module. As computers and testers move into the gigahertz range, corresponding wavelengths are a few millimeters. At such wavelengths, almost any wire is an antenna causing signal radiation. Also, ATEs are now working with lower power levels, with currents in the microampere range. This increases the effects of electrical noise. Where higher powers are used to offset noise, transmission line losses occur thereby reducing efficiency. An advantage of this invention is that the distance from the instrument cards in the test head module to the DUT is kept reasonably short to reduce signal radiation, to improve the signal-to-noise ratio, and to reduce transmission line losses. 
     The instrument cards in the remote test head module are electrically and mechanically connected to each other in a stack-like fashion wherein a male connector on an instrument card is connected to a corresponding female connector on an immediately adjacent instrument card and so on. The connection established by connectors allow the instrument cards to communicate to each other. The instrument cards are connected to the rack console by the cable. The instrument card on top of the stack (a.k.a. the master instrument card) is connected to as many as 64 PE cards. To accommodate 64 PE cards, connectors are arranged in a circle on top of the master instrument card. A disadvantage in connecting instrument cards in a stack is that it does not allow for replacing an instrument card in the stack without disassembling and reconfiguring the instrument card stack. Such disassembly and reconfiguration are likely to result in down time for the ATE which may be undesirable. Another disadvantage in relying on connectors to mechanically connect instrument cards in a stack is that it limits the number of instrument cards that can be stacked and therefore the number of tests that can be carried out by the ATE. While additional mechanical fasteners may be used to secure the instrument cards together thereby allowing more cards to be stacked on top of each other, such fasteners increase costs as well as making it more difficult and time consuming to replace an instrument card. 
     To accommodate the increase number of tests performed by an ATE (e.g., in linear and mixed signals testing) as well as to improve the ability to replace instrument cards and/or reconfigure the test module rapidly, an approach has been developed wherein instrument cards with connectors are connected to corresponding connectors on a backplane such that the instrument cards are parallel to each other. In so doing, any instrument card can be removed and replaced quickly and easily. A prior art ATE  100  that employs this backplane approach is the ASL1000 that is manufactured by TMT Inc. of Sunnyvale, Calif. which is illustrated in FIG.  1 . 
     As shown in FIG. 1, remote test head module  101  is controlled by central processing unit (CPU)  111  with display monitor  112  and keyboard  113 . Power supply  114  supplies the required power to remote test head module  101  which interfaces with DUT  106 . Remote test head module  101  includes back plane  102  having up to twenty-one (21) parallel connectors on one side into which twenty-one instrument cards  103  are plugged. To converge the signals from twenty-one proprietary instrument cards  103  into a small test area that interfaces with DUT  106 , the opposite side of backplane  102  is connected to system interconnect board  104 . On the opposite side of backplane  102 , there are six (6) 96-pin connectors  107  to which six corresponding 96-pins connectors  108  of system interconnect board  104  are plugged. System interconnect board  104  is in turn connected to DUT board  105 . Accordingly, on the opposite side of system interconnect board  104  there are a plurality of connectors  109  to which corresponding connectors  110  of DUT board  105  are connected. 
     In this prior art ATE system, any individual instrument card  103  can be easily and rapid replaced. However, when replacement of a large number of instrument cards is involved, it may be necessary to remove interconnect board  104  from backplane  102  (e.g., for reconfiguration). This is quite challenging given the force required to simultaneously disengage/engage all five-hundred-seventy-six (6×96) pins of six connectors that connect backplane  102  to system interconnect board  104 . Accordingly, mechanical assistance may be required. Even with such a mechanical tool, it is still difficult to remove and replace interconnect board  104  rapidly. 
     Moreover, a test head module that is designed to seat multiple instrument cards like test head module  101  can be rather large in terms of size and weight (as much as 200 lbs) which makes it very difficult to move it close to a DUT let alone maneuvering, even with mechanical aids (e.g., manipulator, wheels, etc.), the test head module in a precise manner to properly connect the test head module with the DUT. As such, it may be necessary to connect PE circuitry to the test head module by a cable to get close to the DUT. This almost always degrades the signals. 
     Thus, a need exists for an ATE test head module that houses a large number of instrument cards, that allows for rapid reconfiguration of a backplane and replacement of instrument cards, as well as can be placed in close proximity with a DUT without requiring a mechanical manipulator and without requiring strenuous forces in reconfiguring the test head module. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an Automated Test Equipment (ATE) test head module that houses a large number of instrument cards, that allows for rapid reconfiguration of a backplane and replacement of instrument cards, as well as can be placed in close proximity with a DUT without requiring a mechanical manipulator and without requiring strenuous forces in reconfiguring the test head module. 
     The present invention meets the above objectives with an ATE test head module that comprises a card cage, and a cassette module mechanically joined to the card cage such that the cassette module can be quickly and easily removed from the card cage. The card cage has first backplane (a.k.a. PXI backplane) that is mechanically and electrically connected to a first set of circuit cards such that any card of the first set of circuit cards can be quickly and easily removed from the first backplane. The first backplane is electrically coupled to a Central Processing Unit (CPU). 
     The cassette module has a second backplane that is mechanically and electrically connected to a second set of circuit cards such that any card of the second set of circuit cards can be quickly and easily removed from the second backplane. The cassette module is designed to hold a Device Under Test (DUT) circuit board for interfacing with a DUT. The first set of circuit cards are in communications with the second set of circuit cards. In an embodiment, the cassette module extends beyond the card cage to form a platform for holding the DUT circuit board. The platform has a cutout with an access door on a rear side allowing access to the second backplane and a through hole in the second backplane to allow visual contact and access to the DUT. Such visual contact is important during various activities such as handler and prober docking, and prober wafer alignment. When closed, the access door prevents light and electrical interference from affecting the DUT. 
     In one embodiment, the card cage has a cavity and an access opening for accommodating the second set of circuit cards when the cassette module is mechanically joined to the card cage. The first set of circuit cards is industry standard general-purpose instrument cards and the second set of circuit cards are proprietary personality instrument cards conforming to industry standards. 
     All the features and advantages of the present invention will become apparent from the following detailed description of its preferred embodiment whose description should be taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating a prior art ATE system. 
     FIG. 2 illustrates a block diagram of ATE  200  in accordance with the present invention. 
     FIG. 3 illustrates in greater detail remote test head  201  of FIG. 2 in accordance with the present invention. 
     FIG. 3A illustrates a top view of remote test head  201 . 
     FIG. 3B illustrates a rear view of remote test head  201 . 
     FIG. 3C illustrates a front view of remote test head  201 . 
     FIG. 4 shows the scenario in which card module  301  is released from its latched position relative to cassette module  302  that may be attached to a handler device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one skilled in the art that the present invention may be practiced without these specific details. In other instances well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention. 
     In accordance with the present invention, an Automated Testing Equipment (ATE) test head is modularized into a card cage module having a first backplane for accommodating general purpose instrument cards and a cassette module having a second backplane that is offset relative to the first backplane for accommodating personality (specific purpose) instrument cards. The general-purpose instrument cards and the personality instrument cards communicate with each other by cables connecting them. The general-purpose instrument cards and personality instrument cards can be quickly disengaged from and engaged to the respective backplanes individually or concurrently. This allows the cassette module to be quickly and easily attached to and detached from the card cage module without requiring strenuous forces. Because of its relatively lightweight and small size, a cassette module in accordance to the present invention is very maneuverable. The test head can also be easily and rapidly reconfigured to perform different test functions without almost no ATE down time. When attached to the card cage, the cassette module extends beyond the card cage&#39;s boundary along one direction to form a platform. This platform provides the interface to a Device Under Test (DUT) board. A through hole is provided in the platform to provide visual alignment of the cassette module relative to the DUT and allow direct connections with the DUT by external instruments. 
     Reference is now made to FIG. 2 illustrating a high-level diagram of computer controlled Automatic Test Equipment (ATE)  200  that implements the present invention. ATE  200  comprises remote test head  201 , computer system  202 , and system power supplies  203 . Computer system  202  is the system controller. Computer system  202  controls remote test head  201  which is electrically linked to computer system  202  by an electrical cable. Computer system  202  also acts as a hub to transfer data to/from ATE  200 . Hence, computer system  202  may generally include a central processing unit (CPU), input/output (I/O) interfaces such as parallel and serial ports, communications interface for networking and communicating with the outside world, video/graphics controller, a number of data storage devices such as hard drive and tape drive for locally storing information, I/O devices such as keyboard and video monitor to allow the operator to interact with ATE  200 . It is to be appreciated that computer system  202  can be any one of a number of different computer systems including desk-top computer systems, general purpose computer systems, embedded computer systems, and others. Remote test head  201  carries all the instrument circuitry cards required to generate forced test signals and to monitor responded signals from the DUT before sending them to computer system  202  for analysis. Accordingly, remote test head  201  is used to interface with the DUT. By having the instrument cards in remote test head  201 , the instrument cards are ensured that they will be in close proximity with the DUT thereby minimizing the adverse effects associated with running a cable from the instrument cards located a distance away to the DUT which may include high signal radiation, low signal-to-noise ratio, and transmission line losses. 
     System power supplies  203  provide steady and uninterrupted direct current (DC) power to test head  201 . Depending on its test purposes, it is to be appreciated that an ATE may have more or fewer than the components discussed above. Further, it should be clear that the components of the ATE discussed above are conventional and well known by people of ordinary skill in the art. 
     Referring now to FIG. 3 illustrating in greater detail a remote test head  201  in accordance with the present invention. As shown in FIG. 3 (a side view of remote test head  201 ), remote test head  201  comprises a portable card cage  301  and a portable cassette module  302 . Card cage  301  houses general purpose instrument cards  303  which are plugged into backplane  313  that is fastened to card cage  301 . More specifically, general instrument cards  303  are plugged into connectors  304  that are connected to backplane  313  (a.k.a. PXI backplane). While card cage  301  also “houses” personality instrument cards  312 , personality instrument cards  312  are not plugged into backplane  313  of card cage  301 . As discussed in greater detail below, personality instrument cards  312  are plugged via connectors into a second backplane that is part of cassette module  302 . In other words, the traditional backplane is split into two backplanes in the present invention. When personality instrument cards  312  are disengaged from the backplane of cassette module  302  (i.e., backplane  314 ), they may remain in card cage  301  (kept in place by slot guides) or they may be removed completely from card cage  301 . By splitting the traditional backplane and allowing individual personality instrument cards  312  to easily disengage from backplane  314 , no strenuous forces are required in detaching card cage  301  from cassette module  302 , or vice versa. 
     General-purpose instrument cards  303  are used to produce electrical signals (e.g., voltages, currents, timing functions, etc.) that are generally required in substantially all of the tests performed using ATE. In other words, general purpose instrument cards  303  act as resources for personality instrument cards which are used for specific test functions. Conversely, personality instrument cards  312  are used to generate test functions that are particular to a specific test. In generating the test functions, personality instrument cards  312  may employ the electrical signals generated by general purpose instrument cards  303 . Backplane  313  only extends about half the length of the bottom side of card cage  301 . As such, there is an access opening into card cage  301  that begins where backplane  313  ends. Such an access opening is used to allow personality instrument cards  312  to be plugged into the backplane  314  of cassette module  302 . To maximize the number of general-purpose instrument cards  303  that can be accommodate by backplane  313  as well as facilitate the insertion and removal of general instrument cards  303  to/from backplane  313 , connectors  304  are arranged so that they are parallel to each other. When general instrument cards  303  are plugged into connectors  304 , they are both mechanically and electrically connected to backplane  313  which in turn is electrically connected to computer system  202 . 
     In FIG. 3, cassette module  302  is shown locked to card cage  301 . However, card cage  301  is designed such that it can be easily and rapidly latched to or disengaged from cassette module  302 , or vice versa. While cassette module  302  is likely attached to a device handler (fixture) during test, card cage  301  is free to swing open or close relative to cassette module  302  thereby providing access to instrument cards, backplanes, and others as well as allowing a rapid exchange of cassette module  302 . In one embodiment, cassette module  302  has an upward-curved slot  305  located at one end of cassette module  302  and extends across the width of cassette module  302 . Hinge pir  306 , which is attached to and extends across the width of card cage  301 , is designed to hook into slot  305  that is at the lower corner of cassette module  302  and extends across the width of cassette module  302  thereby allowing card cage  301  to pivot and rotate about slot  305  of cassette module  302  to swing close or open. To allow card cage  301  to easily and rapidly disengage from cassette module  302 , which may be attached to a handler equipment, hinge pine  306  is designed so that card cage  301  can be easily removed from slot  305 . To attach card cage  301  to cassette module  302  (or vice versa), hinge pin  306  is first hooked onto slot  305  thereby allowing one end of card cage  301  to hang on and be supported by slot  305 . This allows the user to easily pull the free end of cassette module  302  up, even with just one hand given the weight of cassette module  302 , to attach cassette module  302  to card cage  301 . Personality instrument cards  312  are then inserted individually into the corresponding connectors on backplane  314 . To detach card cage  301  from cassette module  302  (or vice versa), personality instrument cards  312  are first disengaged individually from backplane  314 . Card cage  301  is then unlatched from cassette module  302  thereby allowing card cage  301  to swing open relative to cassette module  302  about slot  305 . By disengaging personality instrument cards  312  first, less force is required to disengage card cage  301  from cassette module  302  (or vice versa). 
     Latch mechanisms  307  are used to lock cassette module  302  in place relative to card cage  301  in the locked (close) position. FIG. 3A, which is a top view of remote test head  201  (i.e., a top view of FIG.  3 ), illustrates the relative placement of latch mechanisms  307 . In one embodiment, each latch mechanism  307  comprises lever member  308  and hook member  309 . Lever member  308  is attached and pivoted at one end to flange  309  that is fastened to a side flange of card cage  301 . As such, lever member  308  is free to rotate relative to pivot point  310  that is connects lever  308  to flange  316 . Hook member  309  is attached and pivoted at one end to approximately the midpoint of lever member  308  thereby allowing hook member  309  to rotate relative to lever member  308  about pivot point  311 . As its name suggested, hook member  309  has a hook at the free end. In so doing, latch mechanism provides two degrees of freedom to allow the hook of hook member  309  to move freely to engage and disengage with pin  318  in cassette module  302 . To lock cassette module  302  in place relative to card cage  301 , lever member  308  is pulled down to lower hook member  309 . Because hook member  309  is also free to rotate about pivot point  311 , hook member  309  also has lateral movements. The vertical and lateral movements allow the hook of hook member  309  to find and engage with pin  318 . At this point, lever member  308  is pushed up to raise hook member  309  which latches cassette module  302  in place relative to card cage  301 . To release cassette module  302  relative to card cage  301 , lever member  308  is pulled down to lower hood member  309  which is in turn rotated about pivot point  311  to free it from pin  318  thereby releasing cassette module  302 . It should be clear to a person of ordinary skill in the art that other types of latch mechanisms can also be employed and still be within the scope of the present invention. For illustration purpose, FIG. 4 shows cassette module  302  in its released configuration relative to card module  301 . However, in FIG. 4, cassette module  302  is still hooked onto hinge pin  306  of card cage  301  by slot  305 . To completely detach cassette module  302  from card cage  301 , slot  305  still needs to be unhooked from hinge pin  306  which is easy to do. From this position, cassette module  302  can easily be lifted up by the user, using only one hand, to be latched to card cage  301 . 
     Referring now back to FIG. 3, as discussed earlier, cassette module  302  has a different backplane  314  that is offset relative to backplane  313  of card cage  301 . In other words, backplanes  313  and  314  are in different planes. Like backplane  313 , backplane  314  has a row of connectors  315  arranged in parallel to accommodate a greater number personality instrument cards  312  as well as to allow them to be easily and quickly engaged/disengaged to/from backplane  314  on an individual basis. Personality instrument cards  312  may be connected to selected general purpose instrument cards  303  by cables  322  so that common test functions generated by general purpose instrument cards  303  can be shared by different personality instrument cards  312 . In addition to serving as an interface with a DUT board, backplane  314 , which is attached to cassette module  302 , also acts as the top side of cassette module  302 . Cassette module  302  extends beyond the boundary of card cage  301  along one direction to form a platform. This platform provides the interface to a DUT card. As shown in FIG. 3B, which is a back view of remote test head  201 , through hole  320  is provided in backplane  314  to provide visual alignment of cassette module  302  relative to the DUT board, to facilitate probe card/wafer alignment, and provide direct connections with the DUT by external instruments. DUT board connectors  317  are provided on the front side of backplane  314  and in the proximity of through hole  320  to connect backplane  314  to corresponding connectors from DUT board  319  which is in contact with the DUT. When DUT board  319  is plugged into backplane  314 , they are both mechanically and electrically connected to backplane  314  which in turn is electrically connected to personality instrument cards  312  and computer system  202 . As shown in FIG. 3C, a front view of remote test head  201 , cutout  321  is provided in the front panel of cassette module  302  to allow DUT board  319  access to the DUT board connectors  317 . Cutout  321  may be equipped with an access door so that when closed, the access door prevents light and electrical interference from affecting the DUT during various activities. 
     In accordance with the present invention, because cassette module  302  may be replaced in seconds, the ATE user may have multiple numbers of cassette modules  302 , backplanes  314 , and DUT boards  319  which are configured ahead of time for different requirements of different kinds of tests and for different DUTs. Referring to FIG. 3, the configurations of cassette modules  302  may be different in terms of connections, number of personality instrument cards  312 , types of personality instrument cards, and others. When the time comes to reconfigure test head module  201  for a particular test of a particular DUT, personality instruments cards  312  are disengaged from backplane  314  which can easily and quickly done in accordance with the present invention. By disengaging personality instrument cards  312  from backplane  314 , card cage  301  and cassette module  302  can be readily detached from each other. Upon detachment from card cage  301 , cassette module  302  consequently becomes much lighter and smaller in size therefore more maneuverable. The independent maneuverability of cassette module  302  is very desirable when it comes to aligning cassette module  302  relative to DUT board  319  (with a DUT) which may be attached to a device handler (fixture) or prober. Such maneuverability is also desirable in the alternate attachment approach wherein the DUT board  319  (with a DUT) is already attached to cassette module  302  before cassette module  302  is brought to the proximity of the handler. Card cage  301  and cassette module  302  may be made out of aluminum sheet metal or composites materials which make them very light. Cassette module  302  without the personality instrument cards may weigh five (5) lbs or less. Depending on the test, the disengaged personality instrument cards  312  may be left in card cage  301  for subsequent uses or they may be replaced by different cards. Latch mechanism  307  (or another latch mechanism) is then used to quickly release cassette module  302  from its latched condition with card cage  301 . Hinge pin  306  is then disengaged from slot  30  to completely separate card cage  301  from cassette module  302 . A different cassette module  302  can then be attached to card cage  301  in the reverse order within seconds compared to upward of 15 minutes as in the past. In so doing, no extended down time of the ATE is necessary and no excess force is required beyond the normal insertion and removal force of individual instrument cards for test head reconfiguration. 
     An embodiment of the present invention, an ATE test head module that houses a large number of instrument cards, allows for rapid reconfiguration of a backplane and replacement of instrument cards, as well as can be placed into close proximity with a DUT without requiring a mechanical manipulator, is thus described. While the present invention has been described in a particular embodiment, the present invention should not be construed as limited by such an embodiment, but rather construed according to the below claims.