Abstract:
Multi-stage in circuit test of a circuit board has support to reduce strain placed on the circuit board during each test stage. A shuttle plate is disposed between a load plate that supports a circuit board under test and a probe plate that directs test probes towards the circuit board. The shuttle board slides between different positions with each position establishing the distance between the circuit board and the test probes. For instance, in a first position, the shuttle plate aligns intermediary members to rest between the load plate and shuttle plate to keep the probes spaced by a first distance from the circuit board so that only some test probes contact the circuit board. In a second position, the shuttle plate aligns the intermediary members with blind vias to bring the shuttle plate and load plate proximate each other so that all test probes contact the circuit board.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates in general to the field of information handling system circuit board test, and more particularly to a multi-stage in circuit test with strain management. 
         [0003]    2. Description of the Related Art 
         [0004]    As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems. 
         [0005]    Information handling systems are typically built from a variety of components that communicate through a circuit board, such as a printed circuit board (PCB). The circuit board communicates signals, power and ground through wire lines formed in a nonconductive material, such as copper wires printed in laminated layers of plastic. Once the wire lines are prepared and the circuit board lamination is complete, electronic components are connected to the circuit boards in defined positions, such as by soldering electronic components to exposed connection points on the circuit boards. Often, processors and other large components are coupled to the circuit board with sockets that have mechanical coupling devices to hold processors in place. For example, a ball grid array (BGA) socket solders into a circuit board to establish electrical communication between wire lines of the circuit board and balls laid out on the socket surface. A processor is placed over the balls so that processor contacts interface with the balls and, in turn, with the circuit board wire lines. A load mechanism placed over the processor presses against the top of the processor to hold the processor contacts in place relative to the socket balls. 
         [0006]    Circuit boards generally represent a small portion of the overall cost of an information handling system, however, if a circuit board includes a fault then the more expensive components will often fail in unpredictable manners. For this and other reasons, circuit boards are typically tested for faults before assembly of components to the circuit board with a process generally referred to as in circuit testing (ICT). During in circuit testing, electrical probes test a circuit board to check for faults such as shorts, opens, resistance, capacitance and other indicators that will show whether the circuit board is correctly fabricated. Generally, a “bed of nails” configuration of probes is brought into contact with testing pads formed on the circuit board. Probes are brought into contact with testing nodes by pressing the circuit board against the probes. Typically, the circuit board is brought into contact with probes by creating a vacuum in a test space that pulls the circuit board downward into the probes, such as with the Agilent i3070 tester. In some cases, the circuit board is tested in multiple stages by stopping the circuit board&#39;s vacuum-induced motion after a first distance to provided contact with a first set of spring-loaded probes, and then removing the stops to allow the vacuum to pull the circuit board downwards into a second set of probes. The first set of probes is longer than the second set of probes and include spring loading so that the first set of probes recede downward with the circuit board as the board lowers against the second set of probes. 
         [0007]    In order to varying the distance that a circuit board travels during testing, stops are typically inserted along the edges of the load plate at the point where the first set of probes contact the circuit board. After completion of testing by the first set of probes, the stops are withdrawn to allow the circuit board to move so that the vacuum pulls the circuit board downward to the second set of probes. One difficulty that arises in such multi-stage testing is that, during the first stage of testing, the vacuum exerts a force across the circuit board and load plate that introduces flexion distal the stops. The downward force tends to bow the circuit board about its center point, which introduces strain to the circuit board. Strain across the circuit board transfers to wire lines and solder so that cracks and other faults may develop as a result of the testing. The amount of strain increases as the surface area of the circuit board increases and the thickness of the circuit board decreases. In some instances, a bent circuit board becomes unsuitable for use in an information handling system. In other instances, cracks form at socket joints and in other portions of the socket as the circuit board flexes relative to a stiff socket structure. 
       SUMMARY OF THE INVENTION 
       [0008]    Therefore, a need has arisen for a system and method which supports a circuit board test at multiple stages with reduced circuit board strain. 
         [0009]    In accordance with the present invention, a system and method are provided which substantially reduce the disadvantages and problems associated with previous methods and systems for circuit board testing. Intermediate members provide support to a circuit board under test at intermediate test stages and then recede to allow full movement of the circuit board in a test chamber for a final test stage. 
         [0010]    More specifically, an in circuit tester brings a circuit board into first and second test positions relative to a test probe plate that has test probes of first and second heights. In a first test stage, intermediate members intercede with the movement of the circuit board to maintain the circuit board at a height that allows connection of a first set of test probes to the circuit board but not connection of a second set of test probes. In a second test stage, the intermediate members recede or otherwise provide for additional movement of the circuit board so that both the first and second set of probes contact the circuit board. In one embodiment, the intermediate members extend from a load plate that supports the circuit board towards a shuttle plate to rest on the shuttle plate surface in the first test stage. The shuttle plate slides relative to the load plate to align the intermediate members with blind vias formed in the shuttle plate so that the intermediate member recede into the blind vias to allow additional circuit board motion. The intermediate members are distributed across the bottom surface of the load plate to support the load plate evenly so that stress is not unduly introduced to the circuit board during testing. 
         [0011]    The present invention provides a number of important technical advantages. One example of an important technical advantage is that circuit board tests are performed at multiple stages with support provided across the surface of the circuit board at each stage to reduce the introduction of strain to circuit board connection points. A shuttle plate intercedes between the tester lower probe support surface and circuit board under test to provide support across the surface of the circuit board at multiple test stages. Vias formed in the shuttle plate pass through a first set of probes that interface with the circuit board at a first test stage and a second set of probes that interface with the circuit board at a second test stage. Intermediate stop beans support the circuit board under test during interaction with just the first set of probes. Moving the shuttle plate relative to the circuit board aligns the intermediate stop beans with blind vias of the shuttle plate to allow circuit board motion into position for contact with the second set of probes. The intermediate stop beans prevent excessive strain across the circuit board at the first test stage to prevent circuit board failures during test. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element. 
           [0013]      FIG. 1  depicts a side cutaway view of a multi-stage circuit board tester having an intermediary member to provide circuit board support at an intermediary test stage; 
           [0014]      FIG. 2  depicts an example embodiment of a multi-stage tester having a sliding shuttle plate with stop bean intermediary members to provide circuit board support during testing by long test probes; 
           [0015]      FIG. 3  depicts the multi-stage tester of  FIG. 2  having the shuttle plate slid relative to the load plate so that the stop bean intermediary members engage in blind vias of the shuttle board; and 
           [0016]      FIG. 4  depicts a blow-up top view of an example of a multi-stage tester having a sliding shuttle plate to selectively engage intermediary members. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Information handling system multi-stage circuit board testing is performed with intermediate supports that reduce the risk of strain-related damage tai the circuit boards during testing. For purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, an information handling system may be a personal computer, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include random access memory (RAM), one or more processing resources such as a central processing unit (CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the information handling system may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communications between the various hardware components. 
         [0018]    Referring now to  FIG. 1 , a side cutaway view depicts a multi-stage circuit board tester  10  having an intermediary member  12  to provide circuit board  14  and load plate  26  with support at an intermediary test stage. In the example embodiment, an in circuit tester (ICT) selectively engages long test probes  16  and short test probes  18  with circuit board  14  during multiple testing stages. Tester  10  forms a container with a lid  20  that moves vertically relative to a probe plate  22  at the base of tester  10 . A vacuum source  24  generates a vacuum within tester  10  to bias lid  20  in a downward direction against a load plate  26 . Load plate  26  supports circuit board  14  during test and brings circuit board  14  into contact with test probes  16  and  18  by providing downward motion in response to a bias of lid  20 . Test probes  16  and  18  pass through via openings  28  formed in load plate  26  to come into contact with testing pads formed in circuit board  14 . Springs  30  associated with probes  16  and  18  maintain contact between probes  16  and  18  and circuit board  14  by providing a biasing upward force. Long test probe  16  moves downward to the level of short test probe  18  as circuit board  14  moves toward probe plate  22  so that both long test probe  16  and short test probe  18  are in contact with circuit board  14  as load plate  26  approaches probe plate  22 . 
         [0019]    During a first test stage, load plate  26  lowers by a distance sufficient to bring circuit board  14  in contact with long test probes  16  but insufficient to bring circuit board  14  into contact with short test probes  18 . Tester logic  32  provides test signals through long test probe  16  during the first test stage, while short test probe  18  remain idle. After first stage tests are complete, load plate  26  lowers further towards probe plate  22  so that both long test probes  16  and short test probes  18  are in contact with circuit board  14  to allow a second test stage. Tester logic  32  provides test signals through both long test probe  16  and short test probe  18  during the second test stage. The example embodiment is simplified for illustration purposes by show just a single long and short test probe, while ICT testers typically include a bed of test probes of different lengths. 
         [0020]    Generally, as circuit board  14  is pulled down towards probe plate  22 , load plate  26  will flex and thereby introduce strain to circuit board  14 . Flexing of circuit board  14  can result in the creation of defects as solder or wire lines bend and crack, especially if solid structures are couple to circuit board  14 , such as a processor socket structure  34 . In order to reduce stress across circuit board  14 , intermediate members  12  disposed between probe plate  22  and load plate  26  provide additional support that prevents or reduces flexing of load plate  26 . For example, intermediate members  12  have a length that allows support of load plate  26  translated from probe plate  22  when long test probe  16  engages circuit board  14  at a first test stage. Once the first test stage is complete, intermediate members  12  are removed or otherwise neutralized to allow movement of load plate  26  to a second test stage at which probe plate  22  more directly translates support to load plate  26 . In various embodiments, intermediate members may retract into probe plate  22 , rotate to a shorter profile, retract into load plate  26  or otherwise alter their footprint within tester  10 , such as in the example embodiment depicted by  FIGS. 2 through 4  as set forth below. 
         [0021]    Referring now to  FIG. 2 , an example embodiment is depicted of a. multi-stage tester  10  having a sliding shuttle plate  36  with stop bean intermediary members  12  to provide load plate  26  with support during testing by long test probes  16 . At a first test stage, vacuum within tester  10  pulls lid  20  towards probe plate  22  to bring long test probes  16  into contact with circuit board  14 . Before load plate  26  lowers by a distance sufficient to bring short test probes  18  into contact with circuit board  14 , intermediate stop bean members  14  intervene to stop movement of load plate  26  by resting on the upper surface of a shuttle plate  36 . Intermediate stop bean members are distributed on the bottom surface of load plate  26  to reduce the risk of flexing of load plate  26  at the first test stage. In one example embodiment, intermediate stop bean members  12  are coupled to the bottom surface of load plate  26  in a pattern that provides additional support at sensitive locations of circuit board  14 , such as at the location of structures like processor sockets soldered to circuit board  14 . The force exerted against intermediate stop bean members  12  at the first test stage is translated through shuttle plate  36  to probe plate  22 . 
         [0022]    Shuttle plate  36  includes vias  28  that allow test probes to pass through from probe plate  22  towards circuit board  14 . Vias  28  are formed with sufficient room to allow a sliding motion of shuttle plate  36 , as indicated by motion arrow  40 , without having shuttle plate  36  interfere with test probes  16  and  18 . Intermediate stop bean members  12  have a height sufficient to maintain load plate  26  above short test probes  18  during first stage testing but short enough so that long test probes  16  contact circuit board  14 . Upon introduction of a lateral sliding motion of shuttle plate  36  relative to load plate  26 , intermediate stop bean members  12  align with blind vias formed in shuttle plate  36  to allow further movement of load plate  26  towards probe plate  22  so that short test probes  18  come into contact with circuit board  14  to allow second stage testing. In the second stage testing, circuit board  14  is prevented from excessive flexing by support translated from probe plate  22 , through shuttle plate  36  and load plate  26 . 
         [0023]    Referring now to  FIG. 3 , the multi-stage tester  10  of  FIG. 2  is depicted having the shuttle plate  36  slid relative to the load plate  26  so that the stop bean intermediary members  12  engage in blind vias  38  of the shuttle plate  36 . Although the example embodiment extends intermediate members  12  from the bottom of load plate  26  that selectively recede within blind vias  28  of shuttle plate  36 , in alternative embodiments other types of intermediate structure members may be used. For instance, intermediate members  12  by couple to shuttle plate  36  and extend upwards to selectively recede into blind vias of load plate  26 . Alternatively, intermediate members  12  may be disposed between shuttle plate  36  and probe plate  22  and selectively recede into blind vias formed in either the bottom surface of shuttle plate  36  or the top surface of probe plate  22 . In one embodiment, a ball bearing embedded in each intermediate member  12  aids motion of shuttle plate  36  by reducing friction imposed by force applied from lid  20  under vacuum. In other embodiments, intermediate members  12  may recede into full vias instead of blind vias, or may recede into openings formed in the plate from which the intermediate extends. For example, shuttle plate  36  may include intermediate members that retract and extend from shuttle plate  36  rather than having mating members and blind vias in opposing plates. 
         [0024]    Referring now to  FIG. 4 , a blow-up top view depicts an example of a multi-stage tester  10  having a sliding shuttle plate  36  to selectively engage intermediary members  12 . Probe plate  22  has a bed of long and short probes  16  and  18  that extend upwards at plural heights. Shuttle plate  36  slides laterally relative to probe plate  22  and load plate  26 , and includes vias  28  that allow probes  16  and  18  to pass through. In the example, vias  28  are open block areas that have dimensions sufficient to allow probes  16  and  18  to pass through in each position that shuttle plate  36  slides between. Blind vias  38  are formed to align with intermediate members  12  in stage two testing but to be out of alignment with intermediate members  12  in stage one testing. Load plate  26  is depicted to have smaller vias  28  than those of shuttle plate  36  since load plate  26  of the example embodiment does not move relative to probes  16  and  18 . Intermediate members  12  are depicted on load plate  26  but assemble to intercede between load plate  26  and shuttle plate  36  as described above. Circuit board  14  rests stationary on load plate  26 , which selectively rests on intermediate members  12  in stage one testing or directly on shuttle plate  36  in stage two testing. Shuttle plate  36  in turn rests on probe plate  22  so that support is provided to circuit board  14  through the interactive structure. In alternative embodiments, support may be provided to specific areas of circuit board  14  by varying the structure of shuttle plate  36 , such as by aligning intermediate members at the periphery of socket  34  to reduce the risk of movement proximate the socket. 
         [0025]    Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.