Patent Document

FIELD OF THE INVENTION 
       [0001]    The invention relates to the field of testing equipment for electronic components and more particularly to the field of aligning test contacts. 
       BACKGROUND 
       [0002]    Miniature electronic components are tested in a variety of ways. One group of testing that relates to multiple layer capacitance chips (MLCC) involves electrical testing, including, but not limited to cap testing, cross checking, testing for leakage current, and testing for break down voltage. In the example of U.S. Pat. No. 5,842,579 entitled Electrical Circuit Component Handler, which is incorporated herein by reference, there is shown an example of a rotary style electronic testing machine  10 . With reference to  FIG. 2  herein, which is a modification of FIG. 2 from U.S. Pat. No. 5,842,579, an electronic component is captured in a test plate  12 . A vacuum source passes a vacuum through a base plate to draw electronic components into component pockets on test plate  12 . 
         [0003]    As illustrated in  FIG. 2  herein a stepper motor  16  is operatively connected to test plate  10  to index test plate  12  such that electronic components are delivered to test heads  18  located on testing machine  10 . Frequently the test heads are closely spaced. Each test head  18  may include a plurality of test contacts  20 , each test contact configured to conduct the same test. After the testing is complete, test plate  12  continues to index to deliver tested components to blow off zone  22 . In blow off zone  22  the electronic components are blown out of the component pocket that contains them and appropriately sorted as a function of the test results. In the example of U.S. Pat. No. 5,842,579 the blow off is accomplished by passing the component pockets over a plurality of blow off holes such that actuation of an air source through a specific blow off hole operates to sort the electronic components according to their individual test results. 
         [0004]    Other configurations of test machines are also available. For example, the test plate, rather than being circular in shape may be rectangular. Also drums may be used for certain testing arrangements. 
         [0005]    Electronic component testers may be adjusted and/or calibrated such that the individual test contacts properly align over component pockets such that when the test plate  12  is indexed the electronic components are delivered to the contacts so that an acceptable electrical connection is achieved. One way to align the test contacts with the test component pockets is the use of a fixture to assist the placement of test heads. Proper alignment can be more accurately realized by checking the alignment of the test heads with a borescope. In particular, the borescope would be used to visually inspect each contact and its relative positioning against the component pockets on the test plate. This evaluation would include inspection of theta and skew. If a determination was made that the test contact or test head was misaligned, alignment could be achieved by known adjustments. 
         [0006]    Because the test heads may be closely spaced, use of borescope may be difficult and time consuming. A need has arisen to improve the process of determining the alignment of the contact heads. 
       SUMMARY 
       [0007]    Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
         [0008]    A method for determining a position of a plurality of test contacts on an electronic component testing machine is disclosed. The component testing machine includes a component test plate configured to retain a plurality of electronic components. The test plate is movable between a plurality of index positions such that electronic components electrically connect to the testing contacts at each index position. The electrical connectivity between an electronic component and a testing contact is measured at a plurality of microsteps where each the microstep is a fraction of an index. A plurality of electrical measurements is provided for an individual test contact. The plurality of measurements is evaluated to determine the alignment of the test contact. 
         [0009]    A method for aligning at least one of a plurality of test contacts on an electronic component testing machine is also provided. The component testing machine includes a test plate configured to retain a plurality of electronic components and the test plate is movable between a plurality of index positions. Electronic components electrically connect to the plurality of testing contacts at each index. The method includes measuring the electrical connectivity between the electronic component and a testing contact at a plurality of microsteps and a plurality of electrical measurements is provided for a single test contact. The test contact is adjusted based on the plurality of electrical measurements. 
         [0010]    An electronic component testing machine is also provided. The machine includes a test plate configured to retain a plurality of electronic components and includes a plurality of test heads. Each test head has a plurality of test contacts. The test plate is operatively connected to a drive mechanism such that the test plate is movable between a plurality of index positions to deliver a plurality of electronic components to one of the test heads. A motion controller is configured to move the test plate in microsteps where the microsteps are a distance less than an index. A controller is configured to take multiple electrical measurements between an electronic component and an individual test contact for each microstep resulting in a plurality of electrical measurements. Means are provided to adjusting the test contact to bring it into alignment based on the electrical measurements 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0012]      FIG. 1  is a flow chart depicting the process of determining the alignment of test contacts and including an adjustment of the test contacts; 
           [0013]      FIG. 2  is a simplified perspective view of an example of a prior art electrical testing machine; 
           [0014]      FIG. 2A  is a simplified perspective view of a testing machine configured to carry out the process of  FIG. 1 ; 
           [0015]      FIG. 3  is a close up plan view of a test pocket positioned over a pair of blow off holes; 
           [0016]      FIG. 4  illustrates an optionally graphical output depicting the relative alignment of a plurality of test contacts on a plurality of test heads; 
           [0017]      FIG. 5  is a representative example of an adjustment mechanism that will adjust positioning of a test head; and 
           [0018]      FIG. 6  is a simplistic illustration of different pattern profiles of microstep contact measurements for a test head. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    In normal operation of an electronic test machine a test plate will index from test head to test head. At each test head an electrical measurement will be made. It has been discovered that by dividing the index into a plurality of microsteps an electronic component can be swept underneath a test contact to evaluate the location of a test contact. In one example, the location of the electronic component may be measured relative to a fixed position on the test machine. This fixed position may be at least one blow off hole positioned on a base plate of the test machine. Other fixed locations may be utilized as well. The fixed position may be correlated against the position of a motor driving the test plate to provide a centerline. In the case of a test plate that includes electronic components drawn into component pockets by a vacuum, this fixed position on the machine could possibly become offset relative to the test plate as the test plate becomes loaded with components. In such a case, both a loaded and an unloaded centerline may be provided. For each microstep a determination may be made whether an electrical connection exists between the electronic component and the test contact. Based on the positioning of the plurality of electrical measurements relative to either centerline conclusions may be drawn with respect to alignment. The data derived from the measurements may be graphically presented to a user such that the user can draw conclusions with regard to alignment, or the system may evaluate the data and inform the user whether adjustments are necessary and if so what those adjustments are. 
         [0020]    With reference to  FIG. 1  there is shown a flow chart illustrating the acts of the method of the present invention. With reference to act  31  a test mode is enabled. At act  31  sample components are loaded into test plate  12 . At the test act  31  a motion controller  17  divides each index into a plurality of microsteps. These microsteps may be defined by motor steps of a stepper motor and may be of an arbitrary distance. In one example where the test plate includes eight concentric rings of 200 holes, an index may be approximately 1.8 degrees. In this example, the index of 1.8 degrees may be divided into 200 microsteps, thus enabling the test plate to advance 0.009 degrees for each microstep. As a rule of thumb it has been discovered that dividing the microsteps into a distance approximating 1/20 of the width of the component being tested provides useful results. However, the microstep may be a larger or smaller fraction of the index size. 
         [0021]    At act  33  the test plate is advanced by the above described microstep amounts. At act  34  the alignment system attempts to measure the electronic connection between a test contact  20  and the electronic component for each microstep. In one example the measurement is merely binary, meaning the system determines, yes or no, whether a connection has been made. In act  36  the alignment of the test contact is determined. The alignment may be determined either automatically or with reference to a graphic representation of data. 
         [0022]    With reference to  FIG. 2A  test machine  10  further includes controller  19  configured to receive the data from act  34  and either graphically presents it, as in  FIG. 4 , or makes other calculations. Controller  19  may be part of an overall controller for machine  10  or may be a separate controller. 
         [0023]    With reference to  FIG. 4  there is shown a graphical representation of the output of a microstep evaluation of the alignment of the plurality test contacts. In the illustrative example of  FIG. 4  there is shown the evaluation of nine different contact heads,  40 ,  41 ,  42 ,  43 ,  44 ,  45 ,  46 ,  47 , and  48 . Each contact head includes a plurality of contacts, e.g.  50 ,  51 ,  52 ,  53 ,  54 ,  55 ,  56 , and  57  which have each been individually evaluated. Another example of an evaluation an individual head is seen at  58 . The vertical bar referenced as  58  represents a plurality of successful microstep connections between points A and B. 
         [0024]    Individual contacts may be evaluated to determine whether the connection between the test contact and the electronic component is consistent. With reference to head  59  there is shown a collection of microstep connections where for a portion of the microsteps e.g.  60  where no electrical connection could be made between the test contacts and the electronic component. This illustration would inform the operator that there was intermittent contact between the test contact at  59  and its associated component. An operator may remedy this in a variety of ways including replacement of the test contact at  59 . 
         [0025]      FIG. 4  further illustrates an unloaded nominal center indicator line  70 . Unloaded nominal center indicator line  70  references the positional centerline of the component pocket when the test plate is moving and unloaded. The measurement is made from a fixed position on the machine when the test plate is unloaded and moving. 
         [0026]    One example of determining a centerline is shown in  FIG. 3 . In particular when the test plate is moving a pair of blow off holes  23  may be observed and positionally correlated against a motor count location. In the example of  FIG. 4  the number of motor counts per angle of rotation of the test plate may be determined. The component pockets  21  center themselves over the blow off holes  23  at a repeatable motor count. In the example of  FIG. 4  this repeatable motor count is arbitrarily set at a zero motor count when the test plate is rotating and empty, as noted by reference numeral  70 . It has been observed that in operation of certain electronic component testing machines, such as the model 3430 as sold by Electro Scientific Industries, Inc., the assignee of the instant application, a dynamic shift offset from the centerline occurs as the test plate is loaded with electronic components. That is, the rows of component pockets center themselves over the blow off holes  23  at a slightly different motor count when loaded. One cause of this dynamic shift is the vacuum utilized to retain the electronic component pockets. In the example of  FIG. 4  the dynamic shift was measured as approximately 15 positive motor counts. Thus, in some examples a dynamic centerline  71  may be provided. An upper connect limit  72  and a lower contact limit line  73  may also be provided. In the example of  FIG. 4  the upper contact and lower contact limit lines provide suggestive limits where the test components within which component pockets  21  should be found. In the example of  FIG. 4  a connection between the electronic component and the test contacts is expected to occur between a positive 30 motor counts to a minus 15 motor counts. 
         [0027]    With reference again to  FIG. 1 , act  37  queries as to whether the test heads are aligned. If the test heads are not aligned, the test heads may be aligned at act  38 . Act  38  involves adjusting the test contacts and/or test head such that they would be properly aligned with the test component received in the component pocket  21  in the test plate  12 . With reference to the example of  FIG. 4  one way to make this adjustment would be as follows. Looking to the microstep measurements taken at  48  it can be seen that the measurements are biased in a leading direction. At least some of the microstep measurements in the example did not achieve a connection at the dynamic centerline  71 . Thus an adjustment may be made to shift the test head in the direction of arrow “C”. 
         [0028]    With reference to  FIG. 5  there is shown a simplified test head  18  including a plurality of test contacts  20 . Test head  18  is illustrated with reference to a test plate  12  and component pockets  21 . As is illustrated in  FIG. 5  test head  18  may include adjustments for y skew  75 , a y adjustment  77  and a theta adjustment  79 . Movement of the aforementioned adjustments in the example of  FIG. 5  will move test head  18  in the y skew direction  76 , the y direction  78  and the theta direction  80 . 
         [0029]    In the context of measuring connections at act  34  of  FIG. 1 , the resulting data may inform a user of adjustments to a test head  18  to improve the alignment of the test head relative to the connect pockets. In the example of  FIG. 4  alignment information is graphically displayed to a user who may then interpret the data and adjust the test head. In an alternate example the measurement data may be mathematically interpreted and a user may be specifically informed of the adjustment to bring the test head into alignment. For example, this adjustment may inform the user to turn the theta adjustment one turn clockwise. 
         [0030]    As shown with respect to head  48  in  FIG. 4  the measurement results are preferably in a tapered pattern. This tapered pattern is a function of test plate  12  being circular. It is understood that a non-circular test plate may not yield a tapered pattern of measurement results. The y skew adjustment  75  affects the taper of the measurements. 
         [0031]    With reference to  FIG. 6  there are shown example profile patterns where the taper is skewed and y skew adjustment may be advisable. In the example  82  the y skew is correct for a circular test plate. In the example of  84  y skew is clockwise oriented and needs to be adjusted counter clockwise. In the example of  86  y skew is counter clockwise oriented and needs to be adjusted clockwise. 
         [0032]    With reference again to the example of  FIG. 1 , after an adjustment has been made, act  32  may be reinitiated to confirm alignment. Reinitiating act  32  may not be necessary and may depend on customer preferences. If the query at act  37  indicates alignment, either determined automatically or by reference to a graphic illustration, the process is complete at act  39 . 
         [0033]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.

Technology Category: 7