Abstract:
A probing system has a probing accessory for electrically connecting to a complementary probe accessory connected to a test point where the probing accessory captures and releases the complementary probe accessory by application of only tensile forces.

Description:
BACKGROUND  
       [0001]     As operating frequencies of electronic circuits increase and component geometries decrease, it gets more difficult to probe and measure signals from test points on a printed circuit board (PCB). In addition, the devices used to probe the test points begin to have an effect on the measurement itself. One current solution is to provide one or more header pins that connect to a socketed probe head. The header pins are typically 25 mils square on 100 mils centers. In many applications, these header pins are too physically large and present too much parasitical loading and therefore limit the bandwidth of a signal that may be measured. As geometries of a printed circuit board get smaller, the header pins take up a larger percentage of the PCB surface area which is costly and limits the miniaturization of the device that uses the PCB. Another known solution is to solder probe heads directly to test points on the PCB. Advantageously, the soldered probe head provides for a lower capacitance and a higher bandwidth connection. Disadvantageously, the solution is costly, does not provide for quick easy connection/disconnection, and the number of times it can be soldered and un-soldered is limited.  
         [0002]     There is a need, therefore, for a connection accessory that addresses the disadvantages of the prior art. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]     An understanding of the present teachings can be gained from the following detailed description, taken in conjunction with the accompanying drawings of which:  
         [0004]      FIG. 1  is an enlarged perspective view of an embodiment of a probe head and complementary probing accessory according to the present teachings in an unmated condition.  
         [0005]      FIG. 2  is an enlarged perspective view of an embodiment of a probe head and complementary probing accessory according to the present teachings in an mated condition.  
         [0006]      FIG. 3  is a conceptual view of a printed circuit board with an embodiment of connection accessories according to the present teachings installed.  
         [0007]      FIG. 4  is a graph of the tensile forces applied to the probe head to connect and disconnect a connection accessory according to the present teachings.  
         [0008]      FIG. 5  is an enlarged perspective view of another embodiment of a probe head according to the present teachings in an unmated condition. 
     
    
     DETAILED DESCRIPTION  
       [0009]     With specific reference to  FIG. 1  of the drawings, there is shown an enlarged perspective view of a probe head  100  and complementary probing accessory  101  according to the present teachings. The probe head  100  makes electrical connection to a differential signal and, therefore, includes two identical connections for each one of the differential ports. The probe head  100  includes a housing  102  that holds two capture elements  103 . Each capture element  103  is connected to an impedance element  104  that is electrically disposed between the capture element  103  and the remainder of the probe circuitry in the probe head  100 . The impedance element  104  is typically a resistance to damp the connection parasitics as is known to one of ordinary skill in the art. The remainder of the probe circuitry is similar to that disclosed in U.S. patent application Ser. No. 10/829,725 entitled “Compliant Micro-Browser For A Hand Held Probe” filed Apr. 22, 2004 and U.S. patent application Ser. No. 10/945,146 entitled “High Frequency Oscilloscope Probe With Unitized Probe Tips” filed Sep. 20, 2004 the contents of which are incorporated by reference herein. The capture elements  103  include respective spring elements  105 . In a specific embodiment, each spring element  105  comprises a wire formed into approximately 330 degrees of a circle to create an open loop  106 . Ends  107  of the wire distal from the housing  102  of the probe head  100  are disposed external of the open loop  106  to form a “V” with a large opening end of the “V” disposed away from a center opening  108  of each open loop  106 . The center opening  108  of each open loop  106  is sized and configured to capture a retention element  109 . A distance between the spring elements  105  in a single capture element  103  is shortest at an end that connects to the housing and gradually increases to a largest distance at an end further from the housing  102 . In a specific embodiment, the final length of each of the capture elements  103  is 60 mils.  
         [0010]     In a specific embodiment, the retention element  109  is a sphere mechanically and electrically connected or unitary with an extension shaft  110 . An attachment end  111  of the extension shaft  110  is electrically and mechanically connected via solder or other known electrical/mechanical connection to a test point on a test device such as a printed circuit board (“PCB”). In a specific embodiment, the sphere  109  is metal and approximately 15 mils in diameter and the extension shaft  110  is unitary with the sphere  109  and is approximately 7 mils in diameter.  
         [0011]     As one of ordinary skill in the art appreciates, an extension shaft  110  of the example diameter is not able to take any compressive force without damage to the complementary probe accessory  101 . Because the extension shaft  110  is metal, however, one of ordinary skill in the art can further appreciate that it is able to accept and withstand a tensile force without damage.  
         [0012]     A method of connection between the capture element  103  and the complementary probe accessory  101  further illustrates the relationship between the capture elements  103  and the retention element  109 . Specifically, the method of connection for the embodiment illustrated in  FIG. 1  of the drawings comprises positioning the capture elements  103  close to the attachment end  111  of the extension shaft  110  so that the sphere  109  is free of the capture elements  103 , but the extension shaft  110  is positioned between the capture elements  103 . Because of the relative sizes between the diameter of the extension shaft  110  and the distance between the capture elements  103  distal from the housing  102 , there is room to position the two as described with some margin of adjustment. Minimal tensile force is applied in the process just described.  FIG. 2  of the drawings shows the capture elements  103  retaining the sphere  109  as described.  
         [0013]     With specific reference to  FIG. 3  of the drawings, there is shown a diagram that is more suggestive than it is illustrative of a complementary probe accessory  101  soldered to a PCB  112 .  FIG. 3  of the drawing is included herein to place the present teachings in the context of its application.  
         [0014]     With specific reference to  FIG. 4  of the drawings, there is shown a graph of the tensile forces applied during connection  113  and disconnection  114  of a probe system according to the present teachings as a function of displacement between the capture elements  103  and the sphere  109 . Once positioned, the capture elements  103  are moved away from the attachment end  110  of the extension shaft  110  until the larger open portion of the “V” disposed away from the open loop  106  of each capture element  103  engages the surface of the sphere  109 . As additional and an increasing first tensile force  115  is applied to the probe head  100 , the “V” guides the sphere  109  towards a position that is central to the capture elements  103 . The surface of the sphere  109  in combination with the first tensile force  115  causes displacement of the capture elements  103  outwardly to accept the full diameter of the sphere  109 . As further tensile force is applied to the probe head  100 , the sphere  109  is fully accepted  116  into the space between the capture elements  103 . Because the spring elements  103  are biased inwardly, they return to a neutral position  117  thereby retaining the sphere  109  when something less than a threshold tensile force is applied.  
         [0015]     The capture elements  103  and the sphere  109  are made of electrically conductive material. Accordingly, the retention of the sphere  109  between the capture elements  103  provides electrical continuity between the test point on the PCB  112  and the circuitry in the probe head  100  that performs the probing function. When the sphere  109  is captured between the capture elements  103 , the sphere  109  is able to swivel as it is retained between the capture elements  103  without loss of mechanical or electrical connection. The swivel provides some allowance for movement  117  as the probe head  100  is bumped or wiggled that serves to minimize stress that may be applied to the solder connection between the extension shaft  110  and the PCB while still providing a reliable electrical and mechanical connection between the probe head  100  and the test point.  
         [0016]     A method of disconnection between the probe head  100  and the complementary probe accessory comprises applying a second tensile force  118  to the probe head in the same direction as the first tensile force  115  applied to perform the capture. With specific reference to  FIG. 4  of the drawings, application of the second tensile force  118  after the sphere  109  is captured between the capture elements  103  causes a portion of the open loop  106  that is distal from the housing  102  and opposite the “V” to engage the sphere  109 . The surface of the sphere  109  causes the capture elements  103  to displace outwardly from each other until the full diameter of the sphere  109  is free  119  of the capture elements  103 . The sphere  109  is then able to fully disengage  120  from the capture elements  103  to remove the electrical and mechanical connection between the probe head  100  and complementary probe accessory  101 .  
         [0017]     With specific reference to  FIG. 5  of the drawings, there is shown an alternative embodiment of capture elements  103  according to the present teachings that comprise two plates  121  with a detent  122  to capture the sphere  109 . In a specific embodiment, the detent  122  can also be an opening or other relief area to allow room to capture the retention element when the capture elements  103  return to their neutral position. The capture plates  121  perform the same function as the embodiment of capture elements  103  illustrated in  FIGS. 1 &amp; 2  of the drawings. The capture plates  121  extend past capture arms  123  that connect to the probe head  102 . The capture arms  123  angle away from each other and attach or are unitary with the capture plates  121 . The capture plates  121  are parallel to each other. Relief areas  124  in the capture arms  123  permit positioning of the retention elements  109  prior to application of the first tensile force  115  that captures and retains the retention elements  109  within the openings  122  in the capture plates. The capture plates  121  act as spring elements that are biased inwardly as the surface of the sphere  109  forces them outwardly. When the full diameter of the sphere  109  reaches the detent or opening  122 , the capture plates  121  return to their neutral position thereby capturing the sphere  109 . The second tensile force  118  forces the sphere  109  past the detent or opening  122  to a point where the sphere  109  is free of the capture plates  121 . The capture plates  121  then return to their neutral position as the sphere  109  is free of the capture plates  121 .  
         [0018]     Other embodiments not specifically illustrated will occur to one of ordinary skill in the art with benefit of the present teachings and are considered within the scope of the appended claims. The retention element disclosed is a sphere, but could also have another suitable geometry for a given application such as elliptical, cylindrical or pill shaped. Embodiments disclosed may be differently scaled depending upon requirements of a particular application.