Abstract:
A test fixture includes a pin support plate that have been subjected to an etching process to clean up any pin receiving holes prior to the insertion of test pins into the plate. Cleaning up of the pin receiving holes includes at least partially removing plate materials left in the pin receiving holes after the pin receiving hole formation process.

Description:
FIELD OF THE INVENTION  
         [0001]    The field of the invention is electrical test fixture fabrication.  
         BACKGROUND OF THE INVENTION  
         [0002]    In testing printed wiring boards and other electrical devices, it is not uncommon to use a test fixture to act as the interface between the device to be tested and any cabling or equipment used in the test. Such fixtures often comprise a plate having several holes drilled in it for receiving test pins that are to be placed in electrical contact with the device being tested. It is desirable that such test fixtures be manufacturable with a minimal amount of effort, and operate with a degree of accuracy.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention is directed to test fixtures that include pin support plates that have been subjected to an etching process to clean up any pin receiving holes prior to the insertion of test pins into the plate. It is contemplated that subjecting the pin support plate to an etching process will render the pin receiving holes better suited for receiving test pins such that the pins can be more easily inserted into the holes and allow movement of the pins within the holes. It is contemplated that pin movement into and within the holes results, at least in part, from the removal of plate material which remains in the pin receiving holes after the holes are drilled.  
           [0004]    Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a view of a test fixture embodying the invention  
         [0006]    [0006]FIG. 2 is a diagram of a first method embodying the invention.  
         [0007]    [0007]FIG. 3 is a diagram of a second method embodying the invention.  
         [0008]    [0008]FIG. 4A is a first photograph of a test fixture prior to etching.  
         [0009]    [0009]FIG. 4B is a second photograph of a test fixture prior to etching.  
         [0010]    [0010]FIG. 4C is a third photograph of a test fixture prior to etching.  
         [0011]    [0011]FIG. 4D is a fourth photograph of a test fixture prior to etching.  
         [0012]    [0012]FIG. 5A is a photograph of a test fixture after etching.  
         [0013]    [0013]FIG. 5B is a photograph of a test fixture after etching.  
         [0014]    [0014]FIG. 5C is a photograph of a test fixture after etching. 
     
    
     DETAILED DESCRIPTION  
       [0015]    Referring first to FIGS. 1, a test fixture  10  comprises a pin support plate  11 , pin receiving holes  12 , and test pins  13 . Although plate  11  may be composed of any material or combination of materials, it is currently preferred that plat  11  be composed of G10 epoxy glass material. Similarly, pins  13  may be composed of any suitably conductive material or combination of materials, but it is currently preferred that pins  13  be composed of beryllium copper.  
         [0016]    Although pin holes  12  may be formed in plate  11  by any reasonable method, it is contemplated that the methods disclosed herein will be particularly advantageous when pin receiving holes  12  are mechanically drilled in plate  11 . However, it has been found that, after being drilled, such holes  12  are often at least partially obstructed by plate material that was not completely removed by the drilling process (see FIGS.  4 A- 4 D). Such obstructions are generally undesirable because they tend to increase the force required to insert a test pin into a pin receiving hole and to prevent pins within the holes from making proper contact with a device under test. Such obstructions may be removed (as shown in FIGS.  5 A- 5 C) by subjecting the plate to an etching process (see FIG. 2) after the holes  12  are drilled in plate  11 , but prior to the insertion of pins  13 .  
         [0017]    It is contemplated that subjecting plate  11  to the etching process described herein will result in structural changes to plate  11 . In particular, residues of the etch fluid are likely to be detectable in/on plate  11  after the etching process completes, and the surfaces (including the walls of the pin receiving holes) of plate  11  will likely have detectable surface characteristics caused by the etch process.  
         [0018]    The test fixture of FIG. 1 may be manufactured by providing a support plate; forming pin receiving holes in the support plate; subjecting the support plate to an etch process; and inserting test pins into the pin receiving holes.  
         [0019]    Referring to FIG. 3, subjecting the support plate to an etch process preferably comprises: submerging the support plate in a tank of heated etching fluid; rocking the support plate within the etching fluid for a period sufficient to remove any air trapped in the pin receiving holes and allow fluid to flow into the holes; submerging the support plate in a tank of rinsing fluid; and rocking the support plate within the rinsing fluid for a period sufficient to remove most of any etching fluid trapped in the pin receiving holes. It is currently preferred that the temperature of the etching fluid be at least 110 degrees Fahrenheit before and during the etching process.  
         [0020]    It is currently preferred that the etching fluid be a combination of soft water, M glass etch, and sulfuric acid. In particular, a preferred etching fluid will have 55 gallons of soft water for every 30 pounds of M Glass etch and every 16 litters of sulfuric acid. However, alternative etching fluids may be used so long as they adequately remove the drilling residue from the test pin receiving holes  12 . Using this etching fluid, the preferred temperature, and a plate made from G10 epoxy glass material, it is contemplated that submerging the support plate for 4 minutes in the etching fluid and two minutes in the rinsing fluid will sufficiently clean and polish holes  12  of plate  11 .  
         [0021]    At least some of the benefits of submitting plate  11  to an etching process can be seen by comparing the un-etched plates shown in FIGS.  4 A- 4 D to the etched plates shown in FIGS.  5 A- 5 C. In FIGS.  4 A- 4 D it is clear that a number of the pin receiving holes are partially blocked as previously described, but that the obstructing material has been removed from the plates of FIGS.  5 A- 5 C.  
         [0022]    It is contemplated that submitting plate  11  to an etching process will significantly reduce the force required to insert a test pin into a test pin receiving hole and will result in a decrease in the time required to load pins  13  into plate  11 . Reductions of 50% in pin insertion times have been experienced. Although the maximum force allowed for inserting pins  13  into holes  12  may very between applications, it is contemplated that etching plate  11  may advantageously reduce the force required to insert pins  13  into holes  12  sufficiently so that the pins can be dropped into all of the holes. However, in alternative embodiments the force of gravity may not be sufficient to pull a partially inserted pin completely into a hole for a 100 percent of the holes. In such embodiments, the percentage of holes in which the pins will simply drop into place may be only X percent where X is one of 50, 75, 90, and 95.  
         [0023]    Thus, specific embodiments and applications of test fixtures and methods relating to the formation of test fixtures have been disclosed. It should be apparent, however, to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.