Abstract:
Apparatus for electronically testing printed circuit boards including a plurality of generally parallel test pins which have a section of reduced diameter along their length intermediate the ends thereof, and a plate having a plurality of drilled holes in which the test pins are mounted with the reduced diameter portions being located in the holes, the plate being adapted to interfere with shoulders at the ends of the sections of reduced diameter to retain the test pins in the testing apparatus.

Description:
This is a continuation of application Ser. No. 07/683,872, filed Apr. 11, 1991, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to apparatus for electronically testing printed circuit boards or the like. Such apparatus includes a plurality of substantially parallel test pins or test probes for making electrical contact between respective contact areas on a printed circuit board or the like to be tested and a plurality of corresponding resilient contact elements disposed in accordance with a grid of an array plate or the like against which the apparatus is urged, and a mask plate extending at right angles to the test pins and having therein through-bores through which extend the test pins. First ends or tips of the test pins project through the through-bores in the mask plate to engage the contact areas of the printed circuit board. Such apparatus may include a very large number of such generally parallel test pins or test probes, e.g., 20,000 or more. 
     Apparatus of the above type is rather fully described in Driller et al., U.S. Pat. No. 4,721,908 and Mang et al., U.S. Pat. No. 4,834,659. The principal object of the present invention is to afford improvements over the devices disclosed in the foregoing patents, particularly relative to the design of the test probes, and the manner of retaining such test probes in the apparatus, while readily permitting their removal if desired. 
     In the apparatus disclosed in Driller et al., U.S. Pat. No. 4,721,908, an elastic plate in the nature of a rubber sheet is provided for mounting the plurality of test probes. In such an arrangement, the test probes are in the nature of straight pins without any enlarged or reduced sections. The elastic plate is in the nature of a rubber sheet through which the plurality of test pins are pressed so as to perforate the sheet and thereby mount the test pin. In the foregoing known device, the elastic plate or sheet firmly engages the periphery of each of the test pins extending therethrough, and in that manner prevents them from dropping from the testing apparatus. 
     One disadvantage of the foregoing device is that movement of one test pin can influence movement of several other adjacent test pins due to the manner in which they are mounted in the elastic or rubber sheet in close spacing to one another. Thus, in use of such a device, if one test pin is urged in a longitudinal direction, several other pins could be caused to move with it, which is a disadvantage. It must be borne in mind that such an apparatus may include several thousand such test pins or test probes, and it is preferable that each pin be capable of longitudinal movement independently of the others. 
     In the apparatus of Mang et al., U.S. Pat. No. 4,834,659, there is disclosed a different means of supporting the test pins which represents an attempt to solve the problem discussed above where longitudinal movement of a single test pin can cause similar movement of adjacent pins. In the Mang et al. patent, straight test pins are not used. Instead, each test pin is provided with an enlarged section of relatively short length. One form of enlargement comprises a section which is hammered or deformed. As a result, the normally round test pin will have a flattened area which is enlarged. 
     In the Mang et al. patent, various types of enlarged pin sections are disclosed, but in each case the concept is the same. The pins are mounted in a pair of inner and outer adapter plates formed with a large number of holes or bores which normally would conform to the connection points to be tested on a printed circuit board or the like. Such bores are larger in diameter than the outer diameter of the test pins, but smaller in diameter than the enlarged section of each test pin. The pins are assembled so that the enlarged pin sections are disposed between the inner and outer adapter plates, thereby trapping the pins relative to the two adapter plates and preventing them from falling out of the test apparatus. 
     The main object of the present invention is to provide an improved type of test pin which is neither straight nor has an enlarged section, but rather has a section which is reduced in size compared to the normal pin diameter. 
     A related object of the invention is to provide improved apparatus for retaining test pins or test probes in a testing device which effectively retains the pins in the desired positions, permits independent longitudinal movement of one pin relative to adjacent pins, and yet readily permits removal of pins from the apparatus when desired, such advantages being achieved without providing any enlarged sections along the length of a test pin. 
     An important advantage of the present invention in comparison with test pins having enlarged sections is that it permits the pins to be arrayed in closer proximity to one another. It is highly desirable to be able to provide for greater miniaturization or closer spacing of the test pins, because the industry is continuing to seek higher density in printed circuit boards and associated components, with the result that apparatus for electronically testing such printed circuit boards requires closer spacing of the thousands of test pins or test probes. 
     The foregoing and other objects and advantages of the invention will be apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view, partly in section, illustrating test apparatus embodying the present invention, the showing being somewhat schematic in the sense that only a single one of possibly thousands of test pins or test probes is shown for better understanding of the invention; 
     FIG. 2 is a view similar to FIG. 1, except it shows apparatus designed to simultaneously test opposite sides of a printed circuit board or the like, whereas the apparatus of FIG. 1 is intended to test only one such side; 
     FIG. 3 is a detail view of a test pin or test probe having a recessed section in accordance with the present invention; 
     FIG. 4 is a fragmentary, detail view of a recessed section of a test pin in accordance with the present invention; 
     FIG. 5 is an elevational view, somewhat schematic in form, illustrating the manner in which a test pin is retained and thereby prevented from falling from the test apparatus; 
     FIG. 6 is an enlargement of a portion of FIG. 5 showing the manner in which two horizontally movable plates or sheets cooperate with a reduced section of a test pin to effect retention of the pin in accordance with one embodiment of the invention; 
     FIG. 7 is an enlarged, schematic view demonstrating the manner in which the two slidable sheets of FIG. 6 effect retention of a test pin, the retention areas provided by the two sheets being shown as shaded; and 
     FIG. 8 is an elevational view illustrating an alternative embodiment of the present invention utilizing a single retention sheet which need not be moved horizontally to effect retention. 
    
    
     Now, in order to acquaint those skilled in t he art with the manner of making and using the invention, I shall describe, in conjunction with the accompanying drawings, certain prefer red embodiments of the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, FIG. 1 shows test apparatus for electronically testing printed circuit boards and the like, including a plate  10  having drilled holes  12  which receive therethrough test pins or probes  14 , and which are specially spaced according to the connection points on a printed circuit board  16  or the like to be tested. The printed circuit board  16  is mounted immediately above the plate  10  so that upper ends of test probes  14  can pass through the drilled holes  12  in plate  10  and contact the connection points to be tested on the circuit board  16 . Th e test probe or test pin  14  is longitudinally rigid and made of spring steel or “music wire” as is known in the art. 
     As described previously, there are normally a large number of test probes or test pins  14  in a given test apparatus, as many as 20,000 or more such test probes. Because the drilled holes  12  in the plate  10  are specially arranged to correspond to the connection points on the circuit board  16  to be tested, it is necessary that circuit board  16  be mounted in precise relationship to the testing device, and in particular, to the plate  10 . 
     For that purpose, there is provided apparatus comprising a housing  18 , compression spring  20 , plug  22  and disc member  24  which cooperate with conical pin  26 . In the foregoing manner, conical pin  26  is spring-loaded upwardly so the pin passes through a hole  30  in the plate  10  and the conical upper end of the pin centers in a tooling hole  28  in the circuit board  16 , for the purpose of effecting proper registration between the circuit board  16  and the upper ends of the test probes  14 . 
     At the lower end of the test apparatus, as illustrated in FIG. 1, there are provided a pair of horizontal plates  32  and  34  which have a plurality of drilled holes  36  which receive the test probes  14  therethrough. As more fully described in the above-mentioned Driller et al. and Mang et al. patents, the lower ends of such test probes engage corresponding ones of an array of contact elements of the testing apparatus. Of course, a plurality of the board registration pins  26  may be provided to effect proper registration of the circuit board  16  to be tested. 
     The drilled holes  36  in the plates  32  and  34  are arranged corresponding to a specified grid of an electrical test system. The spacing of such holes will not necessarily correspond to the spacing of the holes  12  in the plate  10  which are specially spaced to correspond to the connection points on the circuit board  16  to be tested. As a result, the test pins  14  may have to shift laterally as they pass upwardly from the holes  36  in plates  32  and  34  to the holes  12  in the plate  10 . While the test pins  14  are described as longitudinally rigid, they are capable of such lateral bending. 
     A spacer is shown at  40  having a hole  42  which is drilled through the spacer  40  and tapped. Such spacers do not permit movement between the upper plate  10  and the lower plates  32  and  34 , as distinguished for example from the apparatus disclosed in Mang et al., U.S. Pat. No. 4,834,659 which discloses resilient spacer members which do permit such relative movement. 
     Still referring to FIG. 1, the test probe  14  is provided with a reduced diameter section  44  which extends through a sheet of material identified at  46  which, as more fully described hereinafter, may comprise one or more sheets of material. In accordance with one embodiment, the sheet  46  preferably comprises two sheets, one on top of the other, which are independently slidable horizontally for a purpose to be described. In accordance with an alternative embodiment, the sheet  46  may comprise a single sheet which is not horizontally movable. In either case, the sheet or sheets  46  are preferably made of material such as polyester film or mylar. 
     FIG. 1 shows a further rigid support spacer  50 , the purpose of which is to balance compression when two sides of a circuit board  16  are tested simultaneously as illustrated in FIG.  2 . The spacer  50  passes through a hole  52  formed in the plate  32 . The spacer  50  fits closely within the hole  52 , thereby maintaining the spacer  50  in a perpendicular or upright position with the upper end of the spacer  50  positioned beneath the plate  10 . 
     FIG. 2 shows testing apparatus which is essentially the same as shown in FIG. 1, except it includes two sets of the apparatus of FIG. 1, one disposed on each side of a printed circuit board (not shown) to be tested. Thus, corresponding parts are identified with the same numerals as in FIG.  1 . In FIG. 2, one of the numerous test probes is identified at  14   a  and is shown bent laterally to accommodate the difference in spacing which may occur between the holes in the plate  10 , the latter holes being arranged to correspond to the connection points on a circuit board to be tested. 
     It will be seen in FIG. 2 that the alignment pin  26  has a conical top  54  which cooperates with a bushing  56  to effect proper alignment between the upper and lower test fixtures, there being several such pins  26  as desired. It will be noted from FIG. 2 that the test apparatus disposed to test the top side of a circuit board (not shown) is inverted relative to the apparatus for testing the underside of such a circuit board. As a result, it is important that the test probes  14  be retained in both longitudinal directions, although limited longitudinal movement of a test probe independently of other test probes is an advantage afforded by the present invention. 
     FIG. 3 is a detail view of a steel test probe or test pin  14  having a reduced diameter section  44  of a predetermined length. It is an important feature of the present invention that the test probes have such a reduced diameter section. Such a section may be formed in various ways, although the preferred procedure is to machine a groove  44  for the purpose of creating retention shoulders at each end of the reduced diameter section  44 . The test probe shown in FIG. 3 is of a type having rounded ends. However, it is known in the art to utilize a wide variety of different types of test probes, and the machined groove  44  of the present invention may be utilized with any of those different types. FIG. 4 is a fragmentary view illustrating one example of a particular form of machined groove  44 . 
     Reference is now made to FIGS. 5-7 which illustrate the manner of retention of the test probes  14  in accordance with one embodiment of the present invention. FIG. 5 is a somewhat schematic view which illustrates one of several thousand test pins  14 . As in the illustration of FIG. 1, the upper end of test pin  14  passes through an opening in a plate  10  to make contact with a connection point on a circuit board (not shown) to be tested. The lower end of pin  14  passes through the plates  32  and  34 , which are also shown in FIG. 1 which illustrates the holes  36  in those plates through which the pins  14  pass. The holes  36  in the two plates  32  and  34  are larger in diameter than the outer diameter of the test pin  14 . As a result, a test pin  14  can readily pass through the plates  32  and  34  and is not longitudinally retained thereby, so additional means is required to prevent the test pins  14  from falling out of the test apparatus. 
     As previously described, the sheet shown at  46  in FIG. 5 may take different forms. In one embodiment as shown in FIG. 6, the sheet  46  comprises two separate sheets of mylar material which are positioned one above the other and are horizontally slidable relative to one another. The two mylar sheets are indicated at  46   a  and  46   b , and they have holes  60   a  and  60   b  formed therein. The holes  60   a  and  60   b  are larger in diameter than the diameter of the test pin  14 , with the result that the pin  14  may be readily passed through the mylar sheets  60   a  and  60   b  if those sheets are positioned with the holes  60   a  and  60   b  aligned with the corresponding test pin  14 . However, FIG. 6 illustrates a non-aligned condition where the upper mylar sheet  46   a  has been moved to the right, while the lower mylar sheets  46   b  has been moved to the left. 
     In the latter condition, the sheets  46   a  and  46   b  will interfere with the annular shoulders at the opposite ends of the reduced diameter section  44  thereby retaining the pin  14  and preventing it from falling from the test apparatus. Accordingly, with apparatus as shown in FIG. 6, each of the sheets  46   a  and  46   b  may be slid or horizontally moved to positions which create interference with the test pin  14  and retain it, subject to limited longitudinal movement depending upon the thickness of the sheets  46  and the length of the reduced diameter section  44 . The sheets  46   a  and  46   b  may also be moved to positions where the holes  60   a  and  60   b  are aligned with the test pin  14  so that the pin may readily be inserted in or removed from the test apparatus. 
     FIG. 7 is an enlarged diagrammatic view which aids in understanding the foregoing. It can be seen that the holes  60   a  and  60   b  in plates  46  are larger in diameter than the outer diameter of the test probe  14 . As a result, when the two holes  60   a  and  60   b  are aligned with probe  14 , the probe may readily be inserted or removed. However, if the plate  46   a  is moved to the right as in FIG. 6, it interferes with the annular shoulder at the upper end of the reduced diameter portion  44 , and that area of interference is represented by the shaded portion  61   a  in FIG.  7 . Similarly, if the plate  46   b  is moved to its left-hand position as shown in FIG. 6, it interferes with the annular shoulder at the lower end of the reduced diameter portion  44 , and that area of interference is represented by the shaded portion  61   b  in FIG.  7 . It is within the scope of the present invention to utilize only one of the two slidable plates  46 . However, it is preferred to use two slidable plates because that provides a greater area of interference or retention and thus more securely retains the test probe  14 . 
     FIG. 8 shows an important alternative embodiment of the invention utilizing a single sheet  46  which need not be shifted horizontally. In the embodiment of FIG. 8, as previously described, the holes  36  in the plates  32  and  34  are larger in diameter than the test pin  14  so they do not provide longitudinal retention. However, the hole shown at  64  in the single plate  46  is larger than the diameter of the grooved portion  44 , but smaller than the outer diameter of the probe or pin  14 . 
     As a result, when the test probe  14  is in the position shown in FIG. 8, it will be retained due to interference between the plate  46  and the annular shoulders at both ends of the reduced diameter portion  44  of probe  14 . It will be understood that in order to place the probe  14  in the retained position as illustrated, a portion of the larger diameter of probe  14  must be forced through the smaller opening  64  in sheet  46 , which is possible because the sheet  46  is made of mylar or other compliant material which is capable of the required deformation. 
     Relative to the test pin or probe  14  of the present invention, while a reduced diameter section in accordance with the present invention may take various forms, it is preferred to machine a groove to create the reduced diameter section, as shown for example at  44  in FIG.  4 . 
     The plate or plates  46  which cooperate with the groove may be made of various materials. A preferred form is a sheet of polyester film or mylar or the like having a thickness of 0.007 inch. 
     In the embodiment described herein, three plates  10 ,  32  and  34  are illustrated in addition to the sheet or sheets  46 . Such plates are commonly made of polycarbonate or acrylic materials. The upper plate shown at  10  in FIG. 1 positions the test probes or pins  14  to the circuit board or other product to be tested, and thus the holes  12  in that plate correspond to connection points or the like on a circuit board or product to be tested. 
     The lower two plates shown at  32  and  34  may not be required in all applications. However, they serve to support the sheet or sheets shown at  46 , and they also serve to position the probes  14 . The holes  36  drilled in the plates  32  and  34  are arranged according to a desired grid system of a given test device, and the drilled holes  60   a  and  60   b  in the mylar sheets  46   a  and  46   b  of the FIG. 6 embodiment, or the holes  64  in the FIG. 8 embodiment, correspond to that same grid pattern. 
     As previously described, in the embodiment of FIGS. 1-7, the sheet or sheets  46  are movable laterally so one can position them with their holes in or out of register with the test probes. With such an arrangement, it is a simple matter to load or unload the test pins  14 , and they are effectively retained when the sheet or sheets  46  are moved to the retained or testing position to create interference areas as shown at  61   a  and  61   b  in FIG.  7 . 
     In the embodiment of FIG. 8, the single sheet  46  is not slidable because pins are loaded or unloaded by forcing the outer diameter of the pin  14  through the somewhat smaller hole  64  in the sheet  46 . However, after the pin  14  is positioned as shown in FIG.  8 , the pin is free-floating longitudinally a limited distance. Similarly, in the embodiment of FIGS. 1-7, the pins, as shown in example in FIG. 1, are capable of limited longitudinal movement, depending upon the length of the grooved section  44  and the thickness of the plates  46 . 
     The two plates  32  and  34  comprise rigid base platens which overlie a contact element array (not shown) in the testing apparatus in a planar relationship. The holes  36  in those two base platens are larger than the outer diameter of the test pins  14  to allow for unrestricted movement of the pins in a vertical or longitudinal direction. The various rigid spacer elements as shown at  40  and  42  maintain a fixed relationship between the two base platens  32  and  34  and the upper fixture or mask plate  10 . As previously described, the holes  12  in the upper plate  10  correspond to specific contact points on a circuit board  16  to be tested. Again, the drilled holes  12  are larger than the outer diameter of the test pins  14  to allow for unrestricted vertical movement of such pins. 
     The sheet or sheets  46  are preferably compliant or non-rigid compared to the plates  32  and  34 , and the drilled passages  60   a  and  60   b  of FIG. 6, or the drilled passages  64  in the FIG. 8 embodiment, are arranged in the same grid pattern of the holes  36 , but not necessarily of the same diameter. In the embodiment of FIGS. 1-7, the drilled holes  60   a  and  60   b  (see FIG. 7) are preferably larger than the diameter of the drilled holes  36  in platens  32  and  34 , as well as being larger than the outer diameter of the test pins  14 . In the embodiment of FIG. 8, the drilled holes  64  are smaller than the outer diameter of the test pins  14 , but larger than the reduced diameter of the portion  44  of those pins. 
     It should be understood that in the embodiment of FIGS. 1-7, when the compliant plates or platens  46   a  and  46   b  are moved in opposite directions to the retention or testing position as shown in FIGS. 6 and 7, the pins  14  are securely locked in place allowing only for vertical movement restricted to the length of the reduced diameter portion  44 . A similar result is achieved by the embodiment of FIG. 8 in that the test pin or probe  14  is positioned in place, allowing primarily only for vertical movement restricted to the length of the section  44 .