Patent Publication Number: US-4547960-A

Title: Methods of and fixture for establishing an electrical connection

Description:
This is a continuation of application Ser. No. 373,196 filed Apr. 29, 1982, now abandoned. 
    
    
     TECHNICAL FIELD 
     This invention relates to methods of and a fixture for establishing an electrical connection, and more particularly to methods of and a fixture for connecting a lead of an electrical component to a circuit. 
     BACKGROUND OF THE INVENTION 
     In testing electrical components having a plurality of leads, the leads are frequently inserted into socket-type contacts which are coupled to an associated test circuit. Socket-type contacts typically include spaced contact fingers which provide a resilient opening into which the leads are inserted. Ideally, the resiliency of the fingers insures proper electrical contact between the leads and the test circuit. However, due to constant use, the resiliency of the contact fingers is reduced. Moreover, the leads are coated typically with solder which results in a larger and nonuniform size of the leads. Thereafter, when the solder coated leads are inserted into the socket-type contacts, the contacts tend to (1) wear rapidly, (2) lose their resiliency and (3) permanently separate to a position where proper electrical contact is no longer insured. Additionally, as the leads of successive components are inserted into the socket-type contacts, the contacts tend to make electrical engagement with the leads at different points on the leads thus introducing a variable into the testing process. This is particularly undesirable where sensitive electrical parameters, such as the insertion loss of 100 MHz pulse transformers, are being measured. In addition, as the socket-type contacts wear and have to be replaced, the testing system must be recalibrated. Similarly, the conductors connecting the socket-type contacts to the test circuit also tend to introduce undesirable variables into the testing system. 
     In an attempt to overcome the above-mentioned disadvantages, the use of zero-insertion force test contacts have been used. One known fixture, which facilitates the testing of amplifiers and which utilizes zero-insertion force test contacts, includes a plurality of lead-receiving slots. A test contact is positioned adjacent one end of each of the plurality of slots. A spring biased plunger is positioned adjacent an opposite end of each of the plurality of slots. To insert the leads of the amplifier the plungers are moved in a direction away from the test contacts. The leads are then inserted into the slots and the plungers are released so that the biasing action of each of the plungers forces the associated leads into one of the test contacts. Capacitors, which are coupled to an opposite end of the test contacts, are connected to a test set through electrical jacks. While this fixture helps reduce damage to the leads and to reduce wear on the test contacts, the fixture is still susceptible to the introduction of undesirable variables into the testing system. 
     Accordingly, a purpose of this invention is to provide a method and fixture for establishing an electrical connection to a circuit which avoids the introduction of undersirable variables into the testing system. 
     SUMMARY OF THE INVENTION 
     This invention relates to methods of and a fixture for an establishing electrical connection between a circuit and a lead of an electrical component. The circuit is formed on one major surface of a substrate having a contact mounted thereon which is electrically connected to the circuit and overlaps a portion of an aperture formed therethrough. The lead having a diameter, which is smaller than the diameter of the aperture, is positioned within the aperture. The lead is moved laterally of and within the aperture toward the contact. Thereafter, the lead is urged into engagement with a portion of the contact which overlaps the aperture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an electrical component having a plurality of leads extending therefrom; 
     FIG. 2 is a view showing the fixture embodying certain principles of the invention; 
     FIG. 3 is a bottom view of a top section of the fixture of FIG. 2 and embodying certain principles of the invention; and 
     FIGS. 4 and 5 are sectional views of the fixture of FIG. 2 having the component of FIG. 1 supported thereon and embodying certain principles of the invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, an electrical component, such as a pulse transformer, designated generally by the numeral 20, includes a body 21 having a plurality of leads 22 extending therefrom. Prior to using the electrical component 20 in its ultimate environment, it is desirable to measure its transmission characteristics. During the measurement of the transmission characteristics, the presence of stray inductance and capacitance affect the accuracy of the measured characteristics. Thus, to minimize the effects of stray inductance and capacitance, electrical leads (not shown) utilized to couple the component 20 to a testing system (not shown) must be reduced to a minimum length. 
     Referring to FIG. 2, a test fixture, designated generally by the numeral 24, facilitates the testing of the electrical component 20. The fixture 24 includes an enclosure, designated generally by the numeral 26, having a bottom surface 28 with a pedestal 30 supported thereon. A lead pusher, such as slide 32, having spaced shoulders 34 extending upwardly therefrom, is mounted for reciprocal sliding movement on the pedestal 30 between stops 36 and 38. The stops 36 and 38 are attached fixedly to the pedestal 30 by screws 40 and 42, respectively. A thumb screw 41, which is threadedly mounted in a side wall 44 of the enclosure 26, is coupled to the slide 32 and facilitates the reciprocal sliding movement thereof. Enclosure 26 also includes a top, designated generally by the numeral 46. The top 46 includes two electrically nonconductive boards 48 and 50 each having a layer 52 of solder plated to one major surface thereof. A substrate 54, having a thin film test circuit 56 formed thereon, is positioned between boards 48 and 50, as illustrated in FIG. 3. The substrate 54 is also attached to the layer 52 of solder by strips 58 and 60. 
     Referring to FIG. 3, two coaxial connectors 62 and 64 are also positioned between boards 48 and 50. The connectors 62 and 64 facilitate coupling of the test circuit 56 to a test set (not shown). Each of the connectors 62 and 64 include outer sleeves 66 and 68, respectively, which are attached to the layer 52 of solder and inner-core conductors 70 and 72, respectively, which are attached to the test circuit 56. The substrate 54 includes a plurality of lead-receiving apertures 74. A plurality of test contacts 76 are mounted on the test circuit 56. Each test contact 76 is placed in a position overlapping one edge of an associated one of the plurality of lead-receiving apertures 74. By mounting the test contacts 76 directly on the test circuit 56, the effects of stray inductance and capacitance are minimized by reducing the distance between the test circuit and the plurality of leads 22 subsequently positioned within the apertures 74. 
     In use, the leads 22 of the electrical component 20 are positioned within the lead-receiving apertures 74 and the body 21 of the component rest on an upper surface 78 of the substrate 54 as illustrated in FIG. 4. The diameter of each of the lead receiving apertures 74 is larger than the diameter of each of the leads 22 to facilitate a frictionless insertion of the leads within the apertures. The thumb screw 41 is then rotated to facilitate a left-to-right movement of the slide 32 as viewed in FIG. 4. As a result of the movement of the slide 32, the shoulders 34 engage the leads 22 and facilitate relative movement between the leads 22 and the substrate 54. Moreover, the body 21 of the component 20 slides along upper surface 78 of the substrate 54 as a result of the movement of the leads 22 whereby the component moves from left to right as viewed in FIG. 4. By allowing the body 21 to move along with the leads 22 until the leads engage the test contacts 76, stresses, which would normally be exerted on the leads if the body had been held in a stationary position, are thereby reduced. The movement of the leads 22 continues whereby the leads are urged into engagement with portions of the contacts 76 which overlaps the apertures 74 and until the slide 32 engages stop 38. As illustrated in FIG. 5, the stop 38 is mounted on the pedestal 30 so that the leads 22 are slightly flexed after contacting the appropriate test contact 76 to insure a firm engagement therewith. 
     As noted above, each of the test contacts 76 overlaps its associated lead-receiving aperture 74. Test contacts 76 in this position provides (1) a full surface for the engagement of the leads 22, and (2) permits some wear of the test contact before replacement of the contact is required. Since the test contacts 76 are mounted on the test circuit 56, the distance between the leads 22 and the circuit 48 are at a minimum and the effects of stray inductance and capacitance are reduced. Thereafter, the transmission parameters associated with the component 20 are measured by the test set (not shown). After various transmission parameters of the component 20 have been measured, the thumb screw 41 is rotated in an opposite direction to facilitate a right-to-left movement of the slide 32 as viewed in FIG. 5. The movement of the slide 32 continues until the slide engages stop 36 thus enabling the leads 22 to return to an unflexed position and to permit the removal of the component 20 from the fixture 24.