1. Field of the Invention
The present invention relates generally to electrical contacts, and more particularly to disengageable contacts with dielectric shielding.
2. Discussion of the Prior Art
Electrical circuits are often provided with disengageable contacts for making electrical connections to leads of electronic devices so that the devices can be readily installed and removed to test the device or circuit or to repair or replace the device. In high frequency electronic circuits, electrical "signal path" connections may need to be isolated from external electrical interference by being at least partially surrounded with a non-conductive gap and ground shield. In critical applications, the non-conductive gap dimensions must be precise to provide a specified impedance in the signal path.
FIGS. 1a, 1b, 2a and 2b represent typical prior art disengageable contacts for coupling an electronic device 2 lead 3 to a circuit terminal 4 and to a ground terminal 5 by means of conventional connectors 10 and 20. In FIG. 1a, connector 10 is formed by a base 11 holding a flexible conductive ground shield 12 connected to ground terminal 5, and a flexible conductive "contact finger" 13 connected to circuit terminal 4. Contact finger 13 is a resilient member which is typically either electrically conductive or coated with electrically conductive material. Finger 13 is spaced by a gap 14 from shield 12, and isolated by isolator means 15 in the form of a solid dielectric 16 sandwiched in gap 14. In FIG. 2a, connector 20 is formed by a base 21 holding flexible conductive ground shield 22, flexible conductive contact finger 23, and isolator means 25 in the form of a solid insulating block 26 with a fluid (typically air) as a dielectric 27 in gap 24.
As shown in FIGS. 1b and (2b), actuator 18 directly, or actuator (28) through device 2, moves contact 13 (23), isolator means 15 (25), and shield 12 (22) together, generally maintaining the contact and the shield parallel to and isolated from each other to maintain a specified impedance wherever they stop their movement. The contact finger may be flexed by the actuator 18 (28) through moving the electronic device, the shield, or directly. The contact finger may be formed straight or bent, and then deformed towards or away from the lead of the device. However, in a connector with the contact finger and the shield being curved together, they slide lengthwise against each other, and it is difficult to maintain the consistency of the dielectric isolation between them. Where, as in FIGS. 1a and 1b, the dielectric is a flexible solid material 16 which maintains the size of gap 14, bending the contacting arrangement generates friction which opposes the actuator and wears out the connector. Where, as in FIGS. 2a and 2b, the dielectric is a fluid 27, a spacer such as block 26 is needed to maintain gap 24 between conductors 22 and 23. A solid block 26 generally has a different dielectric value than the fluid 27 and interrupts the electrical relationship between contact 23 and shield 22. In addition, the size of gap 24 is uncontrolled around the fluid dielectric 27 space, and as shown in FIG. 2b shield 22 may become curved to a different radius than contact finger 23, distorting the size of gap 24 and the electrical relationship between conductors 22 and 23.
Conventional connectors in which both the contact finger and the ground shield move are difficult to design, manufacture, install, use and maintain so as to precisely control the electrical relationship between the moving members. When an additional electrical component, such as a decoupling capacitor, must be connected to the contact finger or ground shield as close as possible to the device lead where the finger or shield will be flexed, it is difficult to connect the additional component.
Finally, the contact finger and ground shield must be connected by joints to a circuit terminal 4 and to a ground terminal 5. It is difficult to minimize the discontinuity in impedance of such joints in moving conductors.
Thus, there is a need for a convenient, reliable and economical disengageable contact means with consistent dielectric shielding from external electrical interference.