Connectors for forming separable connections between electrical conductors are well known and useful. Most of these connectors employ a sliding fit between two mating, contact elements. Some connectors utilize the electrical conductors themselves, e.g. traces on a printed circuit board (PCB) or flexible wires, as one of the mating contacts. Such a design simplifies the connector assembly. One type of contact element which has been advantageously used is described as a buckling beam test probe or contact.
A buckling beam probe is formed with a length many times its cross-sectional area so that the probe buckles or deflects when a predetermined axial load is applied thereto. A long buckling beam provides a small force plus a relatively uniform force throughout its deflection or buckling range. This enables the same force to be exerted on each of a plurality of pads on a semiconductor chip regardless of the deflection of the probe produced by variations in the heights of the pads. The forces for contacting the pad must be kept small so that the pads are not damaged. Accordingly, a buckling beam contact or probe is made sufficiently long with respect to its cross-sectional area such that the force applied to the pads would be determined by the resistance to buckling of the beam.
Buckling direction of a buckling beam contact or probe is typically controlled by accomplishing any one of the following techniques:
(a) offsetting the openings in the upper and lower alignment dies; PA1 (b) disposing the opening of the upper alignment die at an angle relative to the corresponding opening in the lower alignment die to slant the longitudinal axis of the wire; or PA1 (c) a combination of offset and angular slanting.
Once the buckling or bending has been initiated by a compressive load perpendicular to the lengthwise beam, a buckling beam probe or contact continues to bend without additional force. Such physical behavior under load is referred to as elastic instability, which typically is considered a structural failure. However, this physical behavior provides a spring contact with uniform force over a wide compliance range which is useful in high density electrical connectors.
Examples of electrical connectors incorporating buckling beam probes or connectors are described in U.S. Pat. Nos. 3,806,801 and 4,066,312.
Although there are many beneficial reasons for employing a buckling beam type connector, a drawback in the employment of such electrical connectors is the ease with which these connectors become damaged, and therefore, not usable. More particularly, because a buckling beam probe must be long and thin to retain elasticity after repeated buckling cycles, and because the ends of such probes typically protrude through the housing structure of an electrical connector, these fragile probes are easily damaged. As may be appreciated by one skilled in the art, in an electrical connector which incorporates buckling beam type probes, achieving and maintaining, over the life of the electrical connector, normal force of the individual probes within a predetermined range is critical for the reliable operation of the electrical connector, and the maintenance of low contact resistance between the mating conductive surfaces.
The foregoing illustrates limitations known to exist in present electrical connectors incorporating buckling beam probes. Thus, it is apparent that it would be advantageous to provide an improved electrical connector directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.