Patent ID: 7116121

Claim:
In a probe assembly for probing a target signal upon a work circuit assembly with a spring pin contact which is electrically connected to a transmission line formed upon and carried by a printed circuit assembly that when urged against the work circuit assembly compresses the spring pin contact into electrical contact with the target signal, the improvement comprising: the transmission line being formed by a signal trace separated from a ground plane by the thickness of an intervening dielectric layer; the intervening dielectric layer having a first edge parallel to a plane formed by the work circuit assembly; the ground plane having an extended portion that extends beyond the first edge of the intervening dielectric layer in a direction toward the work circuit assembly by a selected first distance bounded by a second edge; a housing portion of the spring pin contact being in electrical contact with the signal trace of the transmission line and also having an end proximate with the first edge of the intervening dielectric layer; a plunger portion of the spring pin contact extending out of a housing portion, over the extended portion of the ground plane and beyond the second edge by a selected second distance; and wherein the characteristic impedance of a transmission line formed by the plunger portion and the extended portion of the ground plane is approximately the same as the characteristic impedance of the transmission line formed by the signal trace and the ground plane.