High-frequency probe tip assembly

Abstract

A probe suitable for low-loss microwave frequency operation has a tip assembly including a semi-rigid coaxial cable having a Teflon.TM. dielectric for temperature stability and a freely-suspended end. On this end a semicylindrical recess is formed defining a shelf along which an inner finger and outer pair of fingers are mounted, each made of resilient conductive material, so as to form a coplanar transmission line. Cantilevered portions of the fingers extend past the end of the cable to form an air-dielectric transmission path of uniform and stable characteristic despite exposure to numerous contact cycles and to provide suitable means for probing nonplanar device pads while also offering good visibility of device pads generally. Corresponding sections of the cantilevered portions are equivalently configured in terms of material composition, cross-sectional geometry and spatial orientation to provide a uniform deflection characteristic relative to each finger for even wearing of the pads and fingers and for stability of transmission characteristic despite contact pressure variation. A rearwardly-inclining end face on each finger reflects dark background shading to cause a dark line to form on each extreme finger end in sharp contrast to the device pads thus facilitating finger visibility. The fingers are originally formed in one-piece and are joined by a carrier strip which is trimmed off after the fingers are connected to the cable so that their transverse spacing is precisely determined.