Apparatus for on-wafer testing of electrical circuits

A probe apparatus for on-wafer testing of an electrical circuit, said probe apparatus comprising:

• a base plate formed from an electrically conductive material, said base plate including top and bottom surfaces and defining an aperture extending therethrough, said base plate further defining a plurality of respective substantially cylindrical conduits;
• a substrate formed from a dielectric material, said substrate including top and bottom surfaces, the top surface of the substrate being electrically connected to the bottom surface of the base plate, said substrate defining an aperture therethrough, the apertures defined by said base plate and said substrate being aligned and sized to permit viewing therethrough;
• a plurality of respective microstrip transmission lines secured to the bottom surface of said substrate, each respective microstrip transmission line having a first end and a second end, each second end being disposed adjacent to the aperture defined by said substrate;
• a plurality of respective coaxial connectors, each including an outer conductor in electrical contact with said base plate and each including a corresponding center conductor having diameter substantially equal to the width of a respective microstrip transmission line, each respective center conductor including a respective end segment which extends beyond its corresponding outer conductor and which depends within a respective one of the conduits and which is in electrical contact with a first end of a respective one of the microstrip transmission lines, the radial distance from the surface of each of said respective end segments to a wall defining a respective conduit being substantially equal to the thickness of said substrate;
• and
• a plurality of respective needle probes each electrically connected to a second end of a respective microstrip transmission line and extending in a direction substantially away from said base plate.