A BICMOS active substrate probe-card technology for digital testing

An active substrate silicon probe card has been implemented by forming a po lyimide membrane on a silicon substrate. The probe card combines tungsten p robe tips and aluminum interconnects in the polyimide membrane with active test circuitry integrated in the substrate. A monolithic prototype of the p robe card designed to enhance the capabilities of conventional digital test systems has been fabricated in a 2-mu m BiCMOS technology. The benefits of the proposed probe-card technology could be further exploit ed by integrating the timing measurement unit of a digital tester into the probe-card substrate, An integrated tester architecture based on time digit ization is described. A prototype of a tester combining a time digitizer an d two test channels has been integrated in a 0.6-mu m BiCMOS technology. Th e time digitizer in the experimental circuit employs a two-stage ring oscil lator that is phase-locked to an external reference and makes use of phase interpolation to achieve a timing resolution of 90 ps.