A BiCMOS active substrate probe-card technology for digital testing

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