Thermally actuated microprobes for a new wafer probe card

A new type of MEMS microprobe was designed and fabricated which can be used for a nest generation wafer probe card. A prototype MEMS probe card consisting of an array of microprobes individually actuated by bimorph heating to make contact with the test chip was also fabricated. This probe card is called the CHIPP (Conformable, HIgh-Pin count, Programmable) card and can be designed to contact up to 800 I/O pads along the perimeter of a 1-cm² chip with a microprobe repeat distance of approximately 50 μm. Microprobes for a prototype CHIPP probe card have been fabricated with a variety of cantilever structures including Al-SiO₂, W-SiO₂ and Al-Si bimorphs, and with the resistive heater placed either inside or on the surface of the cantilever. Ohmic contacts between tips and bond pads were tested with contact resistance as low as 250 mΩ. The deflection efficiency varies from 5.23-9.6 μm/mW for cantilever lengths from 300-500 μm. The maximum reversible deflection is in the range of 280 μm. The measured resonant frequency is 8.16 kHz for a 50×500 μm device and 19.4 kHz for a 40×300 μm device. Heat loss for devices operating in air was found to be substantially higher than for vacuum operation with a heat loss ratio of about 2/1 for a heater inside the structure, and 4.25/1 for a structure with the heater as an outer layer of the cantilever