Mercury-probe apparatus

Apparatus for testing semiconductor wafers, including a support for a test wafer and a mercury probe movable into test position overlying the test wafer, said mercury probe comprising a reservoir of mercury and means defining a mercury passage having one end that opens into a submerged portion of said reservoir, the opposite end of the passage being formed in insulation and constituting a contact aperture, means for establishing a pressure difference between the reservoir and the contact aperture to fill the passage with mercury, said contact aperture being below the upper surface of the mercury in the reservoir by a vertial distance, said vertical distance and the cross-section of the passage being so limited that, when said pressure difference is eliminated, surface tension of the mercury causes the mercury in the passage to be emptied automatically into the reservoir, said passage including means for inhibiting escape of mercury from the reservoir via said passage in case the probe is jolted while the contact aperture is unobstructed.