Importance

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Abstract

ATE is mounted directly to a support surrounding and removably receiving probe cards of differing thickness. An electrically heated chuck having a variable heat transfer coefficient heat exchanging face confronting a liquid nitrogen supplied plenum exhibits a temperature that varies with electrical heater load, rate of liquid nitrogen supply, and heat transfer coefficient of the heat exchanging face. The rate of liquid nitrogen supply is varied as a function of whether or not the electrical heater load falls outside predetermined upper and lower bounds to establish and maintain set point temperature over a range of set point temperatures including liquid nitrogen temperature and ambient temperature. The chuck is mounted for X,Y movement on load-balanced air/vacuum bearing, and is mounted for Z movement to accommodate different thickness probe cards. A load-lock having a pivoting cassette receiving tray that pivots with a pivoting transfer arm is mounted for Z movement with the chuck. A vacuum pump selectively lowers the temperature at which the supplied liquid nitrogen boils. A positive pressure of N.sub.2 gas is maintained to prevent moisture condensation in the load-lock and on the operative surfaces of the chuck.

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First Claim