Thermal control unit used to maintain the temperature of IC devices under test

A thermal control unit for maintaining a set point temperature on an IC device under test (DUT) having a substrate having a die attached to an upper surface thereof, comprising:

• a pedestal assembly comprising a heat-conductive pedestal having a bottom end configured to contact the die of the DUT and a temperature sensor in the bottom end for monitoring the die's temperature;
• a temperature-control fluid circulation block having a fluid inlet and a fluid outlet configured to circulate a fluid therethrough, the block in stacked relationship along a z-axis with the heat conductive pedestal;
• a thermoelectric module between the heat-conductive pedestal and the fluid circulation block configured to control heat flow between the pedestal to the fluid circulation block;
• a substrate pusher configured to contact the substrate of the DUT;
• and
• a controllable force distributor configured to receive a z-axis force and controllably distribute such z-axis force between the pedestal assembly and the substrate pusher, wherein said controllable force distributor includes a force distribution block having an actuator configured to change the force transmitted to the heat conductive pedestal relative to the force transmitted to substrate pusher, wherein the actuator includes a plurality of pistons that can be actuated to exerted a z-axis force that is transmitted to the pedestal and that changes the balance of the z-axis forces transmitted to the pedestal and the substrate pusher, and wherein the plurality of pistons are adjustable and capable of providing varying levels of die force.