Automated Contact Resistance Probe

Project Number: C94-04
Point of Contact: pecht@calce.umd.edu

Objective

Develop an automated contact resistance probe (ACRP) to measure the electrical contact resistance, in real time, using a controlled, variable normal force.

Background

The reliability of electronic systems is largely dependent on and significantly impacted by the performance of various metal contacts in the system. Electrical contacts and connectors must have low and stable contact resistances during service life. The useful life of a contact ceases when the contact resistance exceeds a certain limit value. Models have been developed by the CALCE EPRC to assess the reliability of contacts subjected to different ambient conditions. These models need to be evaluated with experimental contact resistance behavior studies.

Work Accomplished

A probe has been developed that enables accurate measurement of contact resistance and provides a deeper insight into the physics of contact surfaces. Modifications in fixtures (for mounting samples on the probe) enables measurements in actual contact geometries. The probe also enables relative motion, or "wipe," between contact surfaces during measurement and provides heating of the contact sample up to 200øC during measurement.

 The instrument includes:

• Automatic x-y positioning of the sample for contact wipe measurements, and multiple measurements using the same test coupon.
• Vibration can also be simulated using the x-y table. The positioning resolution is around 0.254æm.
• Vibration free normal force application using a hydraulic arrangement. A normal force variation of 0 to 2.27 kgs, with a resolution of 2 gm is possible at present. Finer load resolutions could be achieved by including an amplifier in the load sensing circuit. A novel feature of this loading arrangement is the continuously varying loading capability.
• Computer control of all the above processes. Digitally stored and processed data includes contact force vs. resistance, voltage vs. current, and force vs. resistance vs. contact wipe.
• Precision voltage source and measure. The source can deliver 1nA to 1A at a voltage varying between 0.1mV to 110V. The measure unit has a resolution of 10æV. If contact measurements need to be done at a higher current rating, an appropriate source unit can be added to the existing setup. The source-measure unit provides both current and voltage compliance.