<title>Design considerations of the electrical contacts in (micro)relays</title>

Abstract

The electrical contacts are of crucial importance for the ultimate performance of (micro)relays. In this paper, the contact resistance of hard-contact relays is experimentally studied as a function of the contact force, the apparent contact area and the cleanliness of the contact surfaces. A simple test bench set-up is used to measure the contact resistance in air as a function of the contact force and the contact area. Forces range from 50 mgf to several gf. The contacts have a round shape with diameters ranging from 100 micrometers to 500 micrometers . The resistance decreases with increasing force and increasing area. Above force of approximately 2 gf, the contact resistance becomes fairly stable, i.e., independent of the applied force. The contact resistance stabilizes at values varying from 30 to 50 m(Omega) depending on the area. The measured contact resistance values for a 50 mgf contact force scatters between 50 m(Omega) and 0.7 m(Omega) due to the presence of a contaminating film on the contact surfaces. The scatter in measured values reduces to less than 10 m(Omega) when the contact force is around 4 gf, which again emphasizes that a certain minimum force is required for a reliable contact.