Peculiar Phenomenon in Friction Coefficient of Tin Plated Connector Contacts with Application of Lubricant

For tin plated connector contacts, it was found that friction coefficient of the lubricated contacts was higher than that of non-lubricated contacts. This is very different from common knowledge of lubrication. In this paper, size of true contact areas of static contact condition was discussed by FEM analysis under conditions for both lubricated and non-lubricated contacts between platinum (Pt) hemisphere and tin (Sn) plated flat. In the result, it was clarified that the contact area with lubricant became lager than non-lubricated contacts. This is due to indentation depth of the hemisphere into tin plated layer. Projected area for sliding direction of the sunken contact surface was calculated by geometrical contact model. From these discussions, it was concluded that the increase in friction coefficient with lubricant was not caused by increase in adhesion area but by increase in depth of the contact trace and in plowing the flat.