Investigation On Fretting Principle Of The Gold Plating Contact And Test

The electric contact is widely used in communication and electronic industry, so its reliability is very important. Fretting is one of the major reasons that makes electric contact unreliable.In this paper, fretting principle of contact pairs with double sides gold-plated on the contacts (gold-plated coupons with gold-plated probes) is discussed, including adhesive wear, abrasive wear and the transferring process of the materials, as well as the relationship between contact resistance and the fretting stages. The process of fretting can be divided into three stages. 1. The complete protection stage of gold: contact resistance decreases at the early stage of fretting, and is lower than initial resistance value, and no debris appears. 2. The partial protection stage of gold: contact resistance is higher than initial resistance and increases slowly. Wear debris increases gradually, and Au is the main element in debris. 3. The protection failure stage of gold: contact resistance increases rapidly in a short time and oscillates. A large amount of oxidation accumulates between the contact pair, and much wear debris disperses. Oxide with a little gold is the main component in debris.Parameters which affect fretting performance of gold-plated contacts are researched. First, the surface morphology of PCB coupons displays peaks with valleys. Calculation and ANSYS model analysis show that, when contact pairs are contacted at valleys, contact area is large, and stress is small, so wear debris can't be easily formed during fretting. In addition, gold on the probe is transferred to the coupon and accumulates on the valleys of the coupon, therefore, the gold on the coupon becomes thicker and the fretting life of the contacts is prolonged. When contact pairs contact at peaks, stress is larger than the former, gold wear debris can't be accumulated and stay on fretting track, so contact failure occurs easily. Second, the smaller the amplitude is, the longer fretting life of the gold-plated contacts is. Third, if the thickness of gold-plated layer is the same, the harder the coupon is, the larger the initial contact resistance is, and the longer the life of the gold-plated contacts is. Finally, when the thickness of gold-plated layer reaches 0.2μm, coupon with gold-plated probe has good fretting performance and can save reduce production costs effectively.This paper gives discussion on the fretting principle of contact pairs with nickel-plated probes and gold-plated coupons. The probe is harder than the coupon, so the gold on the coupon transfers to the probe in the initial stage of fretting. Part of gold adheres to probe stably, and part of gold becomes wear debris and is pushed out of fretting area with the processing of fretting. The contact resistance is stable because of enough gold accumulating in the contact area.