Research On Reliability Of Electrical Contacts Under Fretting Conditions

Electric contact largely affects the reliability of electronic equipment. Electrical connectors or connect terminals will result in contact failure even in static state after a period of operation. With microanalysis, some very short wear tracks has been found on the electric contact surface and many insulated granules are around the wear tracks. The phenomena is called as fretting failure, which is one kind of common and dangerous contact failures. Therefore, in order to choose the correct materials of electrical connectors and design the structure and environment conditions to ensure that electrical connectors have sufficient life, it is necessary to study the contact resistance of different materials under multiple conditions with the current achievements in reliability science.In this thesis, fretting experiments for variety of material combinations are carried out. Fretting resistance during the process of fretting is recorded. All the original resistance data are dealt and analyzed to obtain fretting behavior. Finally, Fretting mechanism of contact material combinations are studied.Fretting amplitude and contact pressure are important fretting parameters for double sides gold-plated on the contacts (gold-plated coupons with gold-plated probes). This thesis does fretting experiments of double sides gold-placed on the contacts under different conditions, and finds that raising fretting amplitude and contact pressure lead to more oxide in the fretting zones. Because there is Au in the fretting zones, the contact resistance never raise up.In the study of non-noble metal, it is found that the contact resistance of non-noble metal under fretting is very likely to become high. When make copper and nickel sample a contact couple (indicated with Ni /Cu), the contact resistance significantly rise up much more quickly than the nickel and copper contact couple (indicated with Cu/Ni). By an analysis on mechanism level, we propose copper as contact material in the smaller side of connectors. Also find that the contact resistance which is measured on the edge of fretting zones is most easy to increase. By study the numbers of fretting circles when resistance goes to a stated level on the edge of fretting zones, it is verified that Weibull distribution is appropriate to describe the distribution characteristics of the connector's life, and use the best linear unbiased estimator to calculate the Weibull distribution parameters, then get the reliability characteristic parameter.In the study of non-noble metal, it is also found that the fretting frequency will affect the number of fretting lifetime, during which the contact resistance goes to appointed level. In this thesis, experiment is designed to study how the fretting frequency affect the contact resistance, then we sum up two experience formulas. They can respectively describe the frequency's effect to the contact resistance period and estimate the fretting lifetime during the resistance smooth period and resistance rising period.