Characteristics of electric charges carried by dust particles and their effects on electrical contact failures

Dust contamination is one of the major causes of electrical contact failure. The deposition of dust and adhesion of particles are affected by the electric charges carried by the dust particles. This paper describes characteristics of electric charges carried by dust particles and their effects on electrical contact failure. A Millikan testing method was used for measuring the electric charges. The results show that the variation of electric charges carried by dust particles is located in a band region, the trend of charges can be expressed as a third order equation, the results obtained for positive and negative charge are similar. The morphology and surface seem to be the major factors which influence the electric charge. The relative humidity of the environment greatly affects the amount of electric charge. It is found that dust particles carry negative charges or positive charges, those particles will be attracted to both electric contact surfaces respectively, and thereby the probability of causing electrical contact failure is greatly increased. The selective deposition of particle takes place on electrical contact surface. The failed connectors were characterized by using SEM/EDS. Serious contaminants were detected at the contact interfaces, and the contaminants contained the major elements of dust, namely Si, and Al. Dust particles depositing at contact sports can cause electrical contact failure. They can also result in forming tiny holes in the Au film during plating process as well as influencing Au film adhesion. Appropriately controlling the environmental humidity during operation of the electro-mechanical components and protecting the contact interface from dust can effectively lower electrical contact failure.