Investigation On The Detection And Evaluation System Of Micro USB Connector

As the charging interface of the most of smart phones, micro USB connectors are widely used in the market. However, more and more phenomena of ablation failure have been found during the service of micro USB. Experimental investigation on the mechanism of ablation failure and the reasonable methods of detection and evaluation has theoretical and practical significance. It is meaningful for micro USB selection with better reliability to reduce the failure rate (All USB mentioned in this paper are equivalent to Micro USB).In this paper, the research was divided into two parts. On the one hand, it was aimed at the failure phenomena. The failure mechanism and the main influencing factors leading to ablation and the performance of each factor were studied by analyzing the fault tree, combined with the detection of failure samples. On the other hand, the detection method including the main factors was proposed based on the failure mechanism,which was not only able to distinguish the reliability of different products in a short period of time, but also was corresponding to the actual situation. Then based on the statistic and analysis of the test results, a reasonable evaluation system method was built up to assess the reliability of various types of micro USB connectors.The study found that the burned micro USB in mobile was contaminated by dust particles. High content of negative ions and corroded products of Ni and Cu were concentrated on Vbus contact. The insulation material around Vbus was burned heavily. The failure mechanism was deduced that under a certain ambient humidity, water film condensed on the surface of contacts and insulating materials, and the soluble salts depositing in water film formed electrolyte. When the mobile phone was charging, the surface water was electrolyzed, the anion and cation will move to the opposite electrodes. Galvanic corrosion occurred on Vbus contact between Au plating and exposed Ni underplating and substrate Cu, so that corrosion products of copper or nickel increased contact resistance to form high Joul heat. Due to a poor heat dissipation, the rapid increase in temperature near the Vbus contact resulted in the melting of surrounding insulation material. Through the fault tree analysis and analysis of the characteristics of the various factors,it can conclude that the environmental humidity, soluble salt pollution,electrical stress, wear, temperature are the main factors leading to failure.It is confirmed that order of the influence of the latter three factors is salt pollution, electric stress and wear through the analysis of the range of orthogonal experiment. Temperature and humidity is the basic conditions for electrochemical corrosion, the greater the humidity, the more prone to corrosion. Soluble salts react with metals such as copper or nickel to form corrosive substances, the more serious corrosion, the higher the contact resistance. The voltage can make the directional movement of ions pollutants, resulting in corrosion occurred in Vbus, the greater of voltage,the faster the corrosion rate. Plug destroyed the gold plating layer on the surface of the connector, the more serious the wear, the more prone to corrosion. According to the performance of several factors, a accelerated experiment, including wear, salt pollution, temperature,humidity and electrical stress, was established. The contact resistance was taken as the main evaluation index. The distribution of the contact resistance was estimated and the Weibull distribution of the two parameters was validated. The characteristic value of the Weibull distribution was taken as the main evaluation criterion, combining with the cumulative failure rate and the plating thickness, the reliability of three types of USB was evaluated. Type A was the best, type B was better than type C.