Investigation Of The Failure Mechanism Of Insulation Material In Micro USB Connectors

With the widespread use of smart phones,the development of micro USB connector is promoted.But meanwhile,it was found that the connector insulator was often burned and failed after its application.Exploring the failure mechanism of insulating material ablation is an effective way to prevent connector from the insulation failure and will play an important role on the security implications of production.Since dielectric properties of the insulating material and operating environment are the main factors affecting the micro USB connector insulation performance.In this paper,two aspects have been studied.Firstly,the dielectric properties of two kinds of insulating materials(including Liquid Crystal Polymer(LCP)and Polyamides 9T(PA9T))are studied to evaluate their ablation resistance.Four performances,including surface insulation resistance(SIR),volume insulation resistivity(VIR),breakdown strength(BDS)and comparative tracking index(CTI),of insulating materials will be measured and compared.Secondly,the effects of environmental factors(including environmental temperature and humidity,electric stress,pollutants,mechanical wear)on the dielectric characteristics of insulation material in micro USB connector are investigated respectively.Micro USB connectors made with LCP or PA9T material will be taken to be the test samples.A multi-channel of insulation resistance measurement system is adopted to monitor the surface insulation resistance of test samples during every environmental experiment.Finally,the ablation failure mechanism of micro USB connector insulator will be also discussed.According to the investigation,some conclusions are drawn.Both performances(including SIR,VIR and BDS)of LCP and PA9T material are good,and there is small difference between the two materials.But the CTI of PA9T is much higher than that of LCP.However,the tracking failure is difficult to happen in the case of low-voltage condition,which indicates that comparative tracking is not the ablation failure mechanism of micro USB connectors.Environmental factors of ambient temperature and humidity,electrical stress and mechanical wear do affect the insulation resistance of connector insulating material but they are not severe enough to cause the ablation failure of insulation material.The combined effects of pollutant and electrical stress are the main factor leading to the ablation failure of micro USB material.When contaminants deposited upon the connector absorb moisture from the air,a conductive liquid will be formed.Under the effect of electrical stress,water electrolysis and electrochemical corrosion reaction will occur in micro USB connector.Heat released from chemical reaction will accelerate the material aging of connector.In addition,large amount of Joule heat generated by both increasing of the leakage current due to the change of ion concentration on the connector surface and the contact resistance significantly increased by electrochemical corrosion will remarkably increase the temperature of insulation material.When the temperature reaches the melting point,ablative insulator failure of the material will occur.