The Characteristic And Formation Mechanism Of Contaminants On Failed Connector Contacts Of Mobile Phones

As the terminal unit of mobile communication, mobile phones have been complained about their high failure rate in recent years. Based on the test of manufacturer, it is found that the performance of electronic components in many failed mobile phones is well. So there must be failed connector contacts between electronic components, which result in the failure of mobile phones.Many failed mobile phones had been collected in this dissertation. The electrical and morphological characteristics of contaminants on the failed connector contacts were analyzed. The mechanism of contact failure owing to the contaminants was discussed. The reason for the formation of contaminants was studied and some simulated tests were accomplished. Some important and new findings are summarized and listed as follows:1. The microcosmic characteristics of contaminants on the failed connector contacts of mobile phones are concluded.(1) Fretting take place on the failed connector contacts. The contaminants mostly locate at the end of the contact areas on PWB.(2) The contaminants are mainly accumulated by microparticles, including wear debris, dusts, corrosion products and organic materials. The energy to accumulate the different particles is provided by the micro-motion between connector contacts.(3) In the contaminants, plenty of organic materials such as sodium lactate can be found, and chloride can be detected more than sulphide. So the contaminants on the failed connector contacts are closely related to the environment of human body.(4) Some contaminants have muti-layer structure. A layer of organic materials is covered on the surface, and corrosion products and dusts consist in the contaminants.2. Accumulation of particles and trapping of dusts are the reasons for high contact resistance on the contaminants.(1) The contaminants on the failed connector contacts can result in high contact resistance. The testing points of high resistance mostly locate on the accumulated contaminants at the end of contact areas.(2) High resistance is caused by the high thickness of the contaminants and the dust particles in the contaminants.3. The test method to estimate the thickness of contaminants by X-EDS detection is studied.According to the Anderson/Hasler's formula:R(x)=(?)(E01.68-Fc1.68), as the voltage increases, X-ray penetrates deeper. E0 is the voltage where the element content of basal metal evidently increases, andρis the density of the matrix. After testing the percentage of different elements in the comtaminants at different voltage, the thickness of contaminants can be calculated. It is proved that the calculated thickness of the contaminants is roughly equal to the testing thickness by three-dimensional profile apparatus. A convenient testing method for the thickness of contaminants is verified.4. The effect of organic materials, especially sodium lactate, to contaminants accumulation and high contact resistance is studied.(1) The perspiration can easily enter the mobile phones, which leads to contaminants abundant in sodium lactate.(2) Because the viscosity of sodium lactate is heavy, the contaminants on the failed connector contacts can be glued together tightly, which results in the accumulation of contaminant particles during micro-motion.(3) The accumulated contaminant particles can withstand the driving force of the probe in micro-motion. The probe has to climb up the contaminant particles, which leads to high contact resistance, and contact failure occur.5. The effect of corrosion products trapping to contact failure is analyzed.(1) According to the statistical data, dusts are found in most of the corrosion contaminants. The dust particles can hardly leave the contact surfaces because of the trapping of corrosion products.(2) The dust particles trapped in corrosion products cann't easily be wiped away by the probe. So fluctuated high resistance appears, and contact failure happen.