Research Of The Thermal Fatigue Life On The Lead-free Solder Jiont Of Micro-USB Connector

With the rapid development of modern industry, Micro-USB connectors have been an integral part of people’s lives, so the Micro-USB connector’s lifetime has been highly put on the agenda. Because the solder joint is the bridges of the electrical and mechanical characteristics, once the solder joint failure will directly cause Micro-USB connector’s failure. So the prediction of solder joint’s life is of great significance.Under the cyclical temperature(-55 ℃ to +125 ℃), the joints solder’s life has been described in this thesis. The solder joint’s materials is Sn3.5Ag0.75 Cu whose melting temperature is about 217 ℃. When the temperature reaches the melting point of 0.5, the solder will creep and stress relaxation, which can effectively predict the service life of the solder joints under extreme operating conditions.Under the cyclical temperature, the life prediction of the Micro-USB connector mainly tasks are: using the 3D modeling software Pro/E establishes the entity model Micro-USB connector which includes the Micro-USB whole connector body, metal Pin, wires and SnAgCu lead-free solder, and removing the sharp partially which do not impact the analysis, then importing it into the finite element analysis software ANSYS for analysis. The mechanical behavior of the solder joints are described by the ANAND unity constitutive equation model under cyclic temperature loads. Using commands of parametric design language APDL writes the cyclic temperature loads and simulating the stress and strain distributions of solder joints by theoretical analysis. As the coefficient of thermal expansion mismatches among all of the materials, the maximum stress-strain has been found at the low temperature. And at the high temperature, the thermal stress-strain is decreased. During the heating or cooling temperature, the stress-strain of solder joints changes greatest, which results in the final solder crack initiation at this period then failure. Using Coffin-Manson empirical formula based on plastic strain calculates the thermal fatigue life of solder joints under thermal cycling temperature effects.Final results showed that under the cycling temperature, the solder joints the Micro-USB connector’ maximum stress-strain is found at the bottom of the solder joints where touch on the metal Pin, while the middle solder joint is the most prominent spot, then we can see that the crack initiation will be started from here. The calculating result indicates that the solder joint life is 1146 times, which confirms the Micro-USB connector quality and reliability.