Under Cyclic Tensile Load, The Failure Of Lead-free Solder Joint Damage

The electronic productions tend toward the miniaturization, less weigh and higher performance. The problem that the electronic productions are inevitable to vibrate or impact when we transport and use them, has become increasingly prominent. 70% of abatement of electronic device has resulted from the electronic packaging, in which the solder joint failure is the main reason. Cyclic stretch and impact can simulate practical vibration and impact well. So it is necessary to study lead-free solder joint's reliability under cyclic stretch and impact. The dissertation performs systemic study on Sn-3.5Ag solder joint's damage failure under cyclic stretch and impact, by online monitoring micro resistance. Main work and conclusions:1. Based on solder joint's mechanic damage and Electrical Characteristics, the relationship between solder joint's mechanic damage and resistance was established to make it feasible to detect solder joint's mechanic damage by measuring resistance.2. Experimentation system used for online monitoring solder joint's mechanic damage under cyclic stretch and impact was designed and carried out. To improve the precision of micro resistance measuring device, two ways were adopted, as follows: 1) Reverse current method base on four-probe method was adopted to weaken or eliminate influence of thermal electromotive force. 2) High precision amplifier and second-order low-pass filter circuit with high common mode rejection ratio and series mode rejection ratio were used in hardware circuit; Gross error was eliminated through distribution method to get the available list range, then the arithmetic mean of data in the available list range was the best estimate value without random error on software DSP.3. Based on analysis of the mass experiment data, the two phases which the solder joints pass through under cyclic stretch and impact were described, as follows: the main crack initiation and stable propagation, accelerated propagation. The process experienced by solder joint's damage failure was revealed further.4. Sn-3.5Ag solder joint's damage process under cyclic stretch and impact was discussed. It was found that the solder joint's damage detected by measuring the resistance of solder joint is consistent with the one estimated by using evolution equation. And in the range from 0.1Hz to 20Hz, as the increase of frequency, the whole trend of the fitting parameters A is first increased and then decreased. It was showed that the frequency of cyclic stretch and impact can Influence Sn-3.5Ag solder joint's damage process.5. Influence of frequency on Sn-3.5Ag solder joint's damage mechanism under cyclic stretch and impact was analyzed and discussed. In the range from 0.1Hz to 20Hz, life-span of solder joint is shorter at 5Hz and 10Hz. As the increase of frequency, deformation not to resumed is first increased and then decreased as the same as the practical damage rate of the main crack initiation and stable propagation. It was showed that deformation not to resumed plays a very important role in influence of frequency on Sn-3.5Ag solder joint's damage mechanism under cyclic stretch and impact.