Component soldering generally requires the use of solder paste as a connecting medium, which forms solder joints after reflow. Due to various impacts that the component may encounter during its regular use, the stress on the solder joint accumulates continuously. Stress can come in various forms, such as thermal stress caused by thermal cycling and mechanical stress caused by tension. The accumulation of stress can cause fatigue in the solder joint, which can have a negative impact on its service life.
Fatigue life experiments
Due to the potential harm caused by stress, it is necessary to deepen our understanding of the fatigue behavior of solder paste alloys. Hani et al. conducted accelerated fatigue experiments to test the fatigue life of Jitian solder joints in actual components. They used three levels of vibration amplitude (16 MPa, 20 MPa, and 24 MPa) and a testing temperature of 25°C as experimental conditions
Figure 1. Equipment for fatigue life testing.
Experimental Results
Hani et al. correlated the fatigue life of solder joints with temperature using the following formula. The formula states the number of cyclic stress amplitudes (N63) required for 63% of the test samples to experience fatigue failure. The formula is highly applicable and can be used to analyze the fatigue life at various temperatures. P represents the stress amplitude, R(t) represents the reliability model, and T is the temperature.
Figure 2 shows the Weibull probability plot of solder joints at different stress amplitudes under 25℃. It can be clearly seen that as the stress amplitude increases, the fatigue life of the solder joint decreases. After identifying the relationship between the characteristic fatigue life and the cyclic stress amplitude, a model for the fatigue life of the solder joint can be established (Figure 3). In addition, according to the fatigue life formula, it can be inferred that as the temperature rises, the solder joint will be subjected to increased stress, and the characteristic life will rapidly decrease.
Figure 2. Weibull probability plot of solder joint under different load cycles at room temperature.
Figure 3. Stress-life model of solder joints at room temperature.
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