A striated deformation feature can be observed in Sn-Pb eutectic solder with higher Sn content or a coarse Sn-rich phase after the solder is subjected to a vibration test. This deformation feature may accelerate the life deterioration of Sn-Pb solder under vibration. A similar feature can be observed in lead-free Sn-3.5 mass%Ag eutectic solder. A very little crack can be observed around the deformation areas of an Sn-3.5 mass%Ag sample, and that is the main reason it possesses a lower crack growth rote than Sn-Pb solder. A comparison of the deflection vs. cyclic number (D-N) curves of Sn-Pb and Sn-Ag solders under an identical vibration push force or identical initial defection amplitude demonstrates that Sn-3.5 mass%Ag solder possesses better vibration fracture resistance than Sn-Pb solders. In the case of an identical vibration push force, the initial deflection amplitude of Sn-3.5 mass%Ag solder is significantly smaller than that of Sn-Pb solder, and it may improve the solder's vibration fracture resistance.
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