| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 96 === It is worthwhile to study the mechanical properties and the fracture resistance of solders, because the solder may fracture by external forces during application. In this study, the effects of Sn-xAg-Cu (x=1,2,3) solders in different Ag addition on tensile and vibrational properties is discussed.
The Sn-xAg-Cu solder alloy can be divided into the primary β-Sn and the eutectic phase according to the observation of microstructure. The intermetallic compound (needle-like Ag3Sn and column-like Cu6Sn5 observed by EDS) and Sn matrix are distributed over the eutectic phase. The eutectic phase area affected the tensile and vibrational properties would increase with the increasing of the Ag content.
According to tensile test, the YS and UTS rose when more Ag is added as well as the strain rate is increased. And the TE are all around 40%, while SAC105 performs the best UE of the three. It will be safe to say that the SAC105 can bear more strain before the non-uniform deformation occurs, On the other hand, after tensile test, the microstructures of samples clearly show that the dynamic recrystallization (DRX) does exist, which affects the degree of material softening. As the Ag content decreases, the engineering stress-strain curve drops more slowly after passing UTS, that is to say, the DRX degree increases.
To observe the micro-cracks on the specimens after vibrational test, we can find that cracks are affected by the intermetallic compound of eutectic area. The IMC will induce cracks propagate along the phase boundaries between β-Sn and eutectic area. The damping capacity of the vibration tests under constant force is SAC105>SAC305>SAC205, while is affected by density, elastic modulus, striated deformation and inner friction. When the vibration tests are operated under constant deflection amplitude, we know the crack resistance is SAC205>SAC305>SAC105. The results affected by the degree of crack branching and the degree of crack transition.
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