Influence of Sn Grain Size and Orientation on the Thermomechanical Response and Reliability of Pb-free Solder Joints

Thermal Fatigue Evaluation of Pb-Free Solder Joints: Results, Lessons Learned, and Future Trends

“…During accelerated thermal cycling the microstructures of SAC alloys evolve continually by coarsening of Ag 3 Sn and Cu 6 Sn 5 particles and recrystallization of Sn grains in areas of stress concentration where most of the strain occurs. [23][24][25][26] The combined effect of this microstructural evolution appears to be a reduction in resistance to creep and thermal fatigue. In the cases where the initial solder microstructure is more resistant to microstructural evolution during thermal exposure, the solder joint resistance to thermal fatigue is much less likely to change over time.…”

“…50,51 Thus, the orientations of the Sn grains are a critical parameter in determining the thermomechanical response of SnAgCu solder joints. 24,44,47 Two common techniques to investigate the Sn grain morphology are polarized light microscopy and electron backscattered diffraction (EBSD). Sn exhibits birefringent properties, resulting in different colors for different crystal orientations under cross-polarized imaging.…”

Characterization Techniques for Film Characteristics

“…Kink formation is related to plastic deformation, such as sliding and twinning [15,21]. Because the sliding and twinning of tin depend on the tin crystal orientation, certain kink angles should be more common than others [24][25][26]. Figure 5.26 shows an example of a whisker with a kink angle of 45 ∘ .…”

“…Young's modulus along the c-axis is about three times greater than that along the a-and b-axes [25,34]. Thus, tin whisker formation is affected by the crystal orientation of tin grains, so understanding the crystal orientation relationship between a whisker and its adjacent grains is important for clarifying the tin whisker formation mechanism.…”

Effect of Crystal Orientation on Sn Whisker-Free Sn–Ag–Cu Plating

“…Young's modulus along the c-axis is about three times greater than that along the a-and baxes. 14,15) Thus, when mechanical stress is applied to Sn grains, excess strain can accumulate between adjacent grains that have different grain orientations. Excessive strain can lead to Sn grain deformation (including twin formation) in specific grains.…”