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In situ synchrotron study of electromigration induced grain rotations in Sn solder joints.

Shen H, Zhu W, Li Y, Tamura N, Chen K - Sci Rep (2016)

Bottom Line: Here we report an in situ study of the early stage of microstructure evolution induced by electromigration in a Pb-free β-Sn based solder joint by synchrotron polychromatic X-ray microdiffraction.Theoretical calculation indicates that the trend of electrical resistance drop still holds under the present conditions in the grain with high electrical resistivity, while the other grain with low resistivity reorients to align its a-axis more parallel with the ones of its neighboring grains.A detailed study of dislocation densities and subgrain boundaries suggests that grain rotation in β-Sn, unlike grain rotation in high melting temperature metals which undergo displacive deformation, is accomplished via diffusional process mainly, due to the high homologous temperature.

View Article: PubMed Central - PubMed

Affiliation: Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 China.

ABSTRACT
Here we report an in situ study of the early stage of microstructure evolution induced by electromigration in a Pb-free β-Sn based solder joint by synchrotron polychromatic X-ray microdiffraction. With this technique, crystal orientation evolution is monitored at intragranular levels with high spatial and angular resolution. During the entire experiment, no crystal growth is detected, and rigid grain rotation is observed only in the two grains within the current crowding region, where high density and divergence of electric current occur. Theoretical calculation indicates that the trend of electrical resistance drop still holds under the present conditions in the grain with high electrical resistivity, while the other grain with low resistivity reorients to align its a-axis more parallel with the ones of its neighboring grains. A detailed study of dislocation densities and subgrain boundaries suggests that grain rotation in β-Sn, unlike grain rotation in high melting temperature metals which undergo displacive deformation, is accomplished via diffusional process mainly, due to the high homologous temperature.

No MeSH data available.


Related in: MedlinePlus

Electrical resistivity evolution resulted from the grain rotation.(a) The time dependence of θc, which is defined as the angle between the crystal c-axis and electric current direction. (b) The calculated electrical resistivity σ of all grains. Both θc and σ are found to change in Grain 1 only, although Grain 2 rotates as well.
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f4: Electrical resistivity evolution resulted from the grain rotation.(a) The time dependence of θc, which is defined as the angle between the crystal c-axis and electric current direction. (b) The calculated electrical resistivity σ of all grains. Both θc and σ are found to change in Grain 1 only, although Grain 2 rotates as well.

Mentions: From eq. (4), it can be seen that the conductivity of Sn is a function of θc only, independent of θa and θb. However, measuring θc is not easy because the local current direction cannot be derived accurately from the measurements, especially considering that the depth information is missing due to the bulky shape of the solder joint. Therefore, the evolution of the angle between the c-axis of all 7 crystal grains and the global electric current direction (Δθc) is measured instead, i.e. it is assumed that the electric current direction at any local position of the solder joint does not change as a function of time throughout the performed EM test. This assumption is easily satisfied in this study because the testing condition is mild and no resistance change is observed during the EM test. As displayed in Fig. 4aΔθc goes positive for Grain 1, indicating that Grain 1 has its c-axis reoriented more perpendicular to the electric current direction. Interestingly, Δθc of Grain 2, similarly to all other grains, remains close to zero throughout the EM test. In other words, the rotation of Grain 2 is mostly about the c-axis, and the angle θa between its a-axis and the current direction decreases (Figure S1).


In situ synchrotron study of electromigration induced grain rotations in Sn solder joints.

Shen H, Zhu W, Li Y, Tamura N, Chen K - Sci Rep (2016)

Electrical resistivity evolution resulted from the grain rotation.(a) The time dependence of θc, which is defined as the angle between the crystal c-axis and electric current direction. (b) The calculated electrical resistivity σ of all grains. Both θc and σ are found to change in Grain 1 only, although Grain 2 rotates as well.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834559&req=5

f4: Electrical resistivity evolution resulted from the grain rotation.(a) The time dependence of θc, which is defined as the angle between the crystal c-axis and electric current direction. (b) The calculated electrical resistivity σ of all grains. Both θc and σ are found to change in Grain 1 only, although Grain 2 rotates as well.
Mentions: From eq. (4), it can be seen that the conductivity of Sn is a function of θc only, independent of θa and θb. However, measuring θc is not easy because the local current direction cannot be derived accurately from the measurements, especially considering that the depth information is missing due to the bulky shape of the solder joint. Therefore, the evolution of the angle between the c-axis of all 7 crystal grains and the global electric current direction (Δθc) is measured instead, i.e. it is assumed that the electric current direction at any local position of the solder joint does not change as a function of time throughout the performed EM test. This assumption is easily satisfied in this study because the testing condition is mild and no resistance change is observed during the EM test. As displayed in Fig. 4aΔθc goes positive for Grain 1, indicating that Grain 1 has its c-axis reoriented more perpendicular to the electric current direction. Interestingly, Δθc of Grain 2, similarly to all other grains, remains close to zero throughout the EM test. In other words, the rotation of Grain 2 is mostly about the c-axis, and the angle θa between its a-axis and the current direction decreases (Figure S1).

Bottom Line: Here we report an in situ study of the early stage of microstructure evolution induced by electromigration in a Pb-free β-Sn based solder joint by synchrotron polychromatic X-ray microdiffraction.Theoretical calculation indicates that the trend of electrical resistance drop still holds under the present conditions in the grain with high electrical resistivity, while the other grain with low resistivity reorients to align its a-axis more parallel with the ones of its neighboring grains.A detailed study of dislocation densities and subgrain boundaries suggests that grain rotation in β-Sn, unlike grain rotation in high melting temperature metals which undergo displacive deformation, is accomplished via diffusional process mainly, due to the high homologous temperature.

View Article: PubMed Central - PubMed

Affiliation: Center for Advancing Materials Performance from the Nanoscale (CAMP-Nano), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 China.

ABSTRACT
Here we report an in situ study of the early stage of microstructure evolution induced by electromigration in a Pb-free β-Sn based solder joint by synchrotron polychromatic X-ray microdiffraction. With this technique, crystal orientation evolution is monitored at intragranular levels with high spatial and angular resolution. During the entire experiment, no crystal growth is detected, and rigid grain rotation is observed only in the two grains within the current crowding region, where high density and divergence of electric current occur. Theoretical calculation indicates that the trend of electrical resistance drop still holds under the present conditions in the grain with high electrical resistivity, while the other grain with low resistivity reorients to align its a-axis more parallel with the ones of its neighboring grains. A detailed study of dislocation densities and subgrain boundaries suggests that grain rotation in β-Sn, unlike grain rotation in high melting temperature metals which undergo displacive deformation, is accomplished via diffusional process mainly, due to the high homologous temperature.

No MeSH data available.


Related in: MedlinePlus