Effects of Sn Anisotropy and Ag Addition on Electromigration
Date Issued
2012
Date
2012
Author(s)
Huang, Ting-Chia
Abstract
Two main topics were discussed in this thesis, including the effect of Ag addition and the Sn grain orientation on the electromigration. The line-type solder joints were designed for the electromigration test in both topics in order to exclude some additional concerns that sometimes disturbed the direct explanation of the electromigration phenomenon, including the thermomigration and the current crowding.
Referring to some previous studies, the studies of the Ag addition largely focused on the mechanical properties and the solification of Ag3Sn. Though the SnAg and SnAgCu solder were acknowledged as one of the most promising candidates in lead-free solders, nearly no studies had discussed about the effect of Ag addition on the electromigration. In this thesis, the Cu/Sn1.2Ag/Cu, Cu/Sn4.0Ag/Cu and Ni/Sn3.0Ag/Ni solder joints were used for discussing the effect of Ag addition on electromigration, especially focusing on the dissolution phenomenon at the cathode interface. With the observation with the scanning ion microscopes (SIM) and the kinetic calculation, we concluded that the Ag3Sn would be competent to repress the grain boundary diffusion through the IMC that once prevailed in the systems without Ag addition. Base on this assumption, the difference of the cathode dissolution morphology between the solder joints that with and without Ag addition was well explained. Besides, the shielding effect in which the Ag3Sn could prevent the underlying IMC from stress-induced dissolution also provided a possible method to suppress the serious metallization consumption in electromigration.
Another topic was related to the Sn grain orientation, and the electron backscattered diffraction (EBSD) was utilized to observe this phenomenon. With the trend of miniaturization of the microelectronic devices, many studies had found that a single solder joint would tend to be simply composed with several large Sn grains, and thus the grain orientation of these Sn grains would highly decide the behavior of electromigration. In this thesis, a unique Sn texture in the Ni/Sn/Ni solder joints was available and shown that some specific Sn grain orientations could not only intensify the dissolution at the cathode but also obstruct the diffusion flux, deciding the location of the IMC precipitation. Additionally, larger Sn grains without unique texture were also achieved by adjusting the manufacturing parameters. In this case, the Sn grains seemed to decide the degrading behavior of the cathode interface that was bordered on them. Striking results had been observed that, a dramatically differential dissolution rate appeared in a 200 micron -wideness solder joint with a uniform current density could simply caused by the the Sn grain orientation. Besides, a strong correlation between the Sn grains and the accumulation of the IMC at the anode interface also suggested that the diffusion flux would get along the c-axis of the Sn grain rather than the direction of the electron flow. With this thesis, the behavior of the electromigration related to the Sn grain orientation was further understood and also provided a strong evidence for the importance of the effect of the Sn grain orientation on electromigration.
Subjects
Sn anisotropy
Ag addition
electromigration
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
index.html
Size
23.49 KB
Format
HTML
Checksum
(MD5):16662e7a313a0fab8836b19efe790a7a