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532 results on '"Tu, K.N."'

28. Preferred orientation relationship between Cu6Sn5 scallop-type grains and Cu substrate in reactions between molten Sn-based solders and Cu

Author

Suh, J. O., Tu, K.N., and Tamura, N.

Subjects
copper copper alloys, crystal orientation crystal structure integrated circuit interconnections tin alloys X-ray diffraction.
Abstract

A strong crystallographic orientation relationship between the Cu6Sn5 scallop-type grains and their Cu substrate has been found by synchrotron micro-X-ray diffraction study. Even though the crystal structures of Cu6Sn5 (monoclinic) and Cu (face-centered-cubic) are very different, angular distributions of crystallographic directions between Cu6Sn5 and Cu revealed a strong orientation relationship. Both SnPb solder and pure Sn showed the same result, indicating that this is general behavior between Sn-based solders and Cu. The strong orientation relation suggests that Cu6Sn5 forms prior to Cu3Sn in the wetting reactions. A total of six different orientation relationships were found. In all the cases, the [1 01] direction of Cu6Sn5 preferred to be parallel to the [110] direction of Cu with a misfit of 0.24percent. Due to pseudohexagonal structure of the Cu6Sn5 , the six relationships can be categorized into two groups. From the orientation distribution, one group was found to be less rigid then the other group. (18 References).

Published
2007

29. Structure and kinetics of Sn whisker growth on Pb-free solder finish

Author

Choi, W.J., Lee, T.Y., Tu, K.N., Tamura, N., Celestre, R.S., MacDowell, A.A., Bong, Y.Y., Nguyen, L., and Sheng, G.T.T.

Subjects
Materials science, advanced light source als
Abstract

Standard Leadframes used in surface mount technology are finished with a layer of eutectic SnPb for passivation and for enhancing solder wetting during reflow. When eutectic SnPb is replaced by Pb-free solder, especially the eutectic SnCu, a large number of Sn whiskers are found on the Pb-free finish. Some of the whiskers are long enough to become shorts between the neighboring legs of the leadframe. How to suppress their growth and how to perform accelerated test of Sn whisker growth are crucial reliability issues in the electronic packaging industry. In this paper, we report the study of spontaneous Sn whisker growth at room temperature on eutectic SnCu and pure Sn finishes. Both compressive stress and surface oxide on Sn are necessary conditions for whisker growth. Structure and stress analyses by using the micro-diffraction in synschrotron radiation are reported. Cross-sectional electron microscopy, with samples prepared by focused ion beam, are included.

Published
2002

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