Tin whiskers studied by synchrotron radiation scanning X-ray micro-diffraction

• Published in: Acta materialia Vol. 51; no. 20; pp. 6253 - 6261
• Main Authors: Choi, W.J., Lee, T.Y., Tu, K.N., Tamura, N., Celestre, R.S., MacDowell, A.A., Bong, Y.Y., Nguyen, Luu
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 08.12.2003; Elsevier Science
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Grain orientation; Metals. Metallurgy; Pb-free solder; Physics; Stress gradient; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Tin whisker; Whiskers and dendrites (growth, structure, and nonelectronic properties); X-ray micro-diffractions; X-ray micro-diffractions; Grain orientation; Tin whisker; Pb-free solder; Stress gradient; XRD; Experimental study; Solder; Stress distribution; Whiskers; Tin; Field gradients; Pole figures; Synchrotron radiation
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/S1359-6454(03)00448-8

A large number of Sn whiskers have been found on the Pb-free solder finish on leadframes used in consumer electronic products. Some of the whiskers on eutectic SnCu finishes are long enough to short the neighboring legs of the leadframe. Tin whisker growth is known to be a stress relief phenomenon. We have performed synchrotron radiation X-ray micro-diffraction analysis to measure the local stress level, the orientation of the grains in the finish around a whisker, and the growth direction of whiskers. The compressive stress in the solder finish is quite low, less than 10 MPa; nevertheless, there exists a stress gradient around the root of a whisker. From the orientation map and pole figure, we found that the growth direction of whiskers is [0 0 1] and there exists a preferred orientation of [3 2 1] grains on the solder finish. In one of the whisker analyzed, we found that the normal orientation of the grain just below the whisker is different; it is [2 1 0].