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Mechanism of Fillet Lifting in Sn-Bi Alloys



William J. Boettinger, C A. Handwerker, B Newbury, TG Y. Pan, J M. Nicholson


The probability of fillet lifting in through-hole solder joints was determined for a series of seven binary Sn-Bi solders with compositions between 2.6 and 65 mass percent Bi. A 20 pin ceramic dual inline package was soldered to printed wiring boards with three thicknesses and two pad sizes. A laboratory scale drag soldering process designed to simulate wave soldering was employed. Composition has the largest effect on failure with a peak in lift-off probability near 8 mass percent Bi. The presence of intermetallic needles of Cu(sub6)Sn(Sub5) attached to the pad side of the separation surface, but pulled from solder side indicate that fillet lifting occurs during solidification. This conclusion is further supported by real time observation of fillet lifting. The solidification of these alloys is analyzed using a Scheil analysis and the tendency for fillet lifting is related o a hot tearing criterion originally developed for castings.
Journal of Electronic Materials
No. 5


Fillet Lifting, Pb-free, Solder, Solidification


Boettinger, W. , Handwerker, C. , Newbury, B. , Pan, T. and Nicholson, J. (2002), Mechanism of Fillet Lifting in Sn-Bi Alloys, Journal of Electronic Materials (Accessed March 5, 2024)
Created May 1, 2002, Updated February 17, 2017