The Study of Dissolution of Bi Precipitates in Sn Using A Novel In Situ Heating Technique in the SEMAuthors: Peter Banh, André M. Delhaise, Doug D. Perovic
Company: University of Toronto and Celestica Inc.
Date Published: 6/5/2018 Conference: ICSR (Soldering and Reliability)
This paper details a study to understand the kinetics of Bi particle dissolution using a novel in situ heating technique in the scanning electron microscope (SEM). Three Sn-Bi samples with 3% Bi, 6% Bi, and 9% (all wt%) Bi were heated at 90°C in the SEM to determine the effects of Bi concentration on dissolution. Three Sn-Bi samples with 6 wt% Bi were subjected to different aging conditions (1 day, 3 days, and 7 days, all at 100°C) to determine the effects of aging on dissolution. Another four Sn-Bi samples with 6 wt% Bi were subjected to different aging conditions (as-cast, 1 day, 3 days, and 7 days, all at 100°C) but heated in the SEM at 65°C to determine the effects of temperature on Bi dissolution. SEM images of the samples were taken periodically, and the area of the Bi over time was analyzed.
It is proposed that the area of Bi precipitates in the field of view when heated could be modeled with either one exponential term or two exponential terms. Each of these terms are hypothesized to be a mode of dissolution. The parameters used in the modes are influenced by the aging condition, concentration, and the in situ heating temperature. When modeled by one exponential term, the dissolution is dominated by a dissolution mode in an unsaturated solid solution. When modeled by two exponential terms, the dissolution is dominated by an unsaturated dissolution mode initially, but transitions into a saturated dissolution mode after.
Using the proposed models, it was found that increasing the concentration of Bi slows the dissolution rate, and changes the dissolution behaviour from one mode to two modes. Increasing the time the sample spent aging increases the dissolution rate and changes the dissolution behaviour from two modes to one. Lastly, it was found that a lower in situ heating temperature will slow down the dissolution rate significantly.
in situ heating, dissolution, aging, SEM, Bismuth
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