This experimental study is devoted to a phenomenological and quantitative investigation of the physics of spreading kinetics of eutectic lead solder systems (Pb-63Sn) over Cu 6 Sn 5 /Cu 3 Sn/Cu (IMC) substrates. The spreading kinetics was studied experimentally by using real-time in situ monitoring of the triple-line movement. Data gathering was facilitated by a hot-stage microscopy system under a controlled atmosphere. Three intermetallic surfaces with different heat treatment conditions were used for this investigation. Dramatically more pronounced spreading of Pb-63Sn on all intermetallic Cu 6 Sn 5 /Cu 3 Sn/Cu substrates compared with Cu substrates was observed, along with a much larger spreading area. Hence the physics/ chemistry of spreading over IMCs significantly differs from the spreading of the same system over a virgin Cu substrate. A power-law initial stage of spreading was confirmed, and the corresponding power-law exponents were determined as a function of substrate topography.
This study is devoted to a phenomenological and quantitative investigation of the physics of spreading of lead-free solder systems (Sn, Sn-0.7Cu, and Sn-3.5Ag) over Cu 6 Sn 5 /Cu 3 Sn/Cu substrates. Wetting kinetics was studied using real-time in situ monitoring of the triple-line kinetics under a controlled atmosphere. Three different intermetallic (IMC) substrates were used for this investigation. It was found that the grain size of the deposited IMC compound coating has a sizable influence on the triple-line movement of the liquid solders considered. More pronounced spreading of solders on IMC substrates was observed for all lead-free solders over an intermetallic with the smallest grain size. Lead-free solder spreading over IMC surfaces exposed to aging at elevated temperatures, hence featuring larger grain size, did not feature a significant improvement of wettability when compared with the behavior of the same solders on virgin copper substrates.
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