Silva, Bismarck Luiz
Cante, Manuel V.
Spinelli, Jose E.
Total Authors: 6
 Fed Univ Sao Carlos UFSCar, Dept Mat Engn, BR-13565905 Sao Carlos, SP - Brazil
 Santa Cecilia Univ UNISANTA, Dept Mech Engn, BR-11045040 Santos, SP - Brazil
 Santa Cecilia Univ UNISANTA, Postgrad Program Mech Engn, BR-11045040 Santos, SP - Brazil
 Univ Estadual Campinas, UNICAMP, Dept Mfg & Mat Engn, BR-13083860 Campinas, SP - Brazil
Total Affiliations: 4
JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS;
Web of Science Citations:
Bi-Ag lead-free alloys are considered interesting alternatives to Pb-based traditional solders due to compatible melting point and strength. During soldering, the ability of a liquid alloy to flow or spread over the substrate is crucial for the formation of a metallic bond driven by the physicochemical properties of the liquid solder/solid substrate system. In addition, the wettability is intimately associated with the solder/substrate thermal conductance represented by a heat transfer coefficient, h(i). In this work, three Bi-Ag alloys (hypoeutectic-1.5 wt%Ag, eutectic-2.5 wt%Ag and hypereutectic-4.0 wt%Ag) were directionally solidified under upward unsteady state heat flow conditions. Both time-dependent h(i) profiles and wetting behavior represented by contact angles (theta) were determined for the three alloys examined. The dependence of theta on the alloy Ag content is assessed experimentally. Also, thermal readings collected during directional solidification of the Bi 1.5, 2.5 and 4.0 wt% Ag alloys are used with a view to permitting h(i) versus time (t) profiles to be computed. It is shown that along a first solidification stage (t < 16 s) the h(i) values followed the trend experimentally observed by the contact angles for the three alloys examined, while for t > 16 s the volumetric expansion of the Bi-rich phase is shown to have a dominant role inducing a sudden increase in h(i). For each alloy a couple of time-dependent h(i) expressions is needed to represent the entire solidification progress. (AU)