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MM: Fachverband Metall- und Materialphysik

MM 41: Interfaces II

MM 41.4: Vortrag

Donnerstag, 26. März 2009, 12:30–12:45, IFW D

Surface Tension andWetting in Solder Connections — •André Wedi and Guido Schmitz — Institut für Materialphysik,Westf.Wilhelms-Universität,Wilhelm- Klemm-Str. 10, 48149 Münster, Germany

Wetting is an important pre-requisite of a reliable solder connection. However, it is only an indirect measure for the important specific energy of the reactive interface between solder and base metallization. In order to quantify this energy, we measured wetting angles of solder drops as well as interface tensions between different SnPb solders and organic flux at a reflow temperature of 250^∘C. For the latter, we used the Lecomte-De-Noüy ring method applying suitable geometric corrections. From the two independent data sets, the important energy of the reactive interface is evaluated based on Young’s equation. Remarkably, although both, the tension between solder and flux and the wetting angle, reveal significant dependence on solder composition, the specific energy of the reactive interface remains almost constant in the range of 0 to 40 at% Pb. This indicates that the properties of the reactive interface are essentially controlled by the Cu₆Sn₅ intermetallic reaction product. Since this phase grows during reflow, the wetting angle should develop in time, but in our in-situ measurements of this angle no time dependence is seen. In the talk the consequences of this contradiction to existing models of reactive wetting are discussed.