In situ scanning electron microscopy study of eutectic SnPb and pure Sn wetting on Au/Cu/Cr multilayered thin films

Abstract

Wetting behavior of eutectic SnPb and pure Sn on Au(500 Å)/Cu(1 μm)/Cr(800 Å) layered thin films were monitored in situ in a ramping temperature profile using a scanning electron microscope (SEM) with a vacuum of 10−5–10−6 Torr. We found that the wetting behavior of these two solders in SEM was dramatically different from their behavior in RMA soldering flux; a smaller wetting angle and rough wetting front morphology were observed. Very surprisingly, no dewetting could be observed inside the SEM chamber, yet dewetting happened to the same sample when it was removed from the SEM and immersed in RMA soldering flux. We estimate the interfacial energy between liquid Sn and solid Cr and assume the reduction of surface and interfacial energies caused by possible oxidation of Cr and liquid Sn surface in the SEM in order to explain the above-mentioned wetting and dewetting behaviors.