Influence of surface segregation on wetting of liquid metal alloys

Abstract

Wetting of transition-metal boride and arsenide liquid metal alloys (Ni5sB,5, Pd72B28, Pt72B28, Pd2As) is strongly influenced by surface segregation of low-level bulk impurities in the alloys. At melting, the impurities segregate to the liquid surface and inhibit wetting, resulting in a poorly wetted drop of alloy. Good wetting is achieved by introducing materials into the contact system with high chemical affinity to the major segregants. The materials suppress the impurity segregation by tying up the impurities as solid phases during liquefaction.

Wetting of carbide ceramics (B4C, SiC, TiC and ZrC) by molten Ni at 1753 K

“…A decreasing of apparent volume in the first dozen seconds shows the effect of dissolution on wetting. The densities of these ceramics were less than molten Ni (even was alloyed by the elements from the substrate, e.g., density of Ni 50 B 50 is 7.2 g·cm -3 [20] which is close to Ni). Therefore, ceramics with low density dissolved into molten metal and did not expand the volume of liquid so much, and then would leave a large space in solid side that needs liquid to fill up.…”

“…In Ni/B 4 C system, the density of B 4 C (~ 2.45 g·cm -3 ) is much smaller than molten Ni, even if Ni 50 B 50 (~ 7.2 g·cm -3 [20]). When B 4 C dissolved into molten metal, the formed crater was filled by liquid with high density.…”

“…Therefore, reaction product control (RPC) model was also considered for the analysis of spreading. RPC model, has two forms, one the velocity for the moving of the triple line is almost constant, and another is described as following which the too strict requirement of "linear spreading" is removed, (20) where k r is a kinetic constant in s −1 . We assumed that the volume of droplet kept constant, and then Equ.…”

Influence of Surface Segregation on Wetting of Sn-Ag-Cu (SAC) Series and Pb-Containing Solder Alloys

“…16 Process engineers who deal with solderability, adhesion, and assembly issues should be aware that segregated impurities (rather than solely native oxides) may be the root cause of poor wetting and adhesion. The existence of surface segregation in molten liquids further calls into question many previous studies of wetting that were conducted blind without the advantage of surface analytical tools such as Auger spectroscopy.…”

Real-time scanning electron microscopy and auger spectroscopy of wetting in Sn-3.3Ag-4.8Bi solder paste wetted to Ni-Au

“…Second, despite the fact that the static balance of surface tensions at the interface critically influences wetting and spreading, there have been few studies of solder wetting using surface analytical techniques. 7,8 We have rectified this shortcoming by extensively employing Auger spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) techniques to examine the leading edge of the wetting front and the liquid alloy surface. Observation of the expanding wetting front and wetting of single solder balls provide a unique opportunity to study the initial surface chemical reactions between alloy and substrate.…”