Investigation of the dynamic reactive wetting of Sn-Ag-Cu solder alloys on Ni(P)/Au coated Cu substrates

In the electronic components and device packaging process, the Cu conductor surface is generally coated with Au and Ni. The Au coating is applied to prevent the oxidation of the Cu surface and enhance the solderability, while the Ni coating is applied as a diffusion barrier between the solder alloy and the Cu substrate, in order to restrict the formation and growth of intermetallic compounds. The dynamic reactive wetting characteristics of Sn-Ag-Cu alloys are related to the properties of the coating materials. In the present study, the dynamic reactive wetting behavior of Sn-Ag-Cu alloys on Cu substrates coated with Ni and Au was firstly investigated on millisecond scale. On the bare Cu surface, the metal droplet rebounded several times due to the poor wettability and started to spread from 1 s and became equilibrated by 20 s, whereas on the Ni/Au coated surface, the metal droplet settled down without rebounding because of the good wettability, which caused it to react instantaneously, and became equilibrated by 1 s.