Wetting behavior of eutectic Au-Sn solder on Ni/Au metallization at different temperatures

Au-Sn solder is a high reliable lead-free solder with excellent oxidation resistance which is commonly used in fluxless soldering. In this paper, the wetting behavior of eutectic Au-Sn solder on Ni/Au metallization was studied by the usage of in situ observation of the wetting process of the solder. The results showed that the spreading area of the solder grew and the spreading time decreased with the increase of temperature. The rapid dissolution of Au layer into Au-Sn solder made the content of Au in the contact line (CL) region to reach saturation. The interfacial reaction products precipitated in the CL region impeded the spreading of the solder. As a result, the maximum spreading area was reached in a short time, indicating the high dimensional stability of the molten solder spreading on the substrate. (Au, Ni)(3)Sn-2 formed between Au5Sn layer and Ni layer was founded in the contact line region during the interfacial reaction after the spreading of the solder tended to a halt.