A significant blocking effect of Ni plating layer on the diffusion of Zn element of brass substrate

With the development of space electronic products, spacecraft electronic devices tend to diversify and the structures become complicated gradually. In addition, the tight expense control of electronic products promotes the localization of devices, In which a variety of domestic devices have been used. The brass(Cu-Zn alloy) pins plated with gold(Au) and tin lead(SnPb) layers have poor solderability and frequent quality problems after a period of storage. By comparison, the main difference between the domestic device and the imported device is the plating layer structure. In this study, 3 kinds of samples are used. By SEM(Scanning Electron Microscope), EDS(Energy Dispersive Spectrometer) and XPS(X-ray Photoelectron Spectroscopy) tests, it was found that the sample with nickel(Ni) plating layer and the copper(Cu) plating layer had the best wettability between the pin and the solder, and the relative content of Zinc(Zn) diffused from the brass in the Au plating layer was below 5%, which was lower than that in the sample with neither Ni plating layer nor Cu plating layer, about 10%. The formation of Zinc oxide(ZnO) on the surface of unplated sample was also confirmed. The conclusion is that the Ni plating layer and the Cu plating layer played a role of the barrier layer, which effectively prevented the diffusion of zinc from brass to the plating layer and the surface oxidation, which resulted in the nonwetting behavior between pins and Pb₃₇Sn₆₃ solder.