Effect of the thickness of Au layer in Au/Ni-Co/W metallization stack on the microstructures and wetting quality of Sn-Pb alloy solder

Thin film metallization is an essential procedure to attach the metal structures to the ceramic base material in the hybrid microcircuits, considering that the molten solder alloy cannot wet and spread fully directly on ceramics. Thus, the quality of metallization stack may have great influence on solder interconnection and the joint reliability. This study focuses on a typical de-wetting case to figure out the effect of thickness of Au layer of the Au/Ni-Co/W metallization stack on the microstructures and wetting quality of Sn-Pb alloy solder. Two different thickness of Au coating layer (namely 0.8 μm and 2.5 μm) of Au/Ni-Co/W metallization stack were selected as the objects, and the surface morphologies and cross section of the metallization stack were observed via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A strong correlation between the micro structure and the Au thickness was found, a more serious tungsten immigration with a thinner Au layer. And the de-wetting of thinner Au layer in the Au/Ni-Co/W metallization was attributed to the combined effects of immigration of tungsten and the oxidation of nickel.