Cu/Ni/Au multilayers by electrochemistry: A crucial system in electronics A critical review

Cu/Ni(Ni-P)/Au systems are extensively used to serve as electrical contacts due to their exceptional combination of excellent electrical conductivity, corrosion resistance, and mechanical behavior. Cu has a unique electrical conductivity that made it the most used metal in electronics. However, protective coatings must be applied on Cu due to its poor corrosion resistance. Au films are widely used to secure a proper lifetime of electrical contacts. Ni barrier films are also essential to avoid the diffusion of Cu into the Au deposits that deteriorate the desired properties of noble metal films. The main aspects for improving these systems are the corrosion and wear resistance, the electrical conductivity, lowering the surface roughness and designing a morphology with hemispherical features. In this review, recent studies about the deposition of different Ni films, including Ni alloys and Ni composites, noble metal films, and possible post-treatments to optimize the performance of multi-layer films are presented with special attention to the above-mentioned criteria.