Influence of crystalline structure on diffusion barrier property of electroless Ni–Fe–P coatings in Zn–Al solder interconnects

Abstract

The rapid growth of interfacial Cu–Zn intermetallic compounds (IMCs) at Zn–Al/Cu solder interfaces significantly deteriorates their integrity due to the physical mismatch of interface materials. Thus, a robust interlayer to inhibit the interactions between solder and substrate at elevated temperature is urgently required. In this work, ternary Ni–Fe–P coatings with various crystalline structure were electroless plated on Cu substrates to investigate their interfacial reactions and diffusion barrier properties in Zn–Al solder interconnects. It was found that Ni–Fe–P coatings can significantly suppress the growth of interfacial IMCs in Zn–Al solder interconnects during liquid-solid reaction. Moreover, crystalline structure of Ni–Fe–P coatings played a vital role in the interfacial reactions and microstructural evolutions at the Zn–Al/Ni–Fe–P interfaces. The Ni–Fe–P coating with mixed structure (amorphous + crystalline) exhibited the best diffusion barrier properties among three types of the coatings for the thinnest and void-free Al3Ni2 layer, while crystalline Ni–Fe–P coating is the worst due to not only the rapidly growth of Al3Ni2 and Fe2Al5 phases but also the spalling phenomenon of Al3Ni2 particles.