The effect of Re addition on the thermal stability and structure of Ni–P electroless coatings

Highlights: • Addition of Re allowed to obtain coatings with higher crystallization temperature. • The thermal stability of the coatings is mostly determined by phosphorus content. • Shift of Ni peak in XRD spectra indicate that Re localizes within Ni crystal lattice. • In-situ heating in TEM confirmed the crystallization of the Ni₅P₄ and Ni₃P phases. The electroless plated nickel (Ni–P) coatings are widely applied in the electronics industry. Addition of a third element, such as Re, to the coatings may improve their thermal stability, their resistance to thermal cycling, and finally, the properties of the soldered interconnections. The paper aims at investigating the properties of newly formulated Ni–P-Re coatings compared to conventional Ni–P ones. Characterization results obtained by X-ray diffraction, calorimetric measurements and in-situ heating conducted in TEM are presented and discussed in terms of the relative content of Ni, P and Re in the coatings and the deposition mechanism. While the structural changes and the crystalline/amorphous structure are determined solely by the P content for both the type of coatings, heating treatments demonstrated that the crystallization of Ni₃P is preceded by the Ni₅P₄ phase in the Re containing coatings. Moreover, the thermal stability, which is limited by the crystallization of Ni₃P and influenced by the P content, resulted to be improved for the Ni–P-Re coatings suggesting for a potential application of the new coatings