Synthesis, composition, morphology, and wettability of electroless Ni-Fe-P coatings with varying microstructures

Thermal stability and wettability are important properties for under bump metalization (UBM) in electronic devices. This study aims at preparing the Ni-Fe-P coatings with varying microstructures and investigating the e ffects of microstructures on their properties including surface morphology, roughness, chemical bonding and wettability. The microstructure of the Ni-Fe-P coatings was mainly controlled by their Fe content. The crystal-linity of these coatings continuously increased to 100% when the Fe content reached 12 wt.%, while they exhibited amorphous structure with a Fe content of below 9 wt.%. The wettability order of these coatings are amorphous, crystalline and mixed structure from the best to the worst, which is mainly due to their surface roughness. Moreover, the Fe addition in the Ni-P coatings can promote their thermal stability, showing a good potential as UBMs at elevated temperature. In a temperature range of 340 degrees C-480 degrees C, the amorphous Ni-Fe-P coatings gradually transformed into Ni3P, FeNi3 and slight Ni phases.