Effect of Heat-Treatment on the Structure and Resistivity of Electroless Ni-W-P Alloy Films

An electroless plating bath for amorphous Ni-W-P alloy films was developed and their heat change properties were investigated from the viewpoint of W codeposition effect. The alloy films kept amorphous state with increasing W content even though the P content decreased. Moreover, the films became more amorphous, and their thermal stability increased with an increase of W content in the deposit. The tungsten content was varied from 0 to 20.8 weight percent (w/o) with a decrease in P content from 14.0 to 6.2 w/o by increasing the Na₂WO₄concentration in the bath. Two characteristic heat change behaviors were observed in the Ni-W-P alloy films. One was the formation of metastable phase in spite of low P content. The other was direct formation of Ni-W alloy phase. The tungsten codeposition increased the thermal stability of amorphous Ni-W-P alloy films plated from the baths with higher Na₂WO4 concentration by suppressing the Ni crystallization prior to the Ni₃P compound formation. The thermal changes of resistivity strongly depended on the crystallization of the Ni₃P compound and Ni alloy phase. Both crystallization reactions were controlled by the P and W contents in the deposits.