Thermal expansion coefficient analyses of electroless nickel with varying phosphorous concentrations

Electroless nickel-phosphorus (NiP) layers with different phosphorous concentrations were deposited using in-situ techniques for measurement and control of the plating process. To achieve a constant Ni-concentration and pH, we utilized a control system including photometric-, pH-sensors and a batch feeder. A decreasing pH value leads to increasing phosphorous concentrations. Furthermore, we devised a complexometric titration technique to analyze the chemical composition of electroless NiP and confirmed its accuracy by comparison to well-established gravimetric analysis. The coefficient of thermal expansion (CTE) at temperatures ranging from 86 K to 373 K of electroless NiP layers containing different phosphorous concentrations was analyzed using a push-rod dilatometer. Finally, we demonstrate that the CTE of electroless NiP is precisely adjustable via the deposition parameters of the electrolyte.