Anisotropic growth of electroless nickel‑phosphorus plating on fine sliver lines for L-shape terminal electrode structure of chip inductor

Abstract The micron-size anisotropic growth of electroless nickel‑phosphorus plating was realized on the fine sliver lines with the width of ≤15 μm. Growth of nickel‑phosphorus alloy occurred preferentially in the width direction at a growth rate approximately twice than that in the thickness direction during electroless plating in a bath with periodical positive and negative rotation. The growth rate in the width direction reaches 15–18 μm in 30 min. The dominant nickel‑phosphorus growth in the width direction is attributed to the enhancement of mass transfer rate for solution at the edge of silver lines or nickel‑phosphorus layer, as a result of the better wettability of ceramic than Pd-activated silver and nickel‑phosphorus layer. The suppression of lead acetate at the layer edge is enhanced by nonlinear diffusion instead of wettability difference. A possible mechanism for the formation of nickel‑phosphorus layer morphology as functions of mass transfer and lead distribution was proposed to explain the growth behavior of anisotropic electroless nickel‑phosphorus plating. Furthermore, this anisotropic electroless nickel‑phosphorus plating process was employed to form a novel L-shape terminal electrode structure of chip inductor.