Electroplating of nickel-iron alloys for uniformity of nickel/iron ratio

Abstract

Electroplating nickel-iron alloys onto objects having complex topographical shapes with projections and hollows such as upper pole pieces of thin film magnetic recording heads has been found to yield a substantial variation in nickel-iron alloy composition from point to point within a single pattern. Providing a low total dischargeable ion concentration in the bath is helpful to reduce such variations when plating in the 80:20 Ni:Fe alloy range. That is, it is desirable to use a low value of Fe.sup.++ and Ni.sup.++ ion concentrations and a relatively low current density to operate at the relatively flat peak of the curve of the iron percentage in the plated alloy vs. current density curve. The curve can be raised or lowered by increasing or decreasing the total dischargeable ion concentration respectively for a given Ni.sup.++ /Fe.sup.++ ion ratio. The preferred Fe.sup.++ ion concentration range for Ni:Fe alloy ratio near 80:20 is about 0.15-0.3 g/l for a range of 10-14 g/l of Ni.sup.++ ion in a solution with a pH of about 3, a temperature of about 20.degree.-35.degree. C. where the Ni.sup.++ /Fe.sup.++ ratio in the solution ranges from about 45 to 1 to about 70 to 1. Preferably, an electrolyte for reducing pitting such as 0-100 g/l of NaCl is employed. The cation (Na.sup.+) of the latter electrolyte should not be a dischargeable ion. Plating current density is preferably between about 2 ma/cm.sup.2 and 12 ma/cm.sup.2, and optimum results are achieved for values from about 4 to 8 ma/cm.sup.2.