Electroless Cobalt Deposition from Acid Baths

Abstract

An acid electroless cobalt plating bath was developed which utilizes di‐methylamine borane (DMAB) as the reducing agent and which provides bright deposits at over 13 μm/hr at 70°C. The bath, slightly modified, is also usable at room temperature for deposition on palladium‐activated nonconductors. Additions of even small quantities of hypophosphite to the DMAB bath resulted in failure to achieve deposition; the effect of hypophosphite additions on the single electrode potentials was determined and the results discussed. Electroless cobalt‐boron deposits were found superior, in some respects, to electroless nickel‐phosphorus for providing protection for steel against corrosive attack. A double layer deposit of electroless nickel plus electroless cobalt topcoat provided more effective protection for steel than either deposit, alone, of the same total thickness. Chromating treatments were found effective for retarding the tendency for tarnishing of cobalt during salt exposure. The magnetic properties of some electroless cobalt‐boron deposits were determined; the coercivity was considerably lower than that of electroless cobalt‐phosphorus deposits.