Commercial process for electroplating nickel-phosphorus coatings

Abstract

An aqueous bath for electroplating NiP coatings is provided comprising, generally, a solution containing nickel salts, either a mixture of nickel sulfate and nickel chloride or an all nickel chloride source, sodium hypophosphite and boric acid. Thiourea is added to an all chloride bath solution for decorative applications or other applications requiring enhanced brightness. Upon dissolution of the bath constituents, the bath pH is adjusted up to a value of 3.5 to 4.5 with sodium hydroxide and maintained for at least 15 minutes at or above room temperature, preferably in the range of 40° to 50° C., then the bath pH is reduced to the bath operating range of 2.0 to 3.0, preferably 2.2 to 2.6. Maintaining the elevated solution pH prior to electroplating a substrate prevents the oxidation of the hypophosphite anions and ensures long-term utilization of the bath.

Description

[0001] Not Applicable[0002] The present invention relates to a bath for electroplating nickel-phosphorus coatings onto substrates and, more specifically, to the pretreatment of the bath for improved bath stability, extended bath life and improved nickel cation-complex formation.[0003] Nickel-phosphorus (NiP) coatings exhibit good corrosion and wear resistance. Many tools are coated with NiP because of the coating's hardness compared to pure nickel coatings. Additional uses are found in catalysis, electrical applications, corrosion protection applications and decorative applications. There are several methods for producing NiP coatings, including rapid quenching of a NiP melt and vapor deposition.[0004] The most widely used commercial method for plating NiP is through electroless deposition, which uses a hypophosphite anion as a reducing agent in the plating solution. The hypophosphite is reduced to elemental phosphorus during the deposition of nickel and is occluded in the nickel co...

AI Technical Summary

Benefits of technology

0019] Accordingly, an aqueous bath for electroplating NiP coatings is provided comprising, generally, a solution containing nickel salts, either a mixture of nickel sulfate and nickel chloride or an all nickel chloride source, sodium hypophosphite and boric acid. Thiourea is added to an all chloride bath solution for decorative applications or other applications requiring enhanced brightness. Upon dissolution of the bath constituents, the bath pH is adjusted up to a value of 3.5 to 4.5 with sodium hydroxide and maintained for at least 15 minutes at or above room temperature, preferably in the range of 40.degree. to 50.degree. C., then the bath pH is reduced to the bath operating range of 2.0 to 3.0, preferably 2.2 to 2.6. Maintaining the elevated solution pH prior to electroplating a s...

Problems solved by technology

However, electroless plating also has several disadvantages including the following: (a) poor utilization of chemicals used in the bath resulting in higher material costs (5 to 10 times the costs of electrolytic reduction); (b) slow deposition rates (generally less than 25 microns, or approximately 1 mil, per hour); (c) limited coating thickness (generally below 100 microns, or approximately 4 mils) due to roughening; and (d) relatively short bath life requiring treatment and disposal of large volumes of spent bath solution.

However, the primary obstacle to commercializing an electrolytic plating process has been poor bath stability.

Instability results in reduced bath life, which in turn increases material costs, increases treatment and disposal costs and generally upsets the electroplating process.

An excessive amount of chloride increases the corrosivity of the solution and the internal stress of the deposit.

One ...