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Hypophosphite as a Brightener for Gold Electrodeposits

IP.com Disclosure Number: IPCOM000084355D
Original Publication Date: 1975-Oct-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Horkans, WJ: AUTHOR [+2]

Abstract

Sulfite-based gold plating baths are preferable to cyanide-based baths, due to the toxicity hazards of the latter. However, sulfite baths without additives give deposits of a dull brown appearance. The quality of the electroplate is generally improved by the addition of a brightener which, for the case of sulfite-gold baths, is generally an inorganic compound. Undesirable results of using brighteners are that they are included in the deposit, increasing its resistivity, and that some brighteners are toxic.

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Hypophosphite as a Brightener for Gold Electrodeposits

Sulfite-based gold plating baths are preferable to cyanide-based baths, due to the toxicity hazards of the latter. However, sulfite baths without additives give deposits of a dull brown appearance. The quality of the electroplate is generally improved by the addition of a brightener which, for the case of sulfite-gold baths, is generally an inorganic compound. Undesirable results of using brighteners are that they are included in the deposit, increasing its resistivity, and that some brighteners are toxic.

Hypophosphite (H(2)PO/-/(2)) salts can be used as brighteners in goldsulfite baths. Since these baths often contain phosphorus compounds, use of H(2)PO/- /(2) as a brightener has the advantage of not introducing additional chemical elements into the solution. It is not highly toxic, rare, or expensive.

A typical example of plating conditions yielding good deposit properties is: Variable Typical Value Range Au (I) about 0.1M any value > = 0.05M H(2)PO(2) 10/-2/M 10/-3/ M to > 0.1M pH
8.5 8 to > 13 Current densitg 1 ma/cm/2/ = 1-5 ma/cm/2/ Temperature room temperature = 20 degrees -70 degree.

The bath may be either still or agitated, with a lower concentration of hypophosphite necessary to cause the same degree of brightening in an agitated bath. Lower concentrations of hypophosphite should also be necessary as the temperature is raised.

Under these conditions, the deposit has a resistivity of about 3.2 mu om...