Hard Gold Plating for Electronics Applications from a Non-Cyanide BathEPA Contract Number: EPD15028
Title: Hard Gold Plating for Electronics Applications from a Non-Cyanide Bath
Investigators: Garich, Holly
Small Business: Faraday Technology, Inc.
EPA Contact: Manager, SBIR Program
Project Period: September 1, 2015 through February 29, 2016
Project Amount: $100,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2015) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Manufacturing
The proposed program addresses the need for a commercialized process to efficiently deposit a hard gold coating from a non-cyanide bath for electronics applications that also does not contain nickel or cobalt. Seventy percent of industrial gold use is in the deposition of gold coatings for electronics applications. Most of the electrodeposited gold is used to provide electrical contact surfaces with good corrosion and wear resistance, hardness, and low contact resistance on printed circuit boards and connectors, so-called “hard” gold. Acid gold cyanide baths are able to achieve the required high hardness levels, high wear resistance, and low electrical contact resistance of the gold deposit due to the incorporation of small amounts of additives, such as nickel and cobalt, in the bath. Although the deposit has the required functional properties, the method for obtaining that deposit is undesirable. Although gold is not a threat to the environment, the cyanide used in the gold plating bath is very toxic and listed as one of 17 “high- priority” chemicals by the U.S. EPA. Furthermore, nickel and cobalt are on the European Community Registration, Evaluation, Authorization and Restriction of Chemical substances (REACH) lists. Therefore, it is environmentally desirable to find an alternative plating bath that does not contain cyanide, nickel or cobalt.
This Phase I project will demonstrate the feasibility of a cost-effective, fast, efficient process for hard gold plating for electronics applications, from a non-toxic, cyanide-free bath that does not contain nickel or cobalt. Coating properties, such as hardness, wear resistance and electrical contact resistance, will be evaluated and compared with properties of deposits from state-of-the-art cyanide baths as well as DC sulfite baths. Ideally, the FARADAYIC® gold sulfite plating process will be a drop-in replacement for acid gold cyanide plating. The only changes to current practice will be the change in chemistry and the purchase of a rectifier capable of delivering a FARADAYIC® waveform. Faraday has engaged two commercial partners, one printed circuit board manufacturer who intends to implement the process in their plants, and a chemistry vendor that has existing bulk formulation capabilities and marketing and distribution channels to drive the technology throughout the electronics market, as well as other applications.
The proposed program addresses the need for a commercialized process to efficiently deposit a hard gold coating from a non-cyanide bath for electronics applications that also does not contain nickel or cobalt. Acid gold cyanide baths are able to achieve the required high hardness levels, high wear resistance and low electrical contact resistance of the gold deposit, due to the incorporation of small amounts of additives, such as nickel and cobalt, in the bath. The cyanide used in the gold plating bath is very toxic and listed as one of 17 “high-priority” chemicals by the U.S. EPA. The wastewater limits for total cyanide under EPA’s Metal Finishing Regulations are 1.3 ppm for any single day and 0.28 ppm as a monthly average. Furthermore, nickel and cobalt are on the European Community Registration, Evaluation, Authorization and Restriction of Chemical substances (REACH) lists. Therefore, it is environmentally desirable to find an alternative plating bath that does not contain cyanide, nickel or cobalt.
Seventy percent of industrial gold use is in the deposition of gold coatings for electronics applications. Most of the electrodeposited gold is used to provide electrical contact surfaces with good corrosion and wear resistance, hardness, and low contact resistance on printed circuit boards and connectors – so-called “hard” gold. For example, a touch telephone in the home typically contains 33 gold-plated contacts. Soft gold is used in semiconductor applications, for example, for die bonding, and must be of high purity. Gold is also used in the decorative plating market for jewelry, watch cases, pens, eyeglasses, wire wheels, and bathroom fixtures. This demand represents approximately ninety tons per year. To Faraday’s knowledge, there is no commercially implemented cyanide-free hard gold plating process. We have engaged two commercial partners who are leaders in the printed circuit board and electroplating chemistry industries, and who believe sufficiently in the concept to commit time and in-kind resources to support this proposed effort. The first market entry point will be to validate the technology in conjunction with Faraday’s partner in the printed circuit board industry, first with an alpha scale pilot facility at Faraday, and subsequently with a beta-scale demonstration at Faraday’s partner’s facility. Faraday’s other commercial partner, a global vendor of plating chemistry, will provide the required plating bath. This level of manufacturing validation is absolutely essential to attract the attention and interest from the electronics industry’s well-entrenched distribution channel, i.e., the chemistry and equipment integrators, who have substantial market in-roads to the printed circuit board, chip-scale package, semiconductor, and decorative metal finishing market segments.
The proposed effort seeks to utilize a non-toxic sulfite-based plating bath typically used for soft gold applications, and by introduction of FARADAYIC® Electrodeposition principles of pulse and pulse reverse process mediation, develop a fast, efficient, non-toxic hard gold plating process that achieves the required functional deposit properties. The FARADAYIC® Electrodeposition approach utilizes an asymmetrical waveform to control the deposition process directly at the substrate/bath interface, i.e., electric field mediation of the process, rather than chemical mediation. Optimization of the waveform parameters enables enhanced performance in environmentally benign chemistries, as the electric field control at the interface controls the deposition processes that require toxic chemistries in conventional DC processes. Compared to DC plating from an alkaline gold sulfite bath, the FARADAYIC® Electrodeposition process will:
- achieve or preferably exceed the same high plating rates as acid gold cyanide baths (in an analogous technology for Trivalent Chromium plating, we have achieved up to 5x higher plating/throughput rates as compared to conventional hexavalent chromium plating);
- improve the current efficiency compared to the acid gold cyanide bath;
- reduce the grain size, by favoring grain nucleation over grain growth, thereby increasing hardness and wear resistance and eliminating the need for nickel and cobalt;
- improve bath life by operating in an acidic pH range; and
- run in a pH range which is compatible with photoresists used in printed circuit board fabrication.
If these functional properties and performance metrics can be achieved, gold sulfite could be substituted for hard acid gold cyanide baths, resulting in a substantial environmental benefit, as well as a cost benefit associated with reduced air, water and waste treatment requirements.
The FARADAYIC® Electrodeposition process for cyanide-free plating processes for hard gold plating not only will have a strong environmental benefit from the elimination of cyanide, nickel and cobalt, but Faraday anticipates an increase in the plating rate and current efficiency of the plating process. Faraday has observed such increases in an analogous process, deposition of hard chrome from an environmentally benign trivalent chromium bath, where the company observed a 5x increase in plating rate. Compared to currently used gold plating from toxic cyanide baths, Faraday’s proposed process will (1) reduce waste disposal cost, (2) reduce ventilation cost and (3) improve working conditions. Since cyanide-containing sludge is considered a hazardous waste, sludge transportation and disposal costs will be greatly reduced if gold is plated from a non-cyanide bath. Ventilation cost will be reduced and working conditions will be improved because exposure limits will be greatly relaxed.