How black zinc nickel plating is bringing RoHS to military connectors

4 mins read

When the Reduction of Hazardous Substances (RoHS) Directive came into force in 2006, the intention was to remove, as far as possible, the use of six chemicals from products on the market.

However, one significant market was excluded from the requirements of the legislation: military. Even though military equipment remains exempt from RoHS, those building systems for use in the sector are finding that RoHS compliant devices are, in some cases, providing better performance than the legacy products. And that's the case with MIL-DTL 38999 circular connectors, where black zinc nickel coated parts are becoming increasingly popular. The six substances banned under RoHS are lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls and polybrominated diphenyl ether. In the case of connectors, cadmium is the problem. One of the leaders behind the move to black zinc nickel is Amphenol – something recognised by its appearance on the shortlist for Materials Application of the Year at the recent British Engineering Excellence Awards (BEEAs). In its BEEAs entry, Amphenol said: 'Since the RoHS Directive came into effect, there has been mounting pressure on manufacturers of electrical equipment to eliminate the use of six hazardous substances, even in markets such as defence and aerospace, which are technically exempt. 'Cadmium is highly toxic, carcinogenic and can cause cardiovascular and renal failure. The potential to cause harm is increased significantly when particles of fine cadmium dust are inhaled or ingested. This can happen when two cadmium plated surfaces wear against each other. The challenge for suppliers to the defence industry has been to find a plating finish which provides a suitable alternative to cadmium'. Black zinc nickel The solution has come in the form of black zinc nickel. Amphenol noted: 'Since 2011, our technical team has developed black zinc nickel as a true RoHS compliant alternative for use on connectors, backshells, caps and other accessories'. Connector manufacturer Souriau says that more than 50% of its 38999 connectors now come with an RoHS compliant plating, claiming this reinforces its position as a 'green leader' in the market. The company notes that it has more than a decade of experience with RoHS zinc nickel plating and says this is now considered a superior RoHS compliant alternative to cadmium by the mil/aero industry. Souriau has industrialised this plating for use with most of its MilAero connector lines, including the D38999, Series I, II and III, MIL-C-26482 Series I, VG96918, micro38999, caps and backshells. Traditionally, cadmium has been selected due to its excellent resistance to wear and corrosion and for its electrical conductivity. Whilst alternative coatings have been available, the challenge has been to get these coatings to the point where their all round performance matches that of cadmium. John Islam, connectors business development manager for Northern Europe with distributor TTI, said: "While the military market was exempt from RoHS, as new designs have become available, the attraction of being RoHS compliant has grown. More importantly, designers have seen the environmental and electrical performance of these more recent connectors is better than that of cadmium plated parts." Islam pointed to a 'definite advantage' of black zinc nickel parts over cadmium when it came to electrical characteristics. But he added: "Another key fact which is changing people's views is that black zinc nickel has a 500 hour salt spray performance, compared to the 200 hours from equivalent cadmium parts." But getting black zinc nickel parts to the point where they can outperform their cadmium equivalents has taken time. "In the early stages, the plating process wasn't as well defined as it is today," said Islam. Amphenol explained: 'There have been many iterations of the plating process over the last two years, with collaboration between engineering, plating, test house and chemistry experts moving the approach forward. 'From the initial installation of one trial tank, Amphenol now has two fully operational production lines'. Having developed the plating process, Amphenol then had to show the connectors met strict technical requirements. Amongst the tests, the connectors needed to show shell to shell continuity of beter than 2.5mV and 'resistance to indirect lightning strike', where a current of 10kA is passed through the device. Islam noted: "We can now state categorically that black zinc nickel plating is compatible with cadmium products, so designers can upgrade their systems. They can also use existing cadmium based connectors alongside black zinc nickel plated parts and get better performance." In this way, systems can feature connectors in which both halves are black zinc nickel plated or ones in which one half is black zinc nickel and the other is cadmium plated. In the latter case, there is no galvanic coupling. Legacy compatible In Souriau's opinion, RoHS zinc nickel is non reflective and can be used at high temperatures (up to 175°C) or with specific fluids, like deicing. It says this combination allows these parts to be used in a range of applications. For military applications, black zinc nickel is widely used because of its backwards compatibility with legacy cadmium parts. Souriau says black zinc nickel coated parts can be used with ruggedised pcs, electrical engines and weapon control boxes. For mil/aero, it adds, the benefit of using the plating is its compatibility with other finishes, such as passivated stainless steel or composite nickel. 'Its outstanding fluid resistance is an additional benefit when used together with actuator systems in unpressurised areas', it notes. So how common is the use of black zinc nickel? Islam said: "The target markets for these parts are aeronautical and ground military vehicles. Take up in these markets has been slow, but this has mainly been due to the economic environment; a lot of projects and new designs have been put on hold. "If companies are building new subsystems for these applications, they can design black zinc nickel connectors into the new system, but have the confidence that the system will work with existing cadmium parts. This is going to continue for quite a while yet." He added that 38999 is the main market opportunity at the moment, but noted that other circular connector variants are using the approach. Because of their growing popularity, black zinc nickel connectors are becoming more widely available. Islam said: "Souriau and Amphenol, for example, have full product lines, as does Deutsch. TTI is stocking military and non military parts from Souriau and non military parts from Amphenol, with military parts being added next year." Industry acceptance Defence contractors such as Selex and BAE Systems are becoming more amenable to black zinc nickel, said Islam, who added that Lockheed Martin was more advanced in its thinking. Amphenol says the final seal of approval for its black zinc nickel plating finish has been its successful qualification to MIL-DTL-38999 Series III Class Z, granted by the US Defense Logistics Agency in June 2013. What about the wider applications? Islam sees opportunities in electric vehicles and the broader industrial world. "Electric vehicles; certainly," he said, "but also mass transit and non automotive transportation – the rugged end of the market. Industrial is holding back at the moment, partly because of cost. But the plating is non magnetic and the connectors are good for 500 mating cycles," he concluded.