Pure tin plating has been almost universally adopted, but the looming expiration of a critical exemption is poised to bite manufacturers of screw machined contacts. Bob Hult examines the continuing impact of RoHS.
Just when you thought the connector industry had bit the bullet and removed all lead from its products, the looming expiration of a critical exemption is poised to bite connector manufacturers that make screw machined contacts. Originally enacted in July of 2006 by the European Union, the Restriction of Hazardous Substances (RoHS) forced the electronics industry to remove lead from all solders and contact plating. After much hand wringing, and a few lingering technical concerns, pure tin plating has been almost universally adopted.
The vast majority of electrical contacts in use today are manufactured from thin strips of copper alloy using a stamp-and-form process. Pure copper, which features exceptionally low electrical resistance, cannot provide the necessary spring characteristics required to produce a reliable interface. Although they exhibit significantly lower conductivity, copper alloys such as beryllium copper and phosphor bronze provide the necessary spring features and have become the materials of choice. Using high-speed multi-station stamping dies, contacts can be economically formed into complex configurations that provide consistent normal forces over a wide range of operating temperatures.
An alternate manufacturing process utilizes precision screw machines to produce contacts that can conduct higher currents and higher levels of reliability. These multi-station machines are fully automated lathes that start with copper alloy wire at one end and produce singulated contacts with multiple profiles, slots, and apertures. A key advantage of screw machined contacts is their ability to utilize copper alloys that offer significantly higher conductivity. In order to avoid chipping of the wire during this forming process, a small amount of lead has been traditionally added to the wire alloy. Contacts that are used in military circular connectors are typically manufactured using the screw machine process.
When RoHS was enacted and lead was banned, the EU commission recognized that there was no readily available or economically viable alternative, so an exemption that allowed up to 4% lead by weight in screw machined copper stock was created. That exemption, known as RoHS II 6C, is set to expire on July 1, 2016. If the exemption is not renewed, wire used in screw machined contacts must meet the 0.1% or 1000 parts per million (ppm) maximum lead content standard after that date. Although all electrical contacts produced by the screw machine process will be impacted, the greatest concern revolves around power contacts that require exceptionally high conductivity to minimize resistive loss.
Electronic connector manufacturers have responded to the challenge in a variety of ways. Smaller suppliers that offer only stamped and formed contacts are unaffected. Large multi-national connector manufacturers may include a relatively small percentage of their products that use screw machined contacts. Discussions with representatives of several industry leaders indicated that the impact would be minimal and that, if necessary, they could begin to use proprietary lead-free copper wire that would add cost but provide a bridge until a more economical alternative can be found. One vendor sees this as an opportunity to create a competitive advantage by selling contacts using a proprietary alloy. Manufacturers of military screw machined contacts would be unaffected as they are exempted from RoHS mandates.
The real hit will be to connector manufacturers that have specialized in offering commercial screw machined contacts. Suppliers in this segment have focused their product lines on power and heavy duty contacts that make extensive use of screw machined contacts. If the exemption is not renewed, the impact could be significant. At least one supplier has chosen to assume that the exemption will not be extended and is currently testing a series of lead-free copper alloys to find a suitable replacement that can be implemented if necessary.
Suppliers of copper alloys are also exhibiting a variety of responses. Although there are some machineable copper wire alloys that contain no lead, they are more expensive and exhibit relatively poor conductivity. Several material vendors stated they are actively working on developing new alloys that offer better performance, but there is no clear solution available today. Domestic suppliers primarily provide strip form products to the connector industry, so they see little impact. In some cases, sister divisions located in Europe manufacture copper wire alloys, and are actively lobbying the EU for an extension. A consortium of impacted organizations based in Europe submitted a formal request for extension in January 2015.
OEM customers want assurance that all components they utilize are in compliance regardless of the pending decision. Several computing equipment manufacturers have hired a consulting firm to analyze their entire bill of materials to determine which components contain leaded copper alloys. Indeed, a new industry focused on monitoring RoHS directives and compliance has sprung up over the past few years.
At this point, most players are counting on another five-year extension of the 6C exemption. The lack of a viable alternative material that offers electrical, mechanical, and cost characteristics similar to the current leaded alloys should be justification to grant a three- to five-year extension. The commission is expected to issue a decision by July 2015. The industry is now in a wait-and-hope/pray mode. If it is denied, current stocks of leaded copper alloy may become scrap, and a race to find an alternative material will heat up.
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