EU RoHS prohibits six groups of substances: lead, mercury, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenylethers are each prohibited above 0.1% by weight, and cadmium is prohibited above 0.01% by weight. Some of these substances are naturally-occurring impurities, so the EU defined acceptable limits. EU RoHS also allows these substances in higher concentrations in certain applications if no alternatives exist; each of these scenarios is an ‘exemption.’
Molex is primarily a manufacturer of components, so EU RoHS does not apply directly to Molex. However, RoHS applies to Molex’s customers, and therefore Molex must provide compliant products. While there was some limited use of cadmium, hexavalent chromium, and decabromodiphenylether in Molex products (as colorants, coatings, and flame retardants, respectively), lead was used significantly by Molex: many terminals were coated with a tin-lead plating on the solderable interface. Once EU RoHS was proposed, it became evident Molex would have to cease using tin-lead plating on many products.
Pure-tin platings have been used for decades by Molex, so we had the experience needed to remove lead. One primary concern of switching to pure tin was the growth of tin whiskers (tin filaments that grow from a plating and, once touching another terminal, can cause a short). To mitigate the growth of tin whiskers, Molex terminals typically have a nickel underplate.
While Molex had the expertise to convert tin-lead to pure tin, EU RoHS, which is continually changing, presented a number of other challenges. One challenge of recent memory is the annulment of the decabromodiphenylether exemption. The EU legislators initially allowed decabromodiphenylether in plastics, but this exemption was overturned; Molex had only three months to convert products to use an acceptable flame retardant. Most exemptions, fortunately, have an expiration date years in advance, and this allows Molex and our suppliers the necessary time to convert products to newer, safer alternatives.
Recently, the EU legislators have been working on re-writing RoHS (referred to as a recast). This process attempts to make the legislation more clear based on how it was implemented and enforced in the past four years. The recast is not yet complete, but we’ll discuss this in a future blog posting.