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RoHS and Sensors: What This Means to You

January 1, 2006 By: Ed Ramsden Sensors

0nly a few months remain before the European Union's Reduction of Hazardous Substances (RoHS) directives take effect. As of July 1, 2006, manufacturers will not be allowed to offer many types of new products on the EU market if they contain more than specified maximum amounts of these restricted substances:

  • 1. Lead
  • 2. Mercury
  • 3. Cadmium
  • 4. Hexavalent chromium
  • 5. Polybrominated biphenyl (PBB)
  • 6. Polybrominated diphenyl ether (PBDE)

Not Just European

Even if your company doesn't currently sell so much as a resistor in the EU, the RoHS directives will affect the way you design and manufacture your goods. Your marketing department will, of course, remind you of the potential multibillion-dollar market just looking for the newest and best products. Sensing elements generally wind up inside somebody else's devices. That somebody else may be doing a fair chunk of their business across the Atlantic. This will result in non-negotiable customer demands for your products to also be RoHS compliant. China is imposing its own RoHS laws. If the EU and China aren't enough to convince you, many U.S. states are looking at adopting RoHS legislation in various forms. So if you haven't started thinking about RoHS compliance, you had better start soon.

ED Ramsden
ED Ramsden


One positive feature of the RoHS directives is their call for self-certification: you will not have to shell out big bucks to have an accredited body "certify" your products as compliant. By placing the products on the EU market you are automatically claiming compliance. One key to determining compliance is ensuring that all homogenous materials in your assembly are compliant. A homogenous material can be thought of as a uniform piece of a given substance. For example, an SMD resistor contains several homogenous materials—ceramic substrate, metal end caps, resistance film, etc. Each component must be individually compliant. The advantage is that if every piece of your assembly is compliant, the assembly as a whole should also be. Conversely, if one part of your product, such as a mercury relay, fails compliance then the whole product fails. A mercury relay is also a good example of the difference between "lead-free" and RoHS compliant. If it had tin-plated leads, it could very well be lead-free but fail to meet the RoHS directives.


Self-certification could be a big drawback in compliance determination. If your product's RoHS status is challenged, you will have to provide supporting documentation. While it is theoretically possible to send something out to be taken apart and analyzed, this option could get horrifically expensive because each homogenous material would have to be scrutinized. You are more likely to build a technical file of compliance documentation from each of your component and subassembly suppliers, but again there's a speed bump: getting this information into a usable form.

I have received components whose packing label trumpets RoHS compliance, but finding any other documentation has been an exercise in frustration. You may be able to build an RoHS-compatible product, but documentation is key. Component manufacturers, however, have been getting better at providing this material as the July deadline closes in.

To help with the chore of building and maintaining technical files, IPC (best known for PCB standards), is developing guidelines and reporting templates that will provide a standard means of reporting RoHS compliance. IPC-1751 is a set of reporting guidelines, and IPC-1752 is the proposed form to be used. If enough people buy into the IPC uniform reporting guidelines, RoHS documentation should become much simpler for many, if not most OEMs. These guidelines are expected to be available by the time you read this column.


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