We all know the basics of Moore’s law, right? Every new process node brings a bounty of the three “Ps” – Price, Performance and Power. Most of us can recite them like the alphabet. Missing from our recitation, however, might be some other things that come with a new process node – Lead, Mercury, Cadmium, Chromium, PBBs and PBDE – now THOSE will taste nice on your breakfast cereal. Electronic waste is a major polluter, and, thanks to Moore’s Law, we always have better, faster, cooler products to offer the public – inspiring them to take our last year’s products and dispose of them irresponsibly. As a result, in the US, electronic waste is estimated at two percent of the contents of landfills, and 70 percent of toxic waste.
Yes, I see your hands in the back again. (Why is it always the people in the back who raise their hands?) “Aren’t we all RoHS now? Isn’t this problem gone?” Well, the answer is that many of us are RoHS now, but our newer, greener, RoHS-er products are mainly the ones consumers are currently purchasing. Once they have these new, shiny, green devices, they’re taking their old lame lead-laced ones and tossing them into the environment.
So – even though we’re engineers and great at problem solving, we can’t do too much to alter the behavior of the public, and we can’t change the products that are already out there in the field. We can, however, understand what all this RoHS stuff means, how Weee is not a new video game console, and what the impact of our design decisions can be on the environment and on our ability to distribute our products globally.
RoHS – or “Restriction of Hazardous Substances Directive” comes to us from Europe. The European Union got together and agreed to restrict the use of specific hazardous materials (most notably lead) in the manufacture of electronic equipment. RoHS’s best buddy is something called the Waste Electrical and Electronic Equipment Directive (WEEE). WEEE addresses the issues of recovery, recycling, and re-use of electronic waste. Both RoHS and WEEE are “directives”. So – electronic waste comes to us courtesy of a “law” (Moore’s) and is mitigated by “directives” which are really just suggestions to EU member countries to make their own law and enforcement decisions.
With Europe playing all nice and green, of course, we still had the remainder of the world using and building “dirty” electronics. Luckily, the electronics industry is one of the most global, and what was required for Europe became good business worldwide. In the US, the federal government has taken little action, but the country’s largest electronics consuming and producing state – California — passed legislation that took effect in January of this year that prohibits the sale of many devices that would be banned under the European RoHS directive. Combined with similar regulation and pending regulation in several Asian countries, the net effect is that RoHS-like standards are being broadly applied at the component level across the industry.
If you’re producing semiconductors, for example, that you want to sell into a wide range of electronic products destined for consumers in a large number of countries – you want to be sure that your devices meet the standards for all of the target markets you’ve identified. You also don’t want to have a different process for each specific geography’s set of regulations. As a result, you adopt a conservative approach where your product meets everyone’s specs at once – or at least the majority that you care about.
Today, most of the semiconductors you’d consider dropping onto your board are RoHS compliant. Your job doesn’t end there, though – the RoHS-ity of your product will depend on the board, the peripherals, the manufacturing technology, and, of course, the case. Although most RoHS promotions focus on the “lead free” aspect of compliance, RoHS actually restricts the concentrations of six substances: lead, mercury, cadmium, hexavalent chromium, Prolybrominated biphenyls (PBBs), and Polybrominated diphenyl ether (PDBE). These six substances are limited to a concentration of no more than 0.1% in any “homogeneous material”. That means that each part of your system – if disassembled, must be in compliance. You can’t rely on the weight of your in-compliance circuit board to help you get by with an out-of-compliance enclosure.
There are some helpful and rational exemptions, however. Since the goal of RoHS is to keep quantities of these materials out of the environment, the directive focuses on items that are likely to be manufactured in high volume. Many products, such as semiconductor manufacturing equipment, don’t have to comply. Some countries also exempt heavy iron, like telecommunications infrastructure.
Batteries are also specifically excluded from RoHS restrictions, although they are covered by their own directives in Europe and other countries. Batteries, of course, represent a special challenge, and much of the focus on battery control is on recycling the hazardous materials.
RoHS is certainly not without its detractors. There are significant debates on the impact of RoHS restrictions on reliability, cost, and even environmental impact. Lead-free solder, for example, requires much higher temperatures in use and therefore puts significant stress on temperature-sensitive components. The mechanical reliability of lead-free solder in the wake of heating and cooling cycles is also an issue. Some have also argued that lead-free solder is more corrosion-prone, which could lead to reliability problems in some applications.
One of the most controversial (and best documented) issues with lead-free solder is the potential for growth of nefarious “tin whiskers” which can – in high density packaging – grow out from one contact point and create a short with an adjacent trace or contact. Tin whiskers have been identified as the culprits in some very high-profile failures of equipment designed to be high-reliability.
Of course, one of the best ways to keep our electronic products (and the hazardous materials they contain) out of landfills is to keep them in active use in consumers’ hands. As convergence continues and many devices are replaced by one, we’ll have fewer obsolete toys to discard in the first place. Also, with the increasing software component of today’s embedded systems, more of the upgrades and feature additions can be done in software – keeping the hardware platforms in active use longer. Finally, as Moore’s law helps us in our continuing quest for integration, the reduction of the BOM in complex devices means that fewer components (and smaller ones) will be discarded when the inevitable end comes.