The EU RoHS/REACH environmental compliance laws are designed to prevent harmful toxins such as lead and mercury getting into the environment � but the area of lead-free solders is a highly controversial one, with repercussions that have reached as far as the US military.

Military-specific PCB designs were the norm up to around 15 years ago, with a number of companies specifically manufacturing military-specific integrated circuits. However, defence cutbacks and the switch to COTS (commercial off-the-shelf) products led to a large number of electronic engineering companies switching to making commercial products in order to stay afloat. With Europe such a lucrative market, and with so many other countries following the EU�s take on environmental compliance � plus a tax incentive from the US government - it made sense to fabricate components which complied with the EU RoHS laws, which are the strictest in the world. One of the biggest impacts was in the widespread switch to lead-free solders and finishes, which today are the norm for COTS manufacturers across the world.

The export of high-profile off-the-shelf electronics is a lucrative one, and not restricted to simple components. For example, there are commercial COTS products incorporating Xilinx FPGA designs, designed for use in signals intelligence, reconnaissance, surveillance and other high-performance applications. Naturally, these products are made to very high specifications, but there is one thing thwarting their reliability � tin whiskers. First reported as a problem in military electrical systems in the 1940s, these unwanted oddities can cause havoc in PCBs, causing short circuits and catastrophic system failures that are totally unpredictable.

Whiskers have occasionally been reported in lead-soldered PCB designs, though this is rare. What is known is that in the absence of lead, tin-plated circuits can spontaneously develop microscopic, crystalline filaments at random points. These grow upwards from the base, sometimes harmlessly. However, if they come into contact with a current-carrying part of the circuit they can cause shorting and failure � often, without leaving any visible trace. Whisker formation isn�t restricted to tin; cadmium and zinc finishes can be affected too.

Lead was added to solders in the 1950s, and has a long history of reliability and longevity. Critics say that lead-free substitutes such as pure tin, tin-zinc or tin-silver-copper alloys can�t compete with traditional tin-lead products, citing a lifespan of one to two years for lead-free components, compared to twenty or more for tin-lead assemblies. This is apart from other problems like brittle joints and thermal stress (though the latter is being addressed.)

Environmental agencies in the EU and US say there is no evidence lead-free solder finishes are any less reliable than lead-tin ones � yet have allowed mission-critical electronic systems, such as those used in military and medical establishments, to be exempt. Since these industries now routinely employ COTS components (which are manufactured to a high degree of environmental compliance), engineers are dependent on rapidly dwindling obsolete stocks to ensure reliability. Currently, more reliable lead-free solders are being tried out, which hopefully will lessen the problem.

If you are having PCB design problems linked to environmental compliance, we at Enventure Technologies offer a full range of services from obsolescence management to FPGA design.

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