Concerns raised over 'lead-free' solder health

14 June 2006 News

The European Union RoHS directive that restricts the use of eight hazardous materials, including leaded solder, in the manufacture of various types of electronic and electrical equipment, is causing considerable concern.

"Initially intended to replace the use of traditional leaded solder with the new, lead free variant, it has had unexpected and alarming health implications," says Lutz Otto, national marketing and sales manager at RS Components, an SA supplier of electronic, electrical and industrial components.

"Recent research has suggested that the fumes and vapours emanating from lead-free solders may be even more dangerous to workers and the environment than those emitted by traditional lead containing solders," explains Otto. "While lead was obviously toxic, silver; a standard constituent of lead-free alloys; was found to be several orders of magnitude more eco-toxic than lead. It seems that the best intentions have had unintended consequences. Most research projects concerning the use of lead assumed that eliminating it will have a positive effect on the health of workers, while ignoring the possible adverse health effects of lead substitutes - particularly at the level of the bench top where workers are 'face to face' with potentially toxic, but invisible, fumes, vapours and gases."

And it is these fumes that seem to pose the most immediate risk. Many of these lead-free solders use rosin as a fluxing agent. Tin-lead solders melt at around 180°C, whereas lead-free solders melt at temperatures 30-40°C higher. The fear is that that the higher temperatures required for lead-free soldering will significantly increase the amount of fume produced. As solder fume is one of the top eight causes of occupational asthma, Britain's Health and Safety Executive is very concerned about workers breathing in fumes from solders containing rosin-based fluxes, also known as 'colophony fume'. Anyone soldering with rosin-based fluxes is at risk of developing asthma.

"But it is not all alarm and despondency," notes Otto. "For one, the RoHS lead-free directive only affects South African suppliers of electronic and electrical equipment to the EU and only comes into effect in July 2006. Secondly, there are measures that can be taken to alleviate the impact of these fume vapours. These fall into the areas of substitution with non-rosin-based flux, fume absorbers, flexible arm extraction and tip extraction."

Substitution is the most effective means of preventing exposure to rosin-based solder flux fume. While new products continue to come on to the market, for technical reasons (eg, product quality, tolerances, performance levels, output and re-work costs) they may not yet be suitable alternatives.

Otto goes on to warn that fume absorber units are rarely appropriate due to the fact that they do not filter out the active fume components that cause the development of occupational asthma. "Tests have shown that the units' coarse carbon filters that are usually fitted remove only a small proportion of the harmful constituents in the fume. Recirculation blows fume at other workers. Flexible arm extraction is a better option. These units extract fumes via an extraction tube situated above the work piece and pass it through a large, central filter system elsewhere on the premises. For efficient control, the extraction collection point needs to be close to the work, and between the work and the operator's breathing zone.

"But tip extraction units," says Otto, "are probably the most efficient of the mechanical methods. These have the advantage of continuous removal of fume, whether the iron is in use or at rest. Also the low volume and flow rate of air avoids significant heat loss. It does, however, require regular and frequent maintenance and cleaning as sticky residues build up and block the small bore tube. The iron must also be held in the right position for the extraction to work; eg, elbow rests may be required."

In the final analysis, Otto notes that education and training is the key to preventing the very real health risks. Key points to remember are:

* Occupational asthma due to solder fume is preventable.

* Where possible, prevent or adequately control exposure to rosin-based solder flux fume.

* Manual soldering with a handheld soldering iron poses the greatest risk of fume exposure.

* Products marketed as 'rosin free' are not necessarily without health risks.

Otto reassures customers by saying that RS is committed to helping them identify and cope with the problem.

"As a market leading company we work closely with our business partners to ensure that their needs in terms of technical and safety requirements are met. Anyone with any concerns is welcome to give us a call. The RS website displays full compliance information on all affected product thereby allowing customers to make the correct combination of an educated decision and product choice. We have now actually taken it a step further. In addition to our RoHS compliant/non-compliant flags, there is a new flag with a question mark. This flag applies to products, which are known to be affected by the RoHS legislation, but their actual status is still under investigation."


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