Topic

Volatile Organic Compounds (VOCs)

Volatile Organic Compounds (VOCs) are used widely in products from paints, primers and coatings, to underarm deodorant and cleaning fluids, but have been found to be a major contributory factor to ground level ozone. Whilst ozone in the upper atmosphere helps protect us from the sun's dangerous ultra-violet rays, ozone at ground level is a highly reactive gas that, according to studies by the US Environmental Protection Agency, “affects the normal function of the lung in many healthy humans.”

These studies show that breathing air with ozone concentrations above air quality standards aggravates symptoms of people with pulmonary diseases and seems to increase rates of asthma attacks. There is also evidence that prolonged exposure to ozone causes permanent damage to lung tissue and interferes with the functioning of the immune system. As you will find at http://www.epa.gov/oar/oaqps/gooduphigh/, ozone is “good up high, bad nearby”.

Ozone has been a difficult pollutant to control because it is not emitted as such, but is actually formed in the atmosphere through a photo-chemical process in which VOCs react with oxides of nitrogen in the presence of sunlight. For this reason, controlling VOCs is an effective way of minimising ozone levels. In fact, the EPA definition of a VOC is any volatile organic compound which participates in atmospheric photo-chemical reactions.

The original concerns started with CFC awareness, accelerated by photo-chemical smog incidents. California was the first state to enact laws limiting the VOC content in paints and coatings, setting a precedence for US federal regulation.

The 1990 Clean Air Act Amendments required that VOCs emitted into the atmosphere be calculated and disclosed to the EPA. Effective from 1993, the legislation aimed at reducing the quantity of VOCs released into the atmosphere over a three year period, placing the burden of proof on the consumer to document their emission level.

Whilst the rules vary, they generally apply to all companies using or storing more than 5 tons per year, and “major stationary sources” have to obtain an operating permit for equipment dealing with chemicals. A major stationary source is one with the “potential to emit” more than 10 tons per year of any one hazardous air pollutant, or 25 tons per year of any combination of pollutants. Note that this “potential to emit” refers to the amount that would be used with the equipment running at full capacity, and not the actual usage.

In the USA, not only VOCs, but also oxides of nitrogen, carbon dioxide, carbon monoxide, sulphur dioxide, and particulate matter need to be tracked, and there are swingeing penalties for non-compliance. The situation in the USA is currently more tightly regulated than in Europe, but the aims and strategies are comparable, and there is continuing regulatory activity to reduce emission levels. For example in the UK, a 10 tonne limit was set in the Environmental Protection Act (Solvent Emissions Directive) (England) Direction 2002, and similar legislation in other regions.

In the printing industry, almost everything using chemicals is covered: printing presses, film processors, plate processors, and proofing presses: in the electronics industry, all companies of a significant size will be obliged to comply with VOC restrictions. Other than affecting cleaning strategies, the major impact if VOC regulation comes from their being a important constituent of fluxes. Note particularly that calling flux ‘water-washable’ only means that the residues may be removed by aqueous processing: such fluxes are not necessarily VOC-free, and will probably contain some solvents at the time of application.

Actions needed by the assembler are:

This is an area where there have been a number of improvements in materials. For example Cookson Electronics have reported the successful development of VOC-free foam and spray fluxes for wave soldering. However, in order to remove all water from board surfaces, components and holes, the amount of flux and the pre-heating process parameters are critical. In combination, the process window for lead-free soldering with VOC-free fluxes is narrower than that for SnPb soldering with VOC-based fluxes.

Self Assessment Question

Explain to your colleagues why VOCs may have an impact on their health and on the processes carried out by your assembly partners.

Compare your answer with this one.

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