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SMT & Inspection | August 31, 2006

Fume Extraction For Healthy Lead-Free Rework

Concerned by the acrid odour given off by lead-free fluxes and solder pastes, rework professionals are increasingly calling for better health and safety measures and better fume extraction.
Lead-free reworking processes require higher temperatures and greater use of more active fluxes, which could account for the stronger smell of the gases released during lead-free rework. The often unpleasant odour is a matter of concern for many electronics manufacturing operators, who
are worried that it may signal an increased health hazard.

Even though the smell of a gas is not necessarily an indicator of its impact on health, the UK's Health and Safety Executive (HSE) concurs that rework professionals are right to be concerned. This is partly thanks to the fact that, after years of no-clean solder fluxes, lead-free has triggered a return to the electronics workbench of rosin-based fluxes. In its booklet "Solder Fume and You"
(www.hse.gov.uk/pubns/indg248.pdf), the H&S underlines the possible health hazards that can arise from the use of rosin-containing flux materials. When they are heated to the higher lead-free processing temperatures, they form fumes, or colophony, that can irritate the skin, respiratory tract and eyes. It warns that "Rosin-based solder flux fume is now regarded as one of the most important causes of occupational asthma in Britain", and adds that if ventilation is poor, the effects
may also be felt by others in the work area even if they are not involved in the soldering process.

Not surprisingly, the UK COSHH regulations include Maximum Exposure Limits (MEL) for rosin-based colophony. The HSE recommends that "exposures should be reduced to as far below the MEL as is reasonably practicable, for example by the provision and use of a suitable local extraction ventilation system".

It is clear that a healthy working environment makes sound economic sense, and by investing in their operators' health businesses guard against the more expensive consequences of staff turnover, sick leave, healthcare and potential legal costs. At the same time they benefit from
increased operator efficiency, quality, throughput and a host of other human-related factors that, although they may be difficult to measure, invariably add significantly to the bottom line.

While health and safety is the top priority in deciding to invest in and optimise fume extraction systems, there are additional advantages to taking this step. One of these advantages, we believe, is extended soldering iron tip life. OK International's Market Development Manager, Craig Brown, explains: "At higher temperatures, lead-free fluxes tend to boil and spit, creating more colophony. Unless this is removed by an effective fume extraction system, it can form "black tip", a solid black
deposit on the solder iron. This acts as a barrier, preventing the solder from wetting and worse still, if it burns onto the tip itself, it reduces the tip's thermal performance and useful life. We are now
conducting tests to prove this theory".

It is essential that companies weigh their options carefully when selecting a fume extraction system, as a raft of variables must be considered. These include the quality of the filtration system, which is classified for the size of the particulates that it will capture. OK International's fume extraction systems all use top ranking multistage filtration with EU14 HEPA filters. Other variables include the type of extraction systems that will optimise air filtration: High Pressure (Tip) Systems fit onto the individual soldering irons, while high volume Arm Systems draw colophony from a general work area.

Other issues to take into account include how many users will be attached to any one extraction system? At what distance? What bore tubes should be used in order to draw the fumes away completely without cooling the soldering iron tip and without the colophony cooling, depositing in and clogging the tubes? At what vacuum or speed should the system operate? Is it better to use a benchtop or a central system?

Brown says that engineering expertise is crucial if all of these variables are to be combined into an efficient, cost effective system. He also warns that opting for a low-cost, off-the-shelf air purifier
will give manufacturers a false sense of security. "These units are often based on simple carbon filtration that removes the visible smoke particles to leave the impression of cleaner air. But they leave behind the more dangerous, smaller and invisible particulates. A good quality unit should offer at least a 99.5% efficiency for removing particles down to 0.3 µm".
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