Hakko - The Purpose Of Fume Extraction

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Soldering work involves both metallic and organic compounds. The solders themselves contain, besides tin and lead, various levels of zinc, arsenic, cadmium, antimony and other metals. Fluxes necessary for soldering contain activators to enhance their cleaning properties; these activators are typically organic acids. Such compounds, when heated, release byproducts of incomplete combustion, which in turn can contain noxious fumes, particulate matter, aerosols, and gasses. Prolonged breathing of these contaminants can lead to both short- and long-term operator irritations and illness. Respiratory tract irritation, sore throats, eye irritation and headache are the most common symptoms. Allergies and asthma are often exacerbated by solder smoke.


Please note that the metals of which solder is made do not themselves vaporize at soldering temperatures. Lead, the metal with the lowest vaporization temperature commonly found in solders, does not become a gas below 2950 degrees F. What you are really getting rid of, and what you want to get rid of, is flux smoke. Scorched board material and conformal coating are extra added attractions.


Types of flux.
  1. Resin-based. The oldest, most popular and still most effective soldering flux. This flux is an organic compound consisting primarily of colophony, a complex resin found in pine trees. The active agents in resin flux are abietic acid and plicatic acid; it is the reaction between these organic acids and metallic oxides on the joint materials that provides the cleaning required for solder to 'wet' the joint. In a world free of stickybeaks and activists it would be sufficient to inform operators that these organic acids, when exposed to soldering temperatures, combine with oxygen and yield products of partial combustion which may be irritating to the skin and eyes, or exacerbate respiratory problems. Abietic acid may also cause skin irritation at room temperature - some people are unable to hug a pine tree - and there is some correlation between colophony and allergic reactions.

    Some resin-based fluxes contain additional chemical activators, usually organic fatty acids, which help the fluxing process along by making the compound even more acidic than usual. This helps soldering, to be sure, but may add even more irritants to the air. Resin-based flux leaves a residue behind, after the soldering operation is finished. This residue must be cleaned from the board, both to allow further operations (such as conformal coating) to be carried out with a minimum of fuss and bother, and for cosmetic reasons - charred flux is abominable in the eyes of an inspector. Isopropyl alcohol & methyl alcohol are the solvents of choice; they are cheap, effective, and quick. Cleaning, alas, requires an increment of time, and 'unproductive' time at that; alcohol fumes are unpleasant to some; we therefore have a choice of:

  2. No clean. These fluxes do not, in theory, require cleaning after use, for they do their work and vanish under the influence of heat. Some of them are organic and some are not; most if not all of them are more active - that is, more acidic - than their resinbased predecessors, and all exude chemical residues and products of partial combustion that are even more likely to irritate sensitive membranes than those derived from trees. Many soi-disant 'no clean' fluxes are organically based, usually on an alcohol, and have a low solid content. Typical constituents of solder smoke from no-clean fluxes arise from the breakdown of alcohols and include ethane, acetone, formaldehyde, toluene, terpenes, carbon monoxide and carbon dioxide and, of course, alcohol fumes. Whoo!...


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