Back in the days? Vapour-phase soldering is still done! The great advantages of perfluorocarbons over other halocarbons are that a) they are chemically extremely stable because the C-F covalent bond requires much energy to break them; b) they are virtually non-toxic (for the same reason: they do not break down in the body). In fact they can be used to replace blood in the body for short periods as they do allow oxygen to be dissolved and some "sportsmen" have even injected PFCs into the bloodstream to improve their endurance performance by a higher oxygenation; c) they are very inert chemically; d) they withstand high temperatures; e) they are NOT ozone-depleting. Teflon is a solid PFC. The disadvantages are a) that they are very expensive; b) they are EXTREMELY global-warming (typically 1 kg of PFC is equivalent to 10 tonnes of carbon dioxide which is roughly equivalent to half the emissions of a medium car during its lifetime); c) their stability (~10,000 years atmospheric residence time) is such that end-of-life disposal is very difficult and costly. The fluids, be they pure PFCs or PFEs, used for soldering are sufficiently stable at 210 - 260°C that there is little significant decomposition. Water hardly enters into the equation because it is boiled off instantaneously, even if there be some condensation on the cooling coils. Theoretically, there may be some hydrogen fluoride generated (no hydrofluoric acid), but I believe that the quantities would be really negligible, in practice. With the presence of other organics from the flux residues, I would personally be more concerned with trifluoroacetic acid, another nasty, but I have not heard of any cases. Carbonyl fluoride is also not to be excluded, also very toxic. There is another fluoro-compound, whose name escapes me for the moment, which did cause some concern in the early days, which is toxic in the ppb range. However, in practice, I have never heard of any of these toxic substances being present in sufficient quantity to be of practical concern. The real crunch comes when there is a secondary blanket, used in the early days to reduce losses of the primary fluid. This was initially always a pure CFC-113 (e.g., Freon TF, Arklone P etc.). Later, because of the ozone depletion potential of CFC-113 being as high as 0.8, a lower BP PFC was also proposed. CFC-113 does decompose at the vapour temperature of the primary fluid, so that the interface zone between the two vapours was always a hotbed of chemical reactions. This certainly produced, especially in the presence of water, whose BP was higher than that of the secondary fluid, a whole panoply of acids and other toxic substances. For this reason, these machines had both a molecular sieve to de-water the condensed vapours, but also a filter to remove the acids, otherwise the stainless steel tank corroded into holes in a matter of months. It is possibly this that you are thinking of. The most important decomposition product was hydrogen chloride, which becomes hydrochloric acid in the presence of water, but there was also phosgene, hydrogen fluoride, trichloroacetic acid and goodness knows what else. I feel reasonably certain (abstraction of any environmental effects), if vapour phase soldering with a CFC-113 secondary blanket were invented for the first time today, it would never be allowed into a workshop because of the H&S aspects. Hope this makes it clear. Brian "Marsico, James" wrote: > > Back in the days of vapor phase soldering, I seem to recall that > hydrofluoric acid was a bi-product of the fluorinert mixed with water, or > was it the Freon mixed with the fluorinert? Could anyone elaborate? > > Jim Marsico > Senior Engineer > Production Engineering > EDO Electronics Systems Group > [log in to unmask] <mailto:[log in to unmask]> > 631-595-5879 > > --------------------------------------------------------------------------------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8d > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL > Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 > --------------------------------------------------------------------------------- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------