The condition of the gold pads sounds like the "Black pad" problem exhibited by circuit boards. The lack of nickel is odd because I thought this phenomenon was related to Phosphor-Nickel oxidation in the plating process... Just a thought, Jeffrey A. McGlaughlin CID Battelle Memorial Institute Columbus Ohio [log in to unmask] -----Original Message----- From: Marsico, James [mailto:[log in to unmask]] Sent: Friday, October 19, 2001 7:31 AM To: [log in to unmask] Subject: Re: [TN] Vapor Phase Soldering material BTW, the reason for my inquiry is that we are using Fluorinert as a medium for a liquid burn-in chamber. We're building a multi-chip module in a 655 BGA ceramic package. These components require 160 hrs of burn-in at 125 C, under power (MIL 883 requirement). The test fixture consists of BGA sockets (clam-shell with gold plated copper pins) soldered to a test board. The liquid is used to prevent oxidation of the solder terminations during burn-in, since the solder balls are not attached yet. The solder termination base material is tungsten which is nickel and gold plated. We recently had a batch, or two, of components which exhibited damage to the solder terminations... anywhere from flaking plating with black metalization underneath to completely black, almost burnt-looking pads. Attempts at cleaning these pads (warm HCL) were fruitless. Surface analysis of the pads where metal was found showed gold, copper and molybdenum, but no nickel. (Where the molybdenum came from is a mystery.) At this stage of the game these components are probably worth a couple of thousand dollars, so you can see the reason for trying to get to the root cause. Someone had mentioned that Fluorinert breaks down and forms acid in the presence of water, so everyone is pointing to this as the cause... I'm not so sure. Jim Marsico Senior Engineer Production Engineering EDO Electronics Systems Group [log in to unmask] <mailto:[log in to unmask]> 631-595-5879 -----Original Message----- From: Brian Ellis [SMTP:[log in to unmask]] Sent: Friday, October 19, 2001 5:25 AM To: [log in to unmask] Subject: Re: [TN] Vapor Phase Soldering material Jim, This surprises me and I'd like to know more. In practice, in VP soldering, I doubt whether there is any great significance. Firstly, the bulk of the vapour is anaerobic, with just the top interface in contact with the air. This air will be heated and therefore the RH, even in humid climates, will become extremely small. Then PFCs are demonstrably resistant to hydrolysis in the presence of free H and OH radicals (this is why they have atmospheric residence times of thousands of years): there is simply not enough energy available to break the F-C bonds. Naturally, Mr Arrhenius will say that, at 200°C, the energy will be much higher so there will be more reactivity, but it would require temps exceeding 300°C for it to become significant. Notwithstanding, I believe that we are talking about 1 molecule in 10^n where n is a very large integer that will decompose at soldering temperature under practical conditions in a given time, unless there is something new that I haven't heard about (always possible, of course). I just looked at Fluorinert data sheets on the 3M web site (requires some searching!) and there is no mention of a hydrolytic reaction in anything I could find. Brian "Marsico, James" wrote: > > Brian, > I'm getting conflicting comments from someone from 3M who is claiming that > Fluorinert will decompose at temperatures of 200C and above and this is not > a good thing in the presence of water (usually available as moisture in the > air). Any comments? > > Jim Marsico > Senior Engineer > Production Engineering > EDO Electronics Systems Group > [log in to unmask] <mailto:[log in to unmask]> > 631-595-5879 > > -----Original Message----- > From: Brian Ellis [SMTP:[log in to unmask]] > Sent: Wednesday, October 17, 2001 2:38 AM > To: [log in to unmask] > Subject: Re: [TN] Vapor Phase Soldering material > > 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 rnnge. 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 > > ---------------------------------------------------------------------------- > ----- > > ---------------------------------------------------------------------------- ----- > 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 ---------------------------------------------------------------------------- ----- ---------------------------------------------------------------------------- ----- 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 ---------------------------------------------------------------------------------