Amen, amen. Excellent response, Doug. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls Sent: Wednesday, May 30, 2007 9:54 AM To: [log in to unmask] Subject: Re: [TN] Flux residue, burnt flux Wee Mei, It would not be accurate to say that flux residue is never a good thing to leave behind on an assembly. We make military product and in select cases, we leave flux residue intact. But, we know exactly what the residue is, we know its characteristics in the end use environment, have a ton of test data behind us, and have many measures in place to control the manufacturing process surrounding those flux residues. The military position on RMA fluxes and cleaning are largely due to inertia or old school mind sets. On the other hand, military programs often have to take low bids and have been severely bit many times from assemblers who do NOT know what they are doing, or where "cost" is the only driver. There is no such thing as a good flux or a bad flux. No flux is "safe". Many of the horror stories that we old war horses can (and do) tell can usually be traced back to one root cause - a failure to understand precisely the materials of manufacture and how the end use environment effects the residues on the assemblies. Or the corollary cause - cost is the only consideration. I would say that someone like Bill Kenyon could take Superior 30 flux and make a reliable heart pacemaker. But for the rest of the world, nooooooo way. Military programs today, at least the ones that I deal with, are more open to something other than RMA fluxes (which technically have not been around since 1995), IF you have the test data and demonstrated expertise to back it up. We use low residue fluxes with aqueous cleanings. There are programs doing true no-clean (not here though). There are programs doing water soluble flux. Granted, it often takes a tremendous amount of effort to educate a customer with an RMA mind set, but it can be done. Doug Pauls Rockwell Collins Lum Wee Mei <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 05/30/2007 07:57 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Lum Wee Mei <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] Flux residue, burnt flux Hello, From what have discussed, I gathered that flux residue is never a good thing to leave behind on the PCBA. Regardless whether it is water soluble, no clean or RMA flux, the chemical compounds in the flux residue can react with whatever present in its surrounding over period of time and "mutate". This mutated power is so powerful that it "eats" away connector housing, give rise to dendrites and cause short, etc. Is that the reason why military products only use RMA flux with IPA or Ensolve or other cleaning agent and never no clean and water soluble flux? Thanks and regards, Wee Mei ------------------------------------------------------------------------ ------------------------- I have seen many, many cases of electrical failure due to flux being left on the board, including no-clean, water soluble, and RMA. I have had to perform as an industry consultant for several companies that had field returns and cancelled contracts due to flux issues causing performance problems (crosstalk, etc.) The worst one I ever had to deal with was many years ago (mid-'80s) when a contract manufacturer used a no-clean flux to add (build-around) a printer connector on a computer motherboard. They liberally spread the flux over the SMT pads and hand-soldered the connector in place. They did not realize that the field returns they were getting shortly afterwards were due to the use of the no-clean flux. The chemicals in the no-clean flux attacked the connector housing material, turning it into a grey powder. Some of the motherboards came back with no connector body left, only the connector leads soldered to the pads, and a grey powder where the body used to be. This company brought me in to find out why the connectors were deteriorating. Upon reviewing the original process travelers, I found that the build-around was approved without qualifying the hand-soldering of the connectors, whereas they had been reflow soldered with water-soluble flux prior to that. This company was forced to take back more than 100,000 computer motherboards, remove the connector, remove all traces of the no-clean flux, assemble a new connector using water-soluble flux, wash the boards, re-test the boards, and replace them into the computers, all on their own nickel. They nearly went bankrupt. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Kathy Kuhlow Sent: Tuesday, May 29, 2007 1:52 PM To: [log in to unmask] Subject: Re: [TN] Flux residue, burnt flux Inge, When NAFTA first came into play, the company I worked for ran to the border for cheaper products to be built. We built industrial computing products at the time so it needed to be pretty durable. We ended up within 9 months scrapping everything built south of the border due to two reasons. One was a dendrite growth on all of the gold (simm sockets mainly) due to water quality (said it was DI but apparently our definitions of DI differed a bit). The second reason was flux under the older 386 and 486 chip sets. There was flux underneath that never was cleaned up. We found that the flux was eating through the traces underneath the chips. I suspect it was due to a solder issue and the boards were flooded for rework but insufficiently cleaned up. About 2000 boards were scrapped because it was impossible to determine the extent of both problems. Left south of the border shortly after that and only used them for cables afterwards. Kat -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar Sent: Wednesday, May 23, 2007 3:11 AM To: [log in to unmask] Subject: Re: [TN] Flux residue, burnt flux What I say now may cause some to think that I'm member of Ku-Flux-Klan, which is not the case. So, we follow the general habit of removing 'all' flux residues. However, I can't deny, that I think this flux removal hysteria is little exaggerated. I've been in the business for so long a time, and I have not seen many reported failures that have been caused by flux residues. In theory, flux residues have many ingredients that can cause corrosion, leakage current, decreased insulation etc, but it seems as that does not happen in reality. 100% cleanliness is satifying and beautiful, but costs a lot to obtain. Just a thought. Would be very interesting if anyone could describe a case with flux residues causing massive failures. Inge -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis Sent: den 23 maj 2007 09:38 To: [log in to unmask] Subject: Re: [TN] Flux residue, burnt flux I'm sure that an eminent co-contributor to this forum will tell you, "it depends". If the flux is truly burnt, i.e., black, this indicates pyrolysis, which is a fancy word meaning decomposed by heat. Pyrolysis indicates that the residues have split apart into numerous compounds, leaving carbon-rich stuff. Elemental carbon can be an electrical conductor; do you want conducting particles in your assembly? They may appear fixed in place now, but will they remain so during the life of the equipment? More important, WHY are they there? It may be because the operators don't keep the bits of their irons clean. Do they wipe them on a wet sponge before each joint is made? It may be that the time/temperature conditions of the joint being made are far from optimal. It may be lack of adequate training of the operators. I can't tell. Whatever, prevention is better than cure; a lttle research into the causes may give you the answer. As to flux flow, maybe your solder wire simply has too much flux. Some manufacturers allow you to choose the percentage. Yes, it is easier to solder with an excess. It's a compromise. What you have not told us is the essential information: what kind of assemblies are you making. You can obviously be more tolerant of imperfections if you are making toys than if you are making inertial guidance or satellite systems. Probably you are somewhere between thes extremes. "It depends"! Brian Sue Powers-hartman wrote: > We fight a constant battle with operators leaving burnt flux in > joints. Maybe only a small speck, but drives the inspectors nuts. The > way I read JStd-001D, if they can not see it at referee inspection power, they have to accept it. > How dangerous is this burnt flux to the PWB? If it's not seen at > inspection power and left on the board, what happens. Also, what about no clean flux? > Our solder training video says that if no clean flux runs out to far > and is not heat activated, it can cause problems. Operators watch this > video, but somehow do not get this. They say that it's no clean, they can leave it all on. > I keep saying that this can be a problem, and then they ask me, how > far out can the flux be away from the joint before it's unacceptable. > > Wow, I'm glad I found this forum, I have so many questions to ask you guys. > Anyway, thanks for the help on this subject. > > --------------------------------------------------- > Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 > or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET > Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the > posts: send e-mail to [log in to unmask]: SET Technet Digest Search the > archives of previous posts at: http://listserv.ipc.org/archives Please > visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 > for additional information, or contact 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