Hi Dave, > Hi Hans! The answer to your problem is elementary! > Good, I like simple answers. > Well, I have a guess anyway. > There have been a number of industry cases documented on the appearance of > tin > and/or lead oxides on various areas of circuit board assemblies coming out > of > cleaning processes. This is most commonly called "white residue" and has > been > associated with rosin fluxes. Many of the reports found the root cause was > the > cleaning process (typically water wash processing) was too hot or the > circuit > boards were being introduced to the cleaning process too hot (i.e. right > from > the wave to the cleaning process). The temperature and the tin and/or lead > oxides interact, the oxides come out of solution from the cleaning water, > deposit on the boards and are virtually impossible to remove. You have > both > ingredients present - RMA flux and if I read between the lines very hot > circuit > boards. Try letting the assemblies cool off prior to being introduced to > cleaning and/or make sure cleaning solution temperature is in the 140-150 > range > (assuming that you are water washing). > You bring up dam good points . . . but, unfortunately for me, it's not quite that simple. We definitely let the assemblies cool down. I wait until it is about room temp say 30 - 40 minutes at the earliest before hitting a solution but I'm shooting for within two hours of soldering so the flux doesn't get hard(er) to remove. In fact, we had a problem cleaning them because the shop was waiting a week or two before trying/expecting to get the boards really clean. Until then they didn't see the need and this process wasn't clearly defined (it will be by the time I finish though). Their philosophy was 'The next step will get the assembly dirty so why bother cleaning it really well - ever?' Our Aqueous Cleaner is set at 130 degrees F in both the wash and the rinse sumps and while it might contribute to the corrosion, it can't be the cause. I see corrosion before it even goes through the Aqueous Cleaner. During an initial clean using a spray or soak of Chemtronics Flux Off Rosin, or a mixture of isopropyl alcohol and Trans-1, 2 Dichloroethylene it appears when I dry it off with shop air. At that stage it hasn't even hit the water yet. > Also - oxidation is not necessarily corrosion unless you are talking about > iron. > Very good point. I never took the corrosion series in grad school (my focus was on microelectronic manufacturing) and I only got 'volunteered' as an assembly/cleaning engineer a couple of months ago. Hans > Good Luck. > > ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################