Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!cica!ctrsol!emory!stiatl!john From: john@stiatl.UUCP (John DeArmond) Newsgroups: sci.electronics Subject: Re: Rosin remover Message-ID: <6236@stiatl.UUCP> Date: 31 Jul 89 23:56:17 GMT Reply-To: john@stiatl.UUCP (John DeArmond) Organization: Sales Technologies Inc., "The Procedure IS the product" Lines: 52 >In article <422@ctycal.UUCP> ingoldsb@ctycal.COM (Terry Ingoldsby) writes: >Having been an electronics hobbiest for some years, I am going to ask >what is probably a *dumb* question. I have seen all the discussion >about methods of removing rosin from PC boards, but I've never had >any trouble with leaving it there. My understanding is that it is >an insulator. Is this not true? Does it have some high frequency >characteristics that I've never run into? Do people just dislike >how it looks? Terry, One of the absolute best solvents for most fluxes is 100% ethanol. This is available at your friendly liquor store as PGA (pure grain alcohol). I've found that not only does this stuff remove roson rather well, it leave no residue. I've tried other alcohols and dilute ethanol and none seem to work as well. The water seems to interefer with the solvent effects. My procedure is to first, before doing the repair, wash the area in Clorothane (1,1,1 tricloroethane) to remove any conformal coating that may be present. 1,1,1 won't remove the silicone or epoxy conformal coatings but these are not seen too much in commercial gear. Next do the repair work. Then, with the board horizontal, soak the area in ethanol and scrub with an acid brush (a cheap organic bristle brush so named because it was designed to apply acid for soldering sheet metal. Obtain at hardware store). The flux will appear to disappear but will actually be in solution. If you stop there, your board will dry with a white, powdery film. Hold the board vertical and hose the board thoroughly with ethanol. I use a lab wash bottle for the task. This will flush the board of the flux-laden fluid. Dry with a hair dryer or oven. I suggest a light conformal coating of Krylon crystal clear spray for non-critical boards and whatever the mfr. recommends for critical ones. I've used this technique for years in repairing even very sensitive nuclear instrumentation boards where no surface conductance at all is tolerated (resistors with >10E10 ohms are common). One final note. Don't get fooled at the liquor store into getting 196 proof votka. The 2% water content will foul up the process. The last time I bought some, I got the Absolut brand (russian, I think) which was the only thing they had. I've found that this works better than any of the freon or freon-alcohol mixes that are so expensive. Besides, if you get in a real mess, you can "deflux" the old stomach :-) John -- John De Armond, WD4OQC | Manual? ... What manual ?!? Sales Technologies, Inc. Atlanta, GA | This is Unix, My son, You ...!gatech!stiatl!john **I am the NRA** | just GOTTA Know!!!