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What is a good flux solvent — Parallax Forums

What is a good flux solvent

T ChapT Chap Posts: 4,223
edited 2006-12-02 14:35 in General Discussion
Just started converting some projects to all SMT, and experienced that on a few boards that have traces underneath the IC, some flux is not completely getting removed when I clean the boards with water. I just started using flux to solder in one tssop .5mm part separately from the others, and it has traces underneath it till I can redo the board design. When flux remains stuck under it, and 27 volts from one of the traces hits the flux, tiny sparks come out, and the chip is done. The flux cleaner I have is brutal, it really makes the boards a mess. I need some type of nondestrucitve solvent for the flux that stays jammed under the IC. Anybody got any suggestions?

Comments

  • ForrestForrest Posts: 1,341
    edited 2006-12-02 10:32
    Traces under the part shouldn't be a problem - as long as they're covered with solder mask.

    The solvent you use depends on the type of solder paste or flux that you're using. Check the solder paste data sheet or flux for the recommended solvent.

    Aqueous flux is best removed with warm water. You should be able to immerse the board for 1-3 minutes in warm water, brush it with a toothbrush and rinse with clean, deionized water and blow dry with air.

    RMA or Rosin flux can be removed with a saponifier mixed with water or isopropyl alcohol. Immerse in isopropyl alcohol for 1-3 minutes and blow dry with air.

    No-clean flux hardens after exposed to heat and typically doesn't need to be removed after soldering. You should minimize the amount of no-clean flux used as unheated no-clean flus IS slightly conductive!
  • T ChapT Chap Posts: 4,223
    edited 2006-12-02 11:55
    Thanks Forrest for the info. The bottle says it needs to be "removed and neutralized", but doesn't say how. It is obviously conducting though, as it has cost me 3 boards already. Once traces are lifted it is better to toss them. I thought I was doing some bad reflowing as it is a new process, but in fact the reflow has been perfect, the flux is blowing stuff up. Since it is underneath the IC, it is hard to remove except by some solvent method.
  • ForrestForrest Posts: 1,341
    edited 2006-12-02 13:04
    I think you should switch to a different flux or solder paste. I recommend Kester R276 no-clean solder paster. A 35g syringe will cost you $12.96 at www.techni-tool.com If you want to use flux instead of solder paste, I'd try Kester Tacky flux = Google for sources.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-12-02 14:35
    isopropyl alcohol, in as high a concentration as possible (drug-store, 90%, check the label/s) --·flood it (soak 'em), rub it, blow it out (get a can of "compressed air"/duster), repeat
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