| We use no clean paste and sometimes experience | flux splattering which gives spot on gold fingers. | Need help in analize the cause. thx. Dominic, That is STILL a problem huh? It's a tough one to solve sometimes...especially when you have as many PCB's going through your plant as you do. There's a few sources that something like that can come from. One of the biggest problems is that visually the gold fingers on the PCB may look clean at first glance, but when the board goes through reflow the tiny solder particles that weren't visually detected has now had a chance to melt and flow out on the fingers, and as you well know it's EASY to see then. Aside from making sure that all the misprints have been cleaned spotless before re-printing them, the next thing that I would look at is the printers themselves, and/or the operators too. I don't think the reflow profile has very much to do with it. Because for that to be the case, I'm sure you would see something else on the board (like solder balls all over the place) or in the finished solder joint (like poor wetting from the flux being exhausted because of too high a temperature) that would also tell you that the profile was too hot, or the ramp too steep. If the profiles are anywhere close to what they were when I was there, I know that they're not too hot. There's a couple of things that I can think of with the printer that might cause this. Look at which way the stencil image is oriented and note which way it sits in the printer when running production. If the panel is sitting in the printer with the fingers for each SIMM sitting directly below or above the apertures. What can sometimes happen if the paper in the stencil cleaner jams and doesn't index properly, is when the printer goes thru it's cleaning cycle, the paste that supposed to be getting cleaned winds-up basically getting smeared on the bottomside of the stencil. When the next board that comes into the printer after the stencil cleaning cycle takes place gets printed, it also recieves the paste on the gold fingers that was smeared on the bottom of the stencil. The same kind of thing can occur if you run the stencil cleaner in the printer without any solvent...dry wiping the stencil with just one or two passes won't clean all of the paste off. One last thing that may be causing a problem is that the alcohol you use in the solvent tanks of your printers (if you are using alcohol), could be absorbing moisture from the air if the containers aren't being kept tightly closed...you know all the trouble that causes with wave soldering when your flux or flux thinner has absorbed moisture... BLOWHOLE CITY!!!
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We use no clean paste and sometimes experience
flux splat...
- Jan 06, 1998
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