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Help With Defective Solder JointsBoard Talk
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TranscriptPhil Jim The bare circuit boards in question are hot air solder leveled. At the problem areas, we notice a yellow stain on the hot air leveled surface on the PCB. Phil So it's obviously something your fabrication shop is throwing into the works. Jim Then it's coated with a water soluble flux. Then it's preheated. Then dipped into a solder pot. It's pulled out. It's blasted with the air nozzles to blow excess solder off the surface pads and out of the plated through holes. At that point, it's completely covered with flux residue and whatever else has been blowing around in the air knife chamber. It has to be cleaned very scrupulously. Likewise on the front end of the process, that water soluble flux has to be properly preheated before it goes into the solder pot. So it's a complex process, but it should give you a really good solderable surface. If you're seeing stains, something was amiss in the way they operated the HASL process, most likely in the final cleaning, but maybe some combination of preheat and airflow or something else, just general contamination. Phil When you start getting below 25 mil pitch parts the topography of the board surface can really throw you for a loop. Another reason you might want to look towards surface finishes other than HASL. Jim All you're doing is melting the solder on the surface of the pad with the solder in the paste. So it's really a much easier task in terms of soldering if the HASL was done right. Phil
Jim Phil |
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