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Solder Balls on Neighboring Components After Rework
Board Talk
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TranscriptPhil And welcome to Board Talk with Jim Hall and Phil Zarrow, the Assembly Brothers, who by day go by ITM Consulting. We are here to help you with electronic assembly problems, questions, and whatever else you are struggling with out there. So Jim, today’s question is from TW. It concerns solder balls. Oh, those insidious little solder balls. During the rework of SMT components on conformal coating boards we see solder balls occurring on neighboring components. How can this be eliminated? Jim First thing I think of is where did that solder metal come from to create that solder ball? Did it come from the solder on the site that you are reworking or did it come from the previously soldered joint on the adjacent component? Phil Right, because this brings up the question of whether you are getting parasitic heating of that adjacent component or not, which could be another problem. Jim For anyone who had dealt with rework, particularly on complex boards, perhaps one of the biggest issues is protecting the adjacent component. That means both components, the obvious right on top of the board on the same side of the board the repair site which are just horizontally adjacent to it. But also the components on the bottom. A repairer’s worst nightmare is a mirrored BGA or large component of any size trying to protect the bottom component and still get the top component hot. Melting can be a real problem. Also, I point out the inner layers of the circuit board under the component that is being repaired. If the solder ball material is coming from the adjacent component, you are obviously overheating it. Then what causes that? We assume it is coming from adjacent components. Solder metal that is creating that solder ball is coming from the adjacent components. Even if you are heating it up, why should it produce solder balls? That raises the question of contamination to me, physical damage. That tells me that you need to remove the conformal coating from the part that you are actually going to rework or repair. Then that throws out the question, how did you do that? Did you do it with heat? Did you do it with chemicals? Did you do it with some mechanical upbraiding process? Depending on the answer of that, is it possible that that technique is damaging or contaminating the solder joints on adjacent components. Phil Take a good look at this TW and everyone else who is suffering form a similar malady. Jim Yeah, the first thing is where is that solder coming from? Maybe setting up a good quality video camera during the rework, and see if you can see where that solder is coming from. If it is ending up on adjacent components and coming from the joint that you are reworking, you should be able to see that solder move if you take a good video of it. Maybe from a couple of angles. Understanding that is going to guide you to where the potential solution is going to be. Phil This is Phil Zarrow and Jim Hall of ITM Consulting and Board Talk wishing you a very good day and thanking you for joining us. Please remember, whether you are getting solder balls or not, don’t solder like my brother. Jim And don’t solder like my brother. |
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