Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

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Solder balls



Solder balls | 2 May, 2001

Can anyone tell me what they think is the main cause of excessive solder at the end of the lead after wave. These are not solder peaks as if the leads were cold. It is a well wetted ball of solder on end of the lead. Also, some times you see excessive solder on bottomside chip caps, could this be the same thing?

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Solder balls | 3 May, 2001

Now, I'm not going to talk solder balls, in a traditional sense. I have an image of bilbous, globs of excess solder near the ends of PTH leads. If that's not what you have, ignore the following [and help us understand your situation better] ...

You're probably correct that the cause of excess solder on second side SM devices is related to the cause of excess solder on PTH leads.

There's a variety of things to suggest, but the basic cause is the leads are too hot relative to the pads on the board. So the first things to consider are: * Uping the conveyor speed. * Lowering the pot temperature. * etc.

Second level things are: * Decreasing the amount the board is immersed into the solder pot. * Checking the solder pot for contamination. * Evaluating the angle of the conveyor to the pot. * Determining if the board pads are contaminated.

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Solder balls | 7 May, 2001

One thing I forgot to add about the globs of solder on your bottom side SMT components after wave soldering: The excess solder is likely reducing the reliability of these components, because of the difference in CTE betweeen the ceramic base on the component and the glob of solder. This problem increases with the size of the component.

Consider taking timely steps to prevent recurrence of this problem and monitor field failures.

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Solder balls | 9 May, 2001

What type of preheaters do you have on you're wave? I have to agree with Dave. Your leads are not cold, they are hotter than the annular ring on the PCB. This would cause the solder to go to the lead only rather than the component and land pad / annular ring. You may also have a problem with your fluxer. Is it ultra-sonic or of the "squirt gun" variety? Ultra sonic fluxers, when not properly set up and maintained, can be the bain of a good wave soldering process. The other thing you may want to look at is the stability of your lambda wave. I'd seen a really crappy wave where the lambda wasn't at all smooth and would cause random solder skips on the assembly. That's my two cents.

Talk to ya soon.


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Solder balls | 17 May, 2001

I would have to agree that the leads are probably geting to hot, but there are many factors that could be the root cause. I would suggest doing a experiment with a solder sample and make 2 recipes. One with a relativly cold profile and one with a relativly hot profile and see what the results are. This will give a general idea of where to start to troubleshoot the problem down to its root cause

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