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Selective Soldering - Barrel Fill

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Selective Soldering - Barrel Fill | 14 October, 2010

Heck, now I look up and see this is SMTdotNET. Do I get banned for asking a TH question?

So here's my first real TH issue after living so long in the SMT world.

We are having a sudden issue in what has been a stable process for quite some time. It appears to be confined to a particular lot of PCBs. Finish is ENIG. Solder is good old SN63/Pb37, flux is DI water washable. PCBs are baked for 24 hours before SMT processes, and all soldering processes are completed within 48 hours.

After the selective soldering process we are suddenly experiencing what I would call a de-wetting issue in the barrels of a particular high pin count connector. Same connector location, but random barrels.

We are required to inspect the barrels by X-Ray for correct fill, and we see 100% fill for a year now, and then suddenly this random lack of fill, although the solder is reaching the topside of the PCB, which we can visually observe.

Again, a mature process, all maintenance on the machine is up to date, and the solder maintenance is up to date and within spec as well. I am thinking some kind of contamination.

Can some folks from this enlightened group share some thoughts on where or what I might be looking for? I am not strong on PTH technology.

Thanks all.



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Selective Soldering - Barrel Fill | 15 October, 2010

What you have is blowholes. Baking your boards prior to soldering will help. Root cause is either barrel plating too thin or barrel cracks allowing laminate moisture to escape.


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Selective Soldering - Barrel Fill | 15 October, 2010

Well, we got the baking part right at least.

I would think that would help to rule out the barrel cracks allowing moisture escape. Plating too thin makes sense to me.

In any case, do you think barrel cracking would be observable on a bare PCB? We have up to 200x available. I don't know if others do an inspection of this sort at Receiving or not.

Thanks Patrick

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Selective Soldering - Barrel Fill | 15 October, 2010

Inspecting for plating problems shouldn’t be part of incoming inspection. Your board manufacturer should have the appropriate process control.

I shouldn’t have said barrel cracks but plating skips. Plating skips are caused by dull drills or a too high drill feeding speed. Both will produce carbon smear in the barrel not allowing plating over the smear.

If you will reheat the defective solder joints you will see bubbling of the molten solder. This is a problem that needs to be addressed with the board manufacturer.


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Selective Soldering - Barrel Fill | 22 October, 2010

To get out of a delivery pinch, I had to pre-tim some connectors because of contaminated leads. Make sure your selective wave speed and XYZ travel are close. Try doing a dry run across the board to preheat the PTH and then go back and solder them.

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Selective Soldering - Barrel Fill | 22 October, 2010

Thanks for the help guys. Nice to think I was basically on the right path.

PCB manufacturer has finally conceded the barrel defects and is remaking the PCBs.

We are big on pre-tinning the leads of TH connectors as well as providing some good preheat before soldering with the Selective sodlering machines.

One thing I have learned from this, is that you have to go with your guts. I could look with my eyes and see there was an issue at the through holes, and still had to endure the litany of lame questions about an established process. What is your solder pot temperature, what kind of flux do you nauseum... sometimes you just want to take these guys out back and cut a switch.

In the end, lost about 6 days to the defect cause investigation, and then another 6 work days to replace the PCBs, not to mention the ($)fight over the 1000's of SMT components already placed on these mixed assemblies...

Live and learn, and thanks again all.

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Selective Soldering - Barrel Fill | 25 October, 2010

Thank you for the feed back. This is many times missing in the forum “how the problem got solved”.


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Selective Soldering - Barrel Fill | 28 October, 2010


An useful information (Bruneel is right) that concluded with a root cause Note. Appreciated Heguman, Bruneel & John.

Many Thanks, David, India.

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