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Flux wave on PCBs

Views: 4506


VB

#73662

Flux wave on PCBs | 10 March, 2015

Hi

I have been struggling with boards for high quality picky customer. I am getting flux waves (like splashed - too hard to clean) after wave, where as we are still using Kester 979 (No clean flux, but as we are getting visible marks which looks similar like dross with flux. I have attached images for reference. In image that's definitely not solder. Its flux and please suggest how to avoid this issue. I have tried changing, flux supply level / pre-heat temps / variant conveyor speeds / solder pot heights. But no luck.

For IMAGES : http://www.keepandshare.com/doc12/show.php?i=2595013

Please help me to solve this.

Thanks

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#73665

Flux wave on PCBs | 10 March, 2015

This doesn't appear on different part number boards does it?

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#73666

Flux wave on PCBs | 10 March, 2015

I know it won't prevent this, but have you tried cleaning with a mix of screen cleaner and isopropyl alcohol in a 1/3rd - 2/3rd solution?

We use this, put on by antistatic brush, and then using an air jet to blow it away. Afterwards, the PCB's look as if they had never had flux on them.

However, it would be better not to get this residue in the first place, but I can't offer any advice for that. It could be something on the PCB that is reacting with the flux?

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VB

#73668

Flux wave on PCBs | 11 March, 2015

Hi

sorry my question may be silly, but am confused by others. That's definitely flux on the board and it's not dross sticking to board isn't it? in images?

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#73673

Flux wave on PCBs | 11 March, 2015

Hi its undercured solder resist which leaves a clear waxy/oily residue and can be seen as brown tar/oil in the molten solder wave. This also causes MicroSolder Balling and some snail trails of solder pick up and worst case bridging and peeling resist. Can be helped with flux choice and can be confirmed with solderMask check wipe. Anymore information please contact me

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#73686

Flux wave on PCBs | 14 March, 2015

The white haze is definitely an indication of moisture being trapped in uncured or improperly applied solder mask. You can verify this by heating up the board using a heat gun on an area of the board with the white haze, and if it clears up that is the issue. And if your not seeing this issue on other assemblies, then it is definitely a raw fab issue. Poor solder mask can cause all kinds of issues. Suspect your picky customer is buying the cheapest fabs they can get.

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