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Solder beading with PCB from different fab

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#64063

Solder beading with PCB from different fab | 31 March, 2011

We recently decided to try using a different source for our bare boards to save money. On two different batches of PCBs now from the new source, we are seeing beading including some serious enough to short out underneath 0805 parts.

We have never really had many problems with beading or balling in the past, and did not change our reflow profile, stencil, paste, etc, or any other parameter other than board source.

Any suggestions on what could be causing the problem and how to fix it (other than just not ordering from the new pcb source again)?

Thanks,

TK

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#64066

Solder beading with PCB from different fab | 1 April, 2011

the cause could be moisture in your pcbs. To check it...pass some bare pcbs through your reflow oven (this is a simple way of drying them out a bit), then paste and place and reflow as normal....if solder beads disappear then the pcbs have too much moisture in them. I have experienced this once....damp pcbs and the only issue was mid ship solder balling no other defect. Then if it solves the issue, dry all the pcbs or get the supplier to dry them.

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#64085

Solder beading with PCB from different fab | 5 April, 2011

Thanks! That definitely seemed to help.

TK

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#64086

Solder beading with PCB from different fab | 5 April, 2011

maybe the pcbs need a proper dry (the quick dry in the reflow oven won't get all the moisture out )...maybe 125 C for 4 hours or speak to the manufacturer to get their recommendations.

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#64094

Solder beading with PCB from different fab | 6 April, 2011

TK,

Hope you got it right only for this round of assemblies.

Well, passing through a Reflow belt is not an ultimate process to dry circuit cards & take out moisture from Solder finished layers.

First of all, if the packs were not unsealed (even sealed packs to go for baking if the validity expires) & falling under the spec which your PCB supplier set for baking them in a humidity chamber, need not go for baking process.

And the best practice to bake them is to go for 125°C for 4 Hours as Cooper stated but to make them stand in vertical direction using trays (withstand able) so that hot air would reach PTHs & make moisture dry out.

If the moisture was not the root cause, check for other factors such as stencil thickness, opening & type, reduction, printing parameters, placement force, thermal profile & finally, rheology of solder paste.

Many Thanks, David.

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#64136

Solder beading with PCB from different fab | 8 April, 2011

Just wanted to say thank you to everyone for your help. We will do a long bake for all future PCBs ordered from this vendor.

TK

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