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Solder buildup inside Relow Oven

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Solder buildup inside Relow Oven | 23 October, 2014

Our reflow oven builds solder on one specific panel type. It will have solder buildup inside the oven. We then end up with small solder balls on our panels.

We think it may be the solder paste, the screen printer is leaving a clean wipe under the panels.

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Solder buildup inside Relow Oven | 23 October, 2014

Generally, excess solder balls found randomly around the board/parts points to either a dirty stencil during printing, or a stencil/board that is shifting during printing (smearing the paste a little, and causing a dirty stencil.

If the apertures are pretty small, the stencil wipe may be cleaning the bottom of the stencil, but, it could be leaving paste inside the aperture, which smears when the next board is run.

If the build up area is consistent, I'd start by inspecting the paste post-printing, and see how clean the job is. You could have snap-off issues, board shift issues, or some other factor there. If nothing is detected at the printer, I'd check on the board post placement, to see how the pick/place operation is affecting the solder.

Cheers, ..rob

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Solder buildup inside Relow Oven | 23 October, 2014

Is this happening on a new product you just introduced to the factory? If so, then I would check stencil design. Many moons ago we had a similar issue and discovered we were applying too much paste on the chip parts. We changed to a homeplate design on those aperatures and the problem went a way.

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Solder buildup inside Relow Oven | 27 October, 2014

Are you doing PIN IN PASTE (intrusive reflow) ? If so, then paste can be dripping through the pcb holes and onto the oven bottom heaters / baffles . Or, if any of the SMT pads have vias in them, paste may drip through them if they are not sealed. Where is the solder building up in the oven ?.. Normally solder will fall off pcbs onto the bottom heater or baffle plates...and then I suppose it can be blown by the hot air onto following pcbs !

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