Barrel fill with Pb Free Wave Solder

Are you using no-clean solder, or just no clean flux?

If you're using a solder with WS flux in the core, and a no-clean flux; we'd suggest switching to a WS flux to help during the soldering.

If you are using a no-clean solder/flux combination, you might try pre-heating the board, or using a hot plate for these areas.

We've experienced the problem that you've noted; but, for us, the fix was to add no-clean flux separately. My solderers typically try not to add flux when soldering no-clean, and try to only use the flux contained in the solder core. For tough to solder joints, the answer has almost always been to use a separate flux on the joint.

You may also consider increasing the iron tip temperature, and ensuring that the solderer stays on the joint long enough. One thing I've found with solderers switching over to lead-free from leaded solder is that they're resistant to staying on the joint longer. To keep the tip temps as low as possible (to minimize damage to parts or boards), we've found that solder time is increased, due to the different performance of the lead-free solder.

cheers ..rob

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on the front end in design, minimize the pth connections to ground planes. this takes alot of work by the pcb designer and the approval of the design engineer.

connect maximum of 4 ground planes to pth, minimum 1 plane. use spoked connections. evely distribute the connected planes vertically in the fab stack-up. increase hole diameter (as pitch allows) to 20 mils over pin diameter. increase hole diameter as pcb thickness increases.

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some lead free solders do not flow well and need encouragment. what are you using solder/flux wise and machine/settings including dwell times cheers greg

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We ran into this problem before, on all of our models. We never quite found out the reason, we do know that if the PCB is passed through a reflow oven that is extremely dirty with evaporated solder paste flux, it will make it extremely difficult (or impossible) to solder through the wave. Oxygem PPM's being too high in reflow can also cause this issue.

The only solution we could find was to crank the flux up to about 2.5x the normal level. This gave us good hole fill on all pins.

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I think the BLT solder joints look very shiny for no-lead. We are getting very good top side solder with ours though. They look like this.

- Gold Enig plating - Alpha EF-6100 Flux - SAC305 - Preheat topside temperatures at 110 to 120C

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