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Pb-Free wave Soldering - With or Without N2 ?


Pb-Free wave Soldering - With or Without N2 ? | 17 May, 2004

Straw pole time folks,

how many have or are doing wave soldering of Lead free products and are you using N2 in the process, what level of solids are you using and are you cleaning?

I've heard a story that soem people in Japan are running a high solids flux of around 10% for the Pb-Free wave and so not having to use N2 ont he bath, anyone any thoughts?


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Pb-Free wave Soldering - With or Without N2 ? | 17 May, 2004

I am an equip mfrs rep. I took a customer to my wave solder principal's factory to run their boards on a wave with no-Pb alloy, (Sn96.5 Ag3.0 Cu0.5) in air environment. The results were excellent with pot temp of 263C (505F). Their boards are low to medium thermal mass. Some are single sided; others double sided with SMT components on the bottom side. My wave applications engineers say you do not have to have N2 to get good soldering and we proved it to this customer. Higher solids fluxes are desirable due to the elevated forced-convection pre-heat settings. Some low-solids fluxes don't hold up well enough. This customer uses Alpha NR330 VOC free 4% solids NC flux and it held up well. So, I can comment for this customer in that they are developing their process with air only. Having about fourteen wave solder machines, you can imagine they�re not wanting to fit $$$$ all those machines with nitrogen. N2 gives you a larger process window for wave soldering, but is not mandatory in all applications. A lot of consumer electronics mfrs. are using an alloy with no Ag. I have no experience with those alloys, but heard from my wave solder machine principal that they create a lot more maintenance issues on the machine, creates more dross and has a smaller process window that SAC305 or SAC307 alloys.

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Pb-Free wave Soldering - With or Without N2 ? | 17 May, 2004

I disagree about the maintenance issues with tin/copper solder. All high tin content solders are hard on machines (silver or not). More dross? Controlling the back flow, front flow velocity and AVOID constant surface cleaning will reduce your dross production (lead or lead-free). Also, only use the chip (turbulant) wave when required. I have noticed a tendency for some to use it for every assembly. This, regardless, if it is warranted or not.

Also, not all machine designs are created equal. Example: I have two diferent machines that run identical alloys and flux. One produces 5X more dross than the other. Both are setup as per the manufacturers instructions.

Oh yeah, if your running a 24 inch machine and 90% of your assemblies are 10 inches wide, yeah your gonna produce piles of dross.

I keep hearing this BS about how sac alloys for wave "improve wetting". Its the flux that will principly affect wetting.

As far as N2...its the same arguement we had in the early 90's. Nitrogen is a great fix all for a defective or marginal process....except it isn't free.

The bottom line here is materials and process evaluation!

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