Electronics Assembly Knowledge, Vision & Wisdom
What is the Best Way to Reduce Dross?
What is the Best Way to Reduce Dross?
What is the best way to reduce dross? What are all the possible options to cut down on solder dross? The Assembly Brothers, Phil Zarrow and Jim Hall, offer some options.
Board Talk

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Board Talk is presented by ITM Consulting
Phil Zarrow
Phil Zarrow, ITM Consulting
With over 35 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis. He has vast experience in SMT equipment, materials and processes.


Jim Hall
Jim Hall, ITM Consulting
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics. He is a pioneer in the science of reflow.
Transcript
Phil
Welcome to Board Talk. This Phil Zarrow and Jim Hall of ITM Consulting, known as Pick and Place - the Assembly Brothers! Here to solve some of your process problems! And today -

Jim
You know Phil, we forget that there are a lot of people out there who are new to the industry. What may be basic to us, are questions to some people. We've had several requests come in about reducing dross in a wave soldering machine.

What is the best way to reduce dross? What are all the possible options to cut down on solder dross? First, I think it's appropriate we do a little overview!

Phil
Wave soldering is a process that has been around 50, 60 years now - longer than us! Wow!

Jim
Longer than us - no - not longer than me, Phil!

Phil
Well, okay, okay, we won't go there.

Dross has been an ongoing problem. For those of you who don't know what dross is, it's basically oxidized solder. You have a turbulent condition where a molten solder bath is going through a fountain and the wave tends to oxidize the solder

Jim
That's a good point. Molten solder will oxidize, even without movement, but it's grossly aggravated by the motion of the wave.

And that leads us to some of the basics of reducing and minimizing dross.

1. Don't turn on your solder wave unless you're actually processing boards. Most machines have controls that allow this.

2. Don't pump your wave any harder, higher, or faster than you have to, because that will increase the dross.

3. Don't use your chip wave unless you have to for glued on surface mount components or other reasons, because that increases the exposure of liquid solder to oxygen and increases dross.

4. There are a variety of chemical processes that have been advocated to apply to the wave, or float on top of the wave. Some people have had good success with it. We're not here to sell anybody's product, but you might want to look at what's available.

Phil
What we understand is in some cases these chemical additives work really well, but in other cases may offer no benefit at all. A lot is apparently relative to design of the solder pot and the wave itself.

One of the things we certainly recommend in the wave process, differentiating from reflow, is the use of a nitrogen, inert atmosphere in the solder fountain area.

Jim
But, Phil! Nitrogen costs money!

Phil
It does add cost due to the consumption of the nitrogen, but we're talking about a very small area compared to reflow as we're only inerting over the wave area. We're generally talking about using a nitrogen gas bottle as opposed to having one of those big towers out back.

The savings you will realize - even just with reduction of tin lead dross pays for the nitrogen itself. When you start talking about lead-free, particularly SAC305, it may pay for itself and actually help the process.

Jim
If you choose to explore nitrogen, understand that you must set it up properly and you must maintain it. Many people become disappointed with the results from nitrogen because they don't maintain it. They don't clean the distribution pipes. They don't make sure that their flows are correct at the solder pot, and check the level of oxygen over the pot.

So it can be very beneficial - a tremendous savings achieved over the cost of nitrogen, but you've got to set it up, and you've got to maintain it. If you're not willing to do that, I suggest don't try it. Use the other means.

Many people waste a lot of nitrogen because they don't set it up right and don't maintain the system.

Phil
Whatever you do, you've got to be very diligent about dross removal. You should have a schedule. Often at the beginning of each shift or at the end of each shift, the dross is removed from the solder pot. Dross is the pond scum of the solder pot. And you don't want it there. You want to remove it.

Aside from that, I think we pretty much got that subject covered.

Whether you're reflowing, or wave soldering, or even hand soldering, whatever you're doing -

Jim
Don't solder like my brother!

Phil
Don't solder like my brother! And keep the kids away from that flux pot!
Reader Comment

I just bought the new EVS 500LF so easy to use and this is a fully automatic system and we are recovering 76% solder from the dross we were previously sending away. Might be worth you also taking a look.

Stanislav Besdak, Invensys
Reader Comment

EVS International have been offering the industry solder recovery systems for over 10 years. EVS Systems use mechanical process that recovers 70-80% solder from dross cycle times are very fast and the process is fully automatic also no chemicals powders or oils are used so you are not adding anything to your process The Solder coming from the EVS system is exactly the same as what is in the solder pot check out www.solderrecovery.com for more information.

Simon Norman, EVS International
Reader Comment

Agreed on all counts gentlemen.

Nitrogen though will give biggest bang for the buck as not only does it reduce dross (because no air is present) but it also greatly opens your process window

You use less flux, weeping forces are higher and wetting occurs in less time, things that had to be readjusted when going lead free. No magic bullet however as just like any other part of wave soldering it needs maintenance & calibration.


Ray Chartrand, CharTrain Consulting
Reader Comment

I have also had good results using a nitrogen generator, It does not provide the optimum percentage of nitrogen and you do have to run a tight hood to minimize the volume of nitrogen enriched atmosphere, but does reduce the dross.

The other thing I noted not mentioned is the maintenance schedule. I cleaned my pot every three months, pulling the nozzles and pumps and cleaning them out. This was beneficial for dross control and resulted in better flow with more consistent solder results.

I also drained my pot every three years and inspected for damage as I removed any metallic residues I was not comfortable with.


Bruce Webster, Iridium Communications
Reader Comment

I totally agree with Richard about EVS system in terms of results of dross reduction. I tried other types of dross reduction, that includes N2 and organic chemical dross inhibiting compound, and the best/cheapest one is the EVS system. I would like to add only a point to Richard's comment. If you decide to use EVS system, it's important to prepare a spare parts list for the system. once EVS system needs some periodic preventive or corrective maintenance to keep it working properly. So it will not cost zero after its implementation, cost of maintenance needs to be considered.

Glayson Figueiredo, Philips Medical Systems
Reader Comment

Phil and Jim, very good. Used correctly, nitrogen can strongly reduce dross production in wave soldering machines. With our system, we are able to reduce dross formation by more than 80% when compared with air (or other N2 injection devices). We dropped flux consumption near 50% as well.

Luiz Felipe Rodrigues, Air Liquide, Brazil
Reader Comment

I have a Hollis TDL12 that is working properly but the last few years the dross production has been overwhelming. I will implement an on/ff switch for the wave, although I have seen that the wave stabilizes after a few minutes after initial heat up and I learned that its important for the wave to work for a while before soldering boards. Thanks.

oswaldo, krontec ltda
Reader Comment

Hello Phil and Jim. I'm suprised that you guys didn't mention the EVS Solder Recovery System. With proper de-drossing, the wave will do it's job and with this system, it's possible to reclaim up to 70% of usable solder from each de-dross. Unlike N2, the machine will pay for itself and will not add cost to your soldering process.

In fact, I've heard claims of companies reducing solder purchase quantities by up to 40%. At an ROI, in many cases, of 12 months and under, this is a product you all should be aware of as a wonderful solution. Thanks guys.... I enjoy your bits.


Richard Wilson, Tritec Sales, Inc.
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