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October 31, 2016

Options for Reducing Dross

What are all the possible options we should explore to cut down on the amount of solder dross we see in our wave soldering system?



V. M.

Experts Comments

Hundreds of customers worldwide and many of the worlds large contract manufactures have found the best way to handle dross on your wave is to mechanically recover the pure solder which will be between 80% and 90% of the dross by weight.

Using and EVS Solder Recovery System is fast and simple and will recover 50% to 70% of this solder from the dross by weight in only a 6 to 10 minute cycle with no extra work than what you are doing now when you dedross.

The ancillary benefits of using a solder recovery system are many and documented. You will get a much cleaner wave which will reduce shorts and bridging on your PCB leading to significant reductions in rework.

As you have a cleaner wave you will get less maintenance on your pumps and nozzles and as you can significantly reduce the time it takes to dedross productivity will improve substantially.

You are putting back in to your wave exactly the same solder that is already there with no additives in to your process.

For full details have a look on the EVS website http://www.solderrecovery.com/

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Simon G. Norman
International Director
EVS International
Simon G. Norman is the international director for EVS International, the Leader in Solder Recovery.

To reduce the dross in the wave machine it is important to keep the active surface as low a possible.

That means the solder level has to be always maintained, the distance to the waveformer should be as short as possible. Every millimeter distance more increases the falling hight and therefore the oxidation surface.

Most wave machines have a standby function in case there is no board present. If thereis a between theboards , the wave goes to a standby level and the wave formers stop flowing. This standby function can safe up to 20% dross formation.

The smartes way isto save dross and cleaning is to use a local N2 cover at the wave. If you run a full shift up to 3 shiftproduction you can implement a full tunnel N2 machine. The invest of a tunnel machine can be justified with 1 max 2 years.

I have customer they running without maintenance for one month on their wave machine. The savings can be up to 50 000USD per year!!

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Christian Ott
Sales Manager
Seho
Christian Ott knows electronic manufacturing companies around the world and their specific requirements. He has hands on experience with Selective, Reflow and Wave soldering processes.

Options to reduce dross in wave soldering systems are:

  1. Use nitrogen blanket over the waves, depending on cost of nitrogen gas,
  2. Use oil blanket over the wave soldering pot (beware of any oil contamination)
  3. Use the narrowest width of wave required, eg, don't buy a 24" wave for 6" width PCB
  4. Use selective wave soldering machine if there are only few components to be soldered
  5. use the lowest wave height required, cut the thru hole lead length to the shortest possible.
  6. use only good quality solder bar, some cheap solder bars are recycled from solder dross
  7. Use solder recovery systems, that squeeze hot solder dross to separate molten solder from oxide
  8. Turn on the waves only when the PCB is near the waves (towards the end of preheating zones), and not permanently on.
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EH Lim
Managing Director, Asia Pacific
ECD
EH Lim has been in the PCB Assy industry since 1985, starting at Thomson/Singapore for 5 years before moving to Electrovert Asia Pacifc. Lim was Sales Director for Vitronics Soltec prior to joining ECD in 2007 as Managing Director for Asia Pacific.

My recommendation is to use the MS2 product from PK Metal. Contact Larry Kay at larrykay@pkaymetal.com

We have done extensive testing and it works great.

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Terry Munson
President/Senior Technical Consultant
Foresite
Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.

I would suggest you contact your solder supplier, most supply a dross reducing fluid that is specific for your formulation of solder.

Most of these fluids float on the top of your solder bath reducing the amount of oxygen that contacts the solder.

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Edward Zamborsky
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
Reader Comment
Insure all the bits & pieces of your wave formers are in place & functional. Some manufacturers provided dross & choke plates to build up a secondary solder level to reduce the vertical fall which in turn reduces dross. I've seen many waves where these parts were removed years ago as those who knew of their function are retired or dead & buried. (I'm the exception)

Another great point touched on by EH Lim an old EV colleague is to raise the pot and lower the wave. Many assemblers have a universal pot setting and that has to account for the longest leads or protrusions meaning 95% of assemblies could probably run with higher pots and lower wave settings. My 2 cents.
Ray Chartrand, Chartrain Consulting, USA
Reader Comment
Mechanical dross "squeezing" does not recover metal, it just separates the oxide from the metal that has not really become dross yet. Liquids come in two categories, some like oils just inhibit oxygen from getting to the solder, they slow down dross formation some but they have other issues. The newer technology, such as MS2 from P.Kay Metal actually breaks the organometallic bond, liberating the oxygen and allowing pure, clean solder to return to the solder pot ready for use.

It works very well and it greatly reduces the consumption on an expensive commodity. solder. This process is now being used on many hundreds of lines world wide and its use is accelerating.
Dan Feinberg, Fein-Line Associates, Inc.
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