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Disposal of ultrasonic cleaning water

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Disposal of ultrasonic cleaning water | 24 June, 2008

We are purchasing an ultrasonic cleaner to clean pcb asseblies that have been produced with water soluble flux based solder. After cleaning a batch of assemblies, the water in the cleaner will need to be disposed of. My question is: Do we need to filter out the flux residues from this water before disposal or can we just pour it down the sink drain as is?

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Disposal of ultrasonic cleaning water | 24 June, 2008

Your flux residues may be acceptable for your drain, but the solder balls won't be. You'll need to filter and dispose of the filters per your local city, county, and state regs. Either that or just boil the water off and dispose of the dry remains with your lead contaminated towels, gloves, etc.

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Disposal of ultrasonic cleaning water | 24 June, 2008

I know it is not what you want to hear, but first and foremost, you must consult your local regulating agencies and here is why: Solder paste contains heavy metals. We are all familiar with the problems associated with lead, but lead free solder paste also contains other heavy metals that are toxic and regulated such as antimony, bismuth, copper, silver, tin and zinc. In many parts of the country, less than 2 ppm of lead is allowable for discharge to drain. Allowable limits for the other heavy metals vary considerably.

These heavy metals are easily filtered using simple micron filtration. However, when exposed to a liquid medium such as water, heavy metals will dissolve (ionize) in solution. My experience is that it takes lead solder balls less than 3 days to ionize in water to a concentration greater than 2 ppm. It takes less than 2 days if high quality DI water is used. In their ionic state, heavy metals will pass through a simple micron filter.

If the wastewater is filtered every day using a 1 or 2 micron filter before the heavy metals have time to ionize, micron filtration may be an answer. But if the solder balls are allowed to stand in solution for more than 24 hours, depending on the allowable discharge levels of each heavy metal, micron filtration may not be effective and more expensive ionic exchange or reverse osmosis filtration may be required.

In any case, discharging filtered heavy metal effluent to drain exposes the user to federal Super Fund regulations and potential liabilities even if the filtration process is 100% effective. In a nutshell, the Super Fund regulations state that if heavy metal contamination is found within a 50 mile radius of the user�s facility and the source of the contamination cannot be identified; all users within the 50 mile radius using the drain system for discharging filtered heavy metal effluent will be responsible for the cleanup. This is why wastewater evaporators and closed-loop systems have become popular; they remove the user from the selection pool of potential liability because the drain is not used.

If you should have any additional questions, please feel free to contact me directly.

Bill Schreiber Smart Sonic Corporation Tel: 1(818) 610-7900

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Disposal of ultrasonic cleaning water | 24 June, 2008

There is also an article in the March 2007 issue of U.S. Tech magazine that reviews ultrasonic cleaning technology for PCBs titled "Reducing the Cost of Misprinted PCBs". The information is also relevant to post reflowed PCBs. A PDF copy of the article is available at:

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Disposal of ultrasonic cleaning water | 2 July, 2008

We use a "water Eater" to boil off the water, it escapes as water vapor. The residue we collect and dispose of as part of out Hazmat process. Keeps everything out of the drains.

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