Ultrasonic Cleaning Solution Recommendation

What cleaning solution would you recommend for cleaning electronic circuit boards using ultrasonic cleaners? What temperature setting would you recommend?

D. D.

Expert Panel Responses

Any water based or solvent based PCB cleaning agents could be used in your ultrasonic equipment depending on the brand / id number of the paste / flux you use and your process requirements. Is this going to be a post solder cleaning or pre-solder (misprint) cleaning? Please contact Zestron Corporation (phone: 703-393-9880) for cleaning agent and wash settings recommendation. We would gladly assist you. For water based cleaning agents, you could go up to as high as 160 degrees F as they are not flammable; however for solvent based cleaning agents, due to the fact that they might have a flash point, you need to operate either at room temperature or 20 degrees C below the product's flash point to be within a safe process window.

Umut Tosun
Application Technology Manager
Zestron America

Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".

The cleaning solution chosen will depend on the residues you are trying to remove. There are many cleaning products available that would be suitable for ultrasonic application. The temperature that these should be used at to effectively remove the residues will depend on both the cleaning chemistry and the application. Your best option would be to discuss the details of your application with a materials supplier so that a suitable process can be developed. If you wish to discuss this further, please do not hesitate to contact me direct.

Jade Bridges
European Technical Support Specialist
Electrolube Ltd

Jade Bridges is the European Technical Support Specialist for Electrolube. She is responsible for technical support within Europe, offering assistance to customers with product selection, implementation and after sales support across the range of Electrolube products. Her expertise is carried over from her position as R&D Manager for Electrolube, where she was responsible for the new product development and technical support across an array of chemical products for the electronics industry, including conformal coatings, encapsulation resins, thermal management products, contact lubrication and electronic cleaning solutions.

My recommendation would be any of a number of well-known, neutral-pH, aqueous-based cleaning fluids. MicroCare has one such product, called the Reflow Oven Cleaner (#MCC-ROC) and it, or many of its competitors, would be a good choice. There are a couple of factors you should keep in mind:

Make sure the fluid is versatile and strong enough for the contamination you're trying to remove. Alcohol actually cures flux residues if they are not completely rinsed away, so cleaning can become harder and less effective. The Reflow Oven Cleaner cuts through the residues. It can be used on PCBs, plus on pallets, conveyors, flux condensers, baffles, heating elements, clamps, chains, pulleys, gears and housings. It is suitable for hand-wiping or ultrasonic dip tanks.
Make sure it is a non-foaming fluid. Some very good cleaning products when agitated with ultrasonics generate foam in surprisingly large quantities. It can be a mess to clean up. Avoid at all costs.
Make sure the fluid leaves no residues. So (many) aqueous cleaners contain additives to help the water clean better. These additives (basically soap etc) can linger on the board, causing more problems than they solve. You want something with almost no residues, even when measured in ppm.
Make sure it is nonflammable. Never, ever put flammable liquids in ultrasonic tanks. It can create an oxygen-rich mixture of flammable vapors over the machine and the slightest spark can cause an explosion. (This includes, by the way, isopropyl alcohol. I can't tell you how many times I've seen people using IPA in an ultrasonic machine and nobody ever told them it was dangerous.)
If possible, get a fluid that works better when warm. Warm fluid clean better than cold ones. That's why the Reflow oven cleaner is engineered to clean best between 40-50 degrees C.

Remember that aqueous cleaning is limited by the chemistry of water. Because of the surface tension, viscosity and density of water, it's limited in its cleaning effectiveness, particularly on denser PCBs with tighter stand-offs. If you're not getting the cleaning results you need, it may be time to upgrade to a modern vapor degreaser with a nonflammable solvent cleaning fluid. Learn more at http://bromothane.com/Bromo_FAQs.html or http://vertrelsolvents.com/faq/FAQ_Q50_BetterThanAqua.html.

Mike Jones
Vice President
Micro Care

Mr. Jones is an electronics cleaning and stencil printing specialist. Averaging over one hundred days a year on the road, Mike visits SMT production sites and circuit board repair facilities in every corner of the globe, helping engineers and technicians work through the complex trade-offs today's demanding electronics require.

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