Ask the Experts
October 4, 2017 - Updated
August 25, 2008 - Originally Posted

Cleaning Water Soluble Flux

I have a problem cleaning water soluble flux. The flux specification as defined is to use hot de ionized water under pressure. My cleaning machine does not apply pressure, it works more like a dishwasher and rinses boards. Is there a way to clean flux with a chemistry and what would the chemistry be?

A. Y.

Expert Panel Responses

The success of a defluxing process relies on two capabilities, the equipment's ability to deliver water (or wash solution) to all areas of the assembly, including under components, and the ability to deliver enough mechanical energy to fully solublize the flux. Additionally, the equipment must provide sufficient water diffusion and impact pressure to remove the newly solublized flux through the rinse cycle. Low impact, low diffusion defluxing equipment such as dishwashers and laboratory glassware cleaners are not ideal defluxers. I would not recommend running a defluxing chemical in a low powered, low impact dishwasher / glassware cleaner. At issue is the fact that all defluxing chemicals lower the surface tension of the wash water. As a result, wash solution, including the chemical, is deposited under components. During a low power, low impact rinse cycle, the higher surface tension rinse water can not get under the same components that the chemical enriched wash solution reached. That means wash solution, including the chemical may be trapped under the component, producing devastating results. Your defluxing equipment should produce significant impact pressure and should provide a spray diffusion pattern that facilitates thorough wash and rinse. I would recommend that you stay away from low powered dishwasher / glassware cleaners and consider high impact spray-in-air defluxing equipment.

Mike Konrad
Aqueous Technologies
Mr. Konrad has been in the electronic assembly equipment industry since 1985. He is founder and CEO of Aqueous Technologies Corporation, a manufacturer of automatic de-fluxing equipment, chemicals, and cleanliness testing systems.

There are many water-based cleaners available on the market which may be suitable for your application. Electrolube have a range of such materials called the Safewash range. These are used throughout the electronics industry for cleaning flux residues, uncured pastes and adhesives and heavy greases. I would suggest SWAP as a good starting point for your application. This product is suitable for use in dishwashers due to its low foam action. I would advise testing with your particular flux and checking the suitability of this product in your particular type of machine. There are other cleaners in the range that may be more suitable for your application, although I think SWAP is a good start. Please see the Electrolube website for more information.

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.

There exist a wide variety of water soluble flux chemistries and they do not all leave the same residue. My first piece of advice is to call your solder supplier and ask what chemistry is most appropriate for removing their flux residue. My second piece of advice is to call a cleaning chemistry supplier and find out if they have performed cleaning tests with your brand of solder. Several have extensive libraries of test results and can immediately recommend a proven product. Look for their advertisements in anindustry publication. Web searches were disappointing. In the absence input from either, try a bench toptest with DI and ammonia (the concentration required varies.) If the residue is largely spent acid byproducts, the ammonia will crack their bonds, turning them into salts which will dissolve readily. Whatever you end up with as a solution, be mindful of waste water disposal regulations if you choose to add any chemistry to your wash process waste stream.

John Vivari
Application Engineering Supervisor
Nordson EFD
Mr. Vivari has more than 15 years of electronic engineering design and assembly experience. His expertise in fluid dispensing and solder paste technology assists others in identifying the most cost effective method for assembling products.

Dishwasher type batch cleaners do have a certain impact pressure on the board surface which should yield in better cleaning results than a simple soaking process. However, the impact pressure in batch cleaners are not compared to the ones attained in conveyorized inline cleaners. What is your current wash temperature and wash cycle time? For dishwasher type batch cleaners, you could use an aqueous (water) based cleaning agents which would increase the performance of your wash process and remove the flux residues completely. Even at lower wash temperatures and shorter wash cycle times. This would save operational energy costs and increase your washed board throughput at the same time.

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".

To answer your question; cleaning a watersoluble flux with a flux cleaning chemistry at a concentration of 5% is arelatively common practice as it helps to flush cleaning fluid in tight spacesby lowering the surface tension of the cleaning fluid to 1/3 that of wateralone. The alkalinity from the cleaningagent can also help cleaning by forming soluble salts from the organic acidsoften found in water soluble fluxes. Washing and rinsing pressures are very important becausethey provide energy to flush the flux and chemistry from under tightly spacedcomponents. All "Dishwasher" style board cleaners aresubject to lower surface energy, inconsistent energy distribution and shadowingdue to board racking variations. Inline cleaners provide higher, more consistent surfacecleaning pressures and are better than dishwasher style machines at cleaningand rinsing residues in tight spaces. I would recommend looking at an inline water cleaner,possibly with a 3-5% chemistry concentration to improve your cleaning process.l

Steve Stach
Austin American Technology
Founder and President of AAT. Steve holds numerous patents and has authored numerous research papers and articles in cleaning and soldering. Steve is a founding member of the Central Texas Electronics Association and is a past Director of IMAPS. Steve is active on several IPC cleaning committees.
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