Water-soluble solder paste is mostly classified in ORH0 or ORH1 which are highly corrosive. Manual cleaning is a risk to spread the flux residue to contaminate the adjacent area. That area might get the corrosion from the leftover residue and have functional or reliability issues when the time pass by. The full cleaning process is recommended to ensure the water-soluble flux residue is completely removed from the boards.
Patinya Srianan
Customer Technical Support Engineer, Alpha Assembly Solution
Mr. Srianan is a Customer Technical Support Engineer for Alpha Assembly Solution. He has 15-years of experience in SMT and soldering fields. He takes care of all technical inquiries and problems for customers in Southeast Asia and Australia.
IMO, spot cleaning can create additional contamination to the PCB. Re-cleaning the entire PCB is my opinion.
Jerry Karp
President, JSK Associates
Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.
As flux vehicles of water-soluble solder pastes for most water soluble paste are highly activated (ORH0, ORH1), they have high corrosion potential, Any remaining flux residues post-soldering and have to be cleaned , usually using DI-water or an aqueous based cleaning mix. To make sure for post-rework assemblies all contamination is removed for good reliability, a full cleaning process within an aqueous cleaning machine (Inline or batch) is the preferred solution.
Manuel Schöllig
Product Manager Soldering, Inventec Dehon
Product manager for soldering products, including solder pastes, liquid and tacky fluxes.
It depends on the extent of the rework. If the rework is done to a single component, hand cleaning is sufficient. If the rework is on multiple devices or a component such as fine pitch SMT leads, using an inline washer should remove flux and other contaminants efficiently.
Robert Freid
President and Founder, Contract Manufacturing Consultants, Inc.
Robert Fried helps leading electronics OEM's develop world-class sourcing strategies for PCBA, cables, precision metals, plastics, modules and complete end-products. Other service areas are supplier risk assessment, comprehensive outsource ...
As you mentioned, cleaning can be done manually in the rework area or fully clean the PCBA in a washing system. In either case, water-soluble fluxes must be removed, unless they are tested and designated as “safe” to leave on the PCBA. Manual rework with liquid fluxes and gel fluxes lends itself to spreading of the flux away from the rework area. Manual cleaning may not remove all of the flux residue. It is best to fully clean the PCBA in a washing system to ensure that the flux residue is fully removed.
Tony Lentz
Field Applications, FCT Assembly
Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.
I have seen far to many cases where local cleaning is not a removal of residues but a re-distribution of residues and failure follows. If you do not have water intolerant parts on your assembly, it would be best to follow with a pass through an in-line or batch cleaner.
Doug Pauls
Principal Materials and Process Engineer, Collins Aerospace
Doug Pauls has a bachelors in Chemistry & Physics, Carthage College, BSEE, Univ of Wisc Madison. He has 9 years working experience for US Navy - Materials Lab, Naval Avionics Center Indianapolis. 8 years Technical Director, Contamination Studies Laboratories. 11 years Rockwell Collins Advanced Operations Engineering.
With water-soluble fluxes it will be best to clean the whole PCB again. If you already have a water wash system why not use it? Spot, i.e., manual cleaning, especially on WS fluxes can be risky. How can you guarantee that the flux did not migrate away from the work area only to dry down under a flip chip or other low standoff components?
Lastly, isopropyl alcohol and other common solvents used for spot cleaning are not effective on WS fluxes. Using the cleaning theory of “like clean like” WS fluxes require water or water-based solutions to be effective.
Charlie Pitarys
Technical Expert Sales Support, Kyzen Corporation
Charlie Pitarys has over thirty years of industry experience and has been with KYZEN for twenty-one years. Charlie is a former Marine and a retired Sargent First Class in the Army Reserves. His previous employers include Hollis and Electrovert. Charlie continues to use his expertise on cleaning processes and machine mechanics to help KYZEN customers and partners improve their cleaning operations.
The amount of cleaning you do on your parts depends on the level of reliability that you are building your assemblies. If it is an assembly that is going into a system where there could be a risk of life, then by all means clean the boards in some type of cleaning system or machine. It doesn't have to be complicated. It could be an immersion, or quick rinse, in a good blended polar solvent, manufactured by Florachem, Vantage, or Kyzen, followed by a rinse with IPA.
However, if your level of reliability is low, such as for Ground Serviced Equipment, then simply clean the reworked area with a splash of DI water, the follow it with a localized cleaning with a brush and IPA.
The more you clean, the higher the reliability that the assembly will not fail. Leaving contamination on the board will always invite shorts through the dendritic growth, or similar problems.
Rick Perkins
President, Chem Logic
Rick Perkins is a chemical engineer with more than 33 years of Materials & Processes experience. He has worked with Honeywell Aerospace in high-reliability manufacturing, as well as with several oil-field manufacturing companies. He also has a good understanding of environmental, health, and safety regulations.
The standards say get it clean, they do not say how, for the most part. How clean depends on the application and or the customer’s requirements.
A full wash and clean rinse assures the offending materials are completely dissolved and rinsed away. Spot cleaning can leave dissolved contamination behind once the liquid has evaporated. Unless you can fully rinse the spot with clean solution, you’ll just spread the contamination around vs removing it.
Paul Austen
Senior Project Engineer, Electronic Controls Design Inc
Paul has been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 45 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, engineer, manufacture, and customer. His focus has been the design and application of measurement tools used to improve manufacturing thermal processes as well as moisture sensitive component storage solutions.
I would strongly recommend full cleaning through an aqueous cleaning system preferably with a Proprietary cleaner to ensure proper cleaning and Neutralisation of the flux medium used. Local cleaning is very likely to spread activators under components and very unlikely you will remove 100% of these which will cause an issue in the field.
Greg York
Technical Sales Manager, BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
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