Ask the Experts
June 13, 2024 - Updated
April 4, 2018 - Originally Posted

OA Flux Turning Blue

We use Organic Acid (OA) Flux with our Selective wave and Wave Soldering operations. I have noticed after some period of time the OA flux turns blue. What might be the reason behind this? The flux isn't expired.


Expert Panel Responses

There is more information needed but I will take a swing at this. If the flux is still in the original container I would ask the Flux manufacture what might be happening. Some Flux products with reacted when exposed to heat or direct sunlight.

If this is happening in the machine I would inspect for something that is being eaten or attacked by the flux in the flux container.

Michael Kaminsky
Sr Field Applications Support Engineer
Kester Inc.
Mr. Kaminsky has 30+ years of circuit board soldering assembly experience along with a patent for wave solder VOC flux process.

I am assuming you are talking about flux in the fluxer and not in its original container - most likely dissolving copper from the non plated portions of device leads exposed post trim and form.

Gerard O'Brien
S T and S Testing and Analysis
Gerald O'Brien is Chairman of ANSI J-STD 003, and Co Chairman of IPC 4-14 Surface Finish Plating Committee. He is a key member of ANSI J-STD 002 and 311 G Committees Expert in Surface finish, Solderability issues and Failure analysis in the PWA, PWB and component fields.

Many ingredients used in organic acid fluxes (OA) combine with copper to form blue colored compounds. It is very likely that some copper has been dissolved into the flux giving it a blue color. An ICP or AAS test for copper would confirm the presence and concentration of copper in the flux.

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.

Since organic acid (OA) fluxes have a high activity level they are generally used for component lead tinning but are typically not used for selective or wave soldering since the post-soldering residues are highly corrosive and immediate removal from a printed circuit board assembly is mandatory. If the OA flux is turning blue over time this could be the result of nickel chloride contamination.

When soldering boards with an ENIG (electroless nickel immersion gold) surface finish, the chloride in the OA flux can combine with the nickel if the gold plating is too thin or if the gold plating is porous. If not properly monitored the gold plating thickness can be as thin as 1 micro-inch which is less than the Class 2 requirement of 2 micro-inches. Since the flux is not expired it's always a good idea to check with your flux supplier.

Carlos Bouras
General Manager
Nordson SELECT
Carlos Bouras is the General Manager of Nordson SELECT and has over 30 years of experience in the electronics manufacturing industry. Carlos's expertise is in process engineering, product development and manufacturing operations. For the past 15 years Carlos has focused specifically on automated assembly issues and is the holder of several US patents for non-contact dispensing and precision dispensing of adhesives for the packaging of microprocessor devices.

The flux is likely corroding copper or other exposed metal. OA flux is meant to be cleaned shortly after soldering so as not to result in corrosion.

In these times, is it really necessary to use OA? A switch to No-Clean would reduce incidence of corrosion.

Gary Freedman
Colab Engineering
A thirty year veteran of electronics assembly with major OEMs including Digital Equipment Corp., Compaq and Hewlett-Packard. President of Colab Engineering, LLC; a consulting agency specializing in electronics manufacturing, root-cause analysis and manufacturing improvement. Holder of six U.S. process patents. Authored several sections and chapters on circuit assembly for industry handbooks. Wrote a treatise on laser soldering for Laser Institute of America's LIA Handbook of Laser Materials Processing. Diverse background includes significant stints and contributions in electrochemistry, photovoltaics, silicon crystal growth and laser processing prior to entering the world of PCAs. Member of SMTA. Member of the Technical Journal Committee of the Surface Mount Technology Association.

1. Soldering fluxes are intended to react with metallic surfaces to facilitate soldering. OA fluxes react much faster and more aggressively with metal surfaces compared to no clean fluxes.

2. If the assembly is immersed into the flux as with a foam fluxing application method there will be a build-up of flux-metal reaction products in the flux over time. As the reaction products increase in concentration the flux may change color.

3. As an example; ammonia and copper salts will form a blue color.

Jim Hevel
Research Chemist
Indium Corporation of America
Jim is a Research Chemist at Indium Corporation of America with 30 years of experience in wave flux product development.

Water soluble fluxes are very aggressive and I would think there is a reaction of the flux to some metal in the container, such as a metal cover, or if it is in a dispensing container, the needle is made of copper and the flux is reacting with the material.

In any case, any flux that changes color like you mention should not be used as it will introduce other contaminants to your product which most likely create reliability issues at a later time.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

A change of color usually means that the flux is reacting with something else. In other words, your flux is going through a chemical reaction. The type of fluxer, tank material & environment could be the initiators. I'd recommend to have the flux analyzed for contents.

Edithel Marietti
Senior Manufacturing Engineer
Northrop Grumman
Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.

Reader Comment
I believe you are talking about the flux in the machine, or residual flux left under the BGA that was not completely cleaned off. If you go down into the basement of your home or apartment and examine the copper plumbing, you will see the same blue-green color on the sweated copper connections.

This is because if OA fluxes are used and not cleaned thoroughly there is a reaction between the flux and the copper, and the resultant oxides that form are typically a blue/green color.

These residues are called Verdigris, and the same reaction that occurs on the plumbing also happens on soldered copper joints where sufficient flux residues are left behind. They will not be seen immediately, but take some time to "grow". They will do this at a much faster rate in a humid or salt-bearing atmosphere.
O. Stadheim, Verdigis Technologies Corp.

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