|Ask the Experts|
May 7, 2020
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.
Sr Fiald Applications Support Engineer
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.
S T and S Testing and Analysis
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.
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.
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.
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.
Indium Corporation of America
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.
Vice President, Technical Director
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.
Senior Manufacturing Engineer
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.O. Stadheim, Verdigis Technologies Corp.
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.
|Submit A Comment|
Free Newsletter Subscription
Circuitnet is built for professionals who bear the responsibility of looking ahead, imagining the future, and preparing for it.
Insert Your Email Address