Ask the Experts
January 22, 2018
Cause of Green/Blue Oxide Buildup
My organization is responsible for performing depot levelrepair to circuit card assemblies. We are encountering some serious oxidebuildup, green and blue in color, on circuit cards that are exposed to a marineenvironment. We are seeing leads on small component package bridged withoxidation. At this point we are using mechanical means to remove it (scrapingwith dental tools under a microscope.) This has proven incrediblytime-intensive. What oxides could we possibly be seeing and is there a chemicalor other method for removing them?
Expert Panel Responses
The colour that youare observing is most likely due to the formation of complex hydrated metal chloride salts which are often blue green in colour. The chloridewill be naturally present in the air in a marine environment and willaccelerate the corrosion of most untreated metals. Assuming you have a complexmixture of different chloride salts, it is unlikely that a single solvent likewater or even a light aqueous acid will dissolve away all the differentmaterials, that have formed.
Also I would be concerned at using thisapproach to remove these materials anyway because of the potential for adversereactions else where on the assembly. In these sorts of harsh corrosiveenvironments it may be worth considering some form of circuit board protection.
Senior Applications Chemist
Dr. Poole is a Senior Applications Chemist in Henkel Technologies, electronics assembly materials application engineering group. He is responsible for all of Henkel's assembly products including soldering products, underfills, PCB protection materials, and thermally conductive adhesives.
What you are seeing are most likely not oxides, but "metalsalts" which are corrosion products. In a marine environment, it is likely thatyou are seeing copper chlorides. The hydrate of copper (II) chloride isblue-green in color. Copper sulfate is also a possibility. Both copper (ii)chloride and copper sulfate have solubility in water. I would recommend usingdeionized water and a brush to remove the material, if the assemblies may beimmersed in deionized water. I would not recommend stronger chemicals to removethe materials.
Once the materials are removed, you still have the issue of exposedcopper, and unless protected it will corrode again when exposed to the marineenvironment. In addition, the corrosion may have removed enough metal tocompromise the leads of components, and you will need to check for this.
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
Bluecopper compounds include copper hydroxide (Cu(OH)2)- light blue, which canconvert to copper carbonate (greenish); copper nitrate (Cu(NO3)2) and coppersulfate (CuSO4).Greencopper compounds include copper chloride (CuCl2) when oxidized and coppercarbonate (CuCO3).
These copper cmpds indicate inadequate cleaning. There are a variety ofsolutions that can dissolve these Cu cmpds. I suggest you contact cleaningcompanies like Kyzen or Zestron as they can identify which specific Cu cmpd youhave and the best cleaning solution to remove it chemically.
Lee Wilmot has 20+ years doing EHS work in the PCB/PCBA industries, including environmental compliance, OSHA compliance, workers compensation, material content declarations, RoHS & REACH compliance. Active on IPC EHS committee and c-chaired committees on IPC-1331, J-STD-609A on labeling & marking, IPC-1758 on packaging and others.
I believe you problem is caused by the marine environment providing a little salt which will catalyze and accelerate basemetal corrosion. I suggest you might tryCO2 blasting to remove the bulk residues and follow with a good aggressive DIwater rinse. Consider conformal coatingto prevent new growth.
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.