Cause of Green/Blue Oxide Buildup

My organization is responsible for performing depot level repair to circuit card assemblies. We are encountering some serious oxide buildup, green and blue in color, on circuit cards that are exposed to a marine environment. We are seeing leads on small component package bridged with oxidation.

At this point we are using mechanical means to remove it (scraping with dental tools under a microscope.) This has proven incredibly time-intensive.

What oxides could we possibly be seeing and is there a chemical or other method for removing them?

M.P.

Expert Panel Responses

The colour that you are observing is most likely due to the formation of complex hydrated metal chloride salts which are often blue green in colour. The chloride will be naturally present in the air in a marine environment and will accelerate the corrosion of most untreated metals.

Assuming you have a complex mixture of different chloride salts, it is unlikely that a single solvent like water or even a light aqueous acid will dissolve away all the different materials, that have formed.

Also I would be concerned at using this approach to remove these materials anyway because of the potential for adverse reactions else where on the assembly. In these sorts of harsh corrosive environments it may be worth considering some form of circuit board protection.

Neil Poole
Senior Applications Chemist
Henkel Electronics

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 "metal salts" which are corrosion products. In a marine environment, it is likely that you are seeing copper chlorides. The hydrate of copper (II) chloride is blue-green in color.

Copper sulfate is also a possibility. Both copper (ii)chloride and copper sulfate have solubility in water. I would recommend using deionized water and a brush to remove the material, if the assemblies may be immersed in deionized water. I would not recommend stronger chemicals to remove the materials.

Once the materials are removed, you still have the issue of exposed copper, and unless protected it will corrode again when exposed to the marine environment. In addition, the corrosion may have removed enough metal to compromise the leads of components, and you will need to check for this.

Fritz Byle
Process Engineer
Astronautics

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.

Blue copper compounds include copper hydroxide (Cu(OH)2)- light blue, which can convert to copper carbonate (greenish); copper nitrate (Cu(NO3)2) and copper sulfate (CuSO4). Green copper compounds include copper chloride (CuCl2) when oxidized and copper carbonate (CuCO3).

These copper cmpds indicate inadequate cleaning. There are a variety of solutions that can dissolve these Cu cmpds. I suggest you contact cleaning companies like Kyzen or Zestron as they can identify which specific Cu cmpd you have and the best cleaning solution to remove it chemically.

Lee Wilmot
Director, EHS
TTM Technologies

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 base metal corrosion.

I suggest you might try CO2 blasting to remove the bulk residues and follow with a good aggressive DI water rinse. Consider conformal coating to prevent new growth.

Steve Stach
President
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.

Reader Comment

Copper compounds are formed and show up blue-green in color when the salt in the marine environment reacts with base metals in the PCB. These compounds must be removed with a natural bristle brush and DI water, then a rinse. The board then should be tested for metals degradation at each component lead (probe test) and, assuming it passes, possibly treated with a copper preservative or conformal coating before it is returned to a marine environment.

Russell Claybrook, MicroCare, LLC

Reader Comment

I am absolutely convinced that with a powered PCBa this effect is greatly enhanced ( electrochemical action ) - the best durability is with tinned copper as opposed to bare copper, very thorough cleaning EtOH followed by de-ionized HOH, oven dried then conformal coated several layers but there always will be some permeable aspects and the higher the voltages present more aggressive activity will result. ...this electrochemical action is not limited to copper as observed with ITO indium tin oxide- a transparent electrical conductor used in LCD displays--

I was blessed with the answer to a very puzzling problem we were having with field failures of the LCD touch screens used in some of our products which was the combination of microscopic pinholes in the polymer material used by the display manufacture combined with the high voltages present to rotate the liquid crystals, and the super small nanogram features of the conductors proved to be the case- the manufacturer modified there process- problem gone.

Rick, Wanco

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