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October 4, 2010

Cleaning PCB's of Oxidation

What would be the best method or product for cleaning bare PCB's that have small amounts of oxidation?

I know that proper storage and handling may solve the problem, but what would you suggest?

H. M.

Experts Comments

Oxidation is simply the combination of a substance with oxygen. The process cannot be stopped. Yes proper storage and handling may prevent or slow it down.

You made no reference to the exact alloy used on your PCB's So I will assume it is a HASL finish with either a tin-lead alloy or a lead free, SAC-305 variant.

Depending on the type of flux you are using this alone may be active enough to remove the oxide layer and still provide good soldering results. If the level of oxide contamination is too high and it is impacting wetting for instance then you may have to pre-clean all your bare boards.

A mildly acid aqueous solution should work well. Another option is an aqueous solution that uses a small amount of silicates (not silicone). This is very effective on oxide removal on many metal surfaces and has an added bonus of surface brightening.

I would however be concerned if this oxidation problem is a recurring problem for you. A visit to your board fab shop is well advised to insure they are providing you with clean boards to begin with.

If you have any further questions please do not hesitate to contact me.

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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.
Presumably, the "bare PCB's" have copper surfaces with no protective coating. Even so, it is a good idea to subject them to a solvent cleaning to be on the safe side and remove any traces of oil, grease, fingerprints or other organic contaminants.
 
Probably the best way to remove the oxidation and render the boards highly solderable is to treat them chemically. There are numerous proprietary cleaners commercially available for this purpose, many of which are mildly acidic and need a good water wash followed by a thorough drying process. Note that boards in this condition are very prone to re-oxidation.
 
Consequently, unless they are to be used immediately, it would be wise to treat the boards with some kind of protective coating - anything from a film of Rosin through OSP (Organic Surface Protection), etc. A wide range of suitable materials for short and long term protectionis available from the usual suppliers.
 
I would steer away from mechanical abrasive cleaners since, although quick and easy, these have a tendency to remove one contaminant (the oxidation) and replace it with another (abrasive particles) which can impair the solderability.
 
Proper handling and storage would be good standard practice to prevent future contamination.
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Harold Hyman
Consultant
VJ Electronix
Harold Hyman has been involved in metallurgical aspects of the electronics industry since the 1950's, and in semiconductor development and engineering for STL, Ediswan & RCA. He later joined HTC, a pioneer of vapor phase soldering and continued industry experience Dynapert, GenRad, Teradyne, SRT and VJ Electronics.

We have seen great success using EnviroGold 816 at 5% in DI at 60 C or use of plasma to remove only surface oxides.

Please contact me at Foresite 765-457-8095.

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Terry Munson
President/Senior Technical Consultant
Foresite
Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.
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