November 12, 2025 - Updated
July 25, 2011 - Originally Posted
What is Causing Oxidation?
After 2-3 months of service in the field we are noticing the silver connectors on our circuit board assemblies have turned black, and appear to have heavy oxidation. We believe the new ROHS standards for our circuit boards, in combination with Barium (present globally in our city air), may be causing this problem. Is anyone familiar with this problem?
V. N.
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Couldnt be due to Nitric Acid residues used to plate the Silver onto the Copper in the first place being left on due to improper rinsing. Most Silver Solutions are dissolved in Nitric as the carrier system.I would have thought this was a very likely candidate OR Silver Brightener being left on in large volumes due to improper rinsing after plating.
Greg York
Technical Sales Manager, BLT Circuit Services Ltd
Greg York has over thirty two years of service in Electronics industry. York has installed over 600 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
It sounds like creep corrosion, well known phenomenon with silver, usually associated with high levels of sulfurous compounds to me.
Phil Kinner
Global Business Director conformal coatings division, Electrolube
Phil Kinner - Electrolube - Global Business Director conformal coatings division.
Black tarnishing on silver is most likely caused by some form of sulphur contamination creating silver sulphide often seen as crystalline needles under a microscope. The origin of the sulphur could be from the local atmosphere or even from a local source such as rubber materials which often contain it. This can be released from rubber through time and is encouraged by increasing temperature.
Bryan Kerr
Principal Engineer - CMA Lab, BAE Systems
Bryan Kerr has 35 years experience in providing technical support to PEC assembly manufacturing. His experience ranges from analysis of materials and components to troubleshooting and optimizing, selecting reflow, cleaning, coating and other associated processes.
I would also be very suspicious of sulfur. For example from a coal fired power plant nearby, and even automobile emissions with catalytic converter. Rubber tubing that is heated may also emit traces of sulfur.
Jim Williams
Chairman, Polyonics, Inc.
Jim Willimas is a PhD Chemist in Polymers and Materials Science. He specialize in printing, cleaning, inks, and coatings used in electronics manufacturng operations. Williams has more than 30 years experience.
Initial observation is that the blackening of the silver is more likely due to the creation of Sulphide rather than Oxide. This could be caused by a high Sulphur content in the atmosphere. Is this the case? If the "Tarnish" is a field problem, perhaps a Conformal Coating as a final process step could be a solution.
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.
You didn't state what type of service the assemblies are in. I assume that they are not hermitically sealed. In industrial areas, sulfur components (commonly hydrogen sulfide) are the main culprits. Look for sources of H2S -- high auto traffic, proximity to manufacturing emission stacks, and (here in Texas) gas well or acid gas flares -- all common sources of heavy sulfur contaminants. As for the barium question, I think it would necessarily need to be a barium salt to force the reaction, ie barium sulfate. It also depends on the purity of the silver or the composition of the alloy. Silver alloys containing copper are notorious for the copper "bleeding" through and oxidizing in the air, but that doesn't seem to be the case since the tarnish is black. Copper/air/sulfur tarnish is generally a green or blue-green. Sealing the connectors would be one way of rectifying the problem, perhaps with an encapsulant of some sort. This essentially blocks out the offending contaminant. The amount of access required for the connector would dictate whether this is a viable solution.
Pierce Pillon
Laboratory Mgr., Techspray
Pierce Pillon is the Laboratory Manager and lead formulations chemist at Techspray, a division of Illinois Tool Works (ITW) and a leading manufacturer of chemical products for the electronics industry.
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