A Case Study of Nickel Dendritic Growth on Printed Circuit Boards
This paper is a case study of nickel dendritic growth under moisture condensation condition on freshly produced circuit boards contaminated with sulfuric acid etchant.
Analysis Lab
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Authored By:
Prabjit Singh, Madhana Sunder, Eric Campbell and Larry Palmer
IBM Corporation
NY, USA
Summary
Dendritic growth is a rare short-circuit electrochemical phenomenon that can occur on printed-circuit boards (PCBs) in the presence of ionic contamination, high humidity and voltage bias. The elevated temperatures at which most electronic hardware operate lowers the relative humidity enough to dry the surface contamination that under humid conditions approaching condensation would result in dendritic growth. Silver is most prone to dendritic growth followed by copper and tin. Nickel dendritic growth has rarely been reported.
This paper is a case study of nickel dendritic growth under moisture condensation condition on freshly produced circuit boards contaminated with sulfuric acid etchant. The sulfuric acid contamination on the as-manufactured PCBs got trapped in the solder mask crevice and under high humidity condition spread out across the gap between gold-on-nickel edge connector contact pads. The paper describes the electrochemistry of nickel dendritic growth phenomenon in some detail and concludes that nickel dendrites will grow only when the relative humidity of the environment is near or higher than the deliquescent relative humidity of the contamination on the printed circuit board.
Conclusions
The freshly produced PCBs had sulfuric acid contaminating the edge connector contact pads. When biased under moisture condensation condition, nickel dendrites grew in the presence of sulfuric acid. As the reaction proceeded, the sulfuric acid got consumed producing nickel hydroxide sulfate which has a very high deliquescent relative humidity (DRH) greater than about 85%. As a result of this high DRH of the contamination between the gold on nickel contact pads, nickel dendrites could not grow during subsequent dendritic growth testing under non-condensing relative humidity levels.
The key conclusion of this case study is that nickel dendrites can grow under moisture condensation condition in presence of sulfate and acidic contamination, but that these already formed dendrites will not grow further when humidity is lowered to normal humidity conditions, under which the DRH of the contamination is higher than the relative humidity of the environment.
Initially Published in the SMTA Proceedings
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Comments
Sulfuric Acid activity requires H2O. If you can reduce the H and O you can reduce the activity of the acid. Should engineers have Dendrite formations, they can conduct simple tests with different types of desiccants and driers to see which technology lowers the amounts of H & O.
Dan Jenkins, Steel Camel
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