In an article on contamination and moisture effects on printed circuit board reliability, ERA Technology* identified moisture; applied voltage, and ionic contamination as leading causes of failure.
According to the article: “Printed circuit boards (pcbs) can suffer from a variety of problems if the surface is contaminated with electrically conducting materials. Combined with moisture, this results in a lowering of resistance between tracks and pads and can lead to corrosion of metals. It can also result in the formation of metal filaments, which grow between pads or tracks on rigid or flexible circuits and between oppositely charged metal terminations of components, such as MLCCs, or between the pins of connectors.
……..The ideal situation is constant temperature and a relative humidity of 40 – 50 %. At relative humidities above 50%RH, there is an increasing likelihood that water condensation will occur on the surface of circuitry when changes in air temperature occur. Where the PCB surface is at a lower temperature than the ambient air, this cools the air adjacent to the surface resulting in an increase in the local relative humidity. Condensation occurs when the temperature reaches the dewpoint. At the dewpoint temperature, the relative humidity reaches 100%RH and liquid water is formed.
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*Failure Investigation & Expert Witness Group is Europe’s leading provider of impartial consultancy for engineering reliability & failure investigation, and consultancy on environmental legislation pertaining to the products sector.