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Download fileCurrent leakage failure of conformally coated electronic assemblies
conference contribution
posted on 2009-01-16, 16:59 authored by Guangbin Dou, Patrick WebbPatrick Webb, David Whalley, David HuttDavid Hutt, Antony R. WilsonConformal coatings are widely used on circuit board
assemblies as an attempt to improve reliability and to
ensure high insulation impedances, which are for example
demanded by low current consumption battery operated
RF circuitry. However, components, such as small
ceramic capacitors, have occasionally been found to fail
in some applications, particularly when covered with a
thick silicone conformal coating. This is thought to be
due to the diffusion of water through the coating to the
capacitor surface where it then combines with solder flux
residue, or other organic or ionic contamination left on
the components, thereby dramatically increasing the
effective component leakage current. The primary
objective of this experimental research is therefore to
establish a clear understanding of the effects of moisture
exposure on the surface insulation resistance (SIR) of
conformally coated printed circuit board (PCB)
assemblies. This has been achieved through leakage
current measurements on multilayer ceramic capacitors
during storage in an environmental chamber during
testing similar to IPC standards for non-component
loaded boards.
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- Mechanical, Electrical and Manufacturing Engineering