Dendritic Growth – Shorts on PCBA

Here is another example of electro-chemical migration that resulted in shorted signals on a printed circuit board assembly.

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These ECM residues can often be hard to see under an optical microscope because there are optically transparent metal oxides present with very small metallic dendrites.

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Backscattered electron SEM images show contrast related to atomic number, so for example lead appears very bright (Pb z=82) and carbon appears dark (C z=6). The dendritic structure is a clue that this was ECM related.

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The elemental map below shows that the dendrites are mostly lead but there is also some tin. Both lead and tin are likely to be involved for Sn-Pb solder joint assemblies.

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Check out SEM Lab, Inc.  to learn more.

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