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Corrosion

Electric migration

Description:
Corrosion (corrosion trees) due to electric migration between conductors with diverging electric potential (notice direction of migration). This defect is due to environmental stress (noxious gases, humidity) in combination with different potentials at uncovered or not sufficiently covered conductors.

Causes/Remedy:
  • lack of solder resist
  • defective solder resist
  • environmental stress unaccounted for

Source: visual, optical inspection - general view
corrosion  on conductors due to electric migration
Description:
Detailed view of context described before. Typical corrosion tree indicating migration of conductive material.

Causes/Remedy:
  • lack of solder resist
  • defective solder resist
  • environmental stress unaccounted for

Source: visual, optical inspection - general view
corrosion trees - detailed view

Black tarnished contact areas

Description:
Black tarnished and uncovered contact areas of a PCB. The surface finish used in this case (NiAu) entered into reaction with the environmental conditions. Corrosion of this kind does not allow solder joints any more. Not acceptable. These PCBs must not be used.

Causes/Remedy:
  • storage of PCB in noxious gas atmosphere
  • best before time exceeded
  • deficiencies in surface finish

Source: visual, optical inspection - general view
black tarnished contact areas of a pcb
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