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Abnormal surface of solder joints

Appearance
surface is butt, rough, granular and/or has burls

Description:
The rough surface of through-holes is due to solder from a previous soldering process mixing with the present solder. Particles of the previous solder, e.g. solder balls, are deposited on the surface of the through-holes as they have not completely interfused with the new solder. After removing these solder balls the surface is rough as seen here.

Causes/Remedy:
  • foreign solder particles within through-hole plating
  • contamination of the solder

Source: visual, optical inspection - general view
rough surface of through-holes

Description:
The surface of the solder joint of this SOT23 is slightlyrough. As the assembly was cooled down too slowly after reflow soldering, a dendritic structure has formed which is also visible on the surface of the solder joint. The quality of the solder joint has not been impaired noticeably.

Causes/Remedy:
  • Cooling-down process after soldering too slow

Source: SEM
rough solder joint surface

Description:
The surface of this CMC solder joint is slightly rough. As the assembly was cooled down too slowly after reflow soldering, a dendritic structure has formed which is also visible on the surface of the solder joint. The quality of the solder joint has not been impaired noticeably.

Causes/Remedy:
  • Cooling-down process after soldering too slow

Source: SEM
rough surface structure on a solder joint of a CMC

Description:
Important depositions of flux residues along this reflow solder joint have made the surface butt and rough shortly after soldering, which can only be detected after removal of the flux residues.

Causes/Remedy:
  • percentage of flux in the solder paste too high
  • properties of flux unfavourable

Source: SEM
butt an rough surface of a solder joint

Description:
This photo shows dross which has been transported on the assembly during wave soldering. Dross has to be removed from assemblies in principle, since loose dross particles can cause electrical defects.

Causes/Remedy:
  • contaminated solder: tin oxide, flux residues
  • solder alloy changes

Source: visual, optical inspection - general view
dross on some pins
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