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Residues of non-conducting substances

Appearance Examples: SMD-adhesive, varnish for marking print on board, resist coating. Contact areas constantly at risk.

Residues at CMC

Description:
Open (right) at a CMC due to deposition of excessive adhesive before wave soldering. The placing of the component made the adhesive come out from under it and reach over the pad. As a consequence the component was not soldered. Rework is necessary in any case.

Causes/Remedy:
  • unsuitable machine parameter for deposition of adhesive
  • adhesive (viscosity) unsuited
  • poor positioning of adhesive


Source: SEM
Open at a CMC due to excessive adhesive

Residues at MiniMELF

Description:
see example CMC; same context as above, however at a MiniMELF resistor.

Causes/Remedy:
  • unsuitable machine parameter for deposition of adhesive
  • adhesive (viscosity) unsuited
  • poor positioning of adhesive


Source: SEM
Open at a MiniMELF due to excessive adhesive

Residues, general

Description:
Clearly visible spilling-out of excessive adhesive from under a square-shaped resistor (center), which, however, did not prevent soldering in this case.It is remarkable that only one component shows this defect. This fact indicates that the process parameter (process stability) have not been monitored closely enough.

Causes/Remedy:
  • unsuitable machine parameter for deposition of adhesive
  • adhesive (viscosity) unsuited
  • process parameter (temperature)


Source: visual, optical inspection - general view

Residues at SOD

Description:
Unidentified residues on the contact metallisation of a SOD after wave soldering. This contamination which occurred during soldering prevented the solder from wetting the complete metallisation area of the component. It could not be established what caused it. Apart from this contamination the solder (alloy) had been polluted beforehand.

Causes/Remedy:
  • polluted solder
  • pollution of the solder alloy
  • contamination of the solder or the board (flux residues or similar)
  • Particles of substances from other components (e.g. plastics)


Source: visual, optical inspection - general view
undefined residues on the contact metallisation of a SOD

Residues at SOT23

Description:
Non-soldered lead of a SOT23. The spilling-out of adhesive impaired the wetting during the wave soldering process. The adhesive is on the pad under the lead . Rework is necessary. The component should be removed completely and the contact areas of the lead cleaned from adhesive residue.

Causes/Remedy:
  • unsuitable machine parameter for deposition of adhesive
  • adhesive (viscosity) unsuited
  • poor positioning of adhesive


Source: SEM
Open at a SOT23 due to excessive adhesive

Description:
Same context as described above. The adhesive spilled out from under the component body is clearly visible.

Causes/Remedy:
  • unsuitable machine parameter for deposition of adhesive
  • adhesive (viscosity) unsuited
  • poor positioning of adhesive


Source: visual, optical inspection - general view
Spilled-out adhesive from under a SOT23
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