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Insufficient solder

Appearance
Lean solder fillet below specification limit.
Attention ! Always compare with current specifications and standards. They often differ from each other. Here DIN EN 61191, Part 1 - 4, and IEC 61191, Part 1 - 4 respectively are taken as reference basis.
The assessment of all solder joints is based on the standards given above.

Insufficient solder at CMC

Description:
Reflow soldering of a 1812 CMC. In this case the layout caused a joint where the solder can be suspected to be insufficient. This soldering result is a borderline case according to IEC 61191 - 2 (Class A and B), however, and thus acceptable. Only for Class C is this solder joint insufficient and thus unacceptable. The fact that the solder joints do not cover the total width of the component suggest faults in dimensioning the pads.

Causes/Remedy:
  • poor layout design
  • use suitable components


Source: SEM

Insufficient solder at MiniMELF

Description:
Borderline case for insufficient solder in accordance with IEC 61197 - 2 (Class A and B). This solder joint can be accepted as a borderline case when compared with the other solder joints. It has to be checked, however, whether this is due to a systematic fault or incidental. A complete wetting of the component has to be discernible in principle. Therefore rework is not necessary.

Causes/Remedy:
  • wave soldering: shadow effect, unfavourable position of component
  • reflow soldering: poor solder paste application
  • disturbed wetting at end of component


Source: SEM

Insufficient solder at PLCC

Description:
For the minimum requirements of Class A this example can be regarded as a borderline case for insufficient solder. For the higher requirements of Class B and C the solder joints (middle, left) must be regarded as having insufficient solder and must therefore be reworked. The principle for J-leads is: The toe as well as the heel of the lead have to have solder fillets which show immaculate wetting.

Causes/Remedy:
  • Reflow soldering: too few / poor solder paste applied
  • Wave soldering: shadow effect


Source: SEM

Insufficient solder at SO

Description:
Reflow soldering of a SO with gullwing-leads. The photo shows very lean solder fillets which are a borderline case for insufficient solder. The properly wetted solder fillets are clearly visible. But the following principle also applies: There has to be a visible solder fillet at the heel of the lead. For leads of Alloy42 the higher-ranking acceptability class should always be taken as reference, since the joining partners normally have worse wettability properties than with other materials.

Causes/Remedy:
  • Reflow soldering: too few / poor solder paste applied
  • poor wetting properties


Source: SEM
Insufficient solder at a SO

Insufficient solder at SOT23

Description:
A processing fault before soldering (adhesive on the pad) caused a solder joint with insufficient solder. The solder joint has be to cleaned of the adhesive and properly reworked. It has to be made sure that there es a solder fillet at the heel of the lead.
Observe precautions for handling ESD!

Causes/Remedy:
  • faulty solder joint due to adhesive on the pad


Source: REM
Insufficient solder at a SOT23

Insufficient solder at DPAK

Description:
Insufficient solder at the (wide) front lead. The reflow process could not produce an acceptable solder fillet at the heel of the lead.

Causes/Remedy:
  • Reflow soldering: too few / poor solder paste applied
  • poor wetting at the lead
  • unsuitable process temperature


Source: SEM

Insufficient solder, general

Description:
Insufficient solder at a HMT solder joint. The solder applied is - with reference to 61191-3 - smaller than 75% of the wettable area. Therefore the solder joint has to be reworked.

Causes/Remedy:
  • poor flux / flux application
  • poor process parameter (soldering angle, temperature)
  • bad wettability of board/pads


Source: visual, optical inspection - general view
Insufficient solder at a HMT solder joint
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