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Opens

Appearance
Missing solder fillet, insufficient or altogether missing wetting of one or both of the surfaces to be joined, no (mechanical) connection.

Opens at BGA

Description:
Open at a BGA. For constructional reasons this defect cannot be seen from outside . It is therefore difficult to locate. The microsection and previous X-ray inspection, however, clearly reveal this defect.

Causes/Remedy:
  • BGA/PCB not coplanar
  • vibration during transport
  • insufficient solder paste application
  • deformation of BGA/PCB during soldering
  • Not: poor wetting (see picture)

Source: Microsection

Opens at CMC

Description:
Open at a CMC during wave soldering. The defect is clearly visible from outside. Rework/Repair is easily done but has to match the sensible components. Soldering tip temperature ≤ 360°C.

Causes/Remedy:
    Shadow effect during soldering, therefore:
  • poor layout
  • locally disturbed flux application
  • bad wettability of component
  • residue of adhesive on pad

Source: REM

Opens at MiniMELF

Description:
Open at a MiniMELF resistor during reflow soldering. The defect is easily detectable from outside. Rework has to match the component. Soldering tip temperature ≤ 360 °C.

Causes/Remedy:
  • too little solder paste applied
  • solder paste missing
  • wetting deficiencies of component

Source: visual, optical inspection - general view

Opens at PLCC

Description:
Open at a PLCC (J-lead). This defect cannot always be easily detected from outside, especially if it is rather located in the middle. Rework, however, is unproblematic. Make sure that repair does not result in excess solder.
Observe precautions for handling ESD!

Causes/Remedy:
  • solder paste missing
  • too little solder paste applied
  • bad wettability of leads (especially with Alloy42)
  • bent, deformed leads

Source: visual, optical inspection - general view
Open at a PLCC

Opens at QFP

Description:
Open at several leads of a QFP. This defect is easily detectable in general, since the leads are visible from outside. Rework has to make sure not to use excess solder.
Observe precautions for handling ESD!

Causes/Remedy:
  • solder paste missing
  • too little solder paste applied
  • component not coplanar
  • wetting deficiencies at leads
  • bent, deformed leads

Source: SEM

Opens at SO

Description:
Open at a SO8. The pads at the corners which are larger than the others are to act as solder thieves during wave soldering. The defect is clearly visible. Rework has to make sure that solder joints are uniform.
Observe precautions for handling ESD!

Causes/Remedy:
  • wetting deficiencies of leads
  • shadow effect during wave soldering
  • poorly dimensioned pads
  • wetting deficiencies at PCB

Source: SEM

Opens at SOT23

Description:
Open at a SOT23 during the reflow process. Visual inspection easily locates this defect. It can be seen that one of the contacts has lifted off so that it could not be wetted any more. Rework has to make sure to achieve geometrically uniform solder joints.
Observe precautions for handling ESD!

Causes/Remedy:
  • bent, deformed leads
  • deficiencies in the placing process
  • melting during reflow not simultaneous
  • beginning tombstone effect
  • wetting deficiencies at leads

Source: SEM

Opens at passives

Description:
Open at a through-hole component (seen from the underside). The wave soldering process did not produce solder joints for either of the contacts nor did the solder fill the through-holes. This defect can be easily located, since it is optically very different from soldered joints.
Observe precautions for handling ESD!

Causes/Remedy:
  • wetting deficiencies at leads
  • wetting deficiencies at through-hole
  • through-hole plating faulty/missing
  • shadow effect during wave soldering

Source: visual, optical inspection - general view

Opens at TO220

Description:
Open at a TO220. (middle, right) It is clearly visible that the solder fillet is missing at two of the pins. Optical control is often difficult, because the component body is in the way. Repair has to make sure that the solder completely fills the through-hole. Pay attention to solder contact time and soldering temperature (≤ 360 °C).
Observe precautions for handling ESD!

Causes/Remedy:
  • wetting deficiencies at leads
  • solder contact time during wave soldering too short
  • shadow effect during wave soldering
  • damaged through-hole
  • soldering temperature insufficient
  • flux does not reach relevant area

Source: visual, optical inspection - general view
Open at a TO220

Opens at DIP

Description:
Open at a DIP component. A poor solder fillet (left) or missing wetting (right) prevent solder joints. The contact is only loosely connected but not soldered. Visually distinct defect. Rework has to make sure that the solder completely fills the through-hole. Pay attention to solder contact time and soldering temperature (≤ 360°C).
Observe precautions for handling ESD!

Causes/Remedy:
  • wetting deficiencies at leads
  • solder contact time during wave soldering too short
  • damaged through-hole
  • soldering temperature insufficient
  • flux does not reach relevant area

Source: visual, optical inspection - general view

Opens at DPAK

Description:
Open at a DPAK component. In this case missing solder paste caused the defect. As the component was soldered on one side (not visible on photo) the leads have slightly lifted off on the other. This facilitates visual inspection, since there is a distinct gap between pad and lead ( also see other examples). It is recommended to remove the component completely and to resolder it by hand. Pay attention to soldering temperature (≤ 360°C).
Observe precautions for handling ESD!

Causes/Remedy:
  • faulty solder paste application
  • In case solder paste has been applied correctly:
  • bear in mind possible tombstone effect
  • wetting deficiencies at leads through contact material (Alloy 42)

Source: visual, optical inspection - general view

Opens at others

Description:
Open at a through-hole during reflow soldering. In this case an increased amount of solder paste was printed on enlarged solder eyes. The solder paste normally withdraws into the through-hole during reflow and thus connects the component with the assembly. On the photo bad heat management prevented the solder joint to form(left).It is clearly visible that the solder paste on the solder eyes and in the through-hole has not completely molten. Easily detectable defect from outside.

Causes/Remedy:
  • insufficient solder paste application
  • solder paste does not withdraw into through-hole
  • too little heat input
  • wetting deficiencies at leads
  • wetting deficiencies at plated through-hole

Source: Microsection
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