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Understand the defects and hazards of PCBA soldering
2021-10-03
View:23
Author:Frank

Understand the defects and hazards of PCBA soldering
   The common soldering defects, appearance characteristics, hazards, and cause analysis of PCBA will be explained in detail.
 
   Welding
  
   Appearance characteristics: There is a clear black boundary between the solder and the lead of the component or with the copper foil, and the solder is recessed toward the boundary.
  
   Hazard: not working properly.
  
  Cause Analysis:
  
  ▶The component leads are not cleaned, tinned or oxidized.
  
  ▶The printed board is not clean, and the sprayed flux is of poor quality.
  
   Solder accumulation
  
   Appearance characteristics: The solder joint structure is loose, white and dull.
  
   Hazard: Insufficient mechanical strength, may be welded.
  
  Cause Analysis:
  

pcb board

  ▶The solder quality is not good.
  
  ▶The soldering temperature is not enough.
  
  ▶When the solder is not solidified, the lead of the component becomes loose.
  
   Too much solder
  
   Appearance characteristics: The solder surface is convex.
  
   Hazard: Waste solder, and may contain defects.
  
  Cause analysis: the solder withdrawal is too late.
  
  Too little solder
  
   Appearance characteristics: The soldering area is less than 80% of the pad, and the solder does not form a smooth transition surface.
  
   Hazard: insufficient mechanical strength.
  
  Cause Analysis:
  
  ▶The solder fluidity is poor or the solder is withdrawn too early.
  
  ▶The flux is insufficient.
  
  ▶The welding time is too short.
  
   rosin welding
  
   Appearance characteristics: Rosin slag is contained in the weld.
  
   Hazard: Insufficient strength, poor continuity, and may be on and off.
  
  Cause Analysis:
  
  ▶Too many welders or have failed.
  
  ▶Insufficient welding time and insufficient heating.
  
  ▶The surface oxide film is not removed.
  
   overheated
  
   Appearance characteristics: white solder joints, no metallic luster, rough surface.
  
   Hazard: The pad is easy to peel off and the strength is reduced.
  
   Reason analysis: The power of the soldering iron is too large, and the heating time is too long.
  
   cold welding
  
  Appearance characteristics: the surface becomes tofu-like particles, and sometimes there may be cracks.
  
   Hazard: low strength, poor electrical conductivity.
  
   Reason analysis: The solder shakes before it solidifies.
  
   poor infiltration
  
   Appearance characteristics: The contact between the solder and the welding parts is too large and not smooth.
  
   Hazard: Low strength, no connection or intermittent connection.
  
  Cause Analysis:
  
  ▶The weldment is not cleaned up.
  
  ▶Insufficient flux or poor quality.
  
  ▶The weldment is not heated sufficiently.
  
   asymmetry
  
   Appearance characteristics: The solder does not flow over the pad.
  
   Hazard: Insufficient strength.
  
  Cause Analysis:
  
  ▶The solder has poor fluidity.
  
  ▶Insufficient flux or poor quality.
  
  ▶Insufficient heating.
  
   loose
  
  Appearance characteristics: The wire or component lead can be moved.
  
   Hazard: Poor or non-conduction.
  
  Cause Analysis:
  
  ▶The lead moves before the solder is solidified, causing voids.
  
  ▶The lead wire is not processed properly (poor or not wetted).
  
   pull the tip
  
   Appearance characteristics: sharp.
  
   Hazard: Poor appearance, easy to cause bridging.
  
  Cause Analysis:
  
  ▶There is too little flux and the heating time is too long.
  
  ▶The evacuation angle of the soldering iron is improper.
  
   bridge
  
   Appearance characteristics: adjacent wires are connected.
  
   Hazard: Electrical short circuit.
  
  Cause Analysis:
  
  ▶Too much solder.
  
  ▶The evacuation angle of the soldering iron is improper.
  
   pinhole
  
   Appearance characteristics: visual inspection or low-power amplifier can see holes.
  
   Hazard: Insufficient strength, solder joints are easy to corrode.
  
   Reason analysis: The gap between the lead and the pad hole is too large.
  
   bubble
  
   Appearance characteristics: There is a spit-fire solder uplift at the root of the lead, and there is a cavity inside.
  
   Hazard: Temporary conduction, but it is easy to cause poor conduction for a long time.
  
  Cause Analysis:
  
   There is a large gap between the lead and the pad hole.
  
   The lead wire is poorly infiltrated.
  
   The welding time of the double-sided board plugging the through hole is long, and the air in the hole expands.
  
  Copper Foil Cocked
  
  Appearance characteristics: The copper foil is peeled off from the printed circuit board.
  

   Hazard: The printed board is damaged.
  
   Reason analysis: the welding time is too long and the temperature is too high.
  
   stripping
  
  Appearance characteristics: The solder joints peel off from the copper foil (not the copper foil and the printed board peeling off).
  
   Hazard: Open circuit.
  
  Cause analysis: bad metal plating on the pad.