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6 - Wave soldering and thermal profiles

6.3 - Troubleshooting wave soldering defects

Main soldering defects of wave soldering and some possible preventing actions are
Insufficient hole fill
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  • Solder temperature is too low
  • Solder is contaminated
  • Solder wave is uneven
  • Preheat temperature is too high/low
  • Flux is contaminated or its specific gravity is low
  • Conveyor speed is too high or the angle is small
  • Board or components have poor solderability
  • Insufficient flux activity
Icicles / bridging
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  • Solder temperature is too low
  • Solder is contaminated
  • Solder wave is uneven
  • Preheat temperature is too high/low
  • Flux is contaminated or its specific gravity is low
  • Fluxer is set incorrectly
  • Conveyor speed is too high or the angle is small
  • Board or components have poor solderability
  • Component leads are  too long
  • Excessive solder deposition
  • Insufficient flux activity
Fillet lifting
Fillet lifting is an effect in which the solder joint appears to lift from the PCB pads as the board cools and shrinkages after the soldering process. The primary reasons for fillet lifting are the mismatch in coefficients of thermal expansion of the solder alloy, copper pad and the PCB. There are three different forms of pad lifting:
  • The solder lifts off the copper pad
  • The pad lifts off the board material
  • The solder joint crack
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Solder balling
  • Preheat temperature is set incorrectly (too high/low)
  • Solder temperature is too high
  • Solder wave is too high or uneven
  • Preheat temperature is too high/low
  • Flux is contaminated or its specific gravity is too low
  • Excessive flux
  • Conveyor speed is too high
  • Poor solder mask - ineffective curing
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Skips – open joints
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  • Solder wave is too low or uneven
  • Preheat is too high
  • Flux is contaminated or its specific gravity is high
  • Flux is not making contact, i.e. fluxer set too low
  • Excessive flux blow-off
  • Conveyor speed is too high
  • Shadowing of components – use dual wave
Cosmetic Appearance
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  • Excess flux deposition
  • Preheat temperature is too low
  • Contact time in solder wave is too low
  • Cleaning process is ineffective
  • Too much time elapsed before cleaning
  • Poor solder mask ineffective curing
Electrochemical migration and reduced SIR values
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  • Chloride or other ionic residue on the bare board and/or components
  • Hygroscopic residue on the bare board and/or components
  • Ineffective cleaning during the bare board fabrication or after soldering the assembly
  • Improper use of no-clean solder flux chemistry
  • Ineffective cleaning process
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