Insufficient Solder Bottom-Side Fillets Print E-mail
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Written by Paul Lotosky   
Tuesday, 02 June 2009 19:58

Wave Soldering TroubleshootingWhen these defects occur, check the flux and conveyor speed.

Last month, we discussed insufficient solder topside fillets. This month, we look at insufficient solder bottom-side fillets (Figure 1). Per IPC-A-610, an acceptable condition is a 100% solder fillet and circumferential wetting present on the secondary (solder source) side of the solder joint. The minimum acceptable condition is a 330° circumferential fillet and wetting present for Class 3 boards, and 270° for Class 1 and 2 boards.
Fig. 1

Primary process setup areas to check are:

  • Conveyor speed too slow.
  • Excessive time over preheat, causing the flux to be burned off.
  • Excessive dwell time, causing flux to be destroyed before exiting the wave.
  • Excessive bottom-side board temperature, causing flux to be burned off before the wave.
  • Insufficient flux or flux activity.
  • Wave height too low on one or both waves.
Other things to look for in the process:
  • Insufficient solder temperature.    
  • Excessive preheat.    
  • Excess flux blow-off.
  • Board not seated properly.    
  • Insufficient preheat.    
  • Insufficient flux blow-off.
  • Solder wave height too low.    
  • Contaminated flux.    
  • Flux not making contact.
  • Solder wave uneven.    
  • Flux SP GR too low.    
  • Conveyor speed high.
  • Solder contaminated.    
  • Flux SP GR too high.     
  • Flux applied unevenly.    

Other things to look for with the assembly:     

  • Board contamination.    
  • Improper board handling.    
  • Component contamination.
  • Component leads too short.
Other things to look for with the bare board:
  • Board oxidized.    
  • Mask in hole.     
  • Board warped.    
  • Board contaminated.    
  • Poor plating in the hole.    
  • Component contamination.
  • Misregistration of the mask.    
  • Hole and pad misregistered.

Other things to look for with the board design:

  • Poor pallet design.    
  • Internal ground plane.    
  • Pad size mismatched.
  • Large ground plane on component side.
  • Lead-to-hole ratio too large.     
  • Weight distribution.
  • Large ground plane on solder side.

Paul Lotosky is global director - customer technical support at Cookson Electronics ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Last Updated on Tuesday, 02 June 2009 20:16


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