Insufficient Solder Topside Fillet Print E-mail
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Written by Paul Lotosky   
Wednesday, 01 April 2009 18:17
Wave Soldering

The dwell time, flux and temperatures are main culprits.

Fig. 1

Insufficient solder topside fillet occurs where the joint has not formed a good topside fillet. Per IPC acceptability standards, a total maximum of 25% depression, including both the primary solder destination and the secondary solder source sides, is permitted.

Fig. 2

When troubleshooting, the primary process setup areas to check include:

  • Conveyor speed too slow
  • Time over preheat too long, causing the flux to be burned off.
  • Dwell time too long, causing flux to be destroyed before exiting the wave.
  • Conveyor speed too fast
  • Dwell time too short/topside board temp too low.
  • Topside board temp too high for flux, causing it to burn off before the wave.
  • Insufficient flux, or flux is not active enough.
  • Solder temperature too low, and it cools in the barrel before it reaches the topside.
  • Wave height too low in one or both waves, so solder does not contact the board properly.
Fig. 3

Other things to look for in the process include:

  • Solder temperature too high or too low.
  • Preheat too high or too low.
  • Excess or insufficient flux blow-off.
  • Board not seated properly.
  • Contaminated flux or solder.
  • Board pallet too hot.
  • Solder wave height low.
  • Flux SP GR too low.
  • Conveyor speed high.
  • Solder wave uneven.
  • Flux SP GR too high.
  • Flux applied unevenly or not making contact.

Other things to look for with the assembly:

  • Board oxidized, warped or contaminated.
  • Mask in hole.
  • Laminate moisture.
  • Poor plating in the hole.
  • Hole and pad misregistration.
  • Mask misregistration.
  • Component contamination.

Other things to look for with the board design:

  • Poor pallet design.
  • Internal ground plane.
  • Pad size mismatched.
  • Large ground plane on component site.
  • Lead-to-hole ratio too large or too small.
  • 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 Wednesday, 01 April 2009 11:48


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