Resolving unwanted solder protrusions.

An icicle or flag (also known as a horn) is defined as an undesirable protrusion of solder from a solidified solder joint or coating.

Primary process setup areas to check:
Conveyor speed too slow.
Time over preheat too long, causing the flux to burn off.
Dwell time too long, causing the flux to be destroyed before exiting the wave.
Solder temperature too low.
Not enough flux.
Nitrogen use will help prevent icicles.

Other things to look for in the process:
Solder temperature too low.    
Preheat too high.    
Excess flux blow-off.
Solder wave height low.    
Preheat too low.    
Insufficient flux blow-off.
Solder wave uneven.    
Contaminated flux.
Board pallet too hot.
Solder contaminated.    
Flux SP GR too low.    
Conveyor speed high.
Flux not making contact.    
Flux applied unevenly.    
Conveyor vibration.
Board not seated properly.

Other things to look for with the assembly:
Board contamination.    
Component lead length too long.
Component contamination.

Things to look for with the bare board:
Oxidation.
Contamination.    

Things to look for with the board design:
Poor pallet design.    
Internal ground plane.    
Large ground plane on solder side. 

Paul Lotosky is global director - customer technical support at Cookson Electronics (cooksonelectronics.com) plotosky@cooksonelectronics.com.