[ Problem Point ]
Gluing of lead free solder would be a problem badly.
[ ⇒Kaizen Point ]
The small spot was preheated by the Air Blow Heater.
After preheating, gluing of solder became good.
Moreover it was also heat damage prevention by preheating of a pinpoint.
Related page:
No.2 Preheat of printed circuit boards 
No.2 Preheating of the printed circuit board 
No.16 Soldering of printed circuit board 
No.75 Aging of Printed Circuit Board 
No.28 Preheating of resin board 
Infrared heating of printed circuit board with a halogen line heaterHLH-60A/f∞ 
No.13 Flow and reflow soldering process for printed circuit board, masking the Gold Plate Contact 
No.1 Soldering of printed circuit boards