www.solderingtraining.com. How to solder a Quad Flat Pack (QFP) for high reliability - IPC Class 3. STC (Soldering Training & Certification) 1-800-903-5309 or (612) 205-8609. John Gammell, Certified IPC Trainer.
The reason it works well is because the flat surface of the tip creates a lot of surface tension that pulls away excess solder from the pins as you drag along them. If you had a round conical tip you wouldn't have much surface tension. Fluxing the pins makes the solder flow much better so the pins only hold as much solder as they need.
