Generally, the BGA position on the pcb will be concave (bend) (the material begins to bend during the high temperature reflow process, and the difference in thermal expansion coefficient is relatively large). BGA is preferred to weld on the four sides of the BGA during welding. After the four sides are welded, the solder balls in the middle part will be welded. At this time, the solder paste may not be able to be soldered due to the difference in furnace temperature. In the complete melting welding, this results in a phenomenon of cold welding or cold welding, which may be re-welded again when heated by a hot air blower to reach the welding temperature.
1. The welding time for reflow can be extended (183 degrees Celsius or 217 degrees Celsius).
2, according to the characteristics of the solder, modulate the reasonable temperature of the constant temperature zone, and promote the conversion of FLUX and its active agent into a liquid state, remove the foreign matter of the metal surface, and protect the component feet. And PAD is not oxidized at high temperatures.