When reworking the solder connections underneath the BGA, its solder needs to be
heated for reflow, without damaging the PCB itself or the other components on the
board. This involves sending the heat to melt the solder through the BGA.
However, so the PCB is not thermally shocked, the rework process starts with preheating
the circuit board. Once the PCB itself has been preheated, just enough extra heat
is applied to the BGA to flow the solder underneath it, and then the BGA is removed
from the PCB.
If the BGA is to be reused, it has to be re-balled; the old solder is removed, the BGA cleaned, and new solder in the form of carefully measured balls is flowed onto the pads.
The newly re-balled BGA is placed on the circuit board. The PCB is preheated again,
and once the PCB is up to temperature, the BGA is given extra heat; reflowing the
solder and forming new connections.
Only after the reworked printed circuit board is cleaned and inspected is it ready