Reworking ICs with BGA and LGA Packages

Solder flows best where solder has gone before.

The key to successfully reworking BGA and LGA  packages is tinning the pads on the PCB and IC with solder.

On the IC

Remove all oxidation using a trichlorofluoromethane cleaning solvent and an acid brush.

Apply and mildly active no clean flux to the IC's pads and bump each pad with a small amount of tin / lead solder.  

Remove all no-clean flux residue using a trichlorofluoromethane cleaning solvent and acid brush.

On the PCB

Repeat the above process to apply a solder bump on the small pads of the PCB.

After the IC and PCB have been prepared as described above. . . 

Brush a thin layer of no clean flux on the IC  and PCB small pads. Do not apply flux to the thermal paddle.

Using a miniature syringe apply an appropriate amount of solder paste to the thermal pad on the PCB. 

The solder paste should be 90% metal and 10% no-clean flux.

Precisely align the IC on the PCB.

Then use a hot air reflow machine with a bottom-side heater and a appropriate top-side hot nozzle.

The reflow process will likely require some practice on a sacrificial board.  

A thermocouple monitored temperature profile should be developed and used to optimize yields and minimize thermal damage to the IC and PCB.

That's it !