BGA Re-heat question

[olewales]

Hello,

I have a device I'd like to try and repair. It's a simple GPS receiver/digital compass which shows direction and distance to previously set point. This one. It is probably some kind of broken solder joint problem, because otherwise dead unit comes alive when I apply some pressure to the PCB. I suspect gps receiver IC which is in small BGA package. I don't have tools nor skills to do full reballing, but I'd like to attempt reheating/reflowing it. What is the best way to approach this? I am going to order cheap hot-air station, so I will have some control over temperature and airflow (I regretted missing this tool so many times already that I may as well buy it now).
One specific question I'd like to ask is: should I pour flux over (under) the IC before heating it? It seems intuitive for me to do so but I came across advice telling me NOT to do it because it will inevitably cause existing balls to form solder bridges.

[zerorisers]

one mistake I made when re-flowing an xbox 360 was that when preheating the board so the traces wouldn't crack it got hot enough that there was enough heat transfer to melt the glue under the pads. after I reheated the chip I looked at it under a scope and saw that the pads where lifted by the tension of the solder. (I will be removing the chip and replacing the traces at my work) But i would suggest applying pressure to different chips on the board because it might not be the BGA. what I usually see is a pin is lifted on an IC after re-flowing or there is a cold solder joint.
(After a while of looking i get frustrated and re-solder everything I can with a soldering iron.)

after that if it still changes with flex it may be the BGA. I would suggest making that BGA a last resort.

[olewales]

Thank you for reply.

I thought you suggestion was reasonable so I touched everything I could on this board with soldering iron. Interestingly, it still does not reliably work but it's "less broken" now. Previously it needed continuous pressure on PCB to even turn on. Now, after pressing on PCB I was able to play with this for a minute or two before it hanged. Maybe it was still warm, though. Anyway, I was trying to apply pressure in different areas and it seems to react best on direct pushing on Sirf IC (BGA). I'll probably have my hot-air station on Wednesday so I am still waiting for suggestions what should I do not to screw this up. (wont be a huge loss, since device does not work anyway, but if I can rescue it then cool). For now I am attaching some photos of the PCB for curious readers.

[tautech]

Confirm how many layers the PCB is first, if only 2 layer you should get away with just hot air, if more, you might need a hot plate too.
If you end up having to lift the IC, be careful not to lift pads too.....gently, gently.

[olewales]

sitrep: Reheating the board fixed the device electrically, but I managed to break SMD switches in the process. Both of them I hope they are generic and I will be able to source them for a reasonable price.