Removing / Replacing ICS in mobile phones

Hello,

Im trying to learn as much as possible about removing ICs from cellular phones, because thats an area with very little success for me.

I have a DIC SC-7000Z soldering gun with hot blow in/out air directions but i am allways afraid to burn each component. As much as i increase the temp., as much flux i put in, the ICs never fall and at the same time they seem to become very toasted.

I had some success on reflow of some ICs and repaired some phones that way, but when it comes to change an 8210 ant. switch that is close to RF shields or changing a PA it is a realy trouble.

Now the qwestions:
Is it ok to use Flux when trying to remove a PA for ex? because flux and long time exposition to low temp air blow doenst seem very compatible.. The air blow seems to dry/evaporate the flux before it can help the solder to fuse

Where can i find a temp. sensor for 100..400ºC for me to know what temp i am putting on phone?

I have a liquid flux and a kind of gel flux.. the liquid one evaporate in seconds.. the second one seems like is never to go out of the PCB anymore.. Can you explain something about flux types?

What pre-heating temp. is good for removing a PA for example? and do you put the component side upside down waiting for them to fall or heat them and push it away from the PCB with a tool?

Thank you for reading this long post