what's right temp for desoldering the IC?

what's right temp for desoldering the BGA? i heard BGA will cooked if more than 220C, is that true? how about I heat up from the back side the circuit board with hight temp around 420C is that going to kill the BGA? how about other's ? I use hot air gun, and I heat up around 382C air blow around 6 ( volume ), on all the type smt,soic,plcc,qfp, except the BGA. ( something like Hakko 850 SMD Reworkstation )

one more question, if i blow the air too long on the lead of IC, on the backside sometime had some wet or water look, and it dose not look like the part is melting, where is that came from? and how I clean that up?
Thank you

The right temperature is not a fixed value. Usually is the lowest temperature where the solder material is melted. It depends on many factor such as the volume of nearby components, the type of solder material used at assembly, etc. Another important issue, besides the max. temperature is the temperature variation speed. If you bring a component quickly from ambient temp to hundreds of degrees without slowly and graduately heating all its mass, probably something inside that component will cr-ack because of dilatation. You can desolder a SO-16 component in 2-3 seconds by heating it at 4-500 degree or in 10 seconds by heating it at approx. 300 degree. Obviously, the second choice is the right one. All this is a matter of practice. Test with disposable components/boards untill you get some experience. If you heat up the PCB at 420 grd with the airblower for more than few seconds, you'll have to throw it afterwards. At that temperature most pcbs delaminate due to excessive heat, and all platings inside holes/vias in the surrounding area will be destroyed.

/pisoiu

anyone can tell me more?

TKS!

When I bought my first IBM PC in 1983 I was an IBM tech and fixed midrange systems, one of which was the System38 which evolved into the AS400. At one point I had to do a memory upgrade on a customer's system and ended of with a couple of memory cards that were to be junked. Ha, they were full of 4164 chips, the same chips that my Tekram memory expansion card needed. To remove them, I used a metal keyboard button removal tool that just fit over each side of the chips pins and applied heat from a propane torch to the other side of the board. They just fell out. Of all the chips I, and a bunch of my buddies desoldered, not one went bad. Today the same method works great on an smd board.