what is the Theta JA (ӨJA) of BGA2771 ?

 

This is what Google tells me:
"Ө JA is the thermal resistance from the junction of the die to the ambient temperature and is therefore
a measure of heat transfer from the die to surrounding air. Ө JA is determined with reference to
JEDEC standard JESD51-9."

Hope that helps.

 

The units of Thermal Resistance are °C/Watt. If you know how much power a chip is dissipating, you can calulate the temperature rise from ambient to the junction. The higher the ambient temperature, the easier it is for the chip to reach it's maximum junction temperature. You do not want to exceed the maximum junction temperature -- that is the road to perdition.

 

Thanks Alec_t and Papabravo according to your suggestions I tried to calculate it and here is what I got does it sound right ?

Ө JA = (150-25)/0.2 (°C/Watt)
Ө JA = 625 °C/Watt)

I have attached the Data Sheet for your reference.

 

Where did you find the P=0.2 figure?
The only thermal data I could see in the datasheet says:
R th j-s = thermal resistance from junction to solder point = 300°K/W (when P tot = 200 mW; T s <= 80°C )

 

I took P tot as P max