As the name of the processor suggests, the CPU is a BGA processor. BGA is short for ball grid array for surface mount.
Another advantage of those BGA1 processors is the availability of low voltage CPUs. A very slim notebook has restrictions in height and surface that lead to a bad thermal dissipation. It is required to decrease the voltage in order to reduce the TDPmax.
The mobile Celeron 400 MHz processor is the hottest BGA1 CPU.
If you have such a BGA1 processor in your notebook, you will not be able to upgrade it because it is soldered to the notebook motherboard.