BGA stands for Ball Grid Array.
A type of high-density electronic component package for integrated circuits.
The BGA has solder balls on its backside, which line up with corresponding contacts on the front side of the PCB. The part and PCB are heated until the solder balls melt.
The surface tension of the molten solder makes the chip “float” on the board, which also aligns it perfectly with the pads on the PCB.