Flip-Chip
Another advantage of flip chip is that you can get a lot more pads on the chip since you have pads over the entire chip, not just on the sides. This can be very good for power and ground connection since you can have low inductance, low resistance power grids, as well as have more signal i/o. Since IR drop & I/O for a large, high power chips are a big problem, microprocessors have been one of the first adopters.
One disadvantage is that it's pretty difficult to do thing like micro probe or FIB the chip if there are problems with the design. All you have access to is back side of the chip, and you have to dig through the substrate to get to your probe points. (Hopefully there's no active under it....)