Hi Dave,
MicroBGA (µBGA) is actually a trademark of Tessera Technologies used for its family of compliant chip scale packages.
MiniBGA was used as a tradename for a while by Sandia.
Area array CSP is a generic term that works.
While area array is clear, the term CSP is a bit more clouded. The first definition was an IC package with a foot print not greater than 1.2 times the size of the die. Presently, some folks use ball pitch as a measure (e.g 0.8mm or less), others use the concept of a package not greater than 1 mm on each side, still others focus on volume (e.g. not greater than 1.5X volume of the die) but it is perhaps most fundamentally to be viewed as a minimally packaged chip that is at or near the size of the die.
Hope that helps a bit.
Kind regards,
Joe