It comes in a Tape & Reel (TR). In the case of 4-UFBGA, WLCSP, it is embedded within the case. There is a recommendation that Surface Mount mounting type should be used for this product.
CAS24S128C4ATR Features
Package / Case: 4-UFBGA, WLCSP
CAS24S128C4ATR Applications
There are a lot of ON Semiconductor CAS24S128C4ATR Memory applications.