Three Letter Acronyms (TLA).. we must love them, only explanation of their massive usage.
SiP .. SIP (single inline packages) as in DIP (dual inline packages)
POP (package on package) yet another variation on Green tape thick film hybrids (Green tape: a variation on un-fired ceramic with conductor pattern printed on it / in it).
Standard thick film packaging.. already fired ceramic with refiring to add screen printed conductors (gold,silver, palladium, etc..), resist (carbon, etc...) and dielectrics (glass insulating layers).. basically a physically small ceramic pcb with un-packaged die and printed resistors in the space of a standard IC package.
I designed and built a lot of Thick film hybrids back in the 70s/80s , till standard SMT took most of the "wind out it's sails". Still hard to beat for highest perfomance. (can mix optimum semiconductor technologies in one package)
Today .... only used in Space products.
Reason: dielectric absorbtion of the insulating materials used, thermal transfer of substrate and density with printed resistors and KGD (Known Good Die - another TLA!)
In other words.. cost no object.. size / performance only concern.
This talk of two chips in a single package reminds me of the early days of micros. There used to be a 1kx8 EPROM, the 2708 that required +5V and -12V to operate. Intel brought out a 2Kx8 EPROM that only needed +5V to operate and called it the 2716. TI brought out a part with two 2708s in the same package and also called it the 2716. For a while the Intel part was in extremely short supply and I suspect more than a few people got the TI part which would have been problematic.