A system in package, or SiP, is a way of bundling two or more ICs inside a single package. This is in contrast to a system on chip, or SoC, where the functions on those chips are integrated onto the same die.
SiP has been around since the 1980s in the form of multi-chip modules. Rather than put chips on a printed circuit board, they can be combined into the same package to lower cost or to shorten distances that electrical signals have to travel. Connections historically have been through wire bonds.
While SiP saw limited adoption in its earliest forms, there has been much work done on improving this concept recently with 2.5D and 3D-ICs, as well as package-on-package and flip-chips. There are several key drivers for these changes:
1. Analog IP doesn't shrink as easily as digital circuits from one process node to the next, making it extremely time-consuming and costly to move IC designs from one process node to the next in accordance to Moore's Law. Being able to shrink just the digital portions and keep analog at older process geometries is increasingly attractive, but it also requires some sophisticated communication between dies.
2. Shrinking features and adding more functionality onto semiconductors requires longer and thinner wires, which increases the time it takes for signals to move around a chip. By packaging different chips together, connected through an interposer or through-silicon via, those signals can be speeded up using shorter wire distances and wider conduits.
3. The need to extend battery life in mobile devices will require ways of reducing the amount of power needed to drive signals. Reducing the distances that signals have to travel, particularly in and out of memory, and increasing the width of the conduits, have a direct effect on the amount of energy expended to drive signals.