3D stacking
Beginner
Putting chips right on top of each other in one package, wired straight up and down.
Novice
Bonding dies face to face or face to back so that connections run vertically across their overlap, using through-silicon vias and microbumps or hybrid bonds.
Expert
Trades the edge-limited bandwidth of side-by-side links for area-scaled bandwidth, at the cost of heat that must cross the upper die, power that must pass through the lower one, and test access for buried dies.
Explained in Packaging and chiplets (Systems).
See also: hybrid bonding, Through-silicon via (TSV).