2.5D integration

2.5D integration places several separate dies side-by-side on top of a shared, ultra-fine-wired carrier (a silicon interposer or a silicon bridge) so they behave almost like one giant chip. It sits between flat 2D (everything on one substrate) and true 3D (dies stacked vertically) — hence the name. Picture a city where, instead of one enormous skyscraper, you build several towers on a single dense subway platform that links them with thousands of fast tracks: the buildings are separate, but the platform underneath makes them feel like one campus.

The win is that you can pair a big logic die with stacks of high-bandwidth memory only millimetres away and connect them with tens of thousands of microbump wires — bandwidth and power efficiency a normal package can't match, which is why almost every modern AI accelerator and high-end GPU is built this way. The catch is cost and yield: the silicon interposer is itself a large, expensive piece of silicon, and packing reticle-busting die areas onto it stretches manufacturing limits.