advanced packaging
For fifty years the way to a faster, cheaper chip was to shrink the transistors and cram more onto one slab of silicon. That escalator is slowing: the wires between transistors now choke speed, a single die can only grow so big before yield collapses, and memory can't feed a processor fast enough. Advanced packaging is the answer to all three at once. Instead of betting everything on one ever-bigger, ever-finer monolithic die, you build the system out of several dies and wire them together so tightly inside the package that they behave almost like one chip. The package stops being a passive plastic box that just protects the silicon and routes a few pins, and becomes an active part of the design — which is why people call it the new scaling.
Advanced packaging is really an umbrella over a family of tricks for connecting dies in very short, very dense paths. In 2.5D, you set several dies side by side on top of an interposer — a slab of silicon (or organic substrate) acting as a high-density circuit board whose ultra-fine wires link the dies far more tightly than a normal motherboard ever could; this is how a processor sits next to its HBM memory stacks. In 3D, you go vertical, stacking dies on top of each other and tunnelling signals straight up through them with through-silicon vias, or fusing two dies copper-pad-to-copper-pad with hybrid bonding for connections finer than any solder bump. Shorter links mean less delay, less energy per bit, and enormously more bandwidth between the pieces.
The payoff is both performance and cost. Splitting a chip into smaller dies (chiplets) lets you test each one before assembly and throw away only the bad ones, rescuing the yield a giant monolithic die would have squandered — and it lets you mix process nodes, putting the logic on a cutting-edge node while memory or analog stays on a cheaper, more suitable one. Packaging has become so central that the most advanced AI accelerators are defined as much by their interposer, their HBM stacks, and their bonding pitch as by the transistors inside — the integration scheme is now a first-class part of the chip's competitiveness, not an afterthought.
2.5D (side by side on interposer) 3D (stacked vertically)
┌──────┐ ┌──────┐ ┌──────┐ ┌──────────────┐ cache/memory
│ Logic│ │ HBM │ │ I/O │ ├──────────────┤ <- bonded face-to-face
└──┬───┘ └──┬───┘ └──┬───┘ │ Logic │ (TSVs + hybrid bond)
┌──┴────────┴────────┴──┐ └──────┬───────┘
│ interposer │ <- fine wires │ package substrate
└───────────┬───────────┘
│ package substrateTwo faces of advanced packaging: 2.5D spreads dies across an interposer's fine wiring; 3D stacks them and connects straight through with TSVs and hybrid bonding. Both shorten the links between dies far below what a normal board allows.
The trade-off is heat and complexity: stacking dies traps the heat of several chips in one place, and the package becomes a co-design problem alongside the silicon — so progress here is increasingly gated by thermal limits and standards like UCIe rather than by lithography alone.