Who makes interposers, silicon bridges, rdl for AI data centers

Interposers and bridges are the wiring layer inside an advanced package: a piece of silicon (or a smaller bridge die) that sits between the compute die and HBM stacks above it and the substrate below (2.5D/3D advanced packaging, ABF / high-layer package substrates), routing the dense set of connections a multi-die AI accelerator package needs. Some of this capacity comes from the same foundries doing the most advanced logic manufacturing, and some from separate interposer-focused suppliers, which makes this sub-category's investor exposure partly overlap with, and partly separate from, foundry exposure itself. The category's importance to investors is proportional to how many discrete dies a given accelerator package combines — more chiplets and more HBM stacks per package means more interposer or bridge area needed per finished accelerator, independent of overall accelerator unit growth. It's a smaller, more technical sub-position than packaging or substrates broadly, but one where a design shift toward more disaggregated, multi-die accelerator architectures would increase demand per chip even if total chip volume held flat.