Interposer Cost Console

In a 2.5D package the spotlight goes to the logic die and the HBM, but the component that quietly governs the cost and the size limit is the interposer beneath them. It is the large slab of silicon — or, increasingly, organic or glass — that carries the dense wiring and the through-silicon vias connecting everything, and it behaves, economically, exactly like the big die it is.

That means yield. Defect-limited yield falls exponentially with area, and an interposer spanning a logic die plus eight HBM stacks can exceed 2,500mm² — three reticle fields. At that size a meaningful fraction of interposers carry a killer defect and are scrapped, and the cost of the dead units spreads across the survivors, so cost per good interposer climbs faster than the area itself. Add that fewer large interposers fit on a wafer, and the size penalty compounds.

There is also a hard ceiling: a lithography reticle exposes about 858mm² at once, so larger interposers require stitching multiple fields, and silicon practically tops out near three reticles. This wall is the reason the field diversified — organic RDL interposers (as in CoWoS-R) yield better and dodge the silicon size limit at slightly lower density, and glass interposers promise large, flat panels that scale past silicon entirely. The choice among them is a density-versus-cost-versus-size triangle this console makes explicit.

Optimize the interposer here — its type, area and layer count — then carry the result into the CoWoS Cost console for the full package including HBM and assembly, and estimate the memory it carries in the HBM Cost console.