An interposer is an electrical interface that sits between two components, routing connections from one to the other. In its simplest form, it’s a thin layer of material covered in tiny wiring that lets chips, memory, and other parts communicate without being directly attached to each other. You’ll find interposers inside the most powerful AI chips on the market today, but the concept also applies to simpler hardware adapters like the piece that lets a SATA drive plug into a SAS backplane.
The term comes up most often in semiconductor packaging, where interposers have become essential for building the kind of high-performance processors that power data centers, AI training, and advanced graphics.
How an Interposer Works
Think of an interposer as a middleman layer. A processor chip needs to talk to memory chips, but their connection points don’t line up directly, or the signals need to travel shorter distances to maintain speed. The interposer sits underneath these chips, providing a dense network of internal wiring that routes electrical signals between them. This shortens the path signals have to travel, which reduces power consumption and boosts performance.
The most common way signals pass through a silicon interposer is via tiny vertical tunnels called through-silicon vias, or TSVs. These are microscopic holes drilled through the silicon and filled with metal, creating electrical pathways that run straight through the interposer from top to bottom. TSVs dramatically shorten interconnect paths compared to traditional packaging, where signals would need to travel out to the edges of a chip and across a circuit board to reach another component.
On the surface of the interposer, redistribution layers (thin metal wiring patterns) fan out horizontally to connect different chips sitting side by side. A silicon interposer built on TSMC’s CoWoS platform, for example, uses wiring with a pitch of just 0.8 micrometers and micro bumps spaced 40 micrometers apart. For context, a human hair is roughly 70 micrometers wide. That density is what allows billions of signals to flow between chips in parallel.
Why Interposers Matter for Modern Chips
Modern processors are too complex and too large to manufacture as a single piece of silicon with acceptable yields. Instead, chipmakers split designs into smaller pieces called chiplets, then reconnect them on an interposer. This approach is known as 2.5D packaging: the chiplets sit side by side on a shared interposer rather than being stacked directly on top of each other (which would be full 3D packaging).
The performance gains are significant. When multiple chips share an interposer, they communicate over short, dense connections instead of driving signals across long PCB traces. One early commercial example was Xilinx (now part of AMD) splitting a large FPGA into four “slices” mounted on a single silicon interposer. Applications that previously needed multiple separate chips on a circuit board could be replaced with one package offering higher bandwidth, lower latency, and better power efficiency.
Silicon, Glass, and Organic Interposers
Silicon is the most established interposer material. It offers the finest wiring density and best overall performance, but it’s expensive. Manufacturing silicon interposers requires many of the same process steps as making chips themselves, including photolithography and etching, plus additional steps for TSV formation. Each added process step increases material consumption and cost.
Glass interposers are a lower-cost alternative with a coefficient of thermal expansion that closely matches silicon chips, which reduces the mechanical stress that causes cracking and warping. The tradeoff is poor thermal conductivity compared to silicon and processing difficulties that have slowed adoption.
Organic interposers use printed-circuit-board-like materials and are the cheapest option. Research from Georgia Tech comparing silicon and organic interposers found meaningful tradeoffs. Silicon interposers produced designs that used about 10% less power and occupied a quarter less area. But organic interposers showed advantages in power delivery, with roughly 40% lower impedance in the power distribution network and 2.3 times more bandwidth before hitting electrical resonance issues. Organic interposers use coarser wiring, with micro bump pitches of 150 micrometers versus 40 micrometers for silicon, so they can’t match silicon’s interconnect density. The choice depends on whether an application prioritizes raw performance or cost and power delivery characteristics.
Passive vs. Active Interposers
Most interposers in production today are passive. They contain no transistors or logic circuits, just wiring and vias that route signals between the chips above and the package substrate below. A passive interposer is essentially a very precise wiring board.
Active interposers go further by embedding actual circuitry into the interposer layer. This can include repeaters to boost signals over longer distances, voltage converters, or even network-on-chip routers that manage data traffic between chiplets. Research from the Technion Institute found that active interposers exhibit less than half the latency of passive interposers when connecting chiplets built on different manufacturing processes. Active interposers add complexity and cost but open the door to more sophisticated multi-chip systems.
The AI Chip Connection
Interposers are the reason modern AI accelerators can access memory fast enough to train large language models. High Bandwidth Memory (HBM) stacks sit on the same interposer as the processor, connected through thousands of parallel links that would be impossible with conventional packaging.
NVIDIA’s H100 GPU uses a silicon interposer to connect its processor to 80 GB of HBM3 memory, delivering 3.35 terabytes per second of bandwidth. AMD’s Instinct MI300X pushes this further with 192 GB of HBM3 and 5.3 terabytes per second. TSMC’s CoWoS-S platform, which manufactures interposers for these kinds of chips, can fit up to eight HBM3 stacks on a single interposer measuring 858 square millimeters, supporting a combined 6.6 terabytes per second of bandwidth while keeping power below 400 watts.
The scale of deployment is enormous. Meta’s infrastructure for training Llama 3 used 16,384 H100 GPUs, each relying on interposer-based packaging to keep memory bandwidth high enough for effective AI training. Without interposers, the memory bottleneck would make these workloads impractical.
Cost and Scaling Challenges
Silicon interposers are one of the most expensive components in advanced chip packaging. They require carrier wafers during manufacturing, additional mask layers for patterning, and increasing numbers of TSVs as designs grow more complex. According to McKinsey, the shift toward advanced packaging processes that rely on interposers could increase total material consumption in the U.S. semiconductor supply chain by as much as 60%, with much of that material sourced internationally.
Yield is another pressure point. Larger interposers (needed to accommodate more chiplets and memory stacks) are harder to manufacture without defects. This is one reason glass and organic alternatives continue to attract research investment, even though silicon remains dominant for high-performance applications. The industry is essentially searching for ways to get interposer-level performance at a fraction of the cost, because demand from AI hardware alone is growing faster than current manufacturing capacity can comfortably support.
Interposers Outside of Semiconductors
The term “interposer” isn’t exclusive to chip packaging. In broader hardware contexts, it refers to any adapter that reroutes or converts one physical connection to another. A common example is a socket adapter that spreads a connection to a wider pitch, letting a component with one pin layout plug into a board designed for a different one. SATA-to-SAS adapters are interposers in this sense. The underlying idea is the same: an intermediate layer that translates between two interfaces that wouldn’t otherwise connect directly.