- SPHBM4 significantly reduces pin count while preserving hyperscale-class bandwidth performance
- Organic Substrates Reduce Packaging Costs and Relax Routing Constraints in HBM Designs
- Serialization shifts complexity to the core signaling and logic silicon layers
High-bandwidth memory evolved around extremely wide parallel interfaces, and this design choice defined both performance and cost constraints.
HBM3 uses 1024 pins, a figure that already pushes the limits of dense silicon interposers and advanced packaging.
The JEDEC Solid State Technology Association is developing an alternative known as Standard Package High Bandwidth Memory 4 (SPHBM4), which reduces the width of the physical interface while preserving total throughput.
HBM4 interface doubles HBM3
The HBM4 standard specification doubles the width of the HBM3 interface to 2,048 pins, with digital signals passing through each contact to increase overall throughput.
This scaling approach improves bandwidth, but it also increases routing complexity, substrate requirements, and manufacturing costs, which are concerns for system designers.
The planned SPHBM4 device uses 512 pins and relies on 4:1 serialization while operating at a higher signaling frequency.
In terms of bandwidth, one SPHBM4 pin should support the equivalent workload of four HBM4 pins.
This approach shifts complexity from pin count to basic signaling technology and logic design.
Reducing the pin count allows for wider spacing between contacts, which directly affects packaging options.
JEDEC states that this relaxed bump pitch allows connection to organic substrates rather than silicon interposers.
Silicon substrates support very high interconnect densities with pitches greater than 10 micrometers, while organic substrates typically operate closer to 20 micrometers and cost less to manufacture.
The interposer connecting the memory stack, its base logic chip and an accelerator would therefore move from a silicon-based design to an organic substrate design.
The HBM4 and SPHBM4 devices should offer the same memory capacity per stack, at least in specification.
However, organic substrate mounting allows for longer channel lengths between the accelerator and memory stacks.
This configuration may allow for more SPHBM4 stacks per package, which could increase total memory capacity compared to conventional HBM4 configurations.
Achieving this requires a redesigned core logic chip, since SPHBM4 memory stacks involve a four-to-one pin count reduction compared to HBM4.
HBM is not general purpose memory and is not intended for consumer systems.
Its use cases remain concentrated in AI accelerators, high-performance computing, and GPUs in data centers operated by hyperscalers.
These buyers work at scales where memory bandwidth directly affects revenue efficiency, justifying continued investment in expensive memory technologies.
SPHBM4 does not change this usage model because it preserves HBM-class bandwidth and capacity while optimizing system-level cost structures that are primarily important for hyperscale deployments.
Despite references to lower cost, SPHBM4 does not point a path to mainstream RAM markets.
Even with organic substrates, SPHBM4 remains a stacked memory with a specialized core logic chip and tight coupling to accelerators.
These features do not match consumer DIMM-based memory architectures, price expectations, or motherboard designs.
Any cost reductions apply within the HBM ecosystem itself rather than the entire broader memory market.
However, for SPHBM4 to become a viable standard, it requires support from major vendors.
“JEDEC members are actively shaping the standards that will define next-generation modules for use in AI data centers…” said Mian Quddus, Chairman of the JEDEC Board of Directors.
Major suppliers, including Micron, Samsung and SK Hynix, are members of JEDEC and are already developing HBM4E technologies.
“Our #NuLink D2D/D2M interconnect solution has demonstrated the ability to achieve 4TB/s of bandwidth in a standard package, up to 2x the bandwidth required by…the HBM4 standard, so we look forward to leveraging the work that JEDEC has done with SPHBM4…” said Eliyan, a core logic chip semiconductor company.
Via Blocks and files
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