HBM Memory Needs “Chimney” Cooling Structures — Semiconductor Industry Shift

High-bandwidth memory (HBM) has become essential for GPUs and AI accelerators. Unlike conventional DRAM, HBM uses a stacked structure to achieve wide bus widths and high bandwidth. HBM2 delivered around 307 GB/s, while HBM3e and later generations exceed 1 TB/s. This progress has driven up power consumption and heat, forcing a rethink of cooling strategies.

📑Table of Contents

1. Why “Chimney” Cooling Became Necessary
2. HBM Thermal Density and Cooling Technology Evolution
3. Impact on the Semiconductor Industry and Future Outlook
4. HBM Generation Comparison Table
5. Frequently Asked Questions (FAQ)
6. Summary and Takeaways for Readers

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Why “Chimney” Cooling Became Necessary

The thermal challenge surfaced when the base die moved to a logic process. To push signal speeds from 6.4 Gbps to over 10 GHz, power draw rose sharply. Stacking 12–16 layers or more multiplied heat output by more than four times. Traditional heat dissipation through DRAM layers could no longer adequately cool the D2D PHY, the hottest section.

SK hynix announced “iHBM” on May 27, 2026. It offsets the D2D PHY from the DRAM and places dedicated cooling paths called ICE (Integrated Cooling Elements) directly above it, cutting thermal resistance by 30 %. Samsung unveiled an HBM5 structure using HPB (Heat Path Block) at COMPUTEX 2026. Source: Impress PC Watch (https://pc.watch.impress.co.jp/docs/column/tidbit/2118676.html)

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HBM Thermal Density and Cooling Technology Evolution

Hybrid bonding is under consideration for HBM3e and beyond. It reduces thermal and electrical resistance compared with micro-bumps while keeping thickness down, though at higher cost. Forecasts for HBM5 suggest up to 20 layers per stack and over 100 W per stack, making chimney-style structures indispensable. Micron is pursuing its own low-power plus TSV cooling approach.

Vertical Power Delivery and EMIB-T (interposer-through power delivery) are also being adopted to avoid large currents inside the silicon interposer. In the future, liquid cooling integrated directly into the HBM stack itself may become necessary.

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Impact on the Semiconductor Industry and Future Outlook

The “chimney” cooling structures for HBM are driving broader changes in packaging technology. In AI servers and data centers, thermal management is increasingly becoming a performance bottleneck. Manufacturers are moving toward standardizing dedicated cooling elements such as iHBM and HPB. For readers evaluating HBM-equipped products, checking the cooling design has become a practical consideration.

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HBM Generation Comparison Table

Generation	Bandwidth (GB/s)	Bus Width (bit)	Speed (Gbps)	Notes
HBM2	307	1,024	2.4	–
HBM3	819	1,024	6.4	Logic process migration begins
HBM3e	1,178	1,024	9.2	Increased power consumption
HBM4	2,048	2,048	8	Wider bus
HBM4e	3,072	2,048	12	>10 GHz, chimney required

Source: Impress PC Watch (https://pc.watch.impress.co.jp/docs/column/tidbit/2118676.html), June 2026, extracted from Ōhara Yūsuke’s column.

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Frequently Asked Questions (FAQ)

Q: What exactly is the “chimney” cooling structure in HBM?

In SK hynix’s iHBM, the D2D PHY is offset from the base die and ICE cooling pillars are placed directly above it. Samsung’s HPB places cooling blocks inside the base die. Both approaches aim to dissipate heat from the D2D PHY efficiently.

Q: Why did conventional cooling methods become insufficient?

After HBM3e, the shift to a logic process and increased layer counts pushed heat output more than fourfold. Traditional dissipation paths through DRAM layers created too much thermal resistance for the D2D PHY.

Q: In which fields is HBM particularly important?

HBM is critical for AI accelerators, GPUs, and data-center servers. Its high bandwidth directly affects large language model training and inference performance.

Q: Can this cooling technology be applied to other memory types?

It is currently tailored to HBM’s stacked structure and high heat output. Direct application to other DRAM or non-HBM memory remains limited, although the packaging insights may be shared more broadly.

Q: What is the status of responses from semiconductor manufacturers?

SK hynix announced iHBM in May 2026, Samsung presented HPB at COMPUTEX, and Micron is advancing low-power plus TSV cooling. Each company is developing its own cooling elements.

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Summary and Takeaways for Readers

HBM “chimney” cooling structures mark the next stage in semiconductor packaging. The growing thermal problem highlights hardware design constraints in the AI era. When evaluating HBM-based products, readers should examine cooling design details to assess the balance between performance and reliability. Refer to the original Impress PC Watch article (https://pc.watch.impress.co.jp/docs/column/tidbit/2118676.html) for the latest developments.

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