[News] The HBM4 Battle Begins! Memory Stacking Challenges Remain, Hybrid Bonding as the Key Breakthrough

According to a report from TechNews, South Korean memory giant SK Hynix is participating in COMPUTEX 2024 for the first time, showcasing the latest HBM3e memory and MR-MUF technology (Mass Re-flow Molded Underfill), and revealing that hybrid bonding will play a crucial role in chip stacking.

MR-MUF technology attaches semiconductor chips to circuits, using EMC (liquid epoxy molding compound) to fill gaps between chips or between chips and bumps during stacking. Currently, MR-MUF technology enables tighter chip stacking, improving heat dissipation performance by 10%, energy efficiency by 10%, achieving a product capacity of 36GB, and allowing for the stacking of up to 12 layers.

In contrast, competitors like Samsung and Micron use TC-NCF technology (thermal compression with non-conductive film), which requires high temperatures and high pressure to solidify materials before melting them, followed by cleaning. This process involves more than 2-3 steps, whereas MR-MUF completes the process in one step without needing cleaning. As per SK Hynix, compared to NCF, MR-MUF has approximately twice the thermal conductivity, significantly impacting process speed and yield.

As the number of stacking layers increases, the HBM package thickness is limited to 775 micrometers (μm). Therefore, memory manufacturers must consider how to stack more layers within a certain height, which poses a significant challenge to current packaging technology. Hybrid bonding is likely to become one of the solutions.

The current technology uses micro bump materials to connect DRAM modules, but hybrid bonding can eliminate the need for micro bumps, significantly reducing chip thickness.

SK Hynix has revealed that in future chip stacking, bumps will be eliminated and special materials will be used to fill and connect the chips. This material, similar to a liquid or glue, will provide both heat dissipation and chip protection, resulting in a thinner overall chip stack.

SK Hynix plans to begin mass production of 16-layer HBM4 memory in 2026, using hybrid bonding to stack more DRAM layers. Kim Gwi-wook, head of SK Hynix’s advanced HBM technology team, noted that they are currently researching hybrid bonding and MR-MUF for HBM4, but yield rates are not yet high. If customers require products with more than 20 layers, due to thickness limitations, new processes might be necessary. However, at COMPUTEX, SK Hynix expressed optimism that hybrid bonding technology could potentially allow stacking of more than 20 layers without exceeding 775 micrometers.

Per a report from Korean media Maeil Business Newspaper, HBM4E is expected to be a 16-20 layer product, potentially debuting in 2028. SK Hynix plans to apply 10nm-class 1c DRAM in HBM4E for the first time, significantly increasing memory capacity.

Read more

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• [News] HBM Boom May Lead to DRAM Shortages in the Second Half of the Year

(Photo credit: SK Hynix)