HBM, short for high bandwidth memory, is a high-performance semiconductor that vertically stacks and connects multiple DRAMs (dynamic random-access memories). Initially developed with four layers, HBM technology has evolved to include configurations with eight and now 12 layers, with a 16-layer version in development. This technology connects multiple DRAMs through vertical electrodes without using metal wires, making advanced connection and protection techniques increasingly important. Leading the field are two South Korean semiconductor giants, SK Hynix and Samsung Electronics, each employing distinctive packaging methods. SK uses the Mass Reflow-Molded Underfill (MR-MUF) method, baking all layers simultaneously in an oven, while Samsung employs the Thermal Compression Non-Conductive Film (TC NCF) technique, stacking chips with a film between each layer.
SK Hynix’s MR-MUF technology packages multiple layers of DRAM at once. Below the DRAM, there are lead-based “bumps” that connect the chips. The MR technique involves heating and simultaneously melting all these bumps to solder them. After connecting all the DRAMs, a process known as MUF follows to protect the chips. An epoxy sealing compound, known for excellent heat dissipation, is injected to fill the gaps between the chips and encapsulate them. The assembly is then hardened by applying heat and pressure, completing the HBM. SK Hynix describes this process as “evenly applying heat like baking in an oven and bonding all chips at once, making it stable and efficient.”
Samsung Electronics’ TC NCF, known as “thermal compression with non-conductive film,” differs slightly. Each time a chip is stacked, a non-conductive adhesive film is placed between the layers. The film, a polymer material, is used to insulate the chips from each other and to protect the connection points from impact. Samsung has progressively reduced the thickness of the NCF material, bringing it down to 7 micrometers (µm) for the 12-layer fifth generation HBM3E. “This approach has the advantage of minimizing warping that can occur as the number of layers increases and chip thickness decreases, making it more suitable for building taller stacks,” the company said.
Leveraging the stable characteristics of MR-MUF, SK Hynix currently leads in the fourth-generation HBM3 market, with HBM3 being supplied almost exclusively to Nvidia. On the other hand, Samsung Electronics underscores the advantages of the TC NCF method for stacking higher layers, aiming to dominate the next-generation HBM competition.
