According to sources in the materials industry, on September 2, TSMC is expected to continue using traditional micro-bump technology rather than hybrid bonding in the short term for connecting high-bandwidth memory (HBM) with AI accelerators in advanced packaging. Considering the development cycle of related materials, finer pitch micro-bumps are expected to be used until the later stages of HBM4 and the early stages of HBM5. TSMC has requested its materials and equipment partners to develop bonding and underfill solutions for approximately 5-micron bumps, with South Korean and Japanese suppliers beginning development, and mass production of 5μm bumps expected to start in the second half of 2028.

Currently, the bump height of the third-generation extended HBM, namely HBM3E, is about 15-25μm, while HBM4 is close to about 10μm. Japanese material suppliers previously stated that it is difficult to guarantee quality below 15μm. The reduction and refinement of bumps are due to the height limitations of HBM cubes and the demand for higher interconnection density. JEDEC specifies that the maximum height for HBM stacks is 775μm. In TSMC’s advanced CoWoS packaging, the HBM stacks assembled by GPU and memory suppliers are mounted onto the silicon interposer via micro-bumps, with 16-layer DRAM chip stacking completed within HBM packaging by companies such as SK hynix and Samsung Electronics.

The first and second generations of HBM used larger solder bumps, while micro-bumps became mainstream around the HBM3 generation. SK hynix uses the MR-MUF process, and Samsung Electronics uses TC-NCF. Hybrid bonding allows for thinner and denser interconnections through direct bonding of copper pads, and TSMC has utilized this on its SoIC platform for logic chip stacking, but HBM still connects to the interposer using micro-bumps.