Thermo-Compression Bonding Technology

Thermo-Compression Bonding (TCB) is a flip-chip bonding process that uses a combination of heat and pressure to create interconnects between chips and substrates. This technology is essential for ultra-fine pitch and high-density packaging, making it a cornerstone for advanced semiconductor nodes below 10 nm. TCB enhances electrical performance by reducing resistance, improving thermal management, and facilitating heterogeneous integration—key for high-performance computing and AI-driven applications.

TCB offers several distinct advantages over conventional flip chip bonding:

1. Achieves sub-micron alignment accuracy through simultaneous up-down alignment
2. Controls die tilt at the micron level
3. Controls die flatness by holding it against the bonding tool during the entire bonding process
4. Reduces device warpage by keeping the bond stage well below the melting point of the solder
5. Follows precise profiles for temperature, force, and vertical position

In combination, these advantages greatly reduce stress and warpage from differences in the thermal expansion properties of the materials and allow for the creation of solder joints that are only a few microns thick with sub-micron lateral precision.

TCB is a key enabling technology for advanced packaging
As front-end transistor scaling and associated cost reductions have become increasingly difficult, maintaining the progress of Moore’s law now depends as much on innovations in Advanced Packaging and Heterogeneous Integration as it does on front-end innovation. The processors that power modern data centers and the amazing advances in AI all rely on Advanced Packaging that utilizes fine and ultra-fine pitch interconnections. In turn, Advanced Packaging relies on Thermo-Compression Bonding.

K&S’s TCB technology equips manufacturers with the tools needed to meet the stringent demands of next-generation semiconductor devices. Our systems offer industry-leading control over temperature, pressure, and tilt, ensuring optimal bond integrity, high yields, and consistent performance. With K&S, manufacturers can confidently tackle the challenges of advanced packaging and ultra-fine interconnects.

K&S continues to drive innovations that are pushing bonding capabilities to below 10 μm pitch, even for large dies. Over the past few years, we have developed fluxless bonding technology, first for solder-based interconnects and most recently for direct copper-to-copper interconnects. Leading packages now have die-to-substrate gaps of below 30 μm, even for 30 mm and larger dies. This 1000:1 aspect ratio makes it very challenging to remove flux from the gap. Fluxless bonding eliminates this issue and, thereby, enables continued progression to finer pitch.

Cu-to-Cu thermocompression bonding is another such innovation. For pitches below about 10 μm (interconnect diameters of less than 5 μm), the process margins for liquid solder joints become too small. Control of the electroplating process to create solder caps on copper pillars becomes exceptionally challenging at this pitch. Beyond that, during TCB bonding, slightly too little compression risks electrical opens, while slightly too much compression risks electrical shorts.

Cu-to-Cu thermocompression bonding creates joints directly between flat, polished surfaces of copper. Since there is no liquid phase involved, the process only needs to ensure that the surfaces are pressed together uniformly. K&S’s formic acid and plasma cleaning options provide oxide-free surfaces that allow for high yield. By creating Cu-Cu joints at higher forces and without the need to bond the surrounding dielectrics as in Cu-dielectric hybrid bonding, the thermocompression process is substantially less sensitive to surface roughness and cleanliness. Thus, Cu-Cu TCB offers a simpler and lower-cost alternative.