Die-to-wafer hybrid bonding is about to penetrate advanced chip systems for servers, data centers and later possibly cell phones. Back-end equipment builder Besi and partner Applied Materials are in the front row with their machines. (…)
K&S recently announced a partnership with UCLA CHIPS (Center for Heterogeneous Integration and Performance Scaling at the University of Los Angeles) to get the TCB pitch below 5 micrometers. “I believe it will be very difficult to get this to high-volume manufacturing in the next ten years”, comments Stefan Chitoraga, technology and market analyst for packaging and assembly at Yole Intelligence. In practice, TCB sits at a pitch above 30 microns. Hybrid bonding achieves 10 microns in die-to-wafer processes and under 1 micron for wafer-to-wafer in the case of 3D NAND.
In addition, K&S is working on a process without solder, using formic acid to make the copper bobbles very clean and then connecting them directly together. Paul Lindner, executive technology director at EV Group, admits that this is a sensible strategy, with a chance of success. He agrees that cheaper solutions that work usually win in the back-end. “The industry will do everything possible to hold on to and expand the established technology.”
Yole’s Chitoraga is more outspoken about the drawbacks of thermo-compression. “It’s true that TCB is less expensive than hybrid bonding, but keep in mind that you’re talking about the current status of thermo-compression machines with a pitch of 40 microns. If we go to 10 micron, which by the way is still under development, then the cost will definitely increase compared to 40 micron.”
The Yole analyst has doubts about the reliability of thermo-compression for small pitches. “If you reduce the pitch, then you also have to reduce the size of the micro-bumps. There are quite a few challenges there, because if those micro-bumps are smaller, then they’re much more sensitive to thermal stress.”…
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