Modeling, design, and demonstration of low-temperature Cu interconnections to ultra-thin glass interposers at 20 μm pitch

This paper reports the first design and demonstration of a manufacturable 20 μm pitch Cu interconnection technology to ultra-thin glass interposers. Bonding is accomplished at temperatures below 200 °C without the need for solders. Manufacturability challenges such as substrate warpage, bump noncoplanarity and assembly throughput with low bonding times are addressed with this technology. The modeling and experimental results indicate that the ultra-fine pitch Cu interconnection offsets more than 3 μm non-coplanarity. Bonding interfaces were characterized to show that metallurgical bonding microstructure is formed even with a bonding time of 5 seconds, with superior electrical properties. A mechanism for low-temperature metallurgical bonding is proposed based on the characterization results.