20 µm Copper Micro-Bump Bonding Through a Silver Metallization for Advanced Packaging Under a Low-Pressure Condition

In this work, we proposed a copper (Cu) micro-bump bonding strategy by using a silver (Ag) metallization layer as an interconnect bridge. Si chips with 20 µm Cu-Ag bumps were bonded under a low pressure (0.4 MPa) and atmospheric conditions at 250°C. By investigating the surface morphology evolution of the Cu-Ag bump, it is found that severe surface deformation caused by Ag abnormal grain growth and hillock generation plays a critical role in the Cu-Ag bump bonding, which facilitates the approach and bonding of top and bottom Ag surface of the bump structure. Moreover, this bonding strategy is expected to be particularly advantageous for fine-pitch interconnect applications. It not only mitigates the severe bonding condition requirements that are used in thermal compression bonding and hybrid bonding, but also provides higher quality bonding structures for advanced packaging.