Towards understanding the copper paste dip-bonding process for fine-pitch copper pillar interconnections in microelectronic packaging

This study presents a comprehensive investigation of the copper paste dip-bonding process for fine-pitch copper pillar interconnections in microelectronic packaging. By systematically adjusting the solid content (40 wt.%–80 wt.%) of ethylene glycol-based nano-copper paste, we achieved stable and uniform dipping morphology on copper pillars with diameter/spacing ranging from 40/40 μm to 200/200 μm. Through detailed characterization of the paste’s rheological properties and wetting behavior, combined with dynamic monitoring of the dipping process, we established a quantitative model to depict the neck structure profile and correlate dipping volume with paste properties. The model showed strong agreement with experimental observations, providing fundamental insights for the quantitative analysis of dipping volume. Both the model and experiments identified 70 wt.% as the optimal solid content, corresponding to a contact angle of 42.8° and enabling the achievement of an ideal dipping volume. Under optimized bonding parameters (260°C, 20 MPa, 8 minute dwell time), the interconnection structures exhibited excellent mechanical strength with a shear strength of 42 MPa and outstanding electrical performance with a resistivity as low as 5.78 μΩ·cm. This research confirms that precise control of paste solid content enables reliable fine-pitch interconnections while preventing both insufficient filling and overflow issues. The work establishes both theoretical foundations and practical methodologies for enhancing process stability in dip-bonding technology, offering promising applications in advanced microelectronic packaging.