Bubble dynamics in microfluidic electroless copper interconnection for advanced 3D chip integration

3D chip integration is critical for achieving high information density and enhanced device performance in rapidly evolving microelectronics. Traditional thermocompression bonding faces significant reliability challenges, prompting the development of the microfluidic electroless interconnection (MELI) technique for low-temperature bonding. However, defect formation remains a substantial barrier to MELI implementation. This work developed the first quantitative framework in the rational design of the MELI system. We initially investigated bubble behavior in microchannels using an analytical force balance model to accurately predict bubble departure, the predictions match the experimental findings well with a Pearson correlation coefficient r = 0.939. The model reveals that flow velocity-controlled shear lift force dominates bubble departure mechanisms. Subsequently, a coupled phase field model (PFM) was developed to examine bubble dynamics and retention effects. Simulations revealed the dynamic process of bubble retention and subsequent void formation, identifying a critical velocity threshold effect on bubble retention behavior where bubble necking deformation counteracts bubble departure. Based on theoretical insights, design rules were established to achieve defect-free interconnections, and the bubble removal efficiency and retention minimization was balanced by flow velocity selection with 5000 μm/s in the developed system. Experimental validation demonstrated the formation of uniform, solid, mechanically robust bonding bumps with superior mechanical and thermal performance. The proposed design rules successfully eliminate defects while maintaining excellent bonding quality. This research advances theoretical understanding of bubble dynamics in micro-scale reactive systems while providing practical solutions for reliability improvement in 3D chip integration technologies, contributing significantly to both fundamental knowledge and industrial applications.