Microstructural and mechanical integrity of Cu/Cu interconnects formed by self-propagating exothermic reaction methods

• Copper is bonded using solder and self-propagating exothermic reaction (SPER).
• The interfacial IMC layers at different interfaces are verified.
• The shear strength of Cu/Cu SPER joining can reach 30 MPa.
• The influence of process parameters on porosity and joint thickness are analysed.
• The fracture mode of SPER joints and the leading cause are verified.

A rapid and flexible Cu/Cu soldering process has been developed through self-propagating exothermic reaction (SPER) using Al–Ni multilayer nano-film as heat source. The localized intensive heat generated by SPER has a short affecting time and thus a low thermal impact, which promises various potential benefits for electronics interconnects, including the reduction of stress caused by CTE (coefficient of thermal expansion) mismatch and the high temperature soldering by reflow process. In this study, the strong metallurgical Cu/Cu joining interfaces of hundreds nanometers IMCs (intermetallic compounds) layers were formed, which exhibit a shear strength greater than 32 MPa. This work has also characterized the interfacial IMC morphology, thickness, porosity and the fracture behaviour of the joint to allow an analysis and evaluation of the feasibility and reliability of SPER interconnects. In addition, the formation mechanisms of defects and the influence of applied pressure, solder thickness and ambient temperature in SPER process have been investigated, which can further assist the optimization of process and the improvement of joining quality.

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