Low-Temperature Bonding of Cu Through Self-Propagating Reaction Under Various Temperatures and Pressures

Abstract

Low temperature soldering has been realized to create a strong metallurgical interconnection between Cu using the self-propagating exothermic reaction by Al–Ni NanoFoil. This technique presents a great potential for electronics integration with a significantly reduced processing temperature (at least 150 °C lower than traditional techniques) and minimal thermal effects to the components. In this study, finite element analysis was performed to predict the temperature profiles across bonding interfaces, which were subsequently correlated with the formation and quality of the bonded structures. It has been revealed that, for nonequilibrium nanosized phases and defects, their formation and distribution were primarily attributed to the solid–liquid interdiffusion and rapid solidification, under the highly transient regime due to a drastic heating/cooling (105–107 °C/s). The preheating and pressure applied to the bonding structure were clearly beneficial to improve the quality of bonding. This was achieved by the thinned solder thickness and the correspondingly improved temperature profiles that enable a sufficient wetting, filling, and interfacial reactions. Through the comparative analysis of the numerical predictions and the experimental results, the solder layers must completely melt across their thickness and have a total heat over 30 K ms on the Cu to ensure robust interconnections with a shear strength of approximately 37 ± 3 MPa and dense continuous bonding interfaces.