Formation and homogenisation of Sn-Cu interconnects by self-propagated exothermic reactive bonding
journal contributionposted on 2019-04-12, 08:02 authored by Wenbo Zhu, Xiaoting Wang, Changqing LiuChangqing Liu, Zhaoxia ZhouZhaoxia Zhou, Fengshun Wu
We produced SnCu interconnects by self-propagated exothermic reactions using AlNi NanoFoil at ambient conditions, through the instantaneous localised heat across the interfaces between Sn electroplated Cu substrates. This technique presents a great potential for electronics integration with minimal thermal effects to the components. However, the metastable phases resulted from the non-equilibrium interfacial reactions and solidification were inevitable under a highly transient regime due to a drastic heating/cooling (over 107 K/s). In this study, Finite Element Analysis was performed to predict the temperature profiles across bonding interfaces, which were subsequently correlated with the formation and homogenisation of the bonded structures during the bonding and post-bonding ageing process. It has been revealed that, for nano-sized metastable phases, their formation, morphologies and distribution were primarily attributed to the convective mass transportation, liquid-solid inter-diffusion, and directional non-equilibrium solidification of Sn in molten zone of the bonding interfaces. The non-equilibrium phases initially formed in the SnCu interconnects can be homogenised towards the equilibrium status by accelerated ageing. This was achieved through the coalescing and subsequent growth of the original nano-sized metastable phases, as a result of the solid-diffusion of Cu and Ag atoms at intergranular boundary regions of Sn grains, AlNi NanoFoil/Sn. and Cu/Sn interfaces.
The authors acknowledge the studentship jointly awarded by Loughborough University (UK) and Huazhong University of Science and Technology, HUST (China), as well as two research grants on “quasi-ambient bonding (QAB)” (Ref: EP/R032203/1) and “heterogeneous integration (HI)” (Ref: EP/R004501/1) funded by EPSRC of the United Kingdom. The research was also partially supported by a research grant of the National Natural Science Foundation of China (NSFC NO. 61574068) and the Fundamental Research Funds for the Central Universities (No. 2016JCTD112).
- Mechanical, Electrical and Manufacturing Engineering