Authored By:
Albert T. Wu, Hung Wang, Ping-Hsuan Chen
National Central University, Taiwan
Kelvin Li, Chang-Meng Wang and Watson Tseng
Shenmao Technology Inc., Taiwan
Summary
Recent developments in copper (Cu)-based bonding techniques have shown promising advancements for low-temperature and pressureless interconnect applications in electronics for both engineered Cu nanoparticles (NPs) and hybrid Cu-SAC pastes. This study synthesizes Cu NPs using an eco-friendly method with ascorbic acid and without capping agents, achieving controlled particle size distribution through pH manipulation. These NPs are then utilized to form Cu NP pastes by mixing with polyethylene glycol (PEG), which is applied in Cu-to-Cu direct bonding.
The optimal bonding properties are achieved with proper particle size and packing density, which directly correlate to increased joint strength. This study also utilizes a hybrid paste composed of Cu particles and SAC alloy paste. By varying the SAC fractions and Cu particle sizes, a detailed analysis is conducted on joint microstructures and mechanical properties. A paste that displays superior mechanical characteristics can be attributed to an ideal formation of the Cu3Sn phase, offering high stability and resistance against external forces.
This phase is particularly noted for its toughening effect within the intermetallic compound matrix, an effect enhanced by a coherent Cu3Sn/Cu interface. Both approaches demonstrate the potential of Cu-based pastes in achieving efficient, robust, and durable joints suitable for high-temperature applications in electronics manufacturing. These innovative methodologies not only enhance mechanical properties but also contribute to the sustainability of materials, presenting a significant step forward in electronic packaging technologies.
Conclusions
This study demonstrated that controlling the synthesis conditions of Cu NPs, particularly the pH of the reducing solution and the sintering temperature, is crucial for optimizing their microstructure and mechanical performance. The hybrid Cu-SAC paste also showed promise as a bonding material, with the best results achieved using a 20 wt% SAC fraction and a Cu particle size of 0.5 μm. These findings have significant implications for the development of cost-effective and reliable bonding materials for electronic packaging and other high-performance applications.
Initially Published in the SMTA Proceedings
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