Investigation of Surface Oxidation Resistance for High Entropy Solder Particles

While the scaling of Si technology is slowing down, the miniaturization in packaging technology is becoming increasingly crucial for advancing computational performance. One of the critical challenges in scaling the packaging technology is the manufacturing of micronized or even nanosized solder joints. As the size of traditional Sn-based solder joints shrinks below 5 μm, issues related to yield and reliability start to become inevitable. High entropy alloy (HEA) solder presents a possible solution for manufacturing solder joints under 5 μm. However, the complex composition of high entropy alloys makes traditional electroplating methods impractical for industrial applications. The most promising approach involves using high entropy alloy solder paste for bonding, necessitating the use of solder nanoparticles (NPs). Nevertheless, Sn-based nanoparticles are highly susceptible to oxidation, making them unsuitable for bonding purposes. The high-entropy feature of HEA solder nanoparticles offers a potential solution to slow down the oxidation rate of nanoparticles, while the mechanism is not clear yet. Therefore, it is essential to investigate the surface oxidation resistance of high entropy solder particles to enable their application in high-density bonding technology. This proposal first aims to develop a novel method for synthesizing high-entropy solder nanoparticles with varying compositions. The process begins with creating five-element high entropy nanoparticles through ultrasonic treatment of the corresponding fiveelement alloy bulk. Subsequently, we will explore the oxidation resistance of nanoparticles with different compositions using ex-situ transmission electron microscope (TEM) studies and on-chip electrochemical microdevices (OCEM). Then, the soldering performance of different composition HEA NP will be studied. By correlating the results of oxidation resistance investigations by OCEM and ex-situ TEM between NP composition and soldering performance, we intend to develop a novel methodology for assessing the oxidation resistance of high entropy solder particles. Meanwhile, the oxidation resistance mechanism will be clarified for these HEA nanoparticles, enabling us to optimize NP compositions and develop high entropy solder particles with superior oxidation resistance and soldering performance. Finally, these oxidation-resistance solder particles will be explored for high-density, ultra-fine pitch bonding technology applications.