Progress on low temperature sintering of nano-silver

Nano-silver is a very potential electronic interconnect material, it has excellent physical and chemical properties, high thermal conductivity, and good electrical conductivity. It is not only widely used in the field of electronics, but also in the fields of medical and catalysis. Due to the size effect, when the silver particles reach nanometer size, they will have high surface energy, resulting in the melting point of nano-silver is much lower than that of metallic silver, so that nano-silver can be sintered at low temperature, and finally form a sintering material that similar to the melting point of bulk material. So nano-silver has the characteristics of low-temperature sintering and high-temperature service, which is very suitable for high-power electronic devices. The preparation of nano-silver particles includes physical, chemical, and biological methods. The preparation of nano-silver paste mainly consists of two methods: uniformly mixing nano-silver powder with various organic substances and centrifuging nano-silver particles. Nano-silver low-temperature sintering is based on powder sintering theory and Herring's law. The former shows that applying auxiliary pressure and reducing the size of powder particles can increase the driving force for sintering, thereby achieving sintering densification of metal powder at a temperature lower than the melting point of the metal element. that the additional driving force required for particle sintering decreases as the particle size decreases, because the smaller the particle size, the greater the surface area and surface curvature of the particle, and the greater the sintering driving force of the particle itself during sintering is larger, the required external driving force will be reduced accordingly. The external driving force for sintering can be achieved by applying auxiliary pressure and increasing the sintering temperature. The problem of the low-temperature sintering technology of nano-silver is that the sintering temperature (250°C-350°C) is still too high, which leads to the incompatibility of certain materials, and the need to apply additional auxiliary pressure to improve the quality of the sintered joints, which easily leads to damage of components. Therefore, the low-temperature sintering of nano-silver needs to further improve the sintering performance This article will describe the research progress in recent years from the preparation of nano-silver particles and nano-silver paste, the development of low-temperature sintering technology, and the research of sintering performance.