Effect of Porosity in Copper Nano-Sintering on the Reliability of Power Devices

With the in-depth research on third-generation semiconductors, many issues related to power devices have begun to emerge, with the foremost being the problem of package interconnection reliability. The chip bonding layer serves as a key component in ensuring the normal operation of power devices, as it facilitates the physical and electrical interconnection between the chip and the substrate. As a result, there has been significant research in the field of interconnection. Currently, nano-metal particles are considered an ideal choice. This is because they possess the ability to fuse between particles at lower temperatures, forming characteristics similar to bulk metals, thereby exhibiting high performance and good reliability. As a novel chip bonding method, nano-silver particles have attracted widespread attention. However, their application is constrained due to issues such as cost and susceptibility to electromigration. In comparison to silver, copper boasts a lower cost and excellent resistance to electromigration. Additionally, it exhibits similar electrical and thermal conductivity properties to silver. These factors have propelled nano-copper particles into the spotlight as a new connecting material. This article aims to optimize the sintering process using the single-factor method. The sintering process optimization includes sintering time and pressure, with sintering temperatures ranging from 200°C, 250°C, to 300°C, and sintering pressures varying from 1 MPa, 3 MPa, to 5 MPa. Sample preparation and sintering experiments will be conducted using the optimized sintering process, and the resulting samples will be tested to calculate the shear strength under different conditions. Subsequently, finite element analysis will be employed, considering the volume of porosity in the sintered layer as part of the sintered layer volume. A perfect sintered layer without voids will be modeled, and the sintered layers with different porosities obtained from experiments will be considered as a new material. Material parameters such as Young's modulus and Poisson's ratio for the sintered layer under different porosities will be calculated. These material parameters will be input into the model to assess the impact of different porosities on the reliability of double-sided heat dissipation power devices, including temperature cycling (TC) and the fatigue life of the sintered layer. Finally, it will be concluded that maintaining the porosity of the sintered layer between 15% to 20% is most appropriate. This will serve as a reference for reducing device stress and enhancing reliability.