Sintering and optimization of copper nanopaste-connected copper array conical microstructures

Abstract

With the advancement of 3D integration technology, the integration density and operational speed of circuits continue to increase. Consequently, there is a corresponding rise in the demand for interconnection reliability. However, traditional interconnection processes and materials are no longer able to meet the requirements for interconnection reliability. This study optimized the interconnection material by utilizing different ratios of organic compounds in nano-copper coating materials. Micro/nanostructures were processed using femtosecond laser and secondary thermal coating to enhance the interconnection process. Firstly, to ensure processing efficiency, we utilized femtosecond laser to create micro/nanostructures with increased surface contact area. Subsequently, varying molar ratios of ascorbic acid and benzimidazole were utilized in the preparation of copper (Cu) pastes to analyze their impact on the dispersion and sphericity of the copper nanoparticles and the shear strength of the interconnections. The ideal combination resulted in well-dispersed spherical copper nanoparticles, copper nano paste with an average shear strength of about 38 MPa was obtained. In addition, optimization was achieved through the femtosecond laser copper interconnection sintering process using a secondary heat coating, which reduced the unfilled rate of surface microstructures from 35.31 % to 11.25 % and increased the copper interconnection strength from 31.42 MPa to 43.65 MPa. Finally, finite element simulation analysis was employed to study the temperature and stress distribution of the copper interconnect during operation and to predict its service life under thermal cycling conditions (−50 °C–300 °C). The results demonstrated that the reliability of the sintered structure meets operational requirements.