Sintering Performance And Strengthening Mechanism Of Mixed Cu-Sn Micro-Nano Particles

Due to the development of chips towards miniaturization,densification,and integration,it posed great challenges to the structure,processes,and interconnected materials of advanced packaging technology.However,the traditional interconnected materials cannot meet the demands of advanced packaging technologies.It is necessary to develop a kind of interconnected materials for advanced packaging.Due to the good electrical and thermal conductivity,reliable mechanical properties,and low cost,Cu particles are promising to be an alternative to the traditional interconnected materials.However,the oxidation of Cu nanoparticles will reduce the sintering performance.Cu microparticles is less sensitive to oxidation but possess poor sintering performance in low temperature.The sintering performance of Cu microparticles can be significantly enhanced by adding low melting point metals or mixing micro-nano particles.However,few studies have combined abovementioned two approaches to improve the sintering performance of Cu microparticles.Aiming at the above problems,a method for synthesis of Cu nanoparticles using a wetchemical redox method under the ultrasound treatment was innovatively proposed in this thesis.At the condition of 0-500 W ultrasonic power,the size of Cu nanoparticles was reduced from 520±94 nm to 167±44 nm,and the morphology and dispersion of particles was good.It was found that there is an exponential relationship between the size refinement of nanoparticles and the effect of ultrasonic power.And a quantitative relationship expression between particle size and ultrasonic power was put forward.the mechanism of specific surface energy and ultrasonic power affecting particle size was revealed.The relationship was highly consistent with the experimental results.This mathematical model provides a reliable theoretical explanation and understanding for the particle size refinement and ultrasound treatment.In this thesis,a methods of mixing Cu-Sn particles to enhance sintering performance was proposed.The sintering properties of 167 nm,520 nm and 1 ?m Cu particles and mixing respectively with 250 nm Sn particles were investigated.At the sintering conditions of260 ?,30 min and 5 MPa,the shear strength of 1 ?m Cu-250 nm Sn particles could reach64 MPa.Because Sn particles are uniformly dispersed in the gaps of Cu particles and formed a Cu-Sn intermetallic compound.It was revealed that the strengthening mechanism of mixed Cu-Sn particles sintering is the second phase strengthening.When the mass fraction of Sn particles was 25 wt.%,the shear strength increased from 33 MPa to 70 MPa.The dispersed Cu-Sn intermetallic compound was found in the joint by the analysis of EDS and SEM.Cu-Sn intermetallic compound could block the propagation of dislocations of Cu lattice and prevent the movement of Cu grain boundaries,thereby enhancing the shear strength of the joint.The results showed that the sintering properties of Cu microparticles could be improved by mixing Sn nanoparticles.