Effects Of Nano-CeO₂ Addition On Interfacial IMC Growth Of Sn-0.3Ag-0.7Cu-xCeO₂/Cu Solder Joints

With the miniaturization of microelectronic packages,improving the reliability of solder joints has become more and more important.Hence,study of microstructures and interfacial reactions of intermetallic compounds?IMC?at the interconnect interface has important meaning for the reliability of solder joints.This thesis systematically studied the effect of nano-CeO₂addition on the interfacial reaction of the Sn-0.3Ag-0.7Cu solder joints during reflow and aging processes.The mechanism that effectively suppressed IMC growth and improved interconnect reliability was discussed.The main findings are as follows.The slightly doping of CeO₂ nanoparticles can suppress the growth of the IMC layer and refine the IMC grains during the reflow process.The growth kinetics of IMC layer and IMC grain at the interface of Sn-0.3Ag-0.7Cu-x CeO₂/Cu solder joint during reflow soldering is studied by curve fitting method.The results show that the growth index of IMC layer ranges from 0.337 to 0.380,which means that the growth of the IMC layer thickness is mainly controlled by the channel diffusion between the IMC grains during reflow time.The growth index of IMC grains is in the range of 0.297 to 0.311.The growth of IMC grains is the result of both interfacial reaction and atomic diffusion.CeO₂ nanoparticles may be the nucleation agent of Cu₆Sn₅ grains during the reflow process.When doping with nanoparticles,the activation energy barrier of the system decreases,and more nuclei grow stably through the barrier.The growth rate of IMC is the lowest,and the effect of inhibiting the growth of IMC layer and refining the IMC grains is most obvious when the content of CeO₂ nanoparticles is about0.15wt.%.Temperature and aging time have an impact on the growth of the IMC layer during aging process.The solder joint interface forms a two-layer IMC structure whose compositions is Cu₆Sn₅ and Cu₃Sn respectively.The growth kinetics of the overall IMC layer was studied by a linear fitting method,which shows that the relationship between the thickness of the IMC layer and the aging time in the aging process meets Fick's law,proving that atomic diffusion is the main driving force for IMC growth.When the CeO₂ nanoparticle doping content is about 0.15wt%,the interfacial reaction of the solder joint has the largest activation energy.The doping of trace amounts of CeO₂ nanoparticles can increase the activation energy of the atoms in the solder joints,reduce the diffusion rate of the atoms,and inhibit the growth of the IMC layer.The main mechanism that the doped CeO₂ nanoparticles can refine the IMC grains might be grain boundary pinning mechanism.It is found that as the CeO₂ nanoparticle content increases,the number of fine particles pinned at the grain boundaries increases,hindering grain consolidation and atomic diffusion,thereby reducing the growth rate of the IMC layer.