Growth And Control Mechanism Of Cu₃Sn At Sn/Cu Soldering Interface

The development of electronic packaging has brought about the miniaturization of integrated circuits,which requires that solder joints should have higher reliability.IMC,as the basis for solder joint connection,strongly influences the reliability of solder joints.In previous studies,most of them focused on Cu₆Sn₅,and few of them did relatively systematic studies on Cu₃Sn.The present work has used the reflow soldering process,combined with the corresponding characterization means,simulation techniques,in-depth study of the reflow process（reflow temperature,time,cooling rate,reflow times）,substrate material orientation,solder joint composition and size role of the soldering liquid-solid reaction process interfacial intermetallic compound of Cu₃Sn phase growth mechanism and kinetics,clearly reveal the soldering interfacial reaction process under each process,and based on this thesis The final all-Cu3Sn solder joints were prepared.The main conclusions are obtained as follows:1.The growth of interfacial Cu₃Sn is positively correlated with reflow temperature and time.Both reflow temperature and reflow time promote the growth of Cu₃Sn,and the proportion of Cu₃Sn thickness in the whole interfacial IMC enhances with increasing soldering time or temperature;as the cooling rate decreases,the proportion of Cu₃Sn thickness in the whole Cu₆Sn₅-Cu₃Sn IMC layer increases.In addition,thin layers of Cu₆Sn₅and Cu₃Sn formed at the interface under air cooling,while thick fan-shaped Cu₆Sn₅and laminated Cu₃Sn appeared under furnace cooling.During multiple reflows,on the one hand,the concentration of Cu in the solder increases with increasing reflow time,which is closely related to the continuous growth and dissolution of IMC;on the other hand,not only the size of Cu₆Sn₅grains increases,but also their morphology changes from scalloped to prismatic as the number of reflows increases,and the change in Cu concentration in the solder during multiple reflows results in the growth rate of Cu₆Sn₅During multiple reflows,the Cu concentration in the solder causes fluctuations in the growth rate of Cu₆Sn₅;during multiple reflows,the Vickers hardness and melting point of the solder also fluctuate due to fluctuations in the Cu concentration.2.Ag in the interfacial reaction during reflow of Sn-x Ag/Cu solder joints,the higher the concentration of Ag within the solder joint the larger the size of the interfacial IMC layer.As one of the main constituent elements of the interfacial IMC,the overall Sn-x Cu/Cu solder joint reflow process tends to increase with the initial Cu concentration of the soldering alloy,the Cu concentration gradient within the soldering alloy decreases,and the interfacial IMC size increases.The IMC layer thickness is also larger.This is due to the higher Cu concentration and higher cooling rate in the small Sn/Cu joints,which is conducive to the lateral growth of the interfacial IMC and its prismatic grains,which tend to show larger size,more complete lateral hexagonal prismatic crystals,and a larger IMC layer thickness.3.Based on the previous study,all-Cu₃Sn intermetallic joints can be obtained by increasing the number of reflows and using a smaller cooling rate at a ramp-up temperature design.