Effect Of Cu/Sn Content On The Properties Of IMC-Cu Composite Micro Solder Joints

With the increasingly severe service conditions of electronic components,people pay more and more attention to the reliability of electronic components.The service temperature of the first generation semiconductors represented by Si based devices is relatively low,which can not meet the current requirements of high temperature and high power.However,the third generation semiconductors represented by Si C can withstand a service temperature of more than 300?and support a power density much higher than that of the first generation semiconductors.At present,the chip mounting method is mainly suitable for the first generation semiconductor,which can not meet the high-temperature service requirements of the current industry for semiconductor power devices.In order to give full play to the excellent performance of the third-generation semiconductor high power devices,this paper studies the matching high temperature micro connection method.In this paper,TLP(transient liquid phase bonding)technology was used.The joints were made of Sn solder and three dimensional through-hole porous copper sheet.The porous copper structure has the characteristics of a large specific surface area.It can significantly increase the effective reaction area of Cu and Sn,improve the generation speed of IMC(intermetallic compound)in the composite joints,and improve the bonding efficiency.The obtained joints meet the requirements of"low temperature connection,high temperature service"for high temperature power device chip mounting.To study the effect of different Cu/Sn contents on the growth behavior of IMC-Cu at the interface of the compositemicro solder joints,the TLP technology combined with pressure was used to prepare IMC-Cu compositemicro solder joints with porous copper,pure Sn and Cu substrate as raw materials to study the effect of different Cu/Sn contents on the growth behavior of the compositemicro solder joints in Cu/Sn.The results show that the Cu/Sn content has a significant effect on the growth behavior of IMC in composite-joints.With the increase of Cu content in the joints,the growth rate of IMC increases,and the decrease of Sn content in the compositemicro solder joints is beneficial to the growth of Cu₃Sn at the reaction interface;the time to obtain Cu₃Sn-Cu compositemicro solder joints decreases with the decrease of Sn content in the joints.Under the same bonding conditions,when the bonding time is 25 min,the bonding time of20wt%Snmicro solder joints is 20%shorter than that of 40wt%Snmicro solder joints.When the Sn content is in the range of 20wt%-40wt%,the growth rate of Cu₃Sn increases with the decrease of Sn content in the joints,and the time to obtain all Cu₃Sn-Cu compositemicro solder joints shortens.The effects of different Cu/Sn contents on the shear strength and hardness of three IMC-Cu compositemicro solder joints were studied by shear test and nanoindentation test.The results show that the shear strength and hardness of the compositemicro solder joints increase with the decrease of Sn content,and the shear strength of the compositemicro solder joints with 20wt%Sn content is the highest,which is 97.52MPa.Brittle fracture is the main failure mode of the three joints.The mechanical properties of joints can be improved by adding porous copper in the micro solder joints.When the Sn content of the compositemicro solder joints is within 20wt%-40wt%,with the decrease of Sn content in the joints,the grains of Cu₃Sn-Cumicro solder joints obtained after bonding will be denser and the hardness of the micro solder joints will be increased.The results show that the shear strength of the joints increases with the increase of bonding time.This is because Sn and Cu₆Sn₅in the joints gradually transform to Cu₃Sn with the increase of bonding time,and the shear strength of Cu₃Snn is higher than that of Sn and Cu₆Sn₅.