Study On Microstructure Evolution And Mechanical Properties Of SnSb-XCuAgNi/Ni Solder Joints During Thermal Aging

With the development of the third-generation semiconductor and electronic packaging technology,higher requirements have been placed on the hightemperature resistance of interconnect pads.The development of new hightemperature lead-free solder has become an urgent demand in the field of power device packaging.In this paper,Sn-5Sb-based solder which is suitable for power device interconnection and Ni-plated substrates are used as research objects.Sn-Sb-based solder Sn-5Sb-0.5Cu-0.1Ni-0.1Ag,is obtained by adding trace elements of Cu,Ni,and Ag.As well as the other two solder Sn-5Sb-1Cu-0.1Ni-0.1Ag and Sn-5Sb-0.5Cu-0.1Ni-0.5Ag.It was soldered on a Cu substrate with a Ni-plated barrier layer by comparing with Sn5 Sb and SAC305 in aspect of microstructure and mechanical properties.The evolution of the matrix structure and the compounds in the matrix solder during the aging process was studied.The growth rate of the interfacial intermetallic(IMC)compound changed with the aging time.The solder joints are subjected to high-temperature aging in a hightemperature aging furnace at 150 ?.The aging time is divided into five time periods: 0h,504 h,1008h,1512 h,and 2016 h.Nanoindentation experiments andshear strength experiments were performed on the prepared samples.For mechanical properties,the hardness,elastic modulus,and shear strength of the solder joints were tested.The mechanical properties of the three solders added with trace metal elements and Sn-5Sb and SAC305 were analysed using the tested results.The microstructures of three solders,Sn5Sb-Cu Ni Ag,Sn-5Sb,and SAC305 were analyzed by SEM and EDX,respectively.The results show that the IMCs in Sn5Sb-Cu Ni Ag and SAC305 bulk solders are mainly(Cu,Ni)6Sn5 and granular compounds Ag3 Sn.IMCs in Sn-5Sb solders are mainly(Cu,Ni)6Sn5.The IMCs in the bulk solder coarsens as the aging time increasing.The interfacial IMC layer became significantly thicker and the IMC morphology gradually changed from an irregular jagged shape to a smooth and uniform layer.The thickness of the interfacial IMCs of the Sn5Sb-Cu Ni Ag solder joint is thinner than that of the Sn-5Sb and SAC305 soldered joints.The Sn5Sb-Cu Ni Ag solder joint has better thermal aging resistance.The addition of 0.5Cu and 0.1Ni can inhibit the growth rate of IMC at the interface.The micro hardness of Sn5Sb-x Cu Ni Ag/Ni solder joints is higher than that of Sn-5Sb and SAC305 solders.Among them,the solder C has the highest hardness and the aging time is prolonged.The elastic modulus is gradually increased from aging 0h.When the aging reaches a high peak after 504 h,it then decreases,and when the aging reaches 1008 h,it is a low valley value.Until the aging reaches2016 h,the elastic modulus of the five solder joints all first increase-decreaseincrease-decrease.The trend,the modulus of elasticity is in the form of "M" curve.As the failure time prolongs,the overall trend of the shear strength of the solder joints increases first,then decreases,and then gradually flattens.When aging to 360 h,the shear strength of the first two types of solder joints,Sn Sbx Cu Ni Ag,both increased,and the third type of Sn Sb-x Cu Ni Ag solder joints reached the highest value at 144 h,and the change did not change much when aging to 360 h.The cutting strength remains the highest.