Preparation And Performance Analysis Of High-temperature Lead-free Solder

With the development of miniaturization,intelligence,integration,and reliability of electronic products,surface mount technology(SMT)has become one of the mainstream technologies for electronic packaging.Solder as an interconnect material effectively provides the electronical and thermal channels and mechanical supports,which is a significant part of surface mount technology.Although the traditional lead-free solders have been widely applied in SMT,there is a potential risk of tin reflow and electro-migration at high temperature,resulting in short circuit.Meanwhile,the lead free of electronic products is constantly developed,the use of high temperature solder containing lead is greatly restricted.Therefore,it is a great challenge for electronic packaging to develop a lead-free solder,which achieves low temperature welding and high temperature service.This paper is devoted to developing a low cost and high reliable lead-free solder.The main contents are described as follows:(1)Firstly,the effect of the preparation process of the Cu-Sn solder on the welding properties was explored.The copper powder and tin powder with particle sizes of 1μm were prepared by atomization method,and the effects of mass ratio of copper and tin and kinds of fluxes on the welding strength were also investigated.As the mass ratio of copper and tin is 1.3:1 and n-butanol is the flux,the Cu-Sn solder have the best welding performances,and the corresponding welding strength value reaches to 30 MPa.(2)Secondly,the effect of welding process on the weldability of Cu-Sn solder was studied.The welding properties of the joints were evaluated by analyzing the welding strength,microstructure and phase composition of the joints.When the welding temperature is 300 C,the heating rate is 3.7 C /s,and the welding time is 60 min,the welding strength is more than 30 MPa,and there are no obvious defects in the welding interface.The crystal phases of the welding interface is composed of Cu6Sn5 and Cu3 Sn intermetallic compound and a small amount of Cu and Sn.(3)Finally,the welding defects of the joints were analyzed.The samples were welded at 300°C for 40 minutes,and conducted to aging test at 300°C for 50 h.The appearance of defects,such as voids and cracks,greatly weaken the welding strength of the joints.After aging test,the welding strength significantly increases without defects and voids,and the distribution of Cu and Sn elements is homogeneous.Therefore,the prepared Cu-Sn solder and the optimized welding parameters have good high temperature reliability in this paper,which has broad application prospects in the field of electronic packaging.