Study On Microstructure,Mechanical Properties And Life Prediction Of Accelerated Aging Of Solder Joints

SnPb eutectic alloys are often widely used in the packaging and assembly of electronic products due to their excellent solderability and high reliability.When an ordinary printed circuit board is assembled,the main buffer metal on the pad connection level is Cu.Due to its excellent chemical stability,oxidation resistance,good conductivity,and low contact resistance,Au is often used as electrode lead or as a coating on the surface of various substrates.However,during the service process of the device,Au atoms easily diffuse with the Sn atoms in the SnPb solder to form Au-Sn intermetallic compounds,especially in devices that operate at high temperatures or higher than normal temperature.Many studies have shown that the growth of Au-Sn intermetallic compounds and their evolution during service have a decisive influence on the reliability of device packaging.Therefore,in order to improve the reliability of packaged devices,it is necessary to essentially study the growth mechanism of Au-Sn IMC during the aging process.Therefore,this paper mainly studies the evolution characteristics of the solder joint interface compound and its characteristics during the accelerated aging process of gold-plated printed boards.Analysis of mechanical properties.Through aging and heating experiments on the solder joints,the evolution of the microstructure of thick gold solder joints with different process parameters at aging temperatures of 75?,100?,125?,150?and aging times of 100h,250h,500h,and1000h was studied..By analyzing the evolution law of interface intermetallic compound(IMC)and calculating the thickness of the IMC layer in 3 SEM pictures under the same experimental parameters through PS software,the diffusion coefficient and activation energy of different phases were calculated,and the aging experiment of thick gold solder joints was established.Life prediction model;This paper analyzes the change law of the solder joint interface under different aging conditions and the mechanical properties of the solder joints,and compares the structure and mechanical properties of the solder joints under different aging conditions.The analysis of the changes in the solder joint interface under different aging conditions shows that after accelerated aging,the thickness of the IMC layer at the solder joint interface is mainly determined by the thickness increase of the Au-Cu-Sn compound layer.At different aging temperatures of the solder joint interface IMC,the thickness of the solder joint interface IMC layer shows an upward trend as the aging time increases.In addition,by calculating the thickness of the IMC layer of different phases under different aging experimental conditions,the diffusion coefficient and activation energy of the different phases are calculated through the Alanlius formula,which explains that Cu₃Sn IMC is relatively(The reason for the slower diffusion of Au,Cu)₆Sn₅ IMC.The equivalent high temperature aging time of electronic devices stored at room temperature for a certain n?mber of years is predicted by formulas.The analysis of the composition of solder joints under different aging conditions shows that with the change of aging conditions,the microstructure of solder joints is still mainly Au Sn₄ phase,Sn-rich phase and Pb-rich phase.The phases of the IMC layer at the solder joint interface are Cu₃Sn and(Au,Cu)₆Sn₅ phases.Especially in the later stage of the aging experiment,the acc?mulation of Pb-rich phase at the solder joint interface is more obvious,and the thickness of the IMC layer changes more obviously.The analysis of the mechanical properties under different aging conditions shows that the mechanical properties under appropriate aging conditions are improved compared with the original mechanical properties,and as the aging temperature and time increase at the same time,the mechanical properties begin to decline gradually,at150?Under the aging condition of-1000h,the mechanical performance drops to about half of the original mechanical performance of the device.In the low-temperature aging experiment,the mechanical properties of the solder joints are not particularly obvious.Under the high-temperature aging experiment,the mechanical properties of the solder joints change more obviously with the increase of aging time.The analysis of the solder joint fracture under different aging conditions shows that with the intensification of aging conditions,the fracture position of the solder joint gradually shifts to the IMC layer.Especially at 150?-1000h,the Pb-rich layer of the solder joint is obvious,and the fracture is often in this position.