Finite Element Analysis And Life Prediction Of Thermal Fatigue And Random Vibration Of Nano Silver Solder Joints

With the rapid progress of science and technology,semiconductor technology has been developing towards micro size,high density and high power.Especially the third generation semiconductor represented by silicon carbide and gallium nitride.This puts forward more stringent requirements for electronic packaging technology.Traditional interconnect materials such as tin-lead solder,lead-free alloy solder and conductive adhesive cannot meet the packaging needs of the third-generation semiconductor devices because of their limitations such as high processing temperature,low melting point and poor wettability,so it is of great significance to develop a new material that can meet the requirements.Nano-silver is a very potential material for electronic interconnection.It has excellent physical and chemical properties,high thermal conductivity and good electrical conductivity.Because of the size effect,nano-silver can be sintered at low temperatures and served at high temperatures,so it is very suitable for high-power electronics.According to statistics,the failure of most electronic products is caused by solder joint failure,so the solder joint directly affects the service life of electronic products.Among the loads that electronic products are subjected to during work,the failure rate of electronic products up to 75%by temperature and vibration loads.Therefore,this paper takes nano-silver as the research object and workbench software as the research tool to study the reliability of nano-silver solder joints under loads of temperature,random vibration and condition of thermal vibration loading.It can provide theoretical guidance for the practical application of nano-silver in electronic packaging.1、The finite element analysis of thermal fatigue is carried out on the simplified model.After five cycles of thermal cycle load,the deformation,stress and strain distribution of the solder joint under the thermal cycle load is obtained,and the outermost solder joint is determined as the dangerous solder joint.According to the Engelmaier formula,the thermal fatigue life of 2368 cycle is calculated by the equivalent plastic strain of dangerous solder joints,which is higher than Sn_3.8Ag_0.7Cu,Sn_3.0Ag_0.5Cu and Sn₆₃Pb₃₇.Through analysis models of different structural parameters,it is found that solder joint height,solder joint diameter,pad height,PCB thickness is proportional to the thermal fatigue life.The height of solder joint has the greatest effect on improving thermal fatigue life.PCB width is inversely proportional to thermal fatigue life.2、The finite element analysis of modal and random vibration is carried out on the complete model,the natural frequencies and modes of the first three orders of the structure are obtained.The distribution of deformation,stress and strain of solder joint under random vibration load was obtained,and the bottom right solder joint was determined to be dangerous.According to the Coffin-Manson high cycle fatigue empirical formula combined with Miner’s linear cumulative damage theory and Steinberg model based on Gaussian distribution,the random vibration fatigue life of8342h is calculated by the normal strain of dangerous solder joints,which is lower than Sn_3.0Ag_0.5Cu and Sn₆₃Pb₃₇.Through the analysis models of different structural parameters,it is found that solder joint diameter and PCB thickness are proportional to random vibration fatigue life,PCB thickness on random vibration life is greater than solder joint diameter.Solder joint height and pad thickness are inversely proportional to random vibration fatigue life,and pad thickness has little effect on random vibration fatigue life.3、The finite element analysis of thermal fatigue and random vibration was carried out on the model,to determine the dangerous solder joints under two kinds of loads.The thermal fatigue and random vibration life of the two dangerous solder joints were calculated.Finally,the total damage was obtained by the linear damage superposition method,and the fatigue life of the structure was 560 h by comparison under thermal vibration loading.