Electromigration Reliability Study Of White Light CSP-LED

In order to meet the requirements of miniaturization and high performance of electronic products,integration and packaging density of IC chips continue to increase,accompanied by the current density of micro-interconnect structure increasing dramatically.Chip Scale Package(CSP)stands out for its advantages of small size,good heat dissipation and high reliability.Using chip scale package(CSP),it can make the ratio of the LED chip area to packaging area close to the 1:1,and it is in full compliance with the development requirements of LED packaging,and will be one of the mainstream trends of high-power LED in the future.Due to the high-power LED working under high temperature and high current condition,solder joints in CSP prone to electromigration failure.Therefore,it is important to study the electromigration phenomenon of high-power CSP-LED devices,and clarify the related reliability problems at the same time,which is of great significance for the reliability design of LED devices.The electromigration aging experiment on CSP-LED samples was carried out,the relationship between electromigration characteristics with the applied current and the ambient temperature is investigated.Current conditions of 800 mA,the environment temperature is 105 ?,85 ? and 85 ? under the incentive level of aging experiment,get the characteristics failure time of the solder joint is respectively: 5.33 hours and 22.75 hours and 22.75 hours.Solder joint electromigration lifetime is affected by environmental temperature,the higher the temperature,the smaller the life.The environment temperature is 85 ?,the current condition of 900 mA and 800 mA and 700 mA aging experiment under incentive levels,get the characteristics failure time of the solder joint is respectively: 3.38 hours?22.75 hours and 322.6 hours.The current density is more sensitive to the current density than the ambient temperature.The larger the current is,the smaller the life is.Through the X-ray detection of failure samples,found after aging LED solder sample void rate increases,through the observation of solder joint void formation,it is found that the void of the solder joint is formed and propagated near the inside of the solder joint near the chip side.The three-dimensional finite element model of flip chip CSP-LED devices is established and the electric-thermal coupling analysis is carried out.The current density and temperature distribution are obtained,then reveals the reason why the temperature gradient and the current gradient generated.The atomic flux divergence(AFD)method is programmed by APDL and combined with finite element simulation to simulate the position of solder joint voids formation and predict the electromigration failure life of solder joints.The simulation results show that the maximum atomic flux divergence appears inside the solder joint near the chip side,the position of electromigration voids is simulated by using the technology of birth and death element,which is basically the same as the X-ray observation results.And the error between the predicted electromigration failure time and the experimental results is small.The electromigration reliability analysis method of LED devices can provide guidance for the electromigration failure analysis of LED devices and the improvement of the electromigration reliability.