Research On Reliability Of CSP LED Solder Layer

As the fourth generation of new energy-saving light sources,semiconductor lightemitting diodes(LEDs)have outstanding advantages such as high-efficiency,energysaving,environmental protection,and long lifespan.They have been widely used in indoor and outdoor lighting,automotive lighting,and backlighting.The packaging of LED devices from the initial in-line package,to the surface-mount package,and the latest chip scale package(CSP)are all toward miniaturization,integration,and high density.In the CSP,the solder layer is not only the mechanical performance support for the chip,but also the function of the transmission current,and the most effective way of distributing the heat from the chip,it is also the place where the reliability problem is most likely to appear at present.Although the reliability of the CSP solder layer is very important in the package,there is less research on the reliability and lifetime of the CSP-packaged LED in China.This work was supported by863 Program(No.2015AA033304)and National Key R&D Program of China(Grant No :2017YFB0403100,2017YFB0403102).The main research contents and results are as follows:1)The aging of CSP LED under high temperature and high humidity was carried out,and the samples were tested for shear performance and thermal properties during the aging process.The mechanical properties of the solder layer under the condition of high temperature and humidity aging were obviously reduced.2)In view of the problem of voids in solder layer,the experimental method is used to analyze the voids in CSP.The size and distribution of the void in the solder layer were measured by X-Ray,and then the shear properties of the solder layer were compared under different voids.It was found that the increase in the void rate in the solder layer would lead to a significant reduction in the shear strength.3)The simulation method is used to research the influence of the void position and the void distribution in the solder layer.The results show that the size and position of the void and the distribution state of the void all affect the reliability of the solder layer.Under the same void rate,the mechanical stress of the solder layer is gradually increased with the increase of the number of voids.4)The influence of void size,location and distribution on the mechanical properties and thermal resistance of solder layer was studied by simulation method.The results show that the size,position and distribution of void will affect the reliability of the solder layer.Under the same void rate,the mechanical stress of the solder layer is gradually increased with the increase of the number of voids.When the hole in the solder layer is closer to the inside of the chip,the heat resistance caused by the void is higher,and the thermal resistance of the flip chip layer increases with the increase of void rate.5)Through the Darveaux fatigue life model,the life of the solder layer under the condition of temperature shock is simulated,and the sample failure speed of the SAC305 solder layer is corrected by the experiment.Finally,the Darveaux crack propagation constant of the CSP package LED and the life of the solder layer are obtained.