Research On POP Stacked Package Realiability Under Thermal Shock Load

Due to the rapid development of electronic science and technology, the replacement of the electronic products becomes increasingly frequent. The consumer’s demand is gradually increasing, which forces the package development to higher density. In recent years, the packaging technology developed to the direction of miniaturization, high-density, and intelligence. The design of electronic products changes from the plane to three-dimensional space to meet the requirements of smaller size and better performance. Stacked package POP (package-on-package) technology is considered to be the major development direction of electronic packaging. It integrates logic and memory devices in the same package,which can greatly reduce the package size and increase the packing density. However, the increasing density makes the heat easily to accumulate,which has negative impact on reliability of electronic products. The research of this article focuses on the reliablity of POP stacked structure by the method of experiments and simulations. The main work is as follows:Aiming at POP stacked structure, the reliability of the package under thermal shock load is theoretically studied. We get the distribution of stress and strain and the variation with time.Based on the calculations results,theoretically predict the lifetime of solder balls.Amkor’s 14mm×14mm POP stacked package is chosen to be the research object. POP stacked structure is reasonably simplified.Since the modle’ centrosymmetric structure,this paper build the 1/4 model of POP stacked structure with the finite element analysis software.Simulation study is carried out under the JEDEC thermal shock stanard.The results show that under the thermal shock load the main stress is concentrated on the chips and solder balls,the maximum stress occurs at the corner of the bottom package.The stress of the bottom solder balls show the gradually increasing trend from the center to the edge,while the top solder balls have no obvious trends.We calculate the reliability life of the solder balls based on the Kencht-Fox life prediction model.Based on the strain testing principle the thermal shock test platform is build,and experimentally studied the strain of solder balls under the thermal shock load. Amkor’s 14mm×14mm and 15mm×15mm POP stacked packages are selected for the experiment. We recorded and analyzed both the top and bottom solder balls strains under thermal shock load. Experimental results show that the bottom layer solder balls have larger strain amplitude than top layer solder balls. The reliablity of bottom layer solder balls is lower than top layer solder balls under the same thermal load. We contrast the simulation data to the experimental results and the results are basically same. We also find that the 15mm×15mm package have larger strain amplitude and lower realiablity than the 14mm×14mm packeage. This maybe indicates the larger package size the lower the reliability of solder balls.In summary, this paper studies the POP stacked package realiablity with the method of experimental and simulation.Comparative analysis of the results of simulation and experiment under the same thermal load,explored new method which replacing experiment to finish reliability test by simulation. Investigated different the package size effects on the realiablity. The results can provide a reference value for the reliability study and provide some guidance for packaging and testing.