Research On The Reliability Of Electromigration In Solder Bump Of Flip Chip Packaging Under Multi-physics Coupling

With the development of micro-electronic technique,the development of integrated circuit packaging technology gradually towards the trend of low-cost,miniaturization,high performance.Flip chip become one of the most attractive technologies in electronic packaging,because of its high density of I/O,short,self-aligned in process of interconnection,the productivity of the advantages of good heat resistance,high productivity.With the decrease of size of flip chip solder bumps electric-migration phenomenon occurred in the solder bumps,which will lead to the open circuit in the cathode of solder bumps and short circuit in the anode of solder bumps,and this has serious influence on the reliability of flip chip packages.Electro-migration in flip chip solder bumps studied in this paper.During actual working condition,flip chip will withstand a force,which is combined with heat,electricity and stress,so finite element analysis is used to analysis the coupling analysis of electric and thermal structure in flip chip package.3D dimensional model of flip chip package is established by using finite element software ANSYS and simulated.The temperature distribution and deformation of the flip chip package is achieved.Because the solder layer of flip chip packages are the most inclined to failure,so the solder layer.The substrate temperature and the stress distribution is discussed emphatically.In flip chip packages,the solder bumps are as mechanical connections and electrical connection at the same time,so its reliability has great influence on the package.Electro-migration is one of the factors affecting the reliability of solder bumps.In order to research on the electro-migration mechanism in solder bumps,the distribution of temperature,current density,temperature gradient and joule heat in flip chip package interconnection structure are achieved by using the finite element analysis,and the results show that the distribution of these physical quantities in solder bumps is uneven.At the entrance of the current into the Al wire,the phenomenon of current crowding occurred in the place having the highest temperature called hot spot.The reason of occurrence of hot spot in solder bumps is explained by formula calculation.The analysis results show that there is a certain deviation between hot spot and the maximum stress.The change of maximum temperature,maximum current density,maximum temperature gradient and maximum joule heat in the solder bumps are researched under different current strength.The influence of Al wire size on electro-migration is analyzed.The influence of thickness of Al wire on the electro-migration mechanism is explored.The influence of the size of passivation layer on electro-migration mechanism is explored.The current density of concentration is defined to measure the uniformity of current density in solder bumps.The influence of the size of flip chip packages interconnection structure on electro-migration are researched,and the mean-time-to-failure formula is used to estimating the change of failure time of solder bumps with the shrink of the size of solder bumps.