| With the development of electronic industry, electronic packaging grows up rapidly as an independent new high-tech calling. Among all the technology options, surface mounted technology (SMT) is the fastest expanding one which was thought as "A Revolution of the Electronic Packaging". However, some of the disadvantages of SM connectors, such as inadequate availability and its less reliable solder joints, are also existing instead of many advantages of SM connectors. Generally, the low-cycle fatigue induced by thermal cycle is the major concern in the reliability of SMT .Due to the fine-small solder joint dimension, existing experiment measures can't be used to monitor the stress and strain of solder inner, when thermal fatigue experiment is processing. So, the finite element model analysis is the most feasible means. Different choice of material has a direct influence on final centralized stress, stress-strain distribution--change and life of solder joints. However international and domestic studies aren't yet toward this direction at present. This text launches the subject to this blank to research in the reliability of the solder joint of BGA (Ball Grid Array ) under different material choice. For the first time, the geometrical model for mechanical analysis of the solder joint is built directly from three-dimensional shape model of the BGA by ANSYS software. An unified viscoplastic constitutive law, the Anand model is applied to represent the inelastic deformation behavior for Sn60Pb40 solder. The mechanical performance is analyzed using finite element method .The distribution characteristics of stress and strain in solder joint are given at every time of thermal cycle. Besides, the variety rule of stress and strain with thermal cycle is acquired. Moreover, based on the strain data of the weakest site of the most dangerous solder ball in the array, fatigue life of thermally loaded BGA solder joints is predicted using the modificative coffin-Masson equation and reliability of the solder joints with different top-bottom material assembly is compared. Results indicate: The material heat matching of top-bottom base plate is more better, the life of assembly is more longer. The life-span of the solder joints assembled with ceramic encapsulation and FR4 base plate is 7 times than the one while adopting plastic encapsulation and FR4 base plate to make up; when sticking the Si chip to the FR4 base plate, the life-span is quite shortened; sticking the Si chip to the ceramic base plate can replace the former, because it not only raise the density of assembling, but also life-span of solder joints is prolonged to 6 times than the former; It is the compounding of ceramic to ceramic that match bestly. Finally, by the same way, adopting the existing mechanical capability data of lead-free solder analyses its thermal reliability in contrast with the one of Sn60Pb40 solder under the ceramic-FR4 material compounding. Results show lead-free solder increases the reliability greatly. Its thermal fatigue life is 4 times than the one of SnPb solder. The conclusion will provide a direction on material choice of electronic packaging in order to suit to different reliable requirement in future.
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