BGA焊点在不同加载方式下的力学行为研究

发布时间：2018-04-26 14:15

本文选题：SAC + 有限元　；参考：《哈尔滨理工大学》2015年硕士论文

【摘要】：焊点的可靠性对封装器件的寿命至关重要。“70%以上的电子器件失效是由焊点失效引起的[1]”焊点作为封装器件中重要的组成部位，焊点的可靠性决定了封装器件功能的实现。随着无铅化研究的不断深入和SMT（表面贴装技术，Surface MountedTechnology）的不断发展，新型无铅钎料要求在综合性能上（如力学行为、焊接性及焊点可靠性等）与63Sn37Pb共晶钎料能媲美，甚至超越63Sn37Pb以应对在各种恶劣环境中服役的电子封装产品对长期稳定运行的可靠性的要求。其中对焊点力学行为分析及研究尤为重要。目前BGA焊点在不同加载方式下的可靠性的研究主要是针对温度循环、振动冲击，如热循环试验、跌落试验、振动试验等，而对无铅BGA单个焊点本身的循环、分级、循环分级行为研究还少见报道。本文将采用统一的幂指数蠕变本构方程描述焊点的应力应变行为对BGA焊点在承受循环、分级、循环分级载荷的机械外载过程进行有限元模拟，预测焊点失效的位置，分析应力应变规律，并讨论了不同加载对BGA焊点力学行为的影响，本研究对微电子封装BGA焊点可靠性评价提供一定理论依据。本文对Sn-3.0Ag-0.5Cu BGA焊点不同加载方式下的加载过程进行数值模拟。研究不同加载方式对BGA焊点力学行为的影响。研究结果表明：在不同加载方式下焊点的易失效位置是相同的，应力集中区域为受力一侧下IMC处；塑性应变最大的区域位于不受力一侧上球颈处；单个互连BGA焊点在承受循环载荷时受力一侧下IMC处残余应力最大，该处最容易导致裂纹扩展失稳；焊点在承受循环分级载荷时，不受力一侧上球颈处产生的塑性变形最大，该处最易因局部塑性应变集中产生疲劳裂纹。对焊点分级力学行为的研究表明：随着峰值载荷的增加，塑性应变成为焊点失效的主要因素；随着加载速率的增加，等效塑性应变区域由中心向两侧颈部骤减，应力分布规律基本不变，应力的累积成为焊点失效的主导因素；随着载荷步数的增加，焊点由于塑性应变集中产生裂纹的可能性增加。对焊点循环行为的研究表明：随着峰值载荷的增大，等效塑性应变量成为焊点失效的主要原因，同时焊点的疲劳寿命减小；保载时间的增加，只能使蠕变过程可以进行的更充分，但并不能产生额外的蠕变。达到临界状态后，焊点的疲劳寿命几乎不受保载时间长短的影响；随着循环次数的增加，焊点的可以充分的发生塑性变形，而不残留，，焊点的损伤累计增加，循环次数的多少对焊点疲劳寿命的影响越来越小。
[Abstract]:The reliability of solder joint is very important to the life of packaging device. "more than 70% of electronic device failure is caused by the failure of solder joint [1]" as an important part of packaging device. The reliability of solder joint determines the realization of packaging device function. With the development of lead-free research and the development of SMT (Surface Mount Technology), the new lead-free solder is required to match the 63Sn37Pb eutectic solder in its comprehensive properties (such as mechanical behavior, weldability and solder joint reliability). It is even beyond 63Sn37Pb to cope with the reliability requirements of long-term and stable operation of electronic packaging products serving in various harsh environments. It is very important to analyze and study the mechanical behavior of solder joint. At present, the reliability of BGA solder joints under different loading modes is mainly focused on temperature cycle, vibration shock, such as thermal cycle test, drop test, vibration test, etc. Cyclic grading behavior is rarely reported. In this paper, a unified exponential creep constitutive equation is used to describe the stress-strain behavior of solder joints. The mechanical external loading process of BGA solder joints under cyclic, graded and cyclic loading is simulated by finite element method, and the failure position of solder joints is predicted. The effect of different loading on the mechanical behavior of BGA solder joint is analyzed. The research provides a theoretical basis for the reliability evaluation of BGA solder joint in microelectronic packaging. In this paper, the loading process of Sn-3.0Ag-0.5Cu BGA solder joints under different loading modes is numerically simulated. The effect of different loading modes on the mechanical behavior of BGA solder joint was studied. The results show that the failure position of solder joints is the same under different loading modes, the stress concentration region is the IMC under the stress side, the region with the largest plastic strain is located at the ball neck on the unloaded side. The residual stress of single interconnect BGA solder joint under cyclic loading on one side of IMC is the largest, which is the most likely to lead to the instability of crack propagation, and the plastic deformation of the upper ball neck on the side without loading is the largest when the solder joint is subjected to cyclic graded load. Fatigue cracks are most likely to occur due to local plastic strain concentration. The study on the mechanical behavior of solder joints shows that with the increase of peak load, plastic strain becomes the main factor of the failure of solder joints, and with the increase of loading rate, the equivalent plastic strain region decreases sharply from the center to the neck of both sides. The stress distribution law is basically unchanged, and the accumulation of stress becomes the dominant factor for the failure of solder joints, and with the increase of load steps, the possibility of cracking in solder joints due to the concentration of plastic strain increases. The study on the cyclic behavior of solder joint shows that with the increase of peak load, the equivalent plastic strain becomes the main reason for the failure of the solder joint, and the fatigue life of the solder joint decreases, and the increase of the loading time can only lead to the increase of the fatigue life of the solder joint. The creep process can be carried out more fully, but no additional creep can be generated. After reaching the critical state, the fatigue life of the solder joint is almost unaffected by the length of the holding time, and with the increase of cycle times, the joint can be fully plastic deformed, but without residual, the damage of the solder joint accumulates, and the fatigue life of the solder joint increases with the increase of cycle times. The effect of the number of cycles on the fatigue life of solder joint is smaller and smaller.
【学位授予单位】：哈尔滨理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN05

【参考文献】