多物理场下烧结纳米银材料及封装互连结构力学行为研究

The current project focus on the mechanical properties of silver nano material and corresponding electronic packaging interconnect under coupled thermal-electric-mechanical loading. The micromechanics constitutive model and fatigue life prediction method under multi-physical fields will be developed. Combing with porosity experiment, the void nucleation and propagation mechanism for sintered nano silver material under multi-physical fields will be investigated. The mathematical relationship between void volume fraction and loading condition will be developed based on the mass diffusion and phase transformation theory. The proposed approach incorporates micromechanics constitutive model for multi-voids structure and based on the thermodynamic theory. The quadratic homogenization method is adopted to develop the multi-scale representative volume elements for micro- and nano- level voids. From the theoretical and experimental analysis, the micromechanics constitutive model for sintered nano silver interconnect can be developed, which could accurately describe the stress-strain relationship of sintered nano silver interconnect. Through the fatigue experiments under multi-physical fields, the fatigue behavior and life of sintered nano silver interconnect under coupled loading can be determined. Combing with the developed micromechanics constitutive model, the mechanical behavior of sintered nano silver interconnect under different working conditions can be predicted with reasonable accuracy. The current project aim at providing theoretical basis, numerical method, and experimental data for the application of nano silver materials in the next generation of electronic packaging devices.

本项目拟研究烧结纳米银材料及相应微电子封装互连结构在热-电-力多物理场耦合作用下的力学性能，开发多场条件下的细观本构模型和疲劳寿命预测模型。首先结合孔隙率测定试验，研究烧结纳米银材料中孔洞在多场条件下的萌生及扩展机理，并基于质量扩散理论和相变理论建立孔洞体积分数与加载条件的关系。然后基于热力学定律，结合多孔结构细观本构理论，采用二次均匀化方法对微米级和纳米级孔洞分别构建不同尺度代表性体积单元，从而开发多场条件下烧结纳米银焊点的细观本构模型，实现烧结纳米银焊点应力-应变关系的准确模拟。拟通过多物理场作用下的疲劳试验研究，探讨多场耦合加载下材料疲劳特性，建立烧结纳米银焊点疲劳寿命预测理论，结合本项目开发的本构模型，最终实现烧结纳米银焊点在不同工作条件下力学行为的准确描述，为该材料在新一代微电子封装器件中的应用提供力学理论支持、仿真方法及相应试验数据。

随着新一代半导体的发展，微电子封装结构所服役的环境变的更为复杂和极端，传统焊料的性能已不再满足极端环境下使电子元器件稳定运行的要求。烧结纳米银材料以其优异的高温服役性能和导电导热性能逐渐受到越来越多的关注，但作为一种新兴的封装材料，烧结纳米银的力学性能和破坏机理尚不完全明晰。为此，本项目针对烧结纳米银在多场作用下的力学行为展开研究，测定了烧结纳米银材料在不同荷载下的力学参数，开发了相应的本构模型和疲劳寿命预测模型。针对纳米银的多孔特性，本项目对纳米银的孔隙率和孔隙分布进行了表征，使用分子动力学研究了不同孔洞结构和不同孔隙率对纳米银试件拉伸性能的影响。针对纳米银材料所面临的高电流服役环境，建立了基于能量方法的孔洞成核模型，可以对电迁移和热迁移引起的失效进行预测。为描述烧结纳米银的力学行为，本项目将宏观唯象统一塑性蠕变本构模型和GTN本构模型结合，将孔洞体积分数引入到塑性屈服准则中，建立了可描述多孔材料的本构模型。为对纳米银结构使用寿命进行评估，本项目从热力学第二定律出发，将相变理论和熵增理论相结合，建立了普适性更强的疲劳裂纹预测模型，该模型可适用于不同类型的金属材料。本项目的研究结果为纳米银在新一代微电子封装中的应用提供了关键数据和理论基础，促进了第三代半导体的应用和发展。