Research On Mechanical Properties Of Typical Heterogeneous Materials Based On Asymptotic Homogenization Method

Along with the rapid development of electronics packaging technology, novel materials are continuously emerging. Heterogeneous materials, including composite, porous media and laminated materials, are widely applied in the field of electronics packaging for their excellent performance. Heterogeneous materials can be regarded as homogeneous materials at macro-scale, while at micro-scale, heterogeneities of the material can be clearly identified. The basic topic of the research of heterogeneous material is to establish the correlation between macro and micro scales, to study the relation of characteristics of microstructure to the effective properties at macro-scale and to analyze the intrinsic connections of material properties at different scales. The investigations of multi-scale issues of heterogeneous materials can result in a deeper understanding of the micro-scale foundation of the macro-scale property, can lead to resonable prediction of macro-scale property from micro-scale characteristics, and most importantly, can facilitate microstructure designing to produce material with desirable properties. This research is of great significance to the performance and reliability of electronics packaging, as well as manufacture process of the product.Based on the asymptotic homogenization theory, a multi-scale approach is adopted to investigate the mechanical properties of typical heterogeneous materials in electronics packaging. Geometry model of the typical heterogeneous materials are generated, expressions of the effective properties and local stress field of the heterogeneous materials are derived, the connections between characteristics of microstructure and effective properties of the materials are investigated. A research framework is established for the multi-scale issues of heterogeneous materials in electronics packaging. The multi-scale asymptotic homogenization mechod is adopted to investigate mechanical properties of three types of heterogeneous material.Firstly, the multi-scale asymptotic homogenization method is used to study the mechanical properties of particulate composites. The representative volume element model of the particulate composite is generated with random sequential addition algorithm. The correlation between microstructure features and effective mechanical properties of silicone-phosphor particulate composite in LED packaging is investigated with the multi-scale asymptotic homogenization method. Experimental measurements, theoretical predictions and numerical simulations are conducted to systematically study the effects of phosphor content, phosphor sizes and spatial distribution of phosphor particles on the effective properties of the composites. Moreover, damage mechanism of the particulate composite is investigated by modeling the interface region with the interfacial cohesive law. The results indicate that, the addition of phosphor will lead to increased effective Young’s modulus of the composites. Stress concentration is intense around regions with dense phosphor dispersion, interfacial debonding and damage of the composite will nucleate and propagate around high stress region.Secondly, the multi-scale asymptotic homogenization method is used to study the mechanical properties of porous media. The representative volume element model of porous media is generated with digital image processing method. The correlation between microstructure features and effective mechanical properties of porous silver in power electronics packaging is investigated with the multi-scale asymptotic homogenization method. Experimental measurements, theoretical predictions and numerical simulations are conducted to systematically study the effects of relative density, micro-scale morphology and load path on the effective properties of porous silver. Since silver material is modeled with elasto-plastic constitutive law, the mechanical behavior of porous silver under large deformation is explored. The results demonstrate that, increased relative density will lead to increased Young’s modulus and enhanced shear strength of porous silver.Thirdly, the multi-scale asymptotic homogenization method is used to study the mechanical properties of laminated material. The representative volume element model of the laminated material is generated according to size and pattern of microstructure of the laminated material. The correlation between microstructure features and effective mechanical properties of laminated material in flexible solar cell packaging is investigated with the multi-scale asymptotic homogenization method. Experimental measurements, theoretical predictions and numerical simulations are conducted to systematically study the effects of size and properties of components on the effective properties of the laminated material. Based on the material properties at various temperatures, effective properties and failure mechanism of the laminated material at room temperature,75℃and125℃are investigated. The results demonstrate that electrode material and interface region are the vulnerable parts of the laminated material in flexible solar cell packaging, and the mechanical performances of the laminated material deteriorate at elevated temperatures.