动载下电子互连导电胶的粘接强度及失效机理研究

As an environmentally friendly interconnected material in the field of electronic packaging, electric conductive adhesive (ECA) has the advantages such as low technological temperature, ultrafine line printing and being easy to connect when compared with solder alloy. Research on the bonding strength and failure mechanism of ECA under dynamic loading are very important for the packaging design of electronic products subjected to mechanical vibration, drop impact, etc. In this research project the bonding strength and failure behaviors of bonding device under dynamic shearing and drop impact are systematically investigated by experimental, theoretical and numerical methods. Influence mechanism of loading rate, drop condition, conductive particles, temperature and hygrothermal aging on the dynamic mechanical behavior of cured ECA and bonding failure mechanism of bonding device are ascertained. The dynamic constitutive relations of cured ECA and theoretical characterization of adhesive joint dynamic shear behavior are obtained. A proportional hazard model of adhesive joint fatigue life is established, as well as the reliability evaluation of flip chip adhesive structure under different drop conditions. Ascertaining the dynamic response law of adhesive structure under drop impact, the optimization design of adhesive structure is carried out to reduce the maximum peeling stress of adhesive joint and to improve the operational reliability. Related research results will provide the theoretical basis and technical support for applications of ECA in the field of electronic industry.

作为绿色环保电子互连材料的导电胶相比于传统合金焊料具有工艺温度低、印刷线条细及可连接性好等优点，其动载下的粘接强度与失效机理研究是承受机械振动、跌落与冲击等因素影响的电子产品封装设计的重要基础与依据。本项目通过实验测试、理论分析和数值模拟系统研究胶连器件在动态剪切与跌落冲击下的互连强度与失效行为，明确加载率、跌落工况、导电颗粒、温度及湿热老化对胶体动态力学行为与胶连器件粘接失效机制的影响机理，得到固化导电胶的动态本构关系并给出导电胶搭接件动态剪切力学行为的理论描述；建立跌落冲击下胶连点寿命的比例风险模型并给出不同跌落工况下倒装芯片胶连结构的可靠性评估，探明跌落冲击下胶连结构的动态响应规律，以降低关键胶连点的最大剥离应力为优化目标，对胶连结构进行优化设计以提高其跌落冲击下的可靠性。为导电胶在电子工业领域的应用提供理论依据与技术支持。

本项目针对电子互连导电胶使役过程中易承受相关动态载荷工况而引起电子器件互连失效的现状，通过实验测试、理论分析及数值模拟开展了固化导电胶的率/温相关变形行为/机理、胶连件剪切力学行为与理论表征及导电胶互连倒装芯片封装结构跌落冲击行为与可靠性分析等方面的研究；结果表明，胶体中银导电颗粒的类“交联点”作用使得较高银含量固化导电胶基体树脂分子链的变形及运动受到更大程度上的限制，粘性常数相对较大，温度升高使得热固性固化导电胶的基体树脂分子链段发生“解冻”、变形与运动能力增强，粘性常数则相对较小，准静态与动态压缩测试下固化导电胶的失效破坏模式分别呈现为沿与试样轴线夹角约为45°的方向出现裂缝及碎裂特征，表现出一定的应变率强化效应及应变率引起的韧脆转变行为，并给出了固化导电胶的动态本构关系；随着加载率提高胶连件的界面剪切断裂能不断增大，得到了胶连件界面断裂能及剪切强度与加载率的定量关系，胶层的剪切应力分布趋势表现为双曲函数形式，均在搭接端部出现剪切应力峰值而中部剪切应力值则较小，给出了基于霍普金森压杆装置开展胶连件动态冲击测试时剪切应力/应变的获取方法，动态高加载速率下银颗粒对胶层剪切变形的抵抗作用较大，而准静态低加载速率下导电胶基体的粘接性能则对剪切变形的抵抗作用较大；水平自由跌落下胶连封装结构的关键胶连点均出现在胶连点阵列的四个外角处，较高银含量关键胶连点的等效应力与z向应力水平高于较低银含量且z向应力主导了关键胶连点的变形，较高银含量胶连点发生塑性变形的自由跌落高度大于较低银含量，其具有较强的抗跌落冲击性能，且小角度倾斜跌落相比于水平跌落更为危险；研究成果为导电胶在我国电子工业领域高装备质量、多功能集成化需求下的高效应用提供了理论与技术支持，具有重要的现实意义与广泛的应用前景。