【作者】 辛东嵘；

【导师】 韩强；

【作者基本信息】 华南理工大学 ， 固体力学， 2013， 博士

【摘要】 树脂与固化剂交联形成的三维网状环氧树脂具有许多优良的热、力学性能，目前已经作为涂料、封装材料、交联剂等广泛应用于国防及民用工业的各个领域。湿热环境下环氧树脂膨胀、老化、力学性能下降及由此导致的界面开裂等问题日益凸显。本文采用分子动力学方法，考虑了温度、含湿量、交联度、应变率及界面粘结剂等的影响，对环氧树脂的力学性能及铜-环氧树脂界面破坏机理做了系统详细的研究，得到了一些富有学术价值的研究成果，对实际工程问题具有指导意义。由于环氧树脂结构的特殊性和重要性，本文首先提出一种新的建模方法，成功实现了环氧树脂的三维网状交联，在此基础上系统研究了环氧树脂玻璃转化温度、热膨胀系数和湿膨胀系数等材料参数，通过静态常应变方法研究了环氧树脂弹性模量、体积模量、剪切模量和泊松比等力学性能参数，分子动力学模拟结果与实验数据吻合较好。研究结果显示，交联度对环氧树脂的热、力学性能的研究有重要意义，以简单的树脂和固化剂共混体系代替交联环氧树脂必然会造成结果偏差；此外，环氧树脂体系所处环境的温度和湿度都会对其性能造成影响，尤其高温、高湿环境对环氧树脂热力学性能有着显著的影响。采用分子动力学方法系统研究了湿气在环氧树脂中的扩散问题，模拟结果表明，随着温度的升高，扩散系数增大；随聚合物中含水量增多及聚合物交联反应程度减小，扩散系数总体呈增大趋势，但同时也发现发生完全交联反应的环氧树脂所含环氧基数目与交联聚合物中所含水分子数目相同时，扩散系数急剧减小。通过分子动力学方法数值模拟，研究了环氧树脂拉伸、压缩时的力学性能，研究结果显示，环氧树脂抗压性能比抗拉性能好；温度升高和含湿量增大都弱化了聚合物的力学性能，高温、高湿环境影响尤其显著；交联度增大和应变率升高强化了聚合物的力学性能，常温下，交联度89%的环氧树脂弹性模量比不交联环氧树脂高2-3GPa。通过分子动力学模拟不仅得到了聚合物材料在高温和高应变率下的力学性能，还从分子能量的微观角度较好地表述了湿热环境中环氧树脂的拉伸和压缩变形过程，这一研究对环氧树脂的改性和性能设计具有重要指导意义。系统分析研究了电子封装中常见的铜-SAM-环氧树脂界面的相互作用能。通过比较，发现与环氧树脂形成化学键的自组装单分子膜SAMA能够提高界面相互作用能，而不与环氧树脂形成化学键的SAME则降低了界面相互作用能，树脂交联程度对基底与环氧树脂界面粘结性基本没有影响，但温度升高、湿气进入和金属氧化都不同程度地减弱了界面的相互作用能。这一研究成果为研究界面粘结剂的粘结作用及评价粘结效果提供了新的研究方法，为选择和设计粘结剂提供了理论依据。界面开裂作为一种典型的封装失效形式，极大地影响了电子封装的可靠性。本文采用分子动力学方法对受拉铜-SAM-环氧树脂的界面破坏进行了系统深入地研究。研究结果表明，树脂交联程度、温度及拉伸速率对受拉环氧树脂-铜界面可靠性影响较小；湿气进入会降低受拉体系的界面强度；高温条件下或湿气的进入都会降低含粘结剂受拉界面的强度；交联度增大加强了受拉铜-SAM-环氧树脂体系的界面可靠性。此外，通过比较铜-SAM-环氧树脂界面相互作用力随拉伸位移的变化趋势及界面破坏形态，揭示了含SAMA界面化学键为界面作用的主要因素，界面受拉过程中，因环氧树脂内部破坏而导致体系失效；含SAME界面间主要作用力为原子间非键力，界面受拉过程中，SAME中原子与环氧树脂原子距离逐渐增大，非键力逐渐减弱直至完全消失，界面失效。分子动力学模拟不仅为研究界面开裂失效这一复杂问题提供了新的方法，而且有助于从分子角度分析界面相互作用能变化的内在原因，对深刻理解界面的相互作用和界面开裂的内在机理具有重要意义。更多还原

【Abstract】 Cross-linked epoxy resin is widely used as coatings, adhesives, composites, and so on inelectronics and aerospace industries because of the excellent thermal and mechanicalproperties. However, the weaker mechanical properties and interfacial delamination caused byexpansion and aging under hygrothermal conditions are also increasingly prominent. In thispaper, the molecular dynamics simulation was performed to study the mechanical propertiesof epoxy resin and the interface failure mechanism of epoxy-SAM-Cu considering the effectsof temperature, moisture content, cross-link conversion, strain rate and SAMs.Cross-linked epoxy resins exhibit much more complexity in molecular structure than thelinear homopolymers and copolymers，which poses significant difficulty to the experimentalcharacterization. In this regard, a new algorithm was thus developed for constructing themolecular model of polymeric network. Then the model was used to predict the thermal andmechanical properties. It was seen that glass transition temperatures, coefficients of thermaland moisture expansion, Young’s modulus, bulk modulus, shear modulus and Poisson’s ratioof the systems are in good agreement with experimental data. In addition, the simulationresults showed that the cross-link conversion, temperature and moisture content affect thethermal mechanical properties of epoxy resin significantly. So the effects of these factors areimportant to improve properties of epoxy resin.Molecular dynamics simulation was performed to study the moisture diffusion incross-linked epoxy resin, with the influence of temperature, water concentration and polymerconversion taken into account. The simulation results showed that the moisture diffusioncoefficients increase with the increase in the temperature. And generally, with the increasedmoisture concentration or decreased polymer conversion, the moisture diffusion coefficientsreduce. However, the moisture diffusion is strongly inhibited when the number of epoxygroups in completely reacted epoxy resins is equal to the number of water molecules.Molecular dynamics method was employed to investigate effects of moisture content,cross-link conversion, strain rate and temperature on the tensile and compressive deformationof epoxy resin. Simulation results showed that the compression performance of cross-linkedepoxy resin is better than its tensile performance. The mechanical properties of epoxy resindecrease obviously with increasing moisture content and temperature. However the highcross-link conversion and strain rate enhance the mechanical properties of resin. At roomtemperature, the Young’s modulus of89%cross-linked epoxy resin is higher than that of non cross-linked resin about2-3GPa. This study obtained the mechanical properties at hightemperature and high strain rate and explained the deformation with the microscopicmolecular energy, providing a guide to the modification of epoxy resin.Due to poor adhesion, the Cu-epoxy interface under hot and humid conditions is a weakpart in electronics and aerospace industries. Molecular dynamics simulation was conducted toinvestigate the interfacial interaction energy of Cu-SAM-epoxy resin, which is widely used inelectronic packages, and the effects of temperature, moisture, crosslink conversion andoxidation degree. The results showed that interaction energy of Cu-SAM-epoxy resin isalmost independent of crosslink conversion of epoxy resin, while is weakened by increasingtemperature, moisture and oxidation. In addition, the simulation revealed that the covalentbonds between SAMA and epoxy enhance the interfacial adhesion of Cu-epoxy. However, thenon-bond interactions of SAME and epoxy resin weaken the interfacial adhesion. This paperprovided a new method for research and valuation the effects of SAM or other adhesive oninterfacial adhesion.Interfacial delamination is one of the typical failure modes in electronic packages. Toobtain good reliability of electronic packages, it is important to study the interface properties.Molecular dynamics simulations of opening mode loading of interfaces are proposed to studysuch interfaces resulting in traction-separation relations that have been used to characterizethe failure process of the interfaces. The results showed that the cross-link conversion,temperature and tensile rate have less effect on the strength of epoxy-Cu interface. But themoisture reduces the interface tensile strength. For the epoxy-SAM-Cu interface, both thehigh temperature and high moisture content reduce the tensile strength, while the highcross-link conversion increases interface reliability. In addition, the interaction force versusdisplacement curve and the interfacial failure mode for epoxy-SAM-Cu system showed thatthe covalent bonds are the main interaction force between cross-linked epoxy and SAMA,while the non-bond interaction is mainly for the interface of epoxy-SAME.更多还原