【作者】 张国尚；

【导师】 荆洪阳；

【作者基本信息】 天津大学 ， 材料加工工程， 2010， 博士

【摘要】 80Au/20Sn钎料合金被广泛用于微电子及光电子封装中,其力学性能对于器件的可靠性分析至关重要。本文通过铸态80Au/20Sn钎料试样的单轴拉伸试验、单轴拉伸蠕变试验、纳米压痕试验以及等温低周疲劳试验,对其力学性能进行了研究。试验发现,80Au/20Sn钎料的拉伸行为受温度和应变率影响显著。25℃、低应变率下以剪切滑移断裂为主,25℃、高应变率下以穿晶断裂为主,75及125℃时以微孔聚合型的韧窝状断裂为主。提出统一型粘塑性Anand本构模型中应考虑温度和应变率对参数的影响,修正后的模型能更好的描述单轴拉伸行为,并能被用于低周疲劳寿命预测中。80Au/20Sn钎料的拉伸蠕变行为在测试温度及应力水平下表现出典型的蠕变特征,随着温度及应力水平的提高,稳态蠕变率显著增加而蠕变寿命显著减小。Norton幂律模型及Garofalo双曲正弦模型都能用来描述80Au/20Sn钎料的蠕变行为,但Garofalo双曲正弦模型更佳。改进的θProjection预测方法能够较好的预测整条蠕变曲线,K-R模型能更好的预测80Au/20Sn钎料的蠕变寿命。测试应力及温度范围内80Au/20Sn钎料合金的蠕变机制并没有发生变化,晶界滑移被认为是80Au/20Sn钎料合金最可能的占主导地位的蠕变变形机制。80Au/20Sn钎料恒加载速率/载荷纳米压痕试验表明微尺度下其热力行为具有较强的加载速率敏感性、显著的尺寸效应以及温度敏感性,在125及200℃下出现了明显的“挤出”现象。基于压痕做功概念得到的蠕变应力指数和蠕变激活能与单轴拉伸/压缩蠕变试验结果具有一定的可比性,表明该测试和分析方法能在一定程度上预测钎料的蠕变参数。80Au/20Sn钎料等温低周疲劳行为强烈依赖于应变率和温度。高应变率下,具有明显的准静态断裂特征;低应变率下,在蠕变与疲劳的交互作用下失效。基于塑性应变的Coffin-Manson模型及基于能量Morrow模型均能对80Au/20Sn钎料的低周疲劳行为进行寿命预测。80Au/20Sn钎料在高温环境下仍能抵抗很高的交变应力,具有极高的抗疲劳性能。更多还原

【Abstract】 80Au/20Sn solder alloy is widely used in high power electronics andoptoelectronics packaging in which the mechanical properties of the solder is essentialto meet the reliability analysis of the components. The mechanical properties of casted80Au/20Sn solder were investigated by uniaxial tensile test, uniaxial tensile creep test,nanoindention test, and isothermal low cycle fatigue test.The uniaxial tensile behavior of 80Au/20Sn solder is dependent on thetemperature and strain rate strongly. The gliding fracture at 25℃and low strain rate,transgranular fracture at 25℃and high strain rate, microvoids at 75 and 125℃aredominant. A modified unified viscoplastic Anand constitutive model considering theeffect of temperature and strain rate on parameters was developed. The new modelcan describe the tensile test curves better and can be used in the prediction of the lowcycle fatigue behavior.The obvious creep characteristic of 80Au/20Sn solder alloy was observed at thetensile creep tests.The creep strain rate increases and creep lifetime decreases as theapplied stress level and temperature increase. The experimental data were successfullyfit with Dorn model and Garofalo model. However, the application of Garofalo modelresulted in a lower estimated variance of error terms as compared to the Dorn model.The modifiedθProjection method can describe the entire creep curve, and the K-Rmodel can be used to predict the creep life. Grain boundarysliding is the mostpossible creep mechanism within the given stress level and temperature.The micro-scale thermomechanical behavior of the 80Au/20Sn solder wasinvestigated by constant loading rate/load nanoindention tests. The loading ratesensitivity, obvious size effect, and pile up at 125 and 200 ?C were observed. Thedifferences of the creep stress exponent and creep activation energy obtained amongon the concept of work of indentation, and by the conventional uniaxialtensile/compressive creep tests are small. It indicates that such nanoindention testsand analysis methods can be used to evaluate the creep parameters of solder alloys insome way.The low cycle fatigue behavior is affected significantly by the strain rate andtemperature. The quasi-static tensile character was observed at low strain rate and theinteraction of creep and fatigue dominates at high strain rate in the fatigue tests. TheCoffin-Mason(C-M) model based on plastic strain and the Morrow model based onenergy can be used to predict the fatigue life of the 80Au/20Sn solder. The 80Au/20Sn solder can still resist high alternating stress, so it has superior fatigue-resistantbehavior.更多还原