【作者】 王珺；

【导师】 陈大鹏；

【作者基本信息】 西南交通大学 ， 固体力学， 2002， 博士

【摘要】 由于高聚物及其复合物材料具有重量轻，强度高等优点，已经广泛应用于各个工程领域。在微电子元件制造中，高聚物及其复合物材料通常用来作为电子元件的封装材料。而在航空、航天工业中，因为它们具有良好的粘接性，又常被用作构件间的粘接剂。由此减低结构的应力集中，降低结构的重量。然而，高聚物材料的一个显著的弱点是其对环境的敏感性，尤其是对湿、热影响敏感。因此，在高温、高湿度的环境中，高聚物的强度明显下降，威胁到结构的安全。在电子元件高温焊接中，受到湿汽侵入的元件常发生“爆米花”式的脱层断裂，严重影响了产品的合格率。这两类问题都需要对湿分扩散，高聚物结构的力学反响进行研究。 湿汽进入到高聚物材料之后，一方面导致其材料强度和耐久性下降。另一方面是纯粹的物理作用，湿汽产生膨胀变形，导致残余应力。有试验发现，高聚物中湿分、温度和应力是相互影响的。并且，高聚物通常具有粘性，其力学行为与时间相关。湿汽对材料性能的影响是可以通过试验测定的，而建立合理的模型描述含有湿、热影响的结构的耦合响应则是对由湿、热导致的破坏问题作出准确的分析和计算模拟的基础和关键。在一般的条件下，对于高聚物吸湿所引发的问题，需要考虑到热传导过程、湿分扩散过程，以及高聚物结构的力学反响。因此，需要发展耦合的本构模型对整个问题进行描述。此外，在含湿、热效应的高聚物材料中，传统的粘弹性或弹性材料的断裂判据不再适用，所以，对该问题进行研究也是十分必要的。 本文由物质守恒，能量守恒以及动量、动量矩平衡原理，采用内变量描述材料的粘性，通过引入Helmholtz自由能和Gibbs自由能，分别导出松弛和蠕变两类湿、热和应力(应变)相互耦合的线性粘弹性本构方程以及普遍的耦合热传导、耦合湿分扩散方程。并针对各向同性材料，导出含湿、热的耦合线性粘弹性本构方程，以及相应的热传导方程和耦合湿分扩散方程。 本文利用内禀断裂能的概念，定义了不含粘性耗散项的临界断裂阻力。由能量的平衡，可以推断出，剔除了粘性耗散的影响，裂纹克服材料内禀断裂能发生扩展所需要的能量完全来自于自由能。由此，作者发展了裂尖自由能释放率的概念及其积分表达式。并建立相应的断裂判据。其中，材料的断裂参数是第 11页 西南交通大学搏士研究生学位论文内禀断裂能。当退化到纯弹性的情形，粘性耗散消失，自由能释放率与经典的能量释放率等价。由此，本文给出含湿、热效应的裂尖能量释放率的积分表达式。并用简单算例验证了其路径无关性。同时，本文将自由能释放率扩展到有多个广延量场作用下的情况，导出统一的表达式。 利用本文提出的断裂判据，通过合理简化，作者对吸湿电子元件在高温焊接过程中发生的“爆米花”式脱层断裂进行了研究分析。目前，电子元件趋于薄型化的发展趋势，由分析计算结果可知，为了避免过高估计裂纹缺陷中的内部压力，直接采用饱和蒸汽压力模型是不恰当的，需要采用本文发展的一般蒸发有限元计算模型进行分析。此外，计算结果还显示：影响“爆米花”式断裂的主要可控因素是扩散系数D。和蒸发系数F卜其中，蒸发系数F。对裂尖能量释放率的影响较大，因此，控制扩散系数DO和蒸发系数F。能有效地降低电子元件发生“爆米花”式脱层断裂的可能性，尤其是控制蒸发系数F。的大小 作者还在 Roy等计算模型的基础上，修正了他们略去 Schpaery单积分粘弹性本构模型中的两个参数的研究工作。据此，作者开发的有限元程序中，保留了SChaPCry模型中的全部三个参数。利用该有限元程序，作者对长时间处于潮湿环境的高聚物粘接接头中，湿分的扩散进行了计算分析。更多还原

【Abstract】 In recent years,polymer has been widely used in engineering applications,including plastic packages in producing micro electric packages,and adhesive joints in aerospace engineering etc. As the polymer is hydrophilic,it will absorb the moisture in high humid environment. The process accelerates as the temperature is rising. Recently,the failure caused by moisture and heat was often observed in package solder reflow and adhesive joints which absorbed moisture. As experiments reveals,the moisture diffusion,heat conduction and mechanical response in polymers are mutually affecting behaviors. A fact that stimulates the effort in developing a set of full coupling constitutive relations with which will have the problem modeled. For the polymer showing time-dependent character in many situations,the viscoelasticity should necessarily be taken into account in the general model. Further,as the conventional J integral is no longer valid for hydrothermal materials cases,investigations on new energy-type fracture criteria are specifically needed.In the present thesis,the constitutive equations of the coupling problem involving heat and moisture effects (HME) were developed on continuum thermodynamics basis,in virtue of Helmholtz free energy. In the endeavor just mentioned,a group of internal variables was introduced to characterize the viscous behaviors of polymers. For isotropic cases,the specific coupling constitutive equations were degenerated from those for general cases thus obtained in the context. With the stress (strain) and coupling coefficient being ignored,the coupling heat conduction equation and the coupling moisture diffusion equation would degenerate to Fourier heat conduction model and Pick diffusion model respectively.In this thesis,the modified critical fracture resistance was defined by excluding the viscoelastic dissipation,which is related to the intrinsic fracture energy. According to the energy balance considerations,the fracture driving energy is uniquely provided by free energy. Hence,it was named free energy release rate in this thesis in tribute to the concept of strain energy release rate. The expression of free energy release rate was derived in this thesis as well. As revealed,it is a path -independent integral and was extended to the multi-field of extensive quantity. With the viscous dissipation being ignored,the free energy release rate would be equivalent to strain energy release rate. As such,the expression of elastic strain energy release rate,which involved the hydrothermal effects,was derived. And,it was employed for delamination analysis of electric packages in the subsequent context.The "popcorn" fracture analysis was studied by introducing reasonable simplifications and taking advantage of the strain energy release rate expression involving the hydrothermal effect. According to the result of analysis,it is advisable to invoke the general evaporation model should the avoidance of the overestimation on the strain energy release rate for very thin package cases be desired. Another important conclusion the present study reached is that the controlling of diffusion coefficient DO and evaporation coefficient F0 is efficient for the deduction of the possibility of the "popcorn" delaminations,in specific with controlling evaporation coefficient.In the appendix,the author of the present thesis included the three parameters of Schapery’s viscoelastic model based on the work of Roy et al. In this aspect,FEM program was developed for implementation of the modified model. By use of this FEM program,analysis of the moisture diffusion in adhesive joint was also conducted.更多还原