Research on Deformation Control Constitutive Model for Lead Free Electronic Devices

本研究针对无铅电子器件，参考纯拉伸、蠕变、应力松弛等基本试验，建立了控制无铅钎料合金变形的本构模型。此外，采用本构模型对免读电子器件进行了结构分析，并进行了可靠性评估和结构优化。本文的研究大纲如下：澄清无铅钎料合金的力学和疲劳寿命特性：采用直径为8mm的60Sn/40Pb和Sn-3.5Ag-0.75Cu小试样，观察了无铅钎料合金宏观力学行为和疲劳失效的基本特征。试验结果表明，无铅和含铅钎料合金具有良好的宏观非弹性变形和疲劳寿命。焊料合金本构模型的构建：综合研究结果(1)适用于解释60Sn/40Pb等含铅焊料合金非弹性变形的本构模型不能用于解释无铅焊料合金的非弹性变形，因为含铅焊料合金的粘塑性变形与无铅焊料合金的粘塑性变形有很大不同。在此基础上，建立了一种新的本构模型来准确地解释无铅钎料合金的非弹性变形。由于用于连接电子器件的焊料合金尺寸为几百微米，因此在本构模型中应考虑焊料合金内部结构的变化。因此，本研究采用基于位错密度的本构模型。采用本构模型构建结构分析方法：将本构模型纳入通用有限元程序进行结构分析。验证了基于位错密度的本构模型的优越性。

In this research, for lead free electronic devices, construction of a constitutive model to control deformation of lead free solder alloys was conducted referring to basic tests such as pure tension, creep and stress relaxation. Moreover, a structural analysis using the constitutive model was proposed for the read free electronic devices, and reliability evaluation and structural optimization were carried out. The outlines of the research are as follows :1. Clarification of mechanical and fatigue life characteristic of lead free solder alloys : Basic characteristic of macroscopic mechanical behavior and fatigue failure were observed using the small specimens, which have the diameter of 8mm and are made of 60Sn/40Pb and Sn-3.5Ag-0.75Cu. The tests results showed the characteristic macroscopic inelastic deformation and fatigue life of lead free and lead solder alloys.2. Construction of constitutive model for solder alloys : Considering the results (1) constitutive models adapted to explain the inelastic deformation of lead solder alloys such as 60Sn/40Pb can not used to explain the inelastic deformation of lead free solder alloys, because the viscoplastic deformation of lead solder alloys is much different from that of lead free solder alloys. Then, construction of a new constitutive model to exactly explain the inelastic deformation of the lead free solder alloys was discussed. Since the solder alloys for connecting electronic devices is a few hundreds micro millimeter the internal structural change in solder alloys should be taken into account in the constitutive model. Therefore, the constitutive model based on dislocation density is employed in this research.3. Construction of structural analysis method using the constitutive model: Structural analysis was conducted by incorporate the model into a general purposed program of FEM. The advantage of the constitutive model based on dislocation density was verified.