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首页> 外文学位 >Grain structure evolution of tin-based lead-free solder joints in electronic packaging assembly and its impacts on the fatigue reliability.
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Grain structure evolution of tin-based lead-free solder joints in electronic packaging assembly and its impacts on the fatigue reliability.

机译：电子包装组件中锡基无铅焊点的晶粒结构演变及其对疲劳可靠性的影响。

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摘要

Solder is one of the main joints materials used in the electronics for decades of years. It is not only the mechanical support but also conducts the electric signals in the electronics. However, the regulation of lead content in electronic devices has driven the transition from lead-tin solder to the lead-free solder that requires lots of research to fill the knowledge gap in the lead-free solder property. At the same time, the reliability issues due to solder failure are of great interest as the miniaturization and mobilization trend of the electronic devices continues. A lot of works have been done to understand the fatigue failure mechanism and its affecting factors with some degree of inconsistence. In this research, the grain structure evolution of tin-based lead free solder in electronic packaging and its relation to the fatigue reliability are studied.;First of all, to evaluate the fatigue reliability and understand the fatigue behavior of the tin-based lead-free solder joints in BGA packaging assembly, isothermal shear fatigue tester was designed. Solder joints under cyclic shear load is found to fail by crack opening mode and crack is fixed at the solder neck area in the package side regardless of the testing conditions.;It is found that the failure of the solder joint under shear follows the Coffin-Manson model and a frequency-modified Coffin-Manson Model was developed for fatigue lifetime prediction. Fatigue property parameters that dictate the fatigue behavior of the solder joints were extracted from this model, namely fatigue ductility coefficient, cyclic strain hardening exponent/cyclic ductility exponent, and frequency exponent. The strain/work hardening rate is found to influence the fatigue resistance of the solder joints more than other parameters.;In the second part of this research, the grain structure evolution on tin-based lead-free solder under one-time thermal exposure (cooling to room temperature) was investigated indicating that recrystallization and mechanical twinning can occur far easier than previously thought. First, it reveals that either the activation energy for recrystallization or the thermal stress in the packaging assembly is higher than expected. Second, it is found that deformation twinning in tin is promoted by hydrostatic pressure stress while dislocation glide is prevented in tin in the packaging assembly. Grain structure sensitivity on the cooling temperature, cooling rate, thermal history, solder composition, and assembly configuration are investigated.;Finally, fatigue tests on solder joints with polygrain and twin structure were carried out showing that recrystallization and twinning improve the fatigue resistance of the solder joints by more than 50%. In summary, first, this research is scientifically important that it gives a new understanding on the mechanism of deformation twinning promoted by hydrostatic pressure stress in tin and tin-alloys.
机译：焊料是数十年来电子产品中使用的主要接头材料之一。它不仅是机械支撑，而且还在电子设备中传导电信号。但是，电子设备中铅含量的规定驱动了从铅锡焊料向无铅焊料的转变，需要大量研究来填补无铅焊料性能方面的知识空白。同时，随着电子设备的小型化和移动化趋势的持续，由于焊接失败而引起的可靠性问题引起了极大的关注。为了理解疲劳破坏机理及其影响因素，已经做了很多工作。本研究研究了电子包装中锡基无铅焊料的晶粒结构演变及其与疲劳可靠性的关系。首先，评估疲劳可靠性并了解锡基铅的疲劳行为，在BGA封装组装中使用免费的焊点，设计了等温剪切疲劳测试仪。发现焊缝在周期性剪切载荷下会因开裂方式而失效，并且无论测试条件如何，裂纹都固定在封装侧的焊锡颈部区域；发现在剪切作用下焊点的失效遵循Coffin-开发了曼森模型和频率修改后的科芬曼森模型来预测疲劳寿命。从该模型中提取了决定焊点疲劳行为的疲劳特性参数，即疲劳延性系数，循环应变硬化指数/循环延性指数和频率指数。发现应变/加工硬化速率对焊点疲劳强度的影响远大于其他参数。;在本研究的第二部分中，在一次热暴露下锡基无铅焊料的晶粒结构演变（研究表明，重结晶和机械孪晶的发生比以前想象的要容易得多。首先，它表明包装组件中用于重结晶的活化能或热应力均高于预期。其次，发现通过静水压力应力促进了锡中的变形孪生，同时防止了包装组件中锡中的位错滑动。研究了晶粒结构对冷却温度，冷却速率，热历程，焊料组成和组装结构的敏感性。最后，对具有晶粒和孪晶结构的焊点进行了疲劳测试，结果表明，再结晶和孪晶可改善合金的疲劳强度。焊点增加了50％以上。总之，首先，这项研究具有科学意义，因为它对锡和锡合金中的静水压力应力促进的孪生变形机理提供了新的认识。

著录项

  • 作者

    Xu, Huili.;

  • 作者单位

    The University of Texas at Arlington.;

  • 授予单位 The University of Texas at Arlington.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 157 p.
  • 总页数 157
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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