Study on Cu Wire Wedge Crack and Fatigue Life Prediction during Thermal Cycling Test (TCT)

2020 IEEE 22nd Electronics Packaging Technology Conference (EPTC) Pub Date : 2020-12-02 DOI:10.1109/EPTC50525.2020.9315045

Billie Xianghong Bi, H. Fan, Jun Yang, Haibin Chen

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Abstract

It is widely believed that wedge crack is resulted from thermal stress occurring at wire bonding area due to coefficient of thermal expansion (CTE) mismatches among epoxy molding compound (EMC), Cu wire, and Leadframe, and wedge bond heel area has the highest risk due to higher stress concentration. To fully understand the wedge crack failure mechanism and the way to improve its fatigue life, in this study, the wedge bond performance under TCT was evaluated in a small outline transistor package with different wire bonding settings, different types of EMC with different CTEs and modulus. The results showed that the TCT performance of Cu wire wedge bond depended on the wire bonding setting, CTE of EMC, adhesion between EMC and Leadframe, wire diameter, etc. Through suitable material selection, package design, process optimization, Cu wire wedge crack during TCT can be avoided to achieve the increasingly higher reliability requirement. Furthermore, numerical modeling was developed to predict Cu wire wedge bond fatigue life with those different factors during TCT. For given packages, modelling can provide a comparison on accumulative plastic strain ($\Delta\varepsilon_{\mathrm{p}}$) at Cu wedge bond to identify the effect of factors on Cu wedge fatigue crack. Fatigue parameters can be derived by simulation results and experimental data. Regarding to these fatigue parameters, TCT fatigue life can be predicted for a given package.

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热循环试验(TCT)中铜丝楔裂及疲劳寿命预测研究

人们普遍认为，由于环氧成型化合物(EMC)与铜线、引线框架之间的热膨胀系数(CTE)不匹配，导致焊丝键合区域产生热应力，导致楔形裂纹产生，而楔形键合后跟区域由于应力集中程度较高，风险最高。为了充分了解楔形裂纹的失效机理和提高其疲劳寿命的途径，本研究在不同的线键合设置、不同类型的电磁兼容、不同cte和模量的小外形晶体管封装中，对TCT下的楔形键合性能进行了评估。结果表明:铜导线楔焊的TCT性能与导线直径、导线楔焊设置、电磁兼容的CTE、电磁兼容与引线架的粘附力等因素有关。通过合适的材料选择、封装设计、工艺优化，可以避免铜丝在TCT过程中产生楔形裂纹，从而达到越来越高的可靠性要求。在此基础上，建立了基于这些因素的铜丝楔键疲劳寿命数值模型。对于给定的包件，通过建模可以比较Cu楔键处的累积塑性应变($\Delta\varepsilon_{\mathrm{p}}$)，从而确定影响Cu楔疲劳裂纹的因素。根据仿真结果和试验数据，可以推导出疲劳参数。根据这些疲劳参数，可以预测给定包件的TCT疲劳寿命。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

2020 IEEE 22nd Electronics Packaging Technology Conference (EPTC)

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