《Investigation on Thermal-Mechanical Reliability and Enhanced Fatigue Life of Indium Thermal Interface Materials for Large-Size Flip Chip Packaging》
Title: Investigation on Thermal-Mechanical Reliability and Enhanced Fatigue Life of Indium Thermal Interface Materials for Large-Size Flip Chip Packaging
Author: Yiou Qiu, Zhen Liu, Linzheng Fu, Mingming Yi, Ping Wu, Linjie Liao, Xiaodong Teng, Wenhui Zhu, Senior Member, IEEE, and Liancheng Wang
Publication time: 2025
DOI: 10.1109/TCPMT.2025.3568526
Journal IEEE TRANSACTIONS ON COMPONENTS, PACKAGING AND MANUFACTURING TECHNOLOGY
Abstract: With the growing demand for thermal management in large-size chips, indium—due to its inherent high thermal conductivity and excellent ductility—is considered an ideal thermal interface material (TIM). For large-size flip-chip packages, enhancing reliability, especially under temperature cycling conditions, remains a significant challenge. This study focuses on large-size flip-chip packaging and employs a combined approach of finite-element simulation and experiments to systematically analyze the creep behavior and morphological evolution of indium under temperature cycling. Based on this analysis, the strain-based Coffin–Manson model was used to predict the fatigue life of indium. To improve the reliability of the indium layer under temperature cycling, design-of-experiments (DOEs) were employed to simulate and analyze the effects of various structural parameters on fatigue life. The results show that the cumulative plastic strain is greatest near the chip edges, which correlates well with the crack locations observed in actual measurements. The fatigue life of the indium layer predicted by the Coffin–Manson model is in good agreement with the experimental results. Signal-to-noise ratio (SNR) analysis indicates that the thickness of the indium layer has the most significant impact on thermal fatigue life, while the adhesive layer thickness has the least influence. Compared to the original model, the optimized package structure exhibits a 135% improvement in fatigue life.
Conclusion: In summary, this study takes large-size flip-chip packaging as its research object and systematically analyzes the reliability of indium under temperature cycling as well as potential improvement methods, combining finite element simulation with experiments. The main research findings are as follows:
1. As the number of temperature cycles increases, the number of microvoids gradually rises and is predominantly concentrated at the corners of the chip. Since the temperature environment has not yet reached the melting point, the effect of solder paste volatilization is not significant. Combined experimental and simulation results indicate that the observed increase in the number of voids is primarily attributable to the cumulative equivalent plastic strain in the indium layer at the corners under temperature cycling.
2. Finite element simulation analysis indicates that, under a constant temperature loading rate, the equivalent stress and equivalent plastic strain exhibit a linear relationship with time. During the holding phase, no variation in the temperature gradient was observed, and the strain rate remained essentially constant. Under temperature cycling, the maximum accumulated plastic strain occurred near the chip edges, which is consistent with the crack locations observed in actual measurements.
3. Based on the strain-based Coffin-Manson model, the predicted fatigue life of the indium layer is 1258.54, which is broadly consistent with the measured values ranging from 800 to 1200. Signal-to-noise ratio (SNR) analysis indicates that the thickness of the indium layer has the greatest impact on thermal fatigue life, while the thickness of the adhesive has the least impact on thermal fatigue life.
4. Simulation analysis of the optimized model shows that the maximum von Mises stress is 0.064 MPa, a reduction of 94.69% compared to the original model. The maximum equivalent plastic strain is 0.3092, a reduction of 65.41% compared to the original model. The range of equivalent plastic strain is 0.018431, which is 49.65% lower than that of the original model. The fatigue life is 2962.60, representing a 135% increase over the original model.
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About the Author: The innovation of this study lies in:
(1) By combining finite element simulation with experimental studies, we systematically revealed the creep behavior and morphological evolution of indium under temperature cycling, and predicted its fatigue life based on the strain-based Coffin–Manson model.
(2) Using experimental design and simulation analysis methods, we evaluated the impact of different structural parameters on the fatigue life of the indium layer and proposed an optimization scheme that significantly improved the fatigue life by 135%.
(3) By comparing the simulated and measured data through warpage analysis, we verified the accuracy of the simulation model and confirmed that the fatigue life predicted by the simulation closely matches the experimental results.