《Influence of surface roughness on interfacial reaction and shear strength ofindium thermal interface materials for FCBGA packaging》
Title: Influence of Surface Roughness on Interfacial Reaction and Shear Strength of Indium Thermal Interface Materials for FCBGA Packaging
Author: Yiou Qiu a, Zhen Liu b, Linzheng Fu a, Minming Yi a, Ping Wu a, Linjie Liao a, Xiaodong Teng b, Wenhui Zhu a,*, Liancheng Wang
Publication Date: 2025
DOI: 10.1016/j.mtcomm.2024.111430
Journal: Materials Today Communications
Abstract: As electronic devices continue to evolve toward higher power consumption, pure indium is gradually emerging as an ideal metal-based thermal interface material (TIM) for flip-chip ball-grid array (FCBGA) packaging, driving strong market demand. However, ensuring the reliability of indium-based thermal interface materials (TIMs) during repeated high-temperature reflow (HTR) processes remains a significant challenge for FCBGA packaging. In this study, we focused on the assembly consisting of a cover plate, indium, and a BSM chip, investigating the wettability between indium and various interfaces within a temperature range of 170–245°C. We also systematically analyzed the effects of different process conditions on interfacial reactions and shear strength. The results show that increasing the temperature and reducing the surface roughness of the coating can enhance the wettability of indium at different interfaces. In contrast, cover plates with a surface roughness of 0.4 < Ra < 0.6 better meet the requirements of the FCBGA manufacturing process. Under low-temperature reflow (LTR) and repeated high-temperature reflow conditions, the primary fracture mode observed was ductile fracture.
Conclusion: This study investigated the wettability of indium on different interfaces within a temperature range of 170–245℃, and examined the effects of low-temperature reflow (LTR) and multiple high-temperature reflows (HTR) on the interfacial reactions and shear strength between indium and cover plates as well as BSM chips. The main conclusions are as follows:
(1) As the welding temperature rises, the contact angle between indium and both the cover plate and the BSM chip decreases, while the spreading area increases. Conversely, the data show that as surface roughness increases, the contact angle also increases, and the spreading area decreases.
(2) In contrast, within the temperature range of 190–245℃, cover plates with a surface roughness of 0.4 < Ra < 0.6 can better meet the process requirements for flip-chip ball grid array (FCBGA). Increasing the surface roughness has a positive effect on both the thickness of intermetallic compounds (IMCs) and grain growth.
(3) During the bonding process, grain spalling was observed at all reaction interfaces between indium and both the cover plate and the chip. Analysis indicates that this phenomenon is related to stress concentration and the morphology of intermetallic compounds (IMCs).
(4) Under multiple high-temperature reflow conditions, when using an indium layer thickness of 230 μm, the thickness and morphology of the IMC layer have relatively little impact on the shear strength.
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About the Author: This study focuses on indium-based thermal interface materials for FCBGA packaging applications. The key innovations are as follows:
1. The wetting behavior of indium on different interfaces under conditions ranging from 170 to 245 ℃ was systematically studied, revealing the coupled effects of temperature and surface roughness. The results indicate that when the surface roughness of the lid is in the range of 0.4 < Ra < 0.6, the wettability is optimal for the FCBGA packaging process.
2. The reaction processes between indium and the interfaces of the lid and chip under different process conditions, as well as the growth kinetics of intermetallic compounds (IMCs), were investigated. The critical role of surface roughness in regulating IMC formation and growth was revealed.
3. It was found that indium exhibits grain delamination at the interface under various process conditions. The study delved into the underlying mechanism of this phenomenon and its impact on interfacial reliability, providing a new perspective for understanding the failure modes of indium-based materials.
4. The system studied the interfacial shear strength and fracture modes after multiple reflows, revealing the underlying mechanisms by which cyclic thermal treatment affects the reliability of indium-based TIMs. This research provides a theoretical basis for enhancing the long-term stability of indium interfaces in FCBGA packages.
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