Low temperature solid-state diffusion bonding of fine pitch Cu/Sn micro-bumps assisted with formic acid vapor for 3D integration

IF 2.6 4区工程技术 Q2 ENGINEERING, ELECTRICAL & ELECTRONIC

Microelectronic Engineering Pub Date : 2025-01-17 DOI:10.1016/j.mee.2025.112319

Hanlin Wan , Qian Wang , Jian Cai , Dejun Wang

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Abstract

Low-temperature solid-state diffusion (SSD) bonding of 5 μm diameter Cu/Sn micro-bumps was achieved with the assistance of formic acid vapor. Efforts were made to overcome surface oxidation of copper and uneven tin morphology, which are two major challenges in SSD bonding. Formic acid vapor was used as pre-treatment gas before bonding and protection gas during bonding. The results demonstrated that formic acid vapor is highly effective in removing surface oxidation on copper and preventing secondary oxidation, thereby facilitating a strong bond. Temperatures of 160 °C and 200 °C in 120 s were identified as ideal for pre-treatment. In SSD thermal compression bonding, 30 MPa TCB pressure was found to be necessary to overcome the uneven tin morphology. Other bonding parameters were also optimized, achieving a die shear strength of up to 59 MPa while reducing bonding temperature and time to 150 °C and 10 min. As bump scale shrinks, the interface analysis revealed a unique “teeth-like” structure in the bonding interface, contributing to improved shear strength due to intermetallic compound (IMC) growth and a favorable stress distribution. The assistance of formic acid vapor and the optimization of bonding parameters enhances the likelihood of future applications of solid-state bonding in industry, which could be an alternative choice for fine-pitch micro-bump bonding application.

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来源期刊

Microelectronic Engineering 工程技术-工程：电子与电气

CiteScore

5.30

自引率

4.30%

发文量

131

审稿时长

29 days

期刊介绍： Microelectronic Engineering is the premier nanoprocessing, and nanotechnology journal focusing on fabrication of electronic, photonic, bioelectronic, electromechanic and fluidic devices and systems, and their applications in the broad areas of electronics, photonics, energy, life sciences, and environment. It covers also the expanding interdisciplinary field of "more than Moore" and "beyond Moore" integrated nanoelectronics / photonics and micro-/nano-/bio-systems. Through its unique mixture of peer-reviewed articles, reviews, accelerated publications, short and Technical notes, and the latest research news on key developments, Microelectronic Engineering provides comprehensive coverage of this exciting, interdisciplinary and dynamic new field for researchers in academia and professionals in industry.