Low-Temperature Cu-Cu Bonding Process Based on the Sn-Cu Multilayer and Self-Propagating Reaction Joining

• Published in: Journal of electronic materials 2019-02, Vol.48 (2), p.1310-1317
• Main Authors: Fan, Jinhu, Shi, Tielin, Tang, Zirong, Gong, Bo, Li, Junjie, Huang, Jie, Li, Tianxiang
• Format: Article
• Language: English
• Subjects: Aluminum; Bond strength; Bonded joints; Bonding strength; Characterization and Evaluation of Materials; Chemistry and Materials Science; Confining; Copper; Electronics and Microelectronics; Electroplating; Instrumentation; Joining; Liquid phases; Low temperature; Materials Science; Morphology; Multilayers; Nickel; Optical and Electronic Materials; Self propagation; Shear strength; Solid State Physics; Substrates; Thickness ratio; Tin; Transient liquid phase bonding
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-018-6827-z

Transient liquid phase bonding can be realized at a relatively low temperature through building an intermetallic interconnection. A self-propagating reaction joint can achieve a low temperature bond by confining the heat at the bonding interface and reduce the thermal effect on other components. In this work, a Sn-Cu alternating multilayer was combined with an Al-Ni self-propagating reaction joint to develop a highly efficient low-temperature Cu-Cu hybrid bonding process. The Sn-Cu alternating multilayer was directly prepared on the Cu substrates by an alternating electroplating process. The Al-Ni multilayer film was sandwiched between two Cu substrates under a pressure of 5 MPa and ignited with a 15-V spark at room temperature. Cu-Cu bonds with three different Sn/Cu thickness ratios were studied. It was found that the Cu 6 Sn 5 layer within the three Sn layers had different thicknesses and decreased with increasing distance from the heat source of the Al-Ni nanofoil. The thickness difference between adjacent Cu 6 Sn 5 layers at first decreased with the increasing Sn/Cu thickness ratio in these three groups and then remained constant. The shear strength of the bonds varied with the thickness of Cu 6 Sn 5 layer and achieved a high shear strength with a Sn/Cu thickness ratio of 1.6  μ m/1  μ m, where fracture occurred within the Cu 6 Sn 5 layer near the Cu substrate. The combination of the Sn-Cu multilayer and self-propagating reaction joining process can achieve a good low-temperature bond between Cu substrates with an optimized Sn/Cu thickness ratio, which has a strong influence on the quality of bonds, the Cu 6 Sn 5 morphology, and shear strength.