Formation of a Diffusion Barrier-Like Intermetallic Compound to Suppress the Formation of Micro-voids at the Sn-0.7Cu/Cu
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https://doi.org/10.1007/s11837-020-04302-5 2020 The Minerals, Metals & Materials Society
INTERFACIAL STABILITY IN MULTI-COMPONENT SYSTEMS
Formation of a Diffusion Barrier-Like Intermetallic Compound to Suppress the Formation of Micro-voids at the Sn-0.7Cu/Cu Interface by Optimal Ga Additions TING-LI YANG,1 YU-CHEN LIU,1 CHIH-HAN YANG,1 YI-KAI KUO,1 and SHIH-KANG LIN 1,2,3,4 1.—Department of Materials Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan. 2.—Hierarchical Green-Energy Materials (Hi-GEM) Research Center, National Cheng Kung University, Tainan 70101, Taiwan. 3.—Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 70101, Taiwan. 4.—e-mail: [email protected]
Kirkendall micro-voids observed within -Cu3Sn or at the bulk Sn solder/Cu interface are undesirable imperfections in solder joints in electronic interconnections that significantly decrease the reliability of the joint. Recent studies have shown that micro-alloying could alter these interfacial reactions and improve the mechanical properties. In this study, we investigated the CuGa-Sn phase equilibria at 200C and the interfacial reactions between Cu substrate and Ga-doped Sn-0.7Cu solders with doping levels of 1.0, 2.0, and 3.0 wt.%. The assembled diffusion couples were isothermally annealed at 200C for different time periods. The results showed that the thickness of the typical Cu-Sn IMCs (g-Cu6Sn5 and -Cu3Sn) progressively decreased along with the formation of the c-Cu9Ga4 phase as the Ga-doping concentration was increased. The g-Cu6Sn5 and -Cu3Sn were completely suppressed and substituted by the c-Cu9Ga4 phase when the Ga-doping concentration was 3 wt.%. More interestingly, the c-Cu9Ga4 was the only IMC formed at the Sn-0.7Cu3.0 Ga/Cu interface even when aging at 200C for up to 1000 h, implying that the undesired defectiveness of Kirkendall micro-voids is possibly prevented by controlling the formation of the interfacial phase.
INTRODUCTION Sn-rich Pb-free solders have been widely used as interconnection materials in the microelectronic package industry.1–5 The eutectic Sn-0.7 wt.% Cu (Sn-0.7Cu) alloy, with its melting temperature at 227C6 and low-cost materials, is one of the most promising Pb-free solders. The interfacial reactions between Sn and Cu have been extensively investigated and reported in the literature.2,7–13 The gCu6Sn5 and -Cu3Sn phases are the two typical intermetallic compounds (IMCs) at the Sn/Cu or Sn0.7Cu/Cu interface. The brittleness of Cu-Sn IMCs
(Received April 14, 2020; accepted July 22, 2020)
and interface micro-voids defects degrade the robustness of solder joints and raise mechanical and electrical reliability concerns during the operation of a device.14–17 Besides, the well-known Kirkendall micro-voids derived from either the divergence of the Cu and Sn atom fluxes due to a non-equilibrium inter-diffusion,18 or the organic impurities incorporated into the Cu during the electroplating process19 are undesirable defects at the Sn-based solder/Cu
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