High Electrical and Thermal Conductivity of Nano-Ag Paste for Power Electronic Applications
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High Electrical and Thermal Conductivity of Nano‑Ag Paste for Power Electronic Applications Hong‑Qiang Zhang1 · Hai‑Lin Bai2 · Qiang Jia1 · Wei Guo1 · Lei Liu1 · Gui‑Sheng Zou1 Received: 20 February 2020 / Revised: 26 March 2020 © The Chinese Society for Metals (CSM) and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The nano-Ag paste consisted of Ag nanoparticles and organic solvents. These organics would be removed by evaporation or decomposition during sintering. When the sintering temperature was 300 °C, the resistivity of sintered bulk was 8.35 × 10−6 Ω cm, and its thermal conductivity was 247 W m−1 K−1. The Si/SiC chips and direct bonding copper (DBC) substrates could be bonded by this nano-Ag paste at low temperature. The bonding interface, sintered microstructure and shear strength of Si/SiC chip attachment were investigated by scanning electron microscopy, transmission electron microscopy and shear tests. Results showed that the sintered Ag layer was porous structure and tightly adhered to the electroless nickel immersion gold surface of DBC substrate and formed the continuous Ag–Au interdiffusion layer. The shear strength of Si and SiC chip attachments was higher than 35 MPa when the sintering pressure was 10 MPa. The fracture occurred inside the sintered Ag layer, and the fracture surface had obvious plastic deformation. Keywords Nano-Ag paste · Sintering process · Interfacial microstructure · Chip attachment · Shear strength
1 Introduction The operating temperature of power electronics in hybrid automotive, aerospace, space exploration, deep oil and gas exploration can reach beyond 300 °C [1, 2]. Silicon carbide (SiC) has the excellent high-temperature performance and been identified as one of the potential semiconductor wafers for the future generation of power electronics [3, 4]. However, traditional die-attach materials, such as Pbbased and Sn-based solders, exhibit the poor bonding reliability at high temperature and low thermal and electrical conductivity [5–7]. Many researches have recently been directed toward developing high-temperature materials for
Available online at http://link.springer.com/journal/40195. * Wei Guo [email protected] * Gui‑Sheng Zou [email protected] 1
School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China
Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
2
power electronics, which can be used to attach chips and have high thermal and electrical conductivity [8, 9]. Nano-Ag paste has been studied as a possible alternative to Pb-free solder [10, 11]. High surface energy of nanoparticles and consequent strong capillary force make it possible to achieve strong bonding [12–15]. After sintering, the melting point of sintered Ag returns to the melting point of bulk Ag so that the sintered chip attachment could operate at high temperature. Currently, nano-Ag paste could achieve bonding chips and substrates pressureless, which avoid chip breaking and shorten processing time [
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