Enhanced copper micro/nano-particle mixed paste sintered at low temperature for 3D interconnects
TL;DR: In this article, an enhanced copper paste, formulated by copper micro-and nano-particles mixture, is reported to prevent paste cracking and obtain an improved packing density, where particle mixture of two different sizes enables reduction in porosity of the micro-paste and resolves the cracking issue in nano-paste.
Abstract: An enhanced copper paste, formulated by copper micro- and nano-particles mixture, is reported to prevent paste cracking and obtain an improved packing density. The particle mixture of two different sizes enables reduction in porosity of the micro-paste and resolves the cracking issue in the nano-paste. In-situ temperature and resistance measurements indicate that the mixed paste has a lower densification temperature. Electrical study also shows a ∼12× lower sheet resistance of 0.27 Ω/sq. In addition, scanning electron microscope image analysis confirms a ∼50% lower porosity, which is consistent with the thermal and electrical results. The 3:1 (micro:nano, wt. %) mixed paste is found to have the strongest synergistic effect. This phenomenon is discussed further. Consequently, the mixed paste is a promising material for potential low temperature 3D interconnects fabrication.
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TL;DR: In this paper, the authors compared the mechanical and thermal-electrical properties of sintered copper (Cu) with Sintered silver (Ag) as bonding materials in the microelectronics joint applications.
71 citations
TL;DR: This study has successfully demonstrated air atmosphere sintering at low temperatures (less than 150 °C) via a simple hot plate heat treatment for producing conductive Cu films on flexible polymer substrates, using a novel Cu-based composite ink with sub-10 nm Cu nanoparticles protected with 1-amino-2-propanol.
Abstract: The development of a thermal sintering method for Cu-based inks under an air atmosphere could greatly expand their application for printed electronics However, it is well-known that Cu-based inks cannot produce conductive Cu films when sintered at low temperatures in air because Cu readily oxidizes under such conditions In this study, we have successfully demonstrated air atmosphere sintering at low temperatures (less than 150 °C) via a simple hot plate heat treatment for producing conductive Cu films on flexible polymer substrates, using a novel Cu-based composite ink with sub-10 nm Cu nanoparticles protected with 1-amino-2-propanol with micrometer-sized Cu particles and submicrometer-sized Cu particles; oxalic acid was also added to prevent the oxidation of the Cu during sintering The Cu films showed a minimum resistivity of 55 × 10–5 Ω·cm when sintered in air at 150 °C for a very short period of 10 s To the best of our knowledge, this is the first report of sintering of Cu-based inks in air at les
70 citations
TL;DR: In this paper, a review summarises the advanced developments of Cu inks in terms of formulations, sintering methods, and long-term reliability, and the mainstream strategies for avoiding oxidation and improving the stability of CU inks and Cu patterns are described.
65 citations
TL;DR: The surface and interface designs for Cu-based conductive inks/pastes are summarized, in which the strategies for the oxidation resistance of Cu and low-temperature sintering are applied to produce highly conductive Cu patterns/electrodes on flexible substrates.
Abstract: Silver (Ag), gold (Au), and copper (Cu) have been utilized as metals for fabricating metal-based inks/pastes for printed/flexible electronics. Among them, Cu is the most promising candidate for metal-based inks/pastes. Cu has high intrinsic electrical/thermal conductivity, which is more cost-effective and abundant, as compared to Ag. Moreover, the migration tendency of Cu is less than that of Ag. Thus, recently, Cu-based inks/pastes have gained increasing attention as conductive inks/pastes for printed/flexible electronics. However, the disadvantages of Cu-based inks/pastes are their instability against oxidation under an ambient condition and tendency to form insulating layers of Cu oxide, such as cuprous oxide (Cu2O) and cupric oxide (CuO). The formation of the Cu oxidation causes a low conductivity in sintered Cu films and interferes with the sintering of Cu particles. In this review, we summarize the surface and interface designs for Cu-based conductive inks/pastes, in which the strategies for the oxidation resistance of Cu and low-temperature sintering are applied to produce highly conductive Cu patterns/electrodes on flexible substrates. First, we classify the Cu-based inks/pastes and briefly describe the surface oxidation behaviors of Cu. Next, we describe various surface control approaches for Cu-based inks/pastes to achieve both the oxidation resistance and low-temperature sintering to produce highly conductive Cu patterns/electrodes on flexible substrates. These surface control approaches include surface designs by polymers, small ligands, core-shell structures, and surface activation. Recently developed Cu-based mixed inks/pastes are also described, and the synergy effect in the mixed inks/pastes offers improved performances compared with the single use of each component. Finally, we offer our perspectives on Cu-based inks/pastes for future efforts.
44 citations
TL;DR: In this article, a joint with a bonding strength of about 20MPa was achieved even at 250°C and under a pressure of 8MPa. But the major oxidation product formed on the surfaces of the nanoparticles was Cu2O and the formation of voids in the sintering structure due to oxidation reduced the shear strength of the joints.
21 citations
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TL;DR: An idealized experimental study of particle packing was made as mentioned in this paper, where spherical metal shot of several discrete, narrow size ranges was efficiently packed in glass containers by mechanical vibration, and the significance and utility of this work to the ceramic and other industries was discussed.
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TL;DR: In this article, the authors achieved robust bonding of Cu wires to Cu pads on polyimide with silver nanopaste cured at 373 K. The bonding is formed by solid state sintering of Ag NPs through neck growth and direct metallic bonding between clean Ag-Cu interfaces.
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283 citations
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Abstract: Drying aqueous suspensions of monodisperse silica nanoparticles can fracture in remarkable patterns. As the material solidifies, evenly spaced cracks invade from the drying surface, with individual cracks undergoing intermittent motion. We show that the growth of cracks is limited by the advancement of the compaction front, which is governed by a balance of evaporation and flow of fluid at the drying surface. Surprisingly, the macroscopic dynamics of drying show signatures of molecular-scale fluid effects.
271 citations