Development of an Antioxidation Copper Paste with Self-Reducing Copper Formate and Molecular Dynamics Analysis of Sintering Mechanisms

doi:10.1007/s40195-025-01869-3

Abstract

Abstract:

This study investigates using an antioxidation copper particle-free paste, formulated with self-reducing copper formate, for Cu-Cu bonding in electronic packaging applications. The research highlights the oxidation resistance of copper formate compared to traditional copper nanoparticles (CuNPs) and its ability to generate CuNPs through thermal decomposition. Experimental results demonstrate that the sintering process benefits from releasing reductive gases during decomposition, improving joint quality with reduced porosity and enhanced mechanical strength at elevated temperatures. Molecular dynamics simulations further elucidate the sintering behavior of CuNPs, providing significant insights into pore collapse, atomic mobility, and neck formation. The findings indicate that increased temperatures enhance surface and bulk diffusion, facilitating robust particle connections. Overall, this work establishes the potential of copper formate for achieving reliable interconnects in semiconductor devices, paving the way for advancements in material formulations for direct copper-copper bonding.

Key words: Copper formate, Cu-to-Cu direct bonding, Sinter bonding, Molecular dynamics simulation, Electronic packaging

Fengyi Wang, Jingyuan Ma, Jiahao Liu, Hongjun Ji, Hongtao Chen. Development of an Antioxidation Copper Paste with Self-Reducing Copper Formate and Molecular Dynamics Analysis of Sintering Mechanisms[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(8): 1351-1360.

Figures/Tables 10

Fig. 1 Preparation of Cu formate paste and sandwich solder joints

Fig. 2 a TG curves of Cu particles and Cu formate in the air at 100 °C; b TG-DSC curves of Cu formate paste at a heating rate of 5 min/°C

Fig. 3 Morphologies of a Cu formate after grinding and b Cu particles formed after heating at 250 °C for 20 min

Fig. 4 TEM morphologies of the thermal decomposition process of Cu formate: a three stages of Cu formate decomposition; b diffraction rings at the green markers in a; c HRTEM image corresponding to b; d and e HRTEM and TEM images of CuNPs; f particle size distribution of CuNPs in e

Fig. 5 Cross-sectional morphologies, porosity, and elemental composition of sintered joints at different temperatures: a-c 250 °C; d-f 300 °C; g-i 350 °C

Fig. 6 Shear strength and fracture morphology of sintering joints at different temperatures: a shear strength; b-d fracture morphology at 250, 300, and 350 °C, respectively

Fig. 7 a MD model of sintering bonding of CuNPs; b sintering simulation process

Fig. 8 Evolution of porosity during the sintering of CuNPs at different temperatures: a-d 250 °C; e-j 300 °C; k-q 350 °C

Fig. 9 a MSD and b sintering neck length of CuNPs at different temperatures

Fig. 10 Displacement vector plot of CuNPs in the sintering process at 350 °C under different times: a 11 ps; b 100 ps; c 300 ps; d 600 ps

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