Structure and properties of low-melting Bi2O3-B2O3-MnO-CuO glasses for conductive silver paste

In this work, the 30Bi2O3-38B2O3-3SiO2-5Al2O3-(24-x)MnO-xCuO (x = 6, 10, 14, 18, 22 mol%) lead-free bismuth borate glasses were prepared by the melt-quenching method. The effects of CuO substitution for MnO on the structure and properties of the bismuth borate glass were investigated. As the CuO content increases from 6 to 22 mol%, the density of the glass gradually increases while the molar volume shows an opposite trend. The FTIR spectra show that [BiO3], [BiO6], [BO3], and [BO4] are the main structural units in the bismuth borate glass network. The vibrations of both [BiO3] and [BO4] units are enhanced with the increasing CuO content. With the increase of CuO content, the glass transition temperature (Tg) decreases from 438 to 417 ℃ and the softening temperature (Tf) decreases from 470 to 452 ℃. The thermal expansion coefficient (CTE) decreases from 7.875 to 7.702 × 10–6 /℃ in the temperature range of 30–300 ℃, which is between the thermal expansion coefficients of Ag (19 × 10–6 /℃) and silicon substrates (2.5 × 10–6 /℃). In addition, the HF resistance of the bismuth borate glasses gradually improves as the CuO content increases, with a minimum dissolution rate of 14.27 × 10–3 g cm−2 min−1. The NaOH resistance of the bismuth borate glasses initially decreases and then remains stable, with a maximum dissolution rate of 14.66 × 10–3 g cm−2 min−1. The results revealed that the investigated Bi2O3-B2O3-MnO-CuO glass can be used as a suitable alternative to lead-based glass for conductive silver paste.