Modification of granulometric composition of ultrafine silver powders

Background. In the modern production of power electronics devices, sintering technology is used for low-temperature connection of their structural elements using special pastes based on ultrafine silver powders. The key problem in the manufacture of such pastes is the agglomeration of silver particles in the powder. The purpose of the work was to develop methods for modifying the granulometric composition of silver powders, leading to an increase in the proportion of submicron particles in them. Materials and methods. The work investigated ultrafine silver powder of domestic production. The granulometric composition of the powder was determined by laser diffraction using a SALD-3101 granulometer. For measurements, suspensions of the studied powder in isopropyl alcohol with concentrations of 50 μg/ml and 75 mg/ml were prepared. Suspensions were subjected to ultrasound treatment at a frequency of 35 kHz in a PSB-5735-05 ultrasonic bath. Results. It was found that the original silver powder consisted of two fractions of particles with sizes from 0.5 to 2.0 μm and from 10 to 500 μm. As a result of ultrasonic (US) treatment of a lowconcentration powder suspension (50 μg/ml) for 80 minutes, the volume fraction of submicron fraction particles increased from 18 to 60%. Long-term (4 hours or more) US treatment of a highly concentrated suspension (75 mg/ml) did not result in the appearance of silver particles smaller than 1 μm in it. Such particles appeared in the suspension upon addition of myristic acid as a dispersant, followed by US-treatment. Dilution of the suspension with isopropyl alcohol to a concentration of 50 μg/ml, followed by US-treatment, made it possible to increase the volume fraction of silver particles with sizes less than 1 μm to 70%. Conclusions. A method has been developed for modifying the granulometric composition of ultrafine silver powders, which makes it possible to increase the volume fraction of submicron particles to 70%.