Copper Sintering Pastes with Various Polar Solvents and Acidic Activators

Devices in the developing semiconductor market require high density, high integration, and detailed processing. Conventional wire bonding is inappropriate for fine-sized devices, and connected wires can be damaged by heat generation and external physical impact. Soldering is also used in advanced packaging technologies. However, disturbances and overhead joints can occur during bonding. Thus, sintering has been extensively utilized to overcome these drawbacks. Sintering pastes are pressurized and bonded, resulting in stable bonding during sintering. In this study, the composition of the Cu sintering material was examined using diverse additives and solvents. We manufactured sintering materials comprising Cu (1 μm), a solvent [methanol (MeOH), ethanol (EtOH), or ethylene glycol (EG)] and an acidic additive (benzoic acid, phthalic acid, or hexanoic acid). After the sintering process, the mechanical and electrical characteristics were compared to determine the optimal composition and bonding conditions. The optimum ratios between the acid and solvent were 4:6 (MeOH and EtOH) and 2:8 (EG) due to the high viscosity and effective long-term storage. All samples using EtOH as the solvent exhibited the highest sintering performances. The aromatic and carboxylic groups substantially improved the sintering performance and increased the electrical conductivity. Based on the O^1s/Cu^2p ratio (2.23%), the best sintering composition was EtOH/PA, which showed the highest electrical conductivity (ca. 10⁴ S/m) and strength (34.0 MPa). The sintering process using various additives and solvents can be helpful to determine the sintering conditions while maintaining the electrical properties.