Sintering of hollow Ag particle paste on bare Cu substrate for die attachment under a nitrogen atmosphere

Hollow nanoparticles have great application potential in the field of nanotechnology, but up to now, few studies have targeted on the sintering process using hollow Ag particles (HAP). It has been shown that hollow particles can melt at a lower temperature level than solid particles, so the hollow particles are easier to coarsen and the potential of hollow particle sintering is worth exploring. In this study, HAP with tunable sizes in a range of 280–910 nm was fabricated. To simulate the joint structure in high-power semiconductor devices, we selected SiC die with Ag metallization as the chip side, while a bare Cu sheet as the substrate side. Then, the HAP pastes with different particle sizes were sintered between the Ag-Cu structure under a nitrogen atmosphere, producing an Ag/HAP/Cu sandwich structure. In shear strength tests, we mixed two-sized HAP of 280 nm and 910 nm with different weight ratios. The ratio of 2:8 displayed a high shear strength of over 25 MPa even at a relatively low bonding temperature of 300 °C and 0.4 MPa added pressure. Results show that the sintered structure by the mix-sized particle paste was denser than that of the single-sized one. Also, a Cu-Ag inter-diffused layer was observed between the mix-sized Ag particles paste and Cu substrate. Therefore, the mix-sized HAP paste achieved a robust interconnection and shear test performance with a bare substrate, which could expand their applications in high-power semiconductor devices.