A lead-free, low-temperature sintering die-attach technique for high-performance and high-temperature packaging

For semiconductor devices to function in products, they need packaging to provide interconnection and protection. Die-attach materials, which join the devices to the rest of the system, play a vital role in ensuring the system performance and reliability. Today, lead-tin and lead-free solder alloys, and conductive epoxies are widely used for attaching the devices because they can be easily processed at a temperature below 300°C. As the electronics industry continues to integrate more functions in smaller packages, the electrical, thermal, and mechanical properties of the existing die-attach materials do not meet the more demanding requirements for performance and reliability. In this talk, a die-attach technique based on sintering of silver pastes to interconnect devices are presented. Two strategies have been adopted to lower the sintering temperature down to 300°C: one involves using quasi-hydrostatic pressure to increase the sintering driving force; while the other relies on nanoscale silver particles to densify the material without pressure. Experimental measurements on the sintered joints show significantly improved electrical, thermal, and mechanical properties over the soldered joints. This silver-sintering die-attach technique opens the possibility for interconnecting wide band gap semiconductor devices (SiC or GaN) that are operable over 350°C where none of the existing solder alloys can be used.