Pressureless transient liquid phase sintering bonding using SAC305 with hybrid Ag particles for high–temperature packaging applications

Transient liquid phase sintering (TLPS) bonding has been widely researched for high temperature interconnection. At TLPS bonding, intermetallic compounds (IMCs) form by solid-liquid interdiffusion between molten low-melting point (MP) metals and high-MP metal particles. This IMC formation reaction occurs simultaneously across the whole joint. Therefore, the growth rate of IMCs is higher than conventional TLP bonding, and the bonding process can be performed in low pressure condition for short time.We investigated hybrid TLPS paste using SAC305 with various size of Ag particles (0.5 - 10 μm in diameter) for pressureless bonding. Hybrid TLPS paste was fabricated using SAC305 powder, hybrid Ag particles, and organic solvent by paste mixer. Then, the pastes (hybrid TLPS paste, SAC305) were printed on Cu substrate, and Cu chip was placed onto printed pastes. Pressureless bonding process was carried out at 300°C for 2 h in air. In cross-sectional micrograph of hybrid TLPS joint, Sn was almost replaced by IMCs, while Sn residue remained after the bonding at SAC305 joint. The mechanical property of joint was evaluated by die shear test. Shear strength of hybrid TLPS joint was 2.5 times higher than that of SAC305. The high-temperature storage test (200 °C) and salt spray test (5 % NaCl at 35 °C) were performed to evaluate the bonding reliability under harsh environment. In both tests, hybrid TLPS joint showed more mechanically and electrochemically robust properties than conventional SAC305 joint.