Silver Sintering Pastes - Improved Bond Performance and Simplified Handling

Silver sintering pastes and films are widely used for attaching SiC dies to their substrates in modern power electronics. They offer mechanical stability to well above the use temperatures (>200C), high thermal conductivity, and do not form brittle inter-metallics. They provide a strong, high reliability bond, especially when sintered with pressure assistance. However, they are not always easy to work with. Developing a product that will sinter at modest temperatures and with modest levels of pressure often results in an unstable formulation that requires cold storage and transport. These products then require conditioning to bring them up to working temperatures before they can be used. If the product cannot be dried before die placement, die size will be limited, or reliability will suffer due to trapped organics left after the sintering process. We have developed several novel paste formulations for sintered silver die, heat sink and top of die attach. They are shelf stable for months at room temperature, offer long open working times with little or no viscosity drift. They can be metal mask stencil printed syringe dispensed, or jetted, and are dried before placement (even when dispensed), allowing large area dies and substrates to be bonded without loss of reliability or thermal performance. We also have new developments in high reliability performance for large area heat sink attachment at reduced temperature and pressure. This allows attachment of encapsulated die/substrate structures onto heat sinks without damage to the organic encapsulant. Extensive reliability test data for these novel formulations will be shared that includes harsh liquid to liquid thermal shock performance.