Development of low-temperature sintering nano-silver die attach materials for bare Cu application

This paper will discuss the fundamental study on nano-silver die attach pastes newly developed with a unique approach using MO (Metallo-organic) technology. MO technology provides a low-temperature sintering capability. The nano-silver pastes show high thermal performance and strong adhesion to the metalized die and substrate without pressure during cure process. In addition, resin reinforcing technology and lowering modulus technology have been developed to improve the mechanical properties. By adding special epoxy resins to the pastes, the porous area is filled with the resin and the sintered structure is reinforced. Additionally, the reliability can be more improved by thermoplastic resin particles. By adding the resin particles to the pastes, the modulus can be lowered and the resin reduces the stress caused by the CTE mismatch between the die and substrate. However, the pastes can only be applied on substrates with Ag or Au plating because the metallic bonding forms without difficulty between the nano-silver particles and the Ag or Au plating. To meet the demand for applications without Ag or Au plating, nano-silver die attach pastes for bare Cu application have newly been developed. Addition of a special additive is effective to form metallic bonding between the nano-silver particles and bare Cu substrates because the additive removes the oxide layer on the surface of Cu substrates. By adjusting the amount of epoxy and thermoplastic resin, adhesion strength on the bare Cu substrate can be more improved. The fundamental investigation for the mechanism and the reliability test results will also be discussed in this study.