Cu₃Sn joint based on transient liquid phase bonding of Cu@Cu₆Sn₅ core–shell particles

With the development of high-integration and high-power electronics, the lack of matching chip connecting materials that can withstand high temperatures has been a challenge. In this manuscript, a Cu@Cu₆Sn₅ core–shell bimetallic particles (approx. 1 μm in diameter) are successfully prepared and introduced as a new solder material for the packaging of power devices to obtain a Cu₃Sn all-IMC solder joint. The joint consisted mainly of equiaxed Cu₃Sn grains, and a small portion of columnar Cu₃Sn grains. In columnar-type growth, Sn is the dominant diffusing species, which comes from the depletion of Sn in Cu₆Sn₅. The depleted Cu₆Sn₅ is transformed into columnar Cu₃Sn. In equiaxed-type growth, Cu is the dominant diffusing species. Cu reacts with Cu₆Sn₅ to grow a Cu₃Sn layer. This conclusion was confirmed by the orientation relationship. The equiaxed Cu₃Sn grain nucleates at the Cu/Cu₃Sn interface have an orientation relationship with the Cu substrate. Columnar Cu₃Sn grains at the Cu₆Sn₅/Cu₃Sn interface have an orientation relationship with Cu₆Sn₅.