Microstructure evolution and properties evaluation of a novel bondline based on Cu@Sn Preform during temperature treatment

The microstructure and properties of Cu@Cu3Sn@Cu6Sn5three-dimensional network bonding interconnections based on Cu@Sn preform was investigated. No through holes were observed at the bulk in as-reflowed, aged and temperature cycling bondlines. Microstructure evolution and phase transformation during thermal treatment test were studied, the shear strength of three-dimensional network bondlines for as-reflowed and thermal treating samples were compared and analyzed. The phase composition of as-reflowed interconnects was Cu/Cu6Sn5 and transformed to Cu/Cu3Sn/Cu6Sn5 after thermal treatment. Different failure modes of as-reflowed, aged and temperature cycling test were found in three-dimensional network structure bondline. The average shear strength of the as-reflowed and the thermal treatment bonding interconnections are 49.5 MPa and 24.9 MPa, respectively, and crack initiated and propagated that perpendicular to substrate during the aging test. The fracture surfaces of the temperature treatment bonding interconnections after shearing test were characterized in detail. The results show that the Cu3Sn phases in Cu@Cu3Sn@Cu6Sn5 three-dimensional network structure affected its strength and fracture mode. The Cu-rich substrate side at the fracture surfaces is always regular while the bulk phases are often accompanied by shear bands and dimples.