Asymmetric Low Temperature Bonding Structure with Thin Solder Layers Using Ultra-Thin Buffer Layer.

Asymmetric Cu to In/Sn bonding structure with Ni ultrathin buffer layer (UBL) on Cu side is investigated in this research. The usage of Ni UBL slows down intermetallic compound (IMC) formation during bonding. Asymmetric structure can separate electrical isolation and solder process to avoid interaction, which can prevent IMC formation during polymer curing. A well-bonded asymmetric structure can be achieved with submicron solder by 150 °C bonding for 15 min. The structure shows the potential for low temperature hybrid bonding technology in high-density three-dimensional (3D) integration.