Copper (Cu)-to-Cu bonding is an essential process for most advanced electronic devices, such as Cu-pillar joining in flip-chip packaging, through-silicon-via interconnections in three-dimensional integrated circuits, and die attachments in wide band-gap electronics. Here we propose an approach for fabricating face-centered cubic solid-solution joints without formation of intermetallic compounds by using a trace amount of gallium (Ga) and nickel (Ni) under-bump-metallurgy (UBM) for the reactive diffusion bonding at 300 °C. The formation of solid-solution joints involves interactions with the Ni[sbnd]Cu[sbnd]Ga mixture at the bonding interface. A shear-strength of 43.5 MPa was achieved in the as-bonded joint due to the formation of grains across the bonding interface, while it does not degrade after prolonged post-annealing at 300 °C for 200 h. Instead, an even stronger joint with a shear-strength of 48.2 MPa was obtained. We demonstrate the fabrication of strong, thermally stable Cu-to-Cu joints using transient molten Ga and Ni UBM.
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry