Synergistically enhanced Si₃N₄/Cu heterostructure bonding by laser surface modification

A bonding approach based on laser surface modification was developed to address the poor bonding between Si₃N₄ ceramic and Cu. The bonding mechanism in Si₃N₄/Cu heterogeneous composite structure fabricated by laser modification-assisted bonding is examined by means of scanning/transmission electron microscopy and thermodynamic analysis. In the bonding process under laser modification, atomic intermixing at the interface is confirmed, as a result of the enhanced diffusion assisted by the dissociation of Si₃N₄ ceramic by laser. The dissociating Si precipitations on the surface, as well as the formation of micro-pores interfacial structure, would be the key concept of the bonding, by which the seamless and robust heterointerfaces were created. By controlling the laser-modifying conditions, we can obtain a reliable heterostructure via the optimization of the trade-off of the surface structure and bonding strength, as determined by the laser-modified surface prior to bonding. The maximum structure depth and S ratio at the Si₃N₄ surface were produced at a laser power of 56 W, corresponding to the maximal shear strength of 15.26 MPa. It is believed that the further development of this bonding technology will advance power electronic substrate fabrication applied in high-power devices.