Novel solid-state pressureless approach for Cu-embedded intermetallic interconnects at low temperature

A pressureless low-temperature Cu-embedded intermetallic joint for interconnects is fabricated using a Cu-based mixed paste containing different amounts of SAC305 (SAC) particles. The highest joint's shear strength reaches 24.2 MPa. The average of the shear strength is 19.2 (±4.3) MPa, which is also high for pressureless solid-state bonding. After a solid-state interdiffusion bonding process, the joint is composed of an intermetallic-compound (IMC) shell and the Cu core particles. TEM analysis indicates a coherent interface between the core and shell. The ductile Cu phase mixed with brittle IMC in the joint enhances its strength. This study validates that void fraction in the joints is not the sole factor that affects the joint's properties. A mathematical model proves that the IMC thickness and IMC interfacial areas make significant contributions for robust interconnects.