Dealloyed nanoporous Cu films on ceramic substrate for low temperature bonding

To realize low temperature thermocompression bonding for 3D packaging and integration is of great significance. This research focuses on Cu-Cu low temperature thermocompression bonding using nanoporous copper films (NPCf) as bonding layer. Cu-Zn alloy as the precursor alloy was fabricated on the ceramic substrate by means of heating-alloy method, then the precursor alloy was immersed into the dilute hydrochloric acid for selective corrosion. Three dimensional bi-continuous nanoporous copper film with ligaments and pores size of 25~65 nm were prepared on the substrate. Nanoindentor was used to study the mechanical properties of NPCf. The results show that the hardness and Young´s modulus of NPCf is far less than that of bulk copper material. Bonding experiments were conducted between two ceramic substrates with NPCf as bonding intermediate. Successful bonding were carried out under the conditions at temperature 250 °C and pressure 20 MPa for 2 h. From uniaxial tensile tests for different samples with and without NPCf structure, it can be found that bonded samples with NPCf have higher bonding strength up to 5 MPa.