FLIP-CHIP BONDING USING SUPERCONDUCTING SOLDER BUMP

Flip-chip bonding using superconducting solder bumps consists of two t echnologies: acid-free thermosonic compression ball bonding and face-d own bonding of the chip on the substrate by means of thermosonic compr ession at 373 K. A superconducting test chip with 68 bumps formed on N b/Pd film pads was bonded on a ceramic substrate. The maximum shear st rength of a single solder bump for the Nb/Pd films was found to be 26. 5 MPa, which was about 3 times higher than that obtained for Nb/Au him pads. The flip-chip module did not undergo catastrophic failures in e ither prototype design or material combination during 20 thermal cycli ngs between 4.2 K and 273 K. Electrical check tests at 4.2 K before an d after the thermal cyclings suggest that the present superconducting solder bump can be put into practical use for superconducting IC chip connection.