Electrical characterization of fine-pitch compliant bumps

The electrical characterization of fine-pitch compliant Au bumps is investigated in this study. Compliant Au bumps of 20 microns pitch were fabricated on a glass substrate for chip-on-glass application. Kelvin probes are fabricated and employed to measure the bump resistance. The resistance ranges from 1.0 to 4.5 ohms, depending on process parameters. Current-carrying capability for these bumps is examined. Electromigration test is performed and it is found that the failure occurs in the wiring Al line on the glass substrate, indicating that the Au bumps have high electromigration resistance. The bump resistance is also measured during thermal cycling from 30 to 100°C, and the resistance increases less than 50% after 6 cycles. Aging test is also carried out at 60°C and 40 mA, and the failure time is 561 hours.