Novel flip-chip bonding technology for W-band interconnections using alternate lead-free solder bumps

A novel lead-free flip-chip technology for mounting high-speed compound semiconductor ICs, which have a relatively severe limitation regarding high-heat treatment, is presented. Solder bump interconnections of 0.95Sn-0.05Au were successfully fabricated by reflowing multilayer metal film at as low a temperature as 220/spl deg/C. The bumps were designed to have a diameter of 36 μm with a gap between the chip and the motherboard of 24 μm. The electrical characteristics of flip-chip-mounted coplanar waveguide chips were measured. The deterioration in reflection loss in the flip chip mounting was less than 3 dB for frequencies up to W-band.