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A flip-chip interconnection technology using novel lead-free solder microbumps with a balling temperature as low as 220 °C is presented. Controllability of newly developed Sn0.95Au0.05 microbumps has been examined experimentally. By varying the bump volume and the diameter of the wettable bump electrodes, Sn0.95Au0.05 microbumps with heights from 11 μm to 37 μm were successfully fabricated with a standard deviation of 1.5 μm. The deviation of on-chip CPW impedance from 50 Ω was lower than 10% for nonmetallization motherboard. The smaller bumps exhibited a better performance since the degradation of reflection properties is ascribed to the bump capacitance, which was estimated 10-20 fF. Because of high process yield and good performance, the flip-chip bonding using Sn0.95Au0.05 microbumps of the order of 20 μm in height may be advantageous for W-band interconnection of InP- or GaAs-based devices. [ABSTRACT FROM PUBLISHER]

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°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. [ABSTRACT FROM PUBLISHER]