Optoelectronic and microwave characteristics of silver coated indium bumps for low temperature flip-chip applications

The effect of silver coating on pure indium bumps for low temperature and high speed flip-chip applications is presented with respect to optoelectronic and microwave characteristics. The current-voltage and light power-current characteristics of flipchip bonded vertical-cavity surface-emitting laser (VCSEL) arrays are improved by coating a thin silver layer of 0.2 (mu)m. The flip-chip assembled coplanar waveguide packages using silver coated bumps show the insertion loss is about 3.3 dB/cm at 20 GHz and the return loss is under 13 dB.