Investigation of optimized high-density flip-chip interconnect design including micro Au bumps for 3-D stacked LSI packaging

The high-speed signal transmission characteristics of high density flip-chip interconnect with micro Au bumps were investigated. A test element group device and substrate was designed and fabricated to measure the properties of the high density interconnect structure. The test chip and substrate had Cu wires patterned to create a controlled impedance coplanar waveguide (CPW) transmission line in order to test the highspeed signal transmission properties. The characteristic impedance and S-parameters (S₂₁, S₁₁) of the flip-chip bonded test chip and substrate was measured. 50-ohm CPWs with two micro bump joints and underfill were successfully fabricated. In this work we have presented a method for designing specific impedance and high frequency properties on Si substrates in the presence of underfill and flip-chip bonded circuits.