Flip Chip Reliability of GaAs on Si Thinfilm Substrates Using AuSn Solder Bumps

An RF and reliability test vehicles compatible with 77 GHz radar sensors comprise a GaAs chip which was flip chip soldered to a silicon substrate having impedance controlled microstrip transmission lines produced by Cu/BCB/Au thinfilm. Daisy-chain and four-point-Kelvin tests structures were designed for monitoring of the electrical contact resistance of the flip chip solder joints. Temperature cycling tests with and without underfiller were performed and the integrity of solder interconnect was electrically measured after defined cycles. Mechanical shear tests and cross-sectioning revealed the different failure modes found in underfilled and non-underfilled test samples.