GHz flip chip interconnect experiments

The flip chip is recognized as the most reliable chip interconnect method and renders an extremely high production yield at very low cost. Furthermore, flip chip gives extraordinary electrical performance, which is vital at GHz frequencies. The flip-chip interconnect is based on three fundamental elements, bumps on a die, chip carrier and the method of joining a die to a carrier. These elements are interdependent, thus important to consider each in order to select the optimal flip-chip system for a specific application. The tentative use of an encapsulant is another consideration. Most obviously, the gold pad and conductor metallurgy of GaAs chips bring the need for alternate bumping methods. Two different joining schemes tentatively suitable for GaAs chip pad metallurgies were tested based on thermocompression joining. Bumps were applied to the chip carrier, a thin film substrate and were either plated gold cylinders or gold ball bond studs. Cross-sections, shear tests, and X-ray imaging were used to determine the joint quality.