Comparison of flip chip and wire bond interconnections and the technology evaluation on 51 GHz transceiver modules

On test vehicles realized in flip chip and wire bond versions, RF-measurements up to 70 GHz had been performed. The evaluation of the results shows the superiority of the flip chip mounting technology. To demonstrate the gain on system performance, two 51 GHz transmitter/receiver modules were realized, one in flip chip and one in wire bond technology. In the flip chip version the low noise amplifier (LNA) and the transmitter chip are directly flip chip mounted on the back structure of a planar patch antenna. In the wire bond version the chips were mounted on one edge of the planar patch antenna to achieve shortest wire bond connections possible. RF-evaluations show the clear advantage of the flip chip version, where a system gain of more than 7 dB could be achieved in comparison to the wire bond version. Further advantages of flip chip mounting technology are a higher reproducibility and an enhanced flexibility for design and construction. In case of transceiver modules, this higher flexibility enables to reduce the length of the feedline drastically in the flip chip version by mounting the MMICs directly on the back structure of the planar patch antenna again leading to reduced losses. The technology used for flip chip assembling consists of a substrate bumping process by Au microplating and a Au/Au-thermocompression bonding process for mounting of the MMICs.