T/R Modules for Automated Assembly and Test Using Flip Chip and LTCC Packaging

This paper discusses the use of Low Temperature Cofired Ceramic (LTCC) packages and flip chip MMICs designed for automated assembly and test in T/R module applications. The reduction of the number of components, elimination of assembly steps, and the automated assembly and test of T/R modules that is thus achieved is also discussed. The use of multi-layer LTCC allows dense packaging. DC lines can be routed on multiple layers, and different types of RF configurations ¿ microstrip, stripline, and coplanar waveguide (CPW) ¿ can be realized on the same substrate. RF cross-overs with high isolation between lines can be achieved by means of buried transmission lines and ground planes. The substrate can be fabricated to be used in a conventional metal housing, or the substrate can be fabricated to function as both the substrate and housing at the same time. With the latter method, walls are built up using the ceramic tape. These walls can also contain circuitry, allowing for higher packaging density. Flipped GaAs chips utilizing CPW structures eliminate costly backside processing of MMIC wafers. Flip chips used in T/R modules are thicker than conventional chips, 25 mils vs. 4 mils, thus providing a much more robust chip for handling by high speed automated assembly equipment. The use of flip chips simplifies the assembly procedure by eliminating wire bonds, since the solder attachment of the flip chip to the substrate serves as both die attach and interconnect.