High Resolution Coplanar Structures on Multilayer LTCC for Applications up to 40 GHz

The announcement of photoimageable metallisation in conjunction with the conventional screen printing process supports the idea to develop passive components for multichip applications up to an estimated frequency limit of 40 GHz. This technique has been developed by DuPont and is called Fodel, which has been printed first in a postfired and later in a cofired process on the LTCC Green Tape 951. In the national supported “4M”-project, which is an abbreviation for multifunctional microand mm-wave modules, a 4x4-inch LTCC tile with 4 substrate layers and a great number of coplanar, microstrip and stripline test structures and circuits has been designed and fabricated. In the first technology run, the postfired test structures show higher fabrication tolerances, which result in a shift of the Fodel metal to the inner thickfilm layers and a higher shrinking than expected. In spite of these drawbacks a number of structures and circuits have been evaluated. In a second technology run, the same layout has been fabricated with a cofired Fodel metallisation. The new tiles show an improved alignment between inner and top layer as well as lower shrinking tolerances. Measured and simulated results from both technology runs will be demonstrated and evaluated. Beside the technology aspects, the focus of these investigations lies on the capability of simulation tools for multilayer circuits as well as on applications aspects for RF circuits up to 40 GHz.