Thick-film fabrication yields thin-film performance

INCREASED use of microwave hybrid circuits for wireless communication syste ms has led to a search for new technologies offering advanced circuit funct ions at low cost. Characteristics such as high electrical conductivity, fin e-line and space resolution, well-defined conductor edges, nearly vertical walls, and smooth upper surfaces are essential for achieving low losses in microwave structures at frequencies above 1 GHz.(1,2,3) Until now, thin-fil m technology has dominated the microwave market because traditional thick f ilm technology yielded poor line resolution and high losses, But rapid deve lopment in novel thick-film materials and advanced thick-film circuit-patte rning techniques has brought improvements that callow current thick-film te chnology to reach beyond its previous limitations, Advanced thick-film tech niques such as photolithography over fired layer, and photoimaging over pho tosensitive dried layer, yield conductor strips with resolution and edge de finition comparable to thin-film technology, Thick-film technology allows d esigners to combine microwave and digital functions on common high-thermal- conductivity alumina substrates and to incorporate capacitors and laser-tri mmable thick-film resistors into the main microwave structures. The self-sm oothing tendency of thick films at the substrate interface permits the use of less-expensive, 96-percent alumina substrates, Additionally, thick-film technology provides significant advantages such as low cost and feasibility for mass production.