A Two-Stage Process for Laser Prototyping of Microwave Circuits in LTCC Technology

An improved technique for laser prototyping of microwave circuits in low-temperature cofired ceramic (LTCC) technology is presented. This builds on the method of laser machining of conductor layers in unfired LTCC tapes. The proposed process presents the hybrid approach of circuit fabrication by employing both unfired and post fired laser machining of LTCC substrate, hence giving more flexibility of realizing multilayer components. This allows the low-tolerance microwave structures like couplers and filters to be fabricated on the outer layers because shrinkage uncertainty is no longer a problem. Track widths and gaps of 30 μm are demonstrated with an edge definition of ±2 μm. A stripline coupler and a four-layer spiral inductor is successfully fabricated using this technique to demonstrate the process. The improved process can produce high-precision microwave and millimeter-wave components on the outer layers and provides rapid system-in-package prototyping for research and development.