PCB Board Design Considerations For Impedance Control And Optimal Signal Integrity In High Speed Digital And RF Systems

By George Qinghua Kang and Michael T. Smith, Arlon, Inc., Materials for Electronics Division

Electrical phase stability and impedance control have become increasingly important in high frequency applications, while trends in electronic industry continue to drive high-speed digital, RF and microwave systems for high-density integration, high system performance and high power operations over a wide range of operating temperatures. Ideal dielectric substrate materials for these challenging applications are highly expected to posses not only desirable electrical properties, such as dielectric temperature stability, dielectric constant consistency and low loss tangent, but also excellent thermal and mechanical properties, such as thin cores for multilayer capability, dimensional stability and low rates of thermal expansion, excellent thickness tolerance and high thermal conductivity (W/m·K). There has been increased focus on material technology development with high frequency substrates to create materials that are dimensionally stable and temperature stable (electrically and mechanically), maintain excellent tolerances (thickness and dielectric constant) and have improved thermal properties over wider temperature swings. Meanwhile, for practical considerations and sometimes for cost concerns over the premium for advanced board materials, robust designs and fabrication processes are also expected to have the capability to accommodate various tolerances and imperfections of board materials as well as PCB processing variations.