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This paper was originally published in the proceedings of IPC APEX EXPO, Las Vegas, Nevada, February 2016. It won the Best Paper Award for the conference.
Currently there is no industry standard test method for measuring dielectric properties of circuit board materials at frequencies greater than about 10 GHz. Various materials vendors and test labs take different approaches to determine these properties. It is common for these different approaches to yield varying values of key properties like permittivity and loss tangent. The D-24C Task Group of IPC has developed this round robin program to assess these various methods from the “bottom up” to determine if standardized methods can be agreed upon to provide the industry with more accurate and valid characteristics of dielectrics used in high-frequency and high-speed applications.
Accurate values of relative permittivity (ɛr) and loss tangent (tan δ) are important characteristics for designers and fabricators in predicting electrical performance of circuits at high frequencies. The most common method for evaluating these parameters at frequencies up to 10 GHz is described in IPC-TM-650-184.108.40.206. This method is equivalent to ASTM-D-3380. This method excites a stripline resonator at both ends with the dielectric under test comprising most of the volume. The stripline is created by establishing intimate contact using a constant clamp force. This method is highly repeatable and is optimized for QA testing at a specific frequency. This method is not well suited for characterizing at frequencies higher than 10 GHz.
To read this entire article, which appeared in the July 2016 issue of The PCB Magazine, click here.