IPC TM-650 2.5.5.6

Abstract

The full sheet resonance (FSR) method is a means for non-destructive measurement of relative permittivity (K') of clad laminates at microwave frequencies. <br>Applicability: The FSR method is applicable to rectangular laminates consisting of dielectric substrate clad with metal foil on both sides, or clad with thick metal on one side and metal foil on the other. Unlike methods using stripline or microstrip resonator elements, the FSR method is sensitive to specimen permittivity only in the Z direction of the material under test. It is useful for comparing the permittivity of clad panels of essentially the same dimensions. No means is provided in this method to account for error caused by fringing capacitance at the open edges of the parallel plate waveguide formed by the metal cladding. For a series of panels of the same length, width, dielectric thickness, and nominal permittivity and measured by the same selection of resonant modes, the fringing errors will be essentially constant and the permittivity values obtained should correlate with performance in stripline or microstrip circuit boards fabricated from the laminates tested. The method may be applied to full size clad laminates as manufactured and trimmed to nominal size or to smaller panels cut from such laminates. <br>Limitations: While it is convenient to estimate the 1/Q or total D value for the specimen under test, this value will be a sum of dissipative losses in the dielectric, resistive losses in the conductors, and radiation losses from the open edges of the resonant cavity. The radiation losses are a large portion of the D value, so the FSR method is not very sensitive to the dissipation factor of the specimen. The FSR is not recommended for dissipation factor measurements. The method is not capable of providing useful information on the variation of K' within a panel.