IPC TM-650 2.5.5.1B

Abstract

This method describes a technique to determine the volume permittivity (dielectric constant) and loss tangent (dissipation factor) of insulating materials at 1 MHz using contacting electrodes. Several techniques are described using the actual thickness of the material measured, the geometry of the test specimen and values for capacitance and conductance of material to calculate the desired properties. The accuracy of this test is inherently limited by the ability to measure thickness accurately, however, use of an estimated value for effective electrode area, stray capacitance and equipment tolerances may also result in significant errors. Use of the preferred method (A) on metal clad materials should reduce errors on permittivity to those associated with thickness measurement (which should be under 2% for material over .005 inch), and an error (under 1%) associated with the effective area determination. Values determined with method B, C or D can be 5% or more from the actual value. Except for thickness determination, errors increase with specimen thickness due to the reduction in actual specimen capacitance. Method B and C are intended for thin materials while Method D is primarily for materials over .020 inch. For more accurate measurement of permittivity (dielectric constant) the two fluid method1 easily permits measurement to better than 1%. For thin films under .005 inch, the two-fluid method IPC-TM-650, Method 2.5.5.3 is recommended.