IPC TM-650 2.2.12.1

Abstract

This method provides a technique for determining the overall thickness of treated or untreated copper foils and for determining the profile factor on foils used for the manufacture of electrical grade laminates and multilayer circuit boards. The profile factor is the difference between the actual mechanical thickness of the foil and the calculated effective thickness based on the weight and density. This method will define the profile factor to about 0.00025 mm [0.01 mil], however, due to variations within the foil the use of values of increments less than 0.00125 mm [0.05 mil] is seldom necessary on treated foils. This method easily achieves this level of precision. A. Background: While for a sample with perfectly flat surfaces the theoretical and actual thickness would be equal, in practice virtually all foils used in such applications are manufactured with one rough surface to enhance adhesion to the substrate. Since this irregular surface reduces the effective electrical thickness of the substrate material and may affect other electrical and mechanical properties, it is often useful to quantify the degree of variation from the theoretical thickness. The technique described herein provides a measure of this variation, which on normal foil generally runs from 0.0025 to 0.025 mm [0.1 mil to 1 mil] and may represent over a 50% increase to the foils theoretical thickness. B. Applications: The effective minimum electrical thickness of a double-sided laminate may be readily determined by subtracting the overall mechanical thickness of the foil (both sides) from the overall thickness of the laminate at a particular location. The actual mechanical thickness of the base material may be estimated by subtracting the effective thickness of the copper foil from the overall mechanical laminate thickness. The Profile Factor may be used to monitor variations of incoming foils of a particular type without time consuming microsectioning. Comparison of different foil types may be made but judgment or performance should be made using the actual criteria of interest.