Printed Circuit Board (PCB) Design Parameters
Many PCB manufacturers still use imperial or mixed imperial and metric units. In the USA imperial is still the preferred choice of units for almost all applications. Both metric and imperial units are quoted here, although some approximations are made between the two. The units are determined from values given in one unit of measure and converted using 25.4 mm = 1 inch conversion factor.
Laminate Material Properties
Values of relative dielectric for laminates can vary with the manufacturer. With FR4 it is dependent on the glass fibre to epoxy resin mix. A typical value of 4.7 is used ...