Surface Insulation Resistance (SIR) is the electrical surface resistance of an insulating surface. The SIR value, also known as insulation resistance (IR), is used in the manufacture of printed circuit boards and is a measure of the cleanliness of the surface of the printed circuit board
. It is measured between two or more adjacent traces or connection pads, and is expressed in ohms
or mega-ohms and giga-ohms. The SIR value can change due to contamination, material changes, corrosion and ionization.leakage currents are measured between several parallel conductor tracks. For this purpose, different voltages are applied to the traces.