Meaning
Measured against electrical potential drop per unit length along an insulating or semi-conductive surface, an electrical property quantifies a material resistance to surface current flow. Surface potential gradients drive leakage currents across substrate surfaces between adjacent high-voltage trace conductors. In printed circuit assemblies and electrostatic discharge protective packaging, surface resistance governs parasitic leakage currents and static charge dissipation rates.
The boundary of this property applies strictly to surface current paths and does not measure volumetric current transport through the bulk interior of the dielectric material.
Material Measurement
Concentric ring electrode fixtures apply calibrated test voltages across substrate surfaces to isolate surface leakage from bulk current paths. Standard test standards measure current flow across specified surface square areas, expressing results in ohms per square. Precision electrometers detect picoampere surface currents on clean dielectric substrates.
Environmental Impact
Ambient humidity severely lowers surface electrical resistance on unsealed printed circuit boards. Moisture absorption forms thin conductive water films across soldermask surfaces, accelerating electrochemical migration between biased copper traces. Conformal coatings seal board surfaces against moisture accumulation to maintain high insulation resistance under humid operating conditions.
Electrostatic Boundary
Static dissipative materials maintain surface resistance values between one megohm and one hundred gigohms per square.
