Surface Insulation Resistance Testing (SIR Testing)

National Technical Systems (NTS)

Surface Insulation Resistance (SIR), as defined by IPC, is the electrical resistance of an insulating material between a pair of contacts, conductors, or grounding devices that is determined under specified environmental and electrical conditions.

In respect to the world of printed circuit boards (PCBs) and printed circuit assemblies (PCAs), SIR testing—also commonly referred to as Temperature Humidity Bias (THB) testing—is used to evaluate a product’s or a process’ ability to resist “failure” by means of current leakage or an electrical short (i.e., dendritic growth). SIR testing is typically performed under elevated temperature and humidity conditions—such as 85°C/85% RH and 40°C/90%—with periodic insulation resistance (IR) measurements obtained.