Surface insulation resistance is a reliability metric that quantifies how well the non-conductive substrate isolates adjacent conductors. It is measured under high temperature and humidity to detect ionic contamination, flux residues, or moisture absorption that could cause leakage currents or dendritic growth.
Heard on the job
The tested batch failed the SIR test after environmental cycling, pointing to active flux residue left on the board.
Related terms
CAF
Conductive anodic filament: copper growth along glass fibers inside a board that shorts holes under voltage.
Coupon
Small test pattern built on the production panel and measured or sectioned to prove the boards meet spec.
Clearance
Minimum spacing between copper features of different nets, or between copper and the board edge or holes.