The two characteristic values Comparative TrackingIndex(CTI) and Proof Tracking Index( PTI) are concerned with tracking resistance. The two dimensionless characteristic values differ only slightly in their test procedure.
The ever-increasing packing density of printed circuit boards means that the structure of the tracks and their spacing from one another are constantly decreasing. Where standard traces were used in the past, we are now talking about fine conductors, ultra-fine conductors and micro-fine conductors with trace structures of less than 50 µm. The reduction of the spaces between the traces can lead to creepage currents. This is why creepage resistance, which is a measure of insulation strength, is an important parameter for the insulating material and thus for PCB development. The metric for this is the performance level category( PLC).
Both the CTI and PTI values are material-dependent and are largely determined by the moisture absorption of the insulating material. While the PTI value works with a specified test voltage of up to 600 V, the CTI index indicates the highest test voltage determined. The CTI values for insulating materials: polyethylene 600, polytetrafluoroethylene 600, polybutylene terephthalate 500 and phenolic resin 125.