What is Comparative Tracking Index (CTI)
The Comparative Tracking Index (CTI) is a quantitative metric that measures the resistance of a material’s insulation to track formation. It evaluates the ability of a PCB surface to resist tracking, which is the breakdown of the insulation material between conductive surface elements like traces and pads. The CTI is determined through a specific test called the comparative tracking index test, where a conductive liquid is applied to the PCB surface and subjected to a high voltage. This liquid simulates the presence of contaminants that can cause tracking, such as moisture or other impurities.
During the CTI test, the voltage is gradually increased until tracking occurs. The CTI value is then determined based on the voltage at which tracking is observed. A higher CTI value indicates better resistance to tracking, meaning that the material is less likely to form conductive paths and maintain its insulation properties.
The CTI value is expressed as a number, typically ranging from 0 to 600. Different materials will have different CTI values, allowing for comparison and selection of materials based on their ability to withstand the intended environment. The CTI value is particularly useful in determining the clearance distance and creepage requirements for PCB designs in high-voltage applications, ensuring electrical safety and reliable operation.