The CTI value indicates how resistant the PCB material is against environmental influences such as dirt and moisture. It is used to assess the proportionate resistance of the PCB base material and helps calculate the high-voltage isolation values between the tracks. It indicates the ability of the PCB substrate to withstand any breakdown between two tracks on the PCB surface. Comparative Tracking Index (CTI) for PCB material selectionĬomparative tracking index (CTI) defines the electrical voltage breakdown of the insulation material of PCB caused due to environmental conditions such as dirt and moisture. The constant high voltage whose comparative tracking index (CTI) is too low will lead to a breakdown of the surface. The breakdown of the surface may be caused due to a voltage spike. This can cause a slow breakdown of the surface of the insulating material between the conductors. The trace gets stemmed due to contamination of dust particles and moisture, resulting in current leakage from one or two conductors. How contamination affects the PCB surface? While dealing with high-voltage designs, it is essential for designers to know the difference between both creepage and clearance rules. Unlike clearance, which is measured in air, creepage is measured along the surface of the insulation material. Clearance and creepage distances between two PCB conductors. What are creepage and clearance distances?Ĭreepage is the shortest distance between conductor traces on a PCB along the surface of the insulation material while clearance is defined as the minimum distance through the air (line of sight) between two conductor traces. The distance between the two PCB traces is measured by various methods and calculations, keeping the standards for clearance and creepage in mind. It is difficult to derive a single solution to specify minimum spacing for multiple applications. Factors such as voltage, application, and the type of PCB assembly play a key role in determining the minimum PCB line spacing requirements. It is defined in terms of creepage and clearance distances.
The minimum line spacing between PCB components and other traces is the distance required to withstand a given voltage. What is the minimum PCB line/trace spacing? Trace width and spacing based on Copper for inner and outer PCB layers. Trace width and spacing which can be manufactured are given in the table. Sierra Circuits has developed certain standards based on the copper weight that mention required PCB line spacing for proper operation. These rules help to find ways for implementing precise circuit formation and reducing overall product size.
The PCB line spacing considerations have become a primary concern for manufacturers as high-voltage circuits require additional rules to form increased electrical clearances and isolation for operator safety. With miniaturization, it is possible to merge multiple boards, which also allows the designer to utilize mixed technologies, including analog, digital, and RF circuits. Earlier, the use of high-voltage boards as a separate board was a common practice in a multi-board system. Most of the electronic circuits require a compact PCB design, whether it is your smartphone or handheld medical imaging systems. The shifting trend towards miniaturization of electronic circuitry poses substantial challenges to the designer, specifically in hybrid technology that includes high-voltage circuits. This process helps to find any issues which may come up in the future during the operation due to environmental conditions or high voltages. To confirm that the board is designed as per the safety standard, one needs to test it in a lab environment using test equipment. These standards are designed considering the safety of human beings operating the product and other equipment in the vicinity.Ī designer will need to have a thorough understanding of parameters such as insulation resistance of dielectric, dielectric breakdown voltage, board material, leakage current, clearance and creepage, and tracking and operating conditions such as humidity and moisture altitude. Following these IPC standards ensures that the final product is safe and functional. Creepage and clearance distances of the traces become important at high voltages.ĭesigning a high-voltage circuit board requires good knowledge of international safety standards and regulations such as IPC 2221A and UL 60950-1. In high-density interconnect PCBs, maintaining a minimum line spacing between traces is quite a challenging task. Voltages above these levels are considered hazardous, and that is why these designs are regarded as high voltage. The PCB line spacing for creepage and clearance becomes an important factor from a product safety viewpoint when the standard operating voltage is above 30VAC or 60VDC.