Comparison of CTI value, grade, model and test of PCB

The leakage tracking resistance of CCL is usually expressed by the comparative tracking index (CTI). Among many properties of copper clad laminate (CCL for short), the resistance to electrIC leakage tracking, as an important safety and reliability index, has been paid more and more attention by PCB designers and PCB manufacturers.

CTI value is tested according to IEC-112 Standard Method Test Method for Comparative Leakage Traceability Index of Substrates, printed boards and Printed Board Assemblies. It refers to the highest voltage value (V) that the substrate surface withstands 50 drops of 0.1% ammonium chloride aqueous solution without forming leakage traces. According to the CTI level of insulating materials, UL and IEC in the United States divide them into 6 grades and 4 grades, as shown in Table 1. CTI ≥ 600 is the highest grade. Copper clad laminate with low CTI value is easy to generate leakage MARKs when it is used for a long time in harsh environments such as high voltage, high temperature, humidity and dirt. Generally, the CTI of ordinary paper based copper clad laminate (XPC, FR-1, etc.) is ≤ 150, and the CTI of ordinary composite based copper clad laminate (CEM-1, CEM-3) and ordinary glass fiber cloth based copper clad laminate (FR-4) is 175~225, which can not meet the requirements for higher safety of electronic and electrical products. The IEC-950 standard also specifies the relationship between the CTI of the copper clad plate and the working voltage of the printed circuit board, the minimum creepage distance (minimum creepage distance). The copper clad plate with high CTI is not only suitable for use in high pollution and high voltage situations, but also very suitable for making high-density printed circuit boards. Compared with ordinary copper clad plate, The wire spacing of the printed circuit board made of the former can be allowed to be SMAller.

Tracking of electric leakage: the process of gradually forming a conductive path on the surface of solid insulating materials under the combined action of electric field and electrolyte.

Comparative Tracking Index (CTI): the highest voltage value of the material surface that can withstand 50 drops of electrolyte (0.1% ammonium chloride aqueous solution) without forming a leakage trace, unit: V.

Proof Tracking Index (PTI): the withstand voltage value of the material surface that can withstand 50 drops of electrolyte without forming leakage traces, expressed in V.

The improvement of plate CTI mainly starts from the resin to minimize the genes that are easy to carbonize and decompose in the molecular structure of the resin.

The above is about PCB manufacturers and PCB designers explaining CTI values, grades, models and test comparisons of PCB.