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What is Comparative Tracking Index(CTI)? |
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Here CTI is a quality item that refers to copper clad laminate which is widely used in home electrical appliance or other high-voltage(110V, 220V) electrical apparatus.It is a simulated conditon that the PCB is polluted in its working environment, which result in leakage or short-circuit at the track gap of the PCB surface, being accompanied by heat releasing and charring. |
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The way of experiment is that continous 50 drops of 0.1% ammonium chloride solution are dropped between two points on the PCB surface,30 seconds per drop,turning on high voltage AC current to do the test. Firstly trying 300V to generate 1A current. There's ammonium chloride solution on the surface, so after current is switched on it will produce resistance who also bring out heat, then the solution is slowly evaporated. 2nd drop is on and till to 50 drops to see if the PCB has leakage or not. Once the PCB has 0.1A creepage and exceeds 0.5 seconds, it's judged Failure. |
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The quality of CTI of laminate refers to the externally applied voltage value and without failure of 50 drops. If abovementioned 300V passed, we can increase the voltage to 400V, 500V or 600V till to the high value before failure, that is the data of the laminite CTI. |
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Bicheng offers high CTI PCB's (high CTI 600V FR-4 and aluminum backed material) which is working in such harsh environment of high voltage, filth and humidity. |
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IEC 112 standard has 3 degrees as follows |
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| Comparative Tracking Index (in Volts) |
Class |
| 600 <= CTI |
I |
| 400 <= CTI < 600 |
II |
| 175 <= CTI < 400 |
IIIA |
| 100 <= CTI < 175 |
IIIB |
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As per the standard of IEC,the smaller a substrate of CTI grade, the better resistance to tracking. Normal FR-4 ranges 175-225V |
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