Comparative Tracking Index (CTI)

Comparative Tracking Index [CTI]. In printed circuit board fabrication, CTI is a measure of the ability of the laminate surface to withstand tracking [carbonneous tracks on the surface, under wet contaminated conditions] across two electrodes placed on the surface, when an electrolyte is dropped between them. It is a test of the bare laminate. Two specified methods are: IEC 112 and ASTM D 3638-85.

CTI is expressed as that voltage which causes tracking after 50 drops of 0.1 percent ammonium cloride solution have fallen on the material. The results of testing the nominal 3 mm thickness are considered representative of the material's performance in any thickness. CTI Range - Tracking Index Assigned PLC (in volts) 600 and greater 0 400 through 599 1 250 through 399 2 175 through 249 3 100 through 174 4 Less than 100 5

[NOTE: PLC=Performance Level Category]

Most laminate suppliers list CTI in their specification sheets. For instance, US suppliers of FR4 commonly give a CTI of 175 � 200. Although, a FR4 with a CTI of 400 is available. FR2 & FR3 have a CTI of 300, CEM1 has a 200 � 300v CTI. Some laminate suppliers that give 600+v CTI are: http://www.gilam.com/GIL_Products/mc3.htm http://www.coates-screen.com/ccp/prodinfo/flyers/Imagecure%20Flyer.pdf

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