The CTI refers to Comparative Tracking Index of Electrical Insulating Materials. Reference documents are ASTM D3638 and test method of IEC 112. This CTI evaluates for low voltage (up to 600V) tracking resistance of an insulating material (laminate) in the presence of aqueous contaminates. You may contact someone at Glasteel Industrial Laminates. These guys appear to have considerable knowledge regarding material attributes necessary to withstand this type of environment. Hadco Printed Circuits Tech Center Two / Watsonville _/_/_/_/_/_/_/ _/_/_/_/ _/_/_/_/_/_/ _/_/_/_/_/_/ _/_/ _/ _/_/ _/_/ _/_/ _/ _/_/ _/_/ _/_/ _/_/_/_/ _/_/_/_/_/_/ _/_/_/_/_/_/ Dave Hoover (408) 728-6677 Senior Process Engineer (408) 728-1728 Fax [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Re: laminate with CTI of 400+ Author: [log in to unmask] at SMTPLINK-HADCO Date: 8/14/95 12:59 PM On 10 August 1995, Dougal Stewart wrote: >> We have a customer who has been asked by his designers to >> provide boards with a CTI of greater than 400 and a flammability >> rating of 94V-1. They also ask if standard FR4 will comply - at >> least I know the answer to that one. >> I am not sure what laminate will meet this requirement - FR3 >> has been suggested, but laminate suppliers always leave off >> the CTI when quoting electrical properties. Dougal, I sent a response Friday to the second-half of your post, but then came across this message that I hadn't read yet. I would like to add a little more to the post I made Friday to help make that information a little more useful. When you speak of CTI, I'm not exactly sure what is meant by that...I don't believe it's coefficient of thermal expansion (CTE) because the values are expressed in parts-per-million...and I can't think of why anyone would want a laminate that has a CTE of 400ppm. So I'm assuming what it is that you're asking for is laminate that has a glass transition temperature (Tg) of 400 degrees F. or above...that works out to 204.44 degrees celsius (400-32 x 5/9=degrees C.)...I'll list below the important properties of the materials I refered to in my last email: (Note: All temperatures are in degrees C.) Reinforcing Materials Dielectric CTE,ppm/degree C. Constant Material @ 1 MHz Long. Radial E-Glass 5.5 5.5 5.5