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                


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                Dave Hoover              (408) 728-6677
                Senior Process Engineer  (408) 728-1728 Fax
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______________________________ 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