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March 1999

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Subject:
From:
Robert Welch <[log in to unmask]>
Reply To:
Date:
Thu, 18 Mar 1999 15:09:05 -0500
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Anne,

Comparitive Tracking Index (CTI} is by definition the voltage at which 50
drops of a 0.1%  solution of ammonium chloride causes failure (ASTM D-3638).
The CTI is used to compare the performance of insulating materials, against
the formation of carbonneous tracks on the surface, under wet contaminated
conditions. From this value a material can be assigned a Perfomance Level
Catergorie (PLC)per UL 746A.  In which 175> is at least a PLC 3.  From this
you can go to EN 60 950?? to determine your minimum spacing at a given
voltage.  I had to read through all the specs for a customer shipping
product to the U.K. Believe you don't want to read them. To me, the
procedure seems as flakey as a 3 $ bill.  Even though there is a huge range
among like materials most fr4 runs from 200-400 volts. See your material
supplier or the materials yellow card under UL QMTS2.
Good luck and hope this helps.


Robert E. Welch
Process Specialist
Waytec Electronics Corp.
Phone 804-237-6391 ext. 138
Fax   804-237-3048

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Anne Ledger
> Sent: Thursday, March 18, 1999 10:21 AM
> To: [log in to unmask]
> Subject: [TN] Comparative Tracking Index?
>
>
> Good Morning TechNet,
>
> I have a fabrication drawing with a note with the following note.
>
> Material:  .062 laminated glass (woven fabric) base, epoxy resin, Flame
> retardent, FR4.
>               copper clad 2 oz./sq ft.  Laminate must be certified to
> have a minimum comparative
>               tracking index of 175.  Microsection demonstrating
> compliance with copper weight,
>               dielectric spacing, line width and use of CTI 175 or
> better material shall be shipped
>               with each lot.
>
> I am at a loss on the CTI 175 stuff.  I have reviewed IPC 4101 and don't
> find a reference.  I have
> placed a call to our material supplier but no response yet.  The TechNet
> seems much faster.
> Can anyone provide me with a clue?  Thanks in advance for the help.
>
> Anne Ledger
> EMDS, Inc.
> [log in to unmask]
>
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