Larry...
 
Damage and failure are two separate things. 'Damage' can happen each
time you cycle the temperature... the cumulative effects over time can
cause a 'failure' of the board material or plating. 
There are many different types of failures... each mode of failure may
have a different effect on the electrical circuit and or the base
material. 
Since FR4 is not really "FR4" anymore and each type of material is
specified by a 'material data sheet', you would first have to consult
the data sheet to see what environmental conditions the material you
want to test was designed to endure... See IPC-4101 if you have a copy
for a list of different 'FR4-like' materials for reference. 
 
Which failure mode are you concerned with? Under what conditions?
What specific material are you testing? 
How wide is the trace feature you are concerned with?  
How thick is the copper? 
Is it internal or external to the board material? 
What is the Tg and Td of the material?
Etc... etc...
It's impossible really to give you a complete and straight answer based
upon the information you have supplied. 
 
Best regards, 
 
 
Bill Brooks
PCB Design Engineer, C.I.D.+
DATRON World Communications, Inc.
"Performance you require - Value you expect"
http://www.dtwc.com <http://www.dtwc.com> 
Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510

<mailto:[log in to unmask]> 
________________________________

From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Pucket, Larry Lee
Sent: Monday, April 21, 2008 6:21 AM
To: [log in to unmask]
Subject: [DC]
 
I have a customer that is doing some trace analysis. He is wondering
what the acceptable trace temperature would be on an FR4 board before
damage would occur (or better yet, the board/trace would be
compromised)? Thanks in advance.
 
 
Larry L. Pucket
Dept. 2992
Sandia National Laboratories
P.O. Box 5800 MS 0628
Albuquerque, NM 87185-0628
phone:(505)844-1711  fax:(505)844-9044
email: [log in to unmask]
 
 
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