80 Amps alone is not really meaningful - the temperature rise needs to 
be measured or calculated based upon the trace widths and copper 
weight. Then you can tell what termperature the product will reach in 
the environment and make a better estimate of the effects.

Blair

On Wed, 12 Nov 2008 09:24:45 -0600, Syed Ahmad 
<[log in to unmask]> wrote:

>Tg being the transition temperature where CTE (commonly designated 
as alpha
>1) shifts to a higher value, FR4 Tg is no longer 14 or 15 ppm past its 
Tg.
>The CTE past the Tg (alpha 2) should be listed on the material 
datasheet.
>Higher CTE will cause more reliability problems than a lower CTE 
depending
>on the operating temperature at a site or for the system. To determine 
the
>effect of Tg, operating temperature needs to be measured or 
simulated.
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Bryan Montney
>Sent: Tuesday, November 11, 2008 1:49 PM
>To: [log in to unmask]
>Subject: [TN] Tg specification
>
>I'm looking for a guideline or resource (IPC spec?) on how to select and
>specify the proper Tg for a given design? I'm not talking about process 
wise
>(Tg140 is acceptable in our lead-free processes), but design wise.
>For example, is Tg140 material sufficient for a board running 80amps 
through
>it and sitting in an enclosure on a hot summer day in Arizona?
>Also, I'm looking for how best to test the Tg robustness during 
production.
>Any help would be greatly appreciated.
>

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