trace peel wouldn't be my first (intuitive) concern. I'd be interested in 
what that specific "FR4" material is, it's max continuous op temp and 
whether the dielectric is decomposing/degrading.

dw

At 10:58 AM 9/18/2007, Croslin, Robert wrote:
>Dear 'Netters,
>
>We have a product used to measure on/off status on flat screen TV's that 
>was designed a few years ago.  Over time, with the newer, bigger TV's, 
>there is a much higher current draw than we'd envisioned way back 
>when.  So, as the devices cycle back through our repair depot, we're 
>making mods to upgrade them to handle these new TV's.  A problem we've 
>seen in testing is that the traces that handle the AC pass-through are now 
>getting quite warm.  We've measured the traces at 105*C at room 
>temperature.  The base is plain old FR4.  We haven't been able to get any 
>to fail in testing, but are concerned about the differential under load 
>possibly causing the trace to peel away from the FR4.  Our concern is 
>thermal cycling over time; could it cause the trace to lift?  If the trace 
>is hot but the board cool in a steady state condition, is there any risk there?
>
>Does anyone know of any specifications that would address this situation?
>
>Bob Croslin
>Nielsen Media Research
>
>
>
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