Hi all,

My experience has been that over about 100C the PCB (FR4) will discolor
over time and a lot of people do not like this!  Below 100C it seems to
be pretty goo with remarkably good adhesion of the copper to the
fibreglass.  Danny's comment is very valid - other components may not
like the high temperatures, plastic capacitors are not good either.
Usually traces that are that hot will have too much voltage drop across
them for most applications.  What happens if a fault (slip with probe or
similar) occurs?  Pop!  you have a nasty repair to do, I think.

Cheers, Hugh.

-----Original Message-----
From: Danny Bishop [mailto:[EMAIL PROTECTED]] 
Sent: Thursday, July 18, 2002 11:21 AM
To: 'Protel EDA Forum'
Subject: Re: [PEDA] 90 degree C?


hi

Basically FR4 should run up to 130degC, and your semiconductor can most
likely handle this temperature (but need to assess the reliability based
on the manufacturers rating and your derating req's). I would consider
thermal transients that can cause

The biggest problem I have had is the conduction across the PCB to other
components that can't handle these temperatures, a bipolar electrolytic
cap was my biggest concern. Also need to consider that at these
temperatures semiconductors have very different parameters, which will
complicate your design.

cheers

> -----Original Message-----
> From: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED]]On
> Behalf Of Jon Elson
> Sent: Thursday, 18 July 2002 8:07 AM
> To: Protel EDA Forum
> Subject: Re: [PEDA] 90 degree C?
>
>
> Michael Biggs wrote:
>
> > Hi all,
> >         Anyone run very hot traces @ like 90 degree C on
> there PWBs and or
> > use surface mount heat sink around the component( like a D-PAK)? 
> > Thanks for any response. I know this is a Protel questions group but

> > everyone seem
> knowledgeable in
> > design layout.
>
> I would assume that over a fairly short time the epoxy holding the 
> copper to the laminate would deteriorate, and the foil would lift off
> the board due to
> the thermal mismatch.  Some cycles of this might cause the
> foil to crack.
>
> I'm pretty sure a recognized safety testing lab would not approve any 
> device designed that way, if they discovered that is what you were 
> doing.
>
> Using a foil area to draw heat away from a heat source is pretty 
> common practice.  I imagine some people let their junctions run at
> 90 C, but I
> suspect the heat sink surface runs cooler than that.
>
> Jon
>
>
> **************************************************************
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> * Tracking #: E17219ECD51CDF48ACDF490FB27BDC77807B5A59
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