PCB trace temperature?

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Hi all,

  I've seen and used the trace temperature vs. current calculators and
seen lots of information on calculating trace temps.  However, I can't
find any information about just how hot you can let a trace get.  I
know that copper melts at about 1100 deg. C, I'm pretty sure that the
board will be damaged before that,...  So, how hot can a trace get and
still be OK on a board?  Where does board damage occur and how hot are
we "allowed" to get a trace?

regards,
DLC
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* Dennis Clark         snipped-for-privacy@frii.com                www.techtoystoday.com   *
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Re: PCB trace temperature?

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Basic rule of thumb: if you can't stand to touch it with your thumb, it's
TOO DAMN HOT.

Hope this helps.

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Re: PCB trace temperature?
 
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Unless you are using a circuit board as a heater, the goal is to keep
the temperature rise as close to zilch as possible.

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Depends on the board: Paper phenolic, fibre glass, kapton, etc.. UL
is the place to look.

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Now that's a question for your lawyer to answer.

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This is, in general, a very good rule of thumb.  In water TDH is ~>115 F.
and is person and situation dependant.  But then in Kuwait it gets to 130F
in the shade.

Transformers sometimes run very hot.  A class H transformer runs at 180C
(measured by the change in winding resistance) - This is arc-welder and
military you-don't-want-know territory.

For a given temperature very small parts will feel cooler, large parts
hotter, water the hottest.

Fahrenheit 451 (~230C) is _way too hot_.

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Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer:  Electronics; Informatics; Photonics.
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Re: PCB trace temperature?
100C on FR4 with good bonding between the copper and substrate. This will
probably discolour the board over a couple of years. 80C if you're being
conservative.

Much hotter on expensive substrates etc.

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Re: PCB trace temperature?
On Fri, 17 Dec 2004 01:18:58 GMT, the renowned "Gary Pace"

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Keep in mind that the temperature rise is above ambient temperature in
the area where the traces are. If it's 45C outside the housing and
65C inside the housing, then that's your base temperature. If you
want to limit it to 80C then you can't have any more than 15C rise.

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Yes, some of the expensive substrates are MUCH better than FR4.


Best regards,
Spehro Pefhany
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Re: PCB trace temperature?
Will this help?

http://www.cooksonpwb.com/laminates/pdf/art_thermal.pdf



Re: PCB trace temperature?
Thanks everyone, all food for thought and most helpful.  Can someone give
me the UL spec to consider for FR4 boards?  I can look up the document if
someone can give me the number.

BTW, that art_thermal.pdf was indeed informative.  I'll check up on the
UL-94 spec, which may be that UL document that I'm looking for, but
regardless, knowing the FR4 delaminates at 140 C is at least a Starting
point in my investigations.

Regards,
DLC
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* Dennis Clark         snipped-for-privacy@frii.com                www.techtoystoday.com   *
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