PCB trace temperature?
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PCB trace temperature?

 
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Dennis Clark
Guest
Posted: Fri Dec 17, 2004 3:01 am    Post subject: PCB trace temperature? Reply with quote
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
--
============================================================================
* Dennis Clark dlc@frii.com www.techtoystoday.com *
* "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 *
============================================================================
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Spehro Pefhany
Guest
Posted: Fri Dec 17, 2004 4:42 am    Post subject: Re: PCB trace temperature? Reply with quote
On Fri, 17 Dec 2004 01:18:58 GMT, the renowned "Gary Pace"
<xxx@yyy.com> wrote:

Quote:
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.

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

Quote:
Much hotter on expensive substrates etc.

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


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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Alan Holt
Guest
Posted: Fri Dec 17, 2004 4:42 am    Post subject: Re: PCB trace temperature? Reply with quote
Will this help?

http://www.cooksonpwb.com/laminates/pdf/art_thermal.pdf
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Nicholas O. Lindan
Guest
Posted: Fri Dec 17, 2004 4:42 am    Post subject: Re: PCB trace temperature? Reply with quote
"Dorsai" <dorsai@mail.com> wrote
Quote:
Dennis Clark <dlc@io.frii.com> banged on the keyboard until producing

I've seen and used the trace temperature vs. current calculators
how hot can a trace get and still be OK on a board?

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

Quote:
Where does board damage occur

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

Quote:
and how hot are we "allowed" to get a trace?

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

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

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_.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/
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Gary Pace
Guest
Posted: Fri Dec 17, 2004 4:42 am    Post subject: Re: PCB trace temperature? Reply with quote
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.

"Dennis Clark" <dlc@io.frii.com> wrote in message
news:41c205d3$0$207$75868355@news.frii.net...
Quote:
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
--
============================================================================
* Dennis Clark dlc@frii.com www.techtoystoday.com
*
* "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003
*
============================================================================
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Dorsai
Guest
Posted: Fri Dec 17, 2004 4:42 am    Post subject: Re: PCB trace temperature? Reply with quote
Dennis Clark <dlc@io.frii.com> banged on the keyboard until producing
news:41c205d3$0$207$75868355@news.frii.net:

Quote:
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
--
========================================================================
====
* Dennis Clark dlc@frii.com
www.techtoystoday.com * * "Programming and Customizing the OOPic
Microcontroller" Mcgraw-Hill 2003 *
========================================================================
====


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

Hope this helps.

--
* * * * * * * * * * * * * * * * *
Dorsai - Author of Erotic Fiction
http://www.asstr.org/~Dorsai
* * * * * * * * * * * * * * * * *
If Bill Gates had a dime for every time Windows crashed...
Oh, wait a minute, he already does.
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Dennis Clark
Guest
Posted: Fri Dec 17, 2004 11:34 am    Post subject: Re: PCB trace temperature? Reply with quote
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
--
============================================================================
* Dennis Clark dlc@frii.com www.techtoystoday.com *
* "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 *
============================================================================
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