PCB trace temperature?

Dennis Clark banged on the keyboard until producing news:41c205d3$0$207$ snipped-for-privacy@news.frii.net:

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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If Bill Gates had a dime for every time Windows crashed... 
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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.

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.

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

Best regards, Spehro Pefhany

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Will this help?

"Dorsai" wrote

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

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

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

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
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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         dlc@frii.com                www.techtoystoday.com   * 
* "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 *    
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