PCB trace temperature?

Question

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 snipped-for-privacy@frii.com
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"Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 * ============================================================================

Dorsai · Accepted Answer

Dennis Clark  banged on the keyboard until producingnews:41c205d3$0$207$ 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* * * * * * * * * * * * * * * * *If Bill Gates had a dime for every time Windows crashed...             Oh, wait a minute, he already does.

Gary Pace · Answer

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.

Spehro Pefhany · Answer

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

Alan Holt · Answer

Will this help?

Nicholas O. Lindan · Answer

"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_.

Dennis Clark · Answer

Thanks everyone, all food for thought and most helpful.  Can someone giveme 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 Startingpoint in my investigations.Regards,DLC-- ============================================================================* Dennis Clark                            * * "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 *    ============================================================================

PCB trace temperature?

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