Confused with Saturn tool kit results

May 11, 2020 10 Replies
J

I have a board on an aluminum plate manufactured by PCBCart. Apparently, the "board" is less than 1 mil thick (because it is actually Kapton film?) while the aluminum plate to which it is firmly attached is a bit less than 32 mils.



My question is why does the Saturn app show less current carrying capacity in 10 mil traces than with a standard PCB? It gives .77A capability (with the default parameters) if I use 1 mil PCB thickness and 1 mil distance to the plane. But, if I change the PCB thickness to



32 mils, the current carrying capacity is ~1.3A.

With a heat sink that close to the traces, this seems intuitively wrong.



What gives?



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L

mandag den 11. maj 2020 kl. 20.43.11 UTC+2 skrev John S:

does it know that the back side is aluminium? otherwise it might make sense the increased spreading resistance of a thinner pcb will result in less current carrying capacity

afaik most of the aluminium PCBs are just thin FR4 bonded to aluminium

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J

Interesting. Got a screen shot?

John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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J

The ones in LED lamps are white. Almost like paint.

John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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L

mandag den 11. maj 2020 kl. 21.31.11 UTC+2 skrev John Larkin:

isn't that just the solder mask?

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J

I can grab the Saturn image and send it to you via email. I have no other way to share at the moment. Is that acceptable?

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J

Sent to what I think is your email address.

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T

That sounds like it's based on IPC-2152. Or god forbid, -2221B. Neither has any understanding of metal core PCBs, based only on glass fiber laminate of typical dimensions.

Needless to say, the allowable heat density is orders of magnitude greater in your situation. Worry more about overall power dissipation, and voltage drop. Both of which can be easily calculated from trace dimensions and the resistivity of copper.

Tim

Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
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J

Yup. The Conductor Properties tab does some goofy things.

John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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J

Yes. It says so. It does some things backwards.

John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
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J

I checked an LED board. It looks like very thin FT4 on aluminum, with white solder mask.

John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
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