Yep, there is no thermal in the calculation.
Make sure you are using the "Internal" setting when calculating the
current.
The value provided by a calculator is probably _quite_ conservative,
considering you have a plane "heatsinking" the spokes of the thermal. I
don't have any evidence, but I would bet that since the calculator
formulas are based on a single trace, you would find their value derated
by as much as 50-60% when applied to a thermal relief.
Anybody have a better "feel" for this?
--
George Patrick
Tektronix, Inc.
Central Engineering, EDS Applications Support
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
* 503-627-5272 (voice) * 503-627-5587 (fax)
http://www.tektronix.com http://www.pcb-designer.com
"Off-Grid and Proud of it!"
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
David Baldwin
Sent: Tuesday, May 08, 2007 16:04
To: [log in to unmask]
Subject: Re: [DC] Current Capacity of Thermal Reliefs
George:
Nice calculator, good job. The via though is just a via,
correct? It doesn't have anything for thermals. Like Bill said, I
can add up the spokes and get the overall width and treat it like a
trace. Or I could just forget about the thermals and let the
assemblers deal with soldering the parts down, not the designers
problem right;-)
Thanks,
Dave
At 03:49 PM 5/8/2007, you wrote:
>http://www.pcb-designer.com/trace.html
>
>--
>George Patrick
>Tektronix, Inc.
>Central Engineering, EDS Applications Support
>P.O. Box 500, M/S 39-512
>Beaverton, OR 97077-0001
>* 503-627-5272 (voice) * 503-627-5587 (fax)
>http://www.tektronix.com http://www.pcb-designer.com
>
>"Off-Grid and Proud of it!"
>
>
>-----Original Message-----
>From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
>Brooks,Bill
>Sent: Tuesday, May 08, 2007 15:39
>To: [log in to unmask]
>Subject: Re: [DC] Current Capacity of Thermal Reliefs
>
>
>Dave,
>
>You will find the formulas for isothermal relief for through hole lands
>in
>the IPC-2222 section 9.1.2 Thermal Relief in Conductor Planes.
>
>Basically it tells you to use 60% of the land size as the 'thermal
>width'
>and then divide it up equally by however many ties you require. The gap
>between the pad and the plane can typically be near the same width as
>the
>web connection width unless you are dealing with some voltage spacing
to
>another conductor which is a different matter all together.
>
>Regarding the current... if you have four .025 in. wide ties to a land,
>you
>would add them together to be equivalent to a .100 in. trace. Figure
out
>what the current carrying capacity is for a .100 in. trace of the
copper
>at
>the thickness you are using and you will be very close.
>
>Also the copper in the hole, if that is your application, can be
>calculated
>by converting the hole into a trace... just imagine splitting the
barrel
>of
>the hole longwise and flattening it out... you then have a sheet of
>copper
>equivalent to the width and length of the rectangle by the thickness of
>the
>plating in the hole... It's not really rocket science... but you do
have
>to
>use Pi in the calculation. :)
>
>I don't know of a calculator for that task but is sounds like a great
>project. Any ambitious programmers out there want to take it on?
>
>Best regards,
>
>Bill Brooks
>PCB Design Engineer, C.I.D.+
>Tel: (760)597-1500 Fax: (760)597-1510
>Datron World Communications, Inc.
>Vista, California
>
>
>-----Original Message-----
>From: David Baldwin [mailto:[log in to unmask]]
>Sent: Tuesday, May 08, 2007 2:35 PM
>To: [log in to unmask]
>Subject: [DC] Current Capacity of Thermal Reliefs
>
>Is there a calculator for the current carrying capacity of a
>component thermal relief?
>
>Thanks,
>
>Dave
>
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