Bill:
Thanks for the feedback.
PCB Libraries has a lot of good documentation (which is to IPC
Standards) on the thermal size, as well as a through hole calculator
to calculate it for you. It's all good stuff.
The formula for calculating the via circumference is 2 x pi (3.14159) x r}.
The main issue is when I need to handle 30 amps, and I have to have a
thermal relief, how do I know it can handle the current required? I
can add up the spokes and say I have a 200 mil (oops, 5.08mm) wide
trace, but since it only is 0.010" (.25mm) long, then there should be
a factor which states it can handle more current due to the extremely
short distance. I did exactly what you said, but how can I be
sure? I'm taking my best educated experience and I believe
everything is fine, but a tool to confirm things would be nice.
Thanks,
Dave
At 03:39 PM 5/8/2007, Brooks,Bill wrote:
>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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