RE: [SI-LIST] : via current carrying capacity

From: Larry Miller ([email protected])
Date: Thu Jan 25 2001 - 11:01:37 PST

I slipped a decimal in my example (early hour, I guess). Chris and I agree:

a 0.015" via would calculate out to: 3.14 * 15 * .01 = 500 mA.

Hope I didn't make anyone put in 10x the number of vias!

Larry Miller

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Heard, Chris
Sent: Thursday, January 25, 2001 8:03 AM
To: 'Larry Miller'; 'Sean Murray'; [email protected]
Subject: RE: [SI-LIST] : via current carrying capacity

This is a classic "rule of thumb" issue. I've been using 3 amps per 0.040"
pth for years. However, the use of thermal reliefs and the number of planes
connecting to the via make all the difference.

Attach 5 or 6 ground planes using 0.020" wide spokes (0.015" long) on a
thermal relief and you can pump over 15A easily into a 0.070" dia hole.

Chris

-----Original Message-----
From: Larry Miller [mailto:[email protected]om]
Sent: Thursday, January 25, 2001 10:37 AM
To: 'Sean Murray'; [email protected]
Subject: RE: [SI-LIST] : via current carrying capacity

I generally use 10 to 30 mA per .001" x .001" of cross-section. You can
calculate the cross-section approximately by calculating the circumference x
plating thickness. I usually assume about 0.001" plating thickness, so this
simplifies to PI * diameter (in mils) * .01. I got this years ago from wire
carrying capacity current densities. They don't seem to blow up.

For reference, a 0.015" via would calculate out to: 3.14 * 15 * .01 = 50 mA.

What do others get/use?

Larry Miller

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Sean Murray
Sent: Thursday, January 25, 2001 6:20 AM
To: [email protected]
Subject: [SI-LIST] : via current carrying capacity

What's the formula to calculate the current carrying capacity of a via?

Sean Murray
General Manager

M&M Specialties, Inc.
1236 W. Southern Ave. #106
Tempe, AZ 85282
1-800-892-8760 x105

www.mmspec.com

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