1. Not sure what's meant except that the hole wall copper is thinner than
the external copper.
2. .001" would be electroplated (total) copper as electroless is typically
less than .0001" thick
3. Tin-lead and gold are negligible conductors relative to copper, due to
the product of their cross-sectional area (esp. for Au) and their
conductance (esp. for Sn-Pb) being so much lower

Timothy Reeves
QA Manager/Process Engineer
ECD Circuit Board Division
13626 S. Freeman Road
Mulino, OR 97042
(800) 228-8198    Fax (503) 829-5482


-----Original Message-----
From: Lum Wee Mei [mailto:[log in to unmask]]
Sent: Thursday, August 10, 2000 10:59 PM
Subject: Via current current capacity


I came across this paragraph in Printed Circuit Handbook by Clyde
Coombs, Jr stating :

"Consider a 0.04" diameter hole plated to a 2oz internal poew plane with
0.001" minimum copper in the hole. The copper hole wall is equivalent to
0.04 x 0.001 x pi = 125 x 10exp -6 sq. in.
"The copper plating of the hole wall is the smallest conductor in the
path and for purposes of calculation in current-carrying capacity,
consider it an internal conductor of a multilayer."

My questions are :
1. Why consider the copper plating of the hole wall as internal layer
and not external?
2. Is the copper plating here which is 0.001" refers to only the
electroless copper thickness or inclusive of copper plating?
3. Why is the tin-lead plating or gold plating never be considered when
calculating current-carrying capacity for component hole or via?

Hope to learn more from your experts out there.
Regards.

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