Re: [PROTEL EDA USERS]: Via size

[Abd ul-Rahman Lomax <marjan@vom.com>]

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One more comment.

At 04:48 PM 9/11/00 -0400, Hans wrote:
>Hi group,
>
>  I was wondering if there are any specific guidelines in setting the via
>size. The bigger the via, the more current can go through ... but the
>gain in cross-sectional area only goes up slightly with increasing
>diameters. Any thoughts on this?

What Hans said about the gain in area was not true. The copper 
cross-section of the via varies roughly with the diameter of the hole; 
double the hole and you double the copper cross-section. To be more exact, 
it could be said that doubling the hole size will almost double the 
cross-sectional area.

Given a via with hole diameter H and plating thickness in the hole T (the 
hole is drilled H + 2 * T and then plated):

the copper cross-sectional area A = PI*(H+2*T)^2 - PI*H^2 (this is the area 
defined by the outer circumference of the copper less the area of the hole 
itself, which has a rather high resistance.... :-); this simplifies to

A = PI*T*(H+T) or PI*H*T(1+T/H)

So if H >> T, A ~ PI*H*T, that is, the area approaches the circumference of 
the hole times the plating thickness.

And if H = 0, A = PI*T^2, which is the area of a circular plugged hole with 
radius T. (You have to use the first equation to avoid dividing by zero....)

marjan@vom.com
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433



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