On behalf of Keith Larson, Circuit Technology, I would like to address your
following questions:


> -----Original Message-----
> From: DeVita, Mike [SMTP:[log in to unmask]]
> Sent: Tuesday, December 21, 1999 6:58 AM
> To:   [log in to unmask]
> Subject:      [DC] Plating limitations
>
> Happy Holidays,
> I am working on a backplane design that requires the ability to handle up
> to
> 50Amps. This brings to mind alot of questions.
>
> To handle that kind of current I need a trace with a width no less than
> .82"
> with 2oz material, or  .55" with 3oz material, with a 20 degree C
> temperature rise. [Dick Berger]   Either circuit width is acceptable,
> depending on the real estate you have available.
>
> 1) What are the ramifications of using 2 or 3oz copper current carrying
> external layers and 1 oz for internal signal layers ie warping, cost,
> manufacturability, hole plating issues. [Dick Berger]   We use both copper
> thickness in our products, however the thinner the copper, the better it
> etches in the fabrication of the board. 3 oz. and up will finish with a
> greater circuit undercut, after etch. The surface copper has no effect on
> the plated through hole. Regarding warpage; if the copper is kept balanced
> in the construction and equally distributed over the surfaces, you should
> have no problem. Cost impact; 2 oz.copper material (2/2) is 40% more
> expensive than 1 oz (1/1), however the material cost only represents
> 10-12% of the boards cost.
>
> 2) If I use the 2 external layers as planes with 1 or 1.5oz copper, I can
> double the heat disipation area (roughly) and half the current load per
> layer, but then I am concerned about current carrying capacity thru the
> plated holes. What is a minimum number of holes if there were 10 pins
> available at a diameter of .035 to carry the current ( 5 Amps per pin)?
        [Dick Berger]  A hole wall should be treaded as a circuit and the
cross sectional area of the copper calculated  to determine the circuit
width. We generally plate .001 min. in the of the hole, however we can plate
.0015 min in the hole's.

        Mike, if you would e-mail your fax number, I will fax you "conductor
resistance nomograph", which may be of some value to you.


> hanks for your feedback