Quote often it is specified exactly the opposite of what you are proposing
(but it probably doesn't matter unless you are doing "heavy copper" designs)

The plating thickness is already implied by calling out your acceptability
requirements, which means you are probably looking at the minimum hole wall
thickness as the driving factor, and the surface plating just ends up being
whatever it ends up being. So the only real variable is what starting
copper they need to use for the surface layers, and that is what is usually
called out. Adding a final thickness to the requirements for the surface
layer is probably not going to help much, unless your design constraints
need a specific minimum and you want to inspect for it.

Where it might matter is where you are doing high currents, heavy copper
designs. If you really need 8oz final thickness, it will really make a
difference if you try to start with two ounce and plate up that much (which
means you want your hole walls to be really thick plating too, so you need
to over-size your holes and clearances) or if you start with 6 oz and plate
up, (which brings it more into the realm of traditional processing, but
thinner hole walls).

hope that helps,
Jack


.
On Wed, Dec 7, 2011 at 1:17 PM, Pete <[log in to unmask]> wrote:

> I am currently reviewing and updating our fabrication notes, and a thought
> just struck me.
>
> Currently, we specify base foil weight, plated to a minumum final weight.
>
> I'm wondering if there really is a reason to specify anything but a final
> weight?  I have gotten calls in the past, vendors asking to change the foil
> weight fo their etching process allowances.  My first thought was to spec
> 1/8 oz. minimum, plated to n/n oz. minimum finished, giving them freedom to
> use whatever is best.  But now I'm thinking, do I even care what foil
> weight they start with?
>
> Does anyone have an idea why it might matter?
>
> Pete
>
>
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