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Ed Current,

          Jack has replied quite effectively as have the other
          reply-eez on this copper thickness issue (Go Team!). The
          only statement I would like to assist Jack on here is the
          etching problems....

          The problem with any 'thick' Copper is the edge definition
          of the trace, but as long as you have loose finished trace
          width requirements when fabbing (say....+/-.006") this will
          allow the fab shop some breathing room as far as undercut
          goes.

                ________________________
               / \                    / \
                  |    trace         |
                 /                    \
          -----/------------------------\------
                    under-cut !

          The other statement that Jack made was that shops add dots
          to allow for even etching.....I think that he was referring
          to "Plating Robbers".  What these Dudes do is to even up the
          plating process....not the etching process.

          Etching is fairly even no matter what densities of copper
          you have across the board.

          -BBBUUUUTTTT ......

          What is definately a problem is one side of your board being
          all Plane, and the other being (wordt case..)  1 - 8 mil
          trace running for 1" in length.
          The Plating current draw in the tank increases as copper
          propegates to the heavier copper area, while that li'l ole 8
          mil trace gets fried completely off the board with about 15
          oz. of copper strapped to his back (instant Ice Scraper as
          we used to refer to these PCB's in the shop !! - the cold
          climate guys should be nodding to this one!)

          This is why they add dots around the open areas... It takes
          some of the 'heat' of the small guys during plating...Then
          naturally when etching, staff will measure all etching
          levels based on the small trace, not plane areas.

          Where this applies to you is in the plating dept...
          You will want to use more 'BASE' material, and less Plated
          material.

          Typical 'high' current apps might require 2.5-3 ounces
          Finished Cu Thickness, but you can rest assured that the
          Plating Line Guy will prefer to plate only .5-.75 oz. of
          copper on top of the balance in Base Copper Material.  This
          reduces line time, as well as build up for via holes.

          Material Issue...

          Not many shops even carry 2 oz. material, so if your
          planning an exotic, allow a very long lead-time.  (My FR-4
          data sheets only go up to 2 oz. base Copper)

          Sorry for the book everyone!

          Les. (X-Fab-Meister turned CAD-Meister)
          [log in to unmask]

          ===========================================

          " He who doesn't have a good E-Mail Program, constantly
            re-types silly Quotes like this one !"
                                    -Les
          ===========================================