Kelly:
               I assume that you are using a 1/2 oz. cu. foil on which
          to build the outer layers. Since 1/2 oz. cu./sq. ft. equates
          to .0007", and the etch occurs on both sides of the pad, a
          maximum etch loss of .0015" would be expected.  This is also
          assuming that the etch is in control, and functioning at a
          ratio of 1:1;i.e., as much is etched inward as it is down.
          There may be a slight growth of the pad width due to
          possible "mushrooming", thus a span of .0025" should be
          quite acceptable to board fabricators.  We like to use
          +.001", -.002" as a maximum with 1/2 oz. cu.  I would guess
          that the pads would be blown up by .001" overall to try to
          more center the tolerance around the finished requirement.
          I don't believe that the finish of either HASL or OSP would
          affect this much, because the typical thickness of solder
          levelled solder is .0001" or less.  Bottom line: if you are
          looking for .011" (+/-.002"), the pads should probably be
          bumped up to .012" on the fabricator's artwork to avoid the
          phenomenon of running at or below the minimum acceptable
          finish.
          Tom Coyle
          Field Services Engineer
          HADCO Corporation
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