In addition to better throughput, foil construction
          eliminates the need for covering what will become the outer
          layer surface with a film etch resist.  Resist would be
          required on an all-core construction on the outer layers to
          keep the copper from being etched away.  In this same vein,
          handling scratches on this protective etch resist would
          cause lower yields.  This is all avoided by adding foil to
          top and bottom after the inner layer etch process, but
          before pressing.
          Tom Coyle
          Field Services Engineer
          HADCO Corporation
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