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1995

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Sat, 10 Jun 95 12:46:24 EST
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          HADCO uses LPI soldermasks almost exclusively, and we also
          "plug" the vias from one side with a wet mask dot pattern.
          Tha only difference is that we perform the process in the
          following sequence:
          LPI soldermask
          hot air solder level
          wet mask via plug
          In this way, the via barrels have a solder coating on them,
          which we consider more reliable.
          I agree with you 100% that this is almost a technology step
          backwards, but it is the best we can do for now for those of
          our customers who need plugged vias, either for vacuum
          purposes at loaded board test, or to reduce bridging vias
          sitting under components.
          Always make sure that you don't plug a via which is needed
          as a test point.  We have also found it difficult to plug
          vias drilled >.020".
          Tom Coyle
          Customer Services Engineer
          HADCO Corporation
          [log in to unmask]



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