John,

Funky indeed. Is there a specified reason provided why they feel immersion
tin needs to be applied to inner-layers? I would suspect this is a fab notes
error. As the tin fuses with the copper over time there may be a reliability
issue, I've not heard of, or read any studies on such a process but I would
certainly question this.

As for gold directly on copper, you can expect bonding and reliability
issues with that.

If I were quoting these requirements I would have a long sit-down with the
customer and try to learn why they feel these unorthodox coating methods are
required, I would guess they were written that way in error. If they insist
personally I would no-bid the project.

Franklin
==========================

  We are quoting on a PCB which has some unique, at least to us,
manufacturing
  requirements and I was hoping that someone might be able to provide
insight
  on some of the challenges we foresee.



  There are many hurdles to clear with this part, two of which are;



  -          This 3 layer PCB must have immersion tin plating on all
  conductors, inner and outer layers.  Does anyone know if the pre-preg will
  successfully bond to the immersion tin plated surfaces?

  -          The outer layers of this part will have areas of selective gold
  plating, 50u",plated directly to copper, no nickel interface.  Are we
likely
  to see problems with bond between the gold and copper?



  John Parsons




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