Markus,
As I recall, the copper plating thickness requirements for blind vias in
IPC-6012 were changed (from 276) to match the copper plating thickness
requirements for PTHs.  The aspect ratio of blind vias can approach or
exceed the aspect ratio of PTHs, and the forces acting on these blind
vias from z-direction expansion mismatch are similar to the forces acting
on PTHs.

Do not have experience with buried vias, but I have seen several high
aspect ratio, class 3 applications where 25 micron copper was
inadequate in blind vias (38 micron was required).

Ted Jones

>>> <[log in to unmask]> 04/15/97 08:10am >>>
Hello !
In IPC specification ANSI/IPC-RB-276, 1992, for "Qualification and
Performance Specification  for Rigid Printed Boards" it is specified a
copper thickness of 15?m for buried and blind vias  with a min.thickness
of 13?m. However this spec. was changed during 1996, IPC-6012, there
the  copper thickness for blind vias were increased to an average
thickness of 25?m with a min.  thickness of 20?m.

Does anyone know why they changed their specifications?  Is there
someone who has any experience of blind and buried vias with thin
copper coatings  (15-13?m)?

Thanks in advance for your help

                 //Markus



Markus Gauffin  M.Sc.
Printed Board Assembly Technology tel: +46 8 719 16 34 fax: +46 8 719
71 99 e-post: [log in to unmask]

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