Since two questions came up about blind vias and the design rules for
microvias I am going to have to switch from lurking mode to responding
mode again.

The minimum blind via with the DYCOstrate (TM) process is approximately
0.002"-0.003" in diameter and is typically in a dielectric thickness of
0.001"-0.003".  The generally accepted rule of thumb for plating a blind
via in a non-sequential process (in other words, a blind via that is 
present when the board gets to plating as opposed to a via that is plated
in an individual layer) is that the maximum aspect ratio is 1:1.

The plasma defined vias are typically smaller than laser defined vias (0.005"
to 0.006") or drilled vias (0.004" or larger) and therefore the pad can
be smaller (pads as small as 0.008" to 0.010" have already been used with plasma
defined vias), but as Mason pointed out, if you want to keep maximum flexibility
around the process that can be used a common set of design rules can be
used for laser or plasma vias.

Merix is currently working with design tool companies to try to make more
design software "Microvia friendly" as well.  That way, in addition to having
common design rules you will have a system that does not have to be tweaked.
In the meantime, several design companies have learned how to cheat the 
current systems to make use of microvias.


Glenn Heath
Merix Corporation
(503)359-2652
[log in to unmask]

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