Brian,

The buried via cores and buried vias (>2 layers) are via types that
originate and end on layers inside the board.  The vias would NOT be
microvias.

The reason for the (2) designations is to take into account the aspect
ratio of the hole and the lack of prepreg in the construction.  The low
aspect ratio and Z axis expansion of the cores (in contrast to thicker
buried vias) tend to be more reliable which resulted in permitting
thinner copper plate thickness for this via type.

Regards,

Randy

Randy Reed, CQE
Reliability/FA Engineer
Global Reliability Group, North America
Merix Corporation
503.992.4421
503.545.0150 mobile
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-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Brian
Madsen
Sent: Thursday, June 05, 2008 2:27 PM
To: [log in to unmask]
Subject: [IPC-600-6012] Definition of Hole types in IPC-6012B, table 3-2

Hello Technical Experts,

In the IPC-6012B document, table 3-2, the Cu plating requirements are
stated 
for 5 different types of holes: through-holes, blind vias, microvias
(blind and 
buried), buried via cores, and buried vias (>2 layers).

I am having a hard time matching these hole types with the types of
holes I 
understand.  Could someone verify/correct the following understandings I
have 
of these 5 types, please?

1) Through-holes = PTH = plated through hole = a plated hole that passes

completely through all dielectric layers of the PCB

2) Blind vias = vias that are drilled into the PCB (from the top layer)
that end 
at an interior layer of the board - but are >= 0.006 inches in diameter
(not 
microvias)

3) Microvias (Blind and Buried) = vias with diameter < 0.006 inches that
are 
formed in HDI outer layers. Blind = outer layer to interior layer,
buried = interior 
layer to interior layer.  These vias are <= 2 layers deep.

4) Buried Via Cores = ?? = through hole in core portion of HDI board?

5) Buried Vias (> 2 layers) = Any via starting on an internal layer and
ending 
on an internal layer that is > 2 layers?? = is this a microvia or
non-microvia?


I am primarily confused by #4 and #5, and am trying to determine which
Cu 
plating thickness is the correct one for the features in my PCBs.
Continental 
uses the term "buried vias" to describe through-holes which are formed
in the 
core of the HDI design (for example, the 6 in a 1-6-1) prior to the
addition of 
the outer HDI layers.  Would that be a #4, or a #5?

Thank you for any assistance,

Brian


Continental Automotive
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