I was trying to express Chris' concern about the definition of hole
diameter.  A .008 hole at the top drilled conically down to .006 at the
bottom.  Is that a microvia?  Your concern about the upper limit of
diameter is another question worth resolving.

Mike Green
Electronic Packaging Design
LMCO-Sunnyvale
408-743-1635
One Corporation, One Team
"Those who have nothing to follow must lead."  M. Green, 2008

-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Wendi
Boger
Sent: Wednesday, January 14, 2009 1:29 PM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Microvias

I would like to discuss this more also. A lot of designs use 6 - 8 mil
laser drills and there seems to be some confusion if they can be
considered a micro via. A number of customer spec I see do allow for the
larger size if the aspect ratio is 1:1 or less.  One other point, the
previous rev of 6012 had them defined as < or = 6 mils. Not sure why we
dropped the = to. 

Wendi


-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Green,
Mike
Sent: Wednesday, January 14, 2009 3:23 PM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Microvias

In talking with Chris an issue is;  Can a laser-drilled hole that is
.008 at the top be classified as a microvia for wrap dimension
requirements?  Have we clearly identified what less than a .006 hole is?

Here is a starting point for discussion:

From IPC-6012 revision B Amendment 1 Table 3-2, Footnote 3.
Blind microvias are vias that <0.15 mm [0.006 in] in diameter and formed
either through laser or mechanical drilling, wet/dry etching, photo
imaging or conductive ink-formation followed by a plating operation. All
performance characteristics for plated holes, as defined in this
document, shall be met. The values given for blind and buried microvias
in Table 3-2 are not applicable for stacked microvias. As of the
publication of this specification, there is little known about this
structure and the reliability results are not consistent with buried and
blind microvias. Stacked microvias may also require different inspection
criteria.


From IPC-T-50 Revision H
Microvia (Build-Up Via) 22.1595
A blind or subsequently buried hole that is < 0.15 mm [< 0.006 in] in
diameter and formed either through laser or mechanical drilling, wet/dry
etching, photo imaging, or conductive ink-formation followed by a
plating operation.


Mike Green
Electronic Packaging Design
LMCO-Sunnyvale
408-743-1635
One Corporation, One Team
"Those who have nothing to follow must lead."  M. Green, 2008
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Chris
Mahanna
Sent: Wednesday, January 14, 2009 11:52 AM
To: [log in to unmask]
Subject: [IPC-600-6012] Microvias

Good afternoon everyone,

I have a customer request to ping this group for a possible redefine of
microvia.  I know that we talked about in Vegas last year.  As I
remember it, we decided that other items were more pressing, but there
was not real objection to the idea.
At issue is wrap (of course) on your typical 8-10 mil (entry side)
ablated hole.

My suggestion is something like: aspect <1.0 and drill/ablation less
than 8 mils deep.
Thoughts?

Thanks,
Chris


Chris Mahanna
Robisan Laboratory Inc.
6502 E 21st Street
Indianapolis, Indiana 46219
317.353.6249