I do not believe there will be any insurmountable issues with building this
board.  We build these types of boards and assemblies all the time.  The
unique thing about this board design is the via in pad design of the BGA
pattern.

My underlying questions are:
1)      Are there any specifications that fully cover this particular type
of board?
2)      Has anyone else had any experience with the IN-PAD-VIA-BGA and
whether there are issues at assembly with tangency or breakout or does there
need to be an annular ring (and how would you verify how much of an annular
ring)?

This board is an R & D project.  I would like to establish whether the
specifics related to the BGA need to be called out on the drawing in the
future or if there is an existing acceptance specification.

Thank you ahead of time for any input.
Dawn D. Patterson

---Original Message -------
From:   Patterson, Dawn D.
Sent:   Wednesday, May 17, 2000 4:42 PM
To:     [log in to unmask]
Subject:        Blind Via BGA Acceptance Criteria?

Thank you for your responses to my "External Blind Via annular ring" query.
I should have explained a little more on why I asked.

The board has already been designed well below reduced producibility.
According to IPC-2221, the external annular ring should have been .024" dia.
at a minimum.  If the hole to pad is tangent on the finished board, I do not
believe it would be detrimental to final assembly.

The board design is more like a Micro Via, but it is a drilled via hole that
will be filled.  The external pads are .018" dia. The Internal pads are
.021"dia.  The drilled blind via hole is .010" dia. The blind via subs are
approximately .035"-.040" thick.  The minimum conductor widths are .005" and
the minimum spacings are .004".  The board has 14 layers and an integral
copper core (.035"-.040" thick). The finished overall thickness of the board
is .125".  The finished outline dimensions are approximately 6" x 9".  The
BGAs (3 of them) will be mounted directly to the plated over surface of the
filled Blind Via.

I have not seen this type of design being discussed on the Tech Net, nor
covered in the specs.  Bits and pieces that are similar, but not all in one
package.

Any comments would be appreciated.

THANK YOU,
Dawn Patterson

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