Tenting is nothing more than having no openings in the solder mask over
vias.  You normally do it on both sides of the board.  I am mystified by
their cost of thousands of dollars.  I do this routinely and specify 100%
electrical test on bare boards.  If you have components on both sides of the
board but the test points for the bottom side pads are not accessible on
top, then you would need a clam shell test fixture.  This can be avoided by
making all nodes accessible through test points on one side of the board.
Even so, a clam shell test fixture shouldn't cost thousands of dollars,
unless it is a large board with lots of 0.5mm spacing pads.

For boards with all the components on one side, tented vias don't cost
anything.  The only caveat is that vias can no longer be used as test
points, so you may have to add some.

Seth Goodman
Goodman & Associates
7687 Leta Way
Verona, WI 53593
Tel (608)833-7687
FAX (608)827-2631

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ryan Jennens
Sent: Monday, November 23, 1998 12:02 PM
To: [log in to unmask]
Subject: [TN] Covering Vias


Howdy all-

        Three more days!
        When I asked our board fab house to mask the vias on the bottom side
of one
of our boards to avoid the shorting which has been plaguing us, I was told
that they could do it, but for a cost of thousands of $.  They said that
they would have to make a clamshell fixture to test the bare board before
they ship it to us.  What are my other options for avoiding shorts to these
vias which are near pads.  This happens under BGA parts and also near some
surface mount parts.  Is tenting more than just covering the vias with
solder mask?  Thanks in advance for the wonderful insight which always
follows these inquiries!

Ryan Jennens
Phoenix Engineering Design, Inc.

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