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August 2004

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Subject:
From:
Ryan Grant <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Mon, 30 Aug 2004 10:51:51 -0600
Content-Type:
text/plain
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text/plain (130 lines)
Cal, it sounds like it doesn't matter whether the via is plugged or
tented.  You just need it to be NON-solderable. (I'm in a similar
situation).  In other words, if the fabricator covers the via with
solder mask, and doesn't etch the via opening, solder will not flow into
the via, even if the via is not sealed closed, because there is nothing
for the solder to wet to.  So you need it neither plugged, filled, nor
tented.  How to convey this in the fab notes is difficult.  I've
resorted to giving the minimum mask dam requirements and let them figure
out the best way to accomplish that.  (I have had several fabricators
tell me they despise covering the vias though)

Ryan Grant

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Cal Driscoll
Sent: Monday, August 30, 2004 8:39 AM
To: [log in to unmask]
Subject: Re: [TN] tented Via


They reason I brought up tented vias as we are seeing an issue in the
manufacturing process.

The via is off a lead of a LCC. The solder needed is filling the via vs.
soldering the lead. The new board vendor does not tent vias (as per
their
specs) and the tolerance is to tight to mask a dam. So currently we
manually
mask the via to produce

cal

-----Original Message-----
From: Jeffrey Bush [mailto:[log in to unmask]]
Sent: Monday, August 30, 2004 8:27 AM
To: TechNet E-Mail Forum; Cal Driscoll
Subject: RE: [TN] tented Via


Of several, 2 main factors - application method and size of via.
Curtain and screen applications tend to move more material into the via
and provides a good base to remain there after image and develop.  Spray
coaters apply a more controlled coating that generally leave the hole
free of mask.  Each type of coating methodologies also have ranges of
material application thickness that will also affect the plugging of the
via.  The second variable if the via size, which can vary by fabricator
- some may drill at different sizes depending on pad-to-hole
capabilities and processing needs.  Smaller vias will plug more readily
than larger.  It is possible that each fabricator is using different
application methods and/or via sizes.

If plugging is important, I would make sure that this condition is
stated on the drawing - ie. "All vias covered by mask to be plugged".
This will allow the fabricator to apply the required processes to ensure
plugging.



Jeffrey Bush
Director, Quality Assurance and Technical Support

                          76 Technology Drive - POB 1890
                             Brattleboro, Vermont 05302-1890
                                Tel. 802.257.4571.21 Fax. 802.257.0011
                                    [log in to unmask]
                              http://www.vtcircuits.com



-----Original Message-----
From: Cal Driscoll [mailto:[log in to unmask]]
Sent: Friday, August 27, 2004 1:15 PM
To: [log in to unmask]
Subject: [TN] tented Via


Hello All-

I am not a board fab person but would like to understand why some LPI
masking processes can not tent vias (non filled).

We have a board house that can tent vias with no issues. When we went to
another board house the are unable to tent vias. Both shops are huge and
have international locations. I would think the technology would be
there to do this.

thanks in advance,
Cal
www.ctdi.com

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