Richard,
I respectfully disagree...I'm the same opinion as Eddie. We had a
problem with BGA solder jumping over a 5.5 mil solder dam to either
short to another via, or suck down its own via because of the required
over printing of solder paste. The problem has been solved since two
years on millions of boards by simply coating LPI over the offending
vias. This has allowed us to reduce the space between the edge of the
BGA pad to the center of the thru-via pad to only 12 mils in some cases,
including with shops that use spray coating and don't fill the via hole
with LPI. Its easier to prevent wetting than it is to get wetting, so
even a thin LPI coating, so thin it can't be seen, will prevent solder
from wetting into the via hole.
Regards,
Ryan
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard
Sent: Wednesday, November 30, 2005 12:45 PM
To: [log in to unmask]
Subject: Re: [TN] Plugging vias necessary?
Agreed. And from the same perspective using LPI alone as a means of
preventing flux and solder from entering the via during reflow and
causing small-ball connections, opens, and other assembly defects is
insufficient, no matter what final finish is used.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Susan Mansilla
Sent: Wednesday, November 30, 2005 1:12 PM
To: [log in to unmask]
Subject: Re: [TN] Plugging vias necessary?
A lot of it is based on common sense. If the hole walls are bare copper
and you want to protect that bare copper from both board fab and
assembly chemicals, you need to completely plug or cover the via. LPI
can flow into the via, but there is no guarantee that there will be a
complete plug or even coverage of the entire hole wall.
If the hole walls are an inert finish such as ENIG, then protecting them
is not the most important aspect of via protection. You would then have
to consider what you are wanting to do and if an incomplete plug would
suffice.
Susan Mansilla
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