Tim,
Search the Technet archives for "via" or "via fill" or "tented", etc.,
for lots of good dialog on this.
A word of caution: The LPI tented vias can blow open during HASL
processing, and the HASL solder will end up in the vias. Then thru
reflow and/or wave solder, the HASL can pop out onto the surface of
your board as solder balls, not a pretty sight. You can talk to your
PCB vendor about "plugging", usually done with SR1000 mask or the
likes, but my favorite option in NO FILL in via holes, keep the LPI
via opening diameter .006" larger then the hole on both sides, then
use a clamping mechanism at test if a reflow-only board, or allow wave
solder to fill holes if wave soldered. This gets rid of the solder
ball possibility, and the contaminants-in-the-hole scenario....both of
which have caused me extreme pain in the past.
Good luck.
Jeff Hempton, Sr. SMD Mfg. Engineer
United Technology Electronic Controls
e-mail: [log in to unmask]
______________________________ Forward Header __________________________________
Subject: [TN] Mask-tented vias
Author: Timothy Reeves <[log in to unmask]> at Internet
Date: 03/03/2000 3:26 PM
Technetters:
What is your opinion on tenting of vias with LPI soldermask? If a design
gives leaves the mask film open over vias, the mask will be UV-exposed,
though not to the degree of the mask on the surface, resulting in some mask
coverage of copper inside the vias, but not as durable/thick as that on the
surface. Some of it will remain, some may end up HASL'ed. What is the
reliability of the "in-between" surfaces that don't coat with solder, but
also don't appear to be covered with mask? The "old specs" used to allow
some "haloing" around pads where thermal cured mask tapered off and left a
coppery ring around the solder-coated pad. Is this the same thing, and is it
a concern?
Designers/end users: If your design allows the vias to be covered with mask,
but the vias don't fill with mask, what problems do you foresee?
Thanks for any and all replies.
G'day
Timothy Reeves
ECD Circuit Board Division
13626 South Freeman Road
Mulino, OR 97042
[log in to unmask]
(503) 829-9108 (800) 228-8198 FAX (503) 829-5482
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