Larry,

Need more information.  What type of SM are you using LPI or Dry film.
 Also what hole size are you using and are you trying to tent the holes.

In general holes over .020 max dia. cannot be reliably tented.  Only Dry
film will tent well but people have hole plugging techniques for LPI.

If not tenting then the holes are open and may have solder splash from HASL
or left over from select solder strip.  We occasionally see patches of
copper with solder which was not well stripped.

Bill Dieffenbacher
Lockheed Martin



----------
From:   [log in to unmask]
Sent:   Wednesday, September 24, 1997 2:47 PM
To:     [log in to unmask]
Subject:        [DESIGNERCOUNCIL] Solder Mask Problems?

I have switched to SMOBC (solder mask over bare copper) and have noticed
that
some of the via's on the board are well covered while others seem to have
only a light coating - I can see the copper hue of the traces - in some
via's
there is a slight splash of solder from the plating process. I don't
require
plugs for vac. fixtures etc.

My main concern is these boards are subject to harsh conditions (coal
mines)
and I'm worried about corrosion at these points.

Has anyone else noticed this with SMOBC?   The board house suggested going
to
a smaller drill size for via's (015). Don't suggest a new house - these
guys
are great and have been working on it.

What is the IPC spec for min coverage for class 2 boards regarding SMOBC?
 Should I be concerned?

Larry Machak (designer, not cad operator!)
Saminco Inc.

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