Larry, Please bear in mind that essentially, a solder resist/mask is a
permanent product to do a temporary job - viz resist solder. (Boy, I bet this
comment stirs up a hornets nest!)

Whereas, a conformal coating is a permanent product to do a permanent job viz:
protect the assembly from the harsh environment.

As you would seem to have a safety critical application, I would sincerely
hope that you are using a suitable coating. This MAY minimise the expressed
concerns about the poor solder mask coverage but you really should take that
up with the board supplier.

Graham Naisbitt


Concoat Ltd                                     Email: [log in to unmask]
Alasan House, Albany Park                       Tel:    +44 (0)1276 691100
Camberley, Surrey GU15 2PL UK           Fax:    +44 (0)1276 691227


-----Original Message-----
From:   DesignerCouncil  On Behalf Of [log in to unmask]
Sent:   Wednesday, September 24, 1997 7:48 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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