I don't know much about your soldermask issue, but I would like to see 
     some discussion of the exposed copper issue.
     
     We have felt for a long time that any exposed copper was unacceptable 
     but with the industry switching over to OSP more and more, we have to 
     accept a limited amount of copper exposure (when SMT pads don't get 
     paste).  If you are making SMT-only boards which don't flow across a 
     wave solder then the amount of exposed copper goes up tremendously.  I 
     recently talked to people at a company which is very prominent in the 
     electronics industry and has been allowing a large amount of exposed 
     copper on their PCB assemblies (look inside your PC and see how much 
     exposed copper you can find).  They have done a significant amount of 
     temperature and life testing and have seen no problems due to exposed 
     copper.
     
     If this is true, isn't it time to stop worrying about exposed copper 
     and start making boards and assemblies cheaper?
     
     Regards,
     
     Roger Held
     Hitachi Computer Products (America), Inc.


______________________________ Reply Separator _________________________________
Subject: Soldermask Tented Vias
Author:  [log in to unmask] at Internet-HICAM-OK
Date:    6/19/96 8:48 AM


     
Good Morning,
     
We usually require soldermask over bare copper and tented vias (less than 
.020").  This typically means that the soldermask is dry film.  If a tented 
via is not required and liquid soldermask is used, it appears that the 
soldermask is suspect to flake off near the via knee, leaving a small amount 
of exposed copper.
     
Is liquid solder mask over bare copper compliant with vias when the plating 
is eletroless nickel - immersion gold?
     
Does the plating type matter?
     
Is the suspect of exposed copper a non-issue?
     
Thank you in advance of any comments.
     
Kevin Thorson
Lockhead Martin
Eagan, Mn