For years the military measured solder coating at the creast of a land. They
also said that the solder coating does not have to wet over the edge of the
land. Therefore, allowing a bit of exposed copper on the edges of a land. If
it worked all these years, we shouldn't be worried about minor exposure now.

At 09:40 AM 6/19/96 -0500, ROGER HELD wrote:
>     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
>     
>
>
Regards,

Gary Ferrari
Tech Circuits
(203)269-3311
[log in to unmask]