Steve,
     
     LPI soldermask can sometimes bleed out (flow) a bit before it cures.  
     This yields a very thin coating of mask which may appear transparent 
     so that bright copper shines through, yet still performs its job and 
     resists solder during the HASL and assy processes.  I haven't seen 
     this in several years so you may want to make sure that your board 
     supplier has their mask process under control.
     
     Frank Hinojos
     Watkins-Johnson Co.


______________________________ Reply Separator _________________________________
Subject: DES: Pads
Author:  "Steve Collins" <[log in to unmask]> at INTERNET
Date:    7/24/97 1:35 PM


I have a .035 dia soldermask pad with no hole in a circular array pattern 
that I use over our mounting holes so we can skip a spot mask process in 
manufacturing. My question is : is this size pad too small to expose or 
develop when using LPI soldermask . I have two vendor who are having 
trouble with this pattern and when I get the boards in I have what looks 
like exposed copper contained on some of the pads. We know that they are 
not really exposed or else they would have covered in the HASL process or 
would be discolored due to contamination. The pads are just as bright 
copper color as you would expect to see before LPI soldermask is applied. 
Anyone have any thoughts.
     
Steve Collins
PCB Design Supervisor
Antec
[log in to unmask]
     
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