Depending on the process used, LPI can effectively plug vias. The
question is how large the vias are and what percent failure is
acceptable. As you state, however, the only way for 100% coverage of
vias is to use a dry film solder mask. Many companies will accept 90%
coverage and use an LPI.

Bob Metcalf
Morton Electronic Materials

>>> <[log in to unmask]> 10/14/96
03:46pm >>>
Item Subject: PLUGGED VIAS -Reply
     The only soldermask I am aware of that can plug vias is dry film mask.

      If there is an LPI mask that can covers vias can someone tell me 
     about this.
     
     Thank You:
     Steve O'Hara
     


______________________________ Reply Separator
_________________________________
Subject: PLUGGED VIAS -Reply
Author:  Non-HP-bmetcalf ([log in to unmask]) at 
HP-Vancouver,shargw2
Date:    10/14/96 11:12 AM


If you are using a photo defined solder mask, you can control which 
pads are covered/filled and which pads are cleared.
      Bob Metcalf  Morton Electronic Materials
      >>> Barry Darnell <[log in to unmask]> 10/14/96 11:41am
>>>
      I have run into a problem with a board that has vias in smt pads.  We 
need all of the vias plugged, and I am told that solder mask is the best 
way to do that.  This is to ensure that a good vacuum is maintained for 
our ATE equipment.  That is the problem.  I can not have a via covered 
with solder mask on top of an smt pad.  The board house I am using says
 this is difficult for them because they have to determine which vias are 
plugged and which are not.  Anyone out there with any suggestions?
      Thanks,
     
    Barry Darnell
(864)627-8800 Ext. 231 [log in to unmask]  CD Electronics, Inc.
Printed Circuit Board Designer
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