There should be a solder mask dam between the SMT device and its via. 
     We place the dam .005" away from the devices pad and .005" away from 
     the via pad for LPISM. We use .007" min. dam width. If the dam is not 
     present you will draw solder away from the device when you reflow the 
     board causing less than desirable solder joint.


______________________________ Reply Separator _________________________________
Subject: ASM Surface mount w/out soldermask
Author:  [log in to unmask] at SMTPpost
Date:    3/15/96 6:52 AM


Please help me resolve a design issue.
     
The board will be assemblied using solderpaste, pick and place, surface 
mount assembly (both sides).  The design has .0135" vias hole centers less 
than .030" from surface mount pads.  The via and pad is connected with a 
short .008" wide trace.  There is no soldermask dam between the surface 
mount pad and the via hole.  Board is a 4 layer .062, which has soldermask 
already on the board.
     
Any assembly concerns?  Should there be a soldermask dam between the land 
and via?  What guidelines do you use/like ?
     
Thanks for your input
     
     
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