I agree with the statement below!
     
     Not only is light coloured LPISM better then dark ones, clear or 
     unpigmented is the best. For reasons largely unknown, the industry 
     (OEMs and Assembly) seems to be indicating through their 
     specifications that a pigment is required for the Solder Mask (usually 
     green).  Clear Solder Mask is the same as green only without the 
     pigment.
     
     Is there any published material on pigmentation verses dendritic 
     growth data or ionic contamination due to straighter sidewalls?


______________________________ Reply Separator _________________________________
Subject: Re (2) PCB Build Dendritic Growth
Author:  [log in to unmask] at corp
Date:    4/26/96 1:34 AM


In our experience, reducing the pigmentation in LPISM's can improve 
undercut considerably.  This can be particularly important in the case of 
nickel gold finishes or when fine pitch solder dams (around 3 mil) are 
required.  (Nickel gold has a tendency to 'get into' LPISM undercuts at 
pad edges reducing adhesion).  The down side used to be strikethrough on 
thin laminates.  Dark coloured LPISM's tend to stop UV passing through the 
laminate and affecting the 'reverse side' image during exposure. The 
advent of substrates containing UV blockers has largely overcome this 
problem.  AS a result most LPISM suppliers are now looking to produce 
masks with lower pigmentation.  Unfortunately such masks don't hide flaws 
in the circuit underneath..... but that's another story!
-- 
Bob Courtney
Coates Circuit Products
Tel (+44) 1761 414471
[log in to unmask]