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]