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| From [log in to unmask] Wed May 1 12: |
49:40 1996 |
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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]
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