Hi Steve,

I am accustomed to thinking of LPI soldermask as a +/- .003" 
material....and for that reason we try to discourage designers from trying 
to have dams less than .006" wide.

Having said that, I will admit that it is my preference is to not use 
soldermask on certain 20 mil pitch components such as BCC48, yet we do use 
soldermask on BGAs at the same pitch.

I will assume you are talking about stripes (dams) between the pads for a 
gull wing QFP leads, and yes, the resolution of LPI allows any good pwb 
fabricator to put a 6 mil wide or larger dam between the pads.

Now if your pads are equal or greater than 14 mils, then the yield at the 
fabricators will be impacted.

Hope this helps,

Phil


12/2007 -0600, Steve Gregory wrote:
>Mornin' All!
>
>What kind of resolution should a LPI be able to give you? Specifically,
>LPI's should be able to give you a solder mask dam between 20-mil pitch
>leads if you have 8-mils of space between the pads shouldn't it?
>
>Thanks!
>
>-Steve Gregory-
>
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