Hi gang,
       A few months ago, I moved to a new employer, and it has been an
     interesting exercise in things I have taken for granted at the
     previous employment.
     An exemple of one of these instances is solder mask between our 20-mil
     (actually .0197") pitch PQFP parts. We are calling out a pad width of
     .012". My previous employers suppliers was no problem...now I am
     hearing whining from the new companies suppliers that they cannot
     produce this for us????
       Recent pad and aperture designs we have put in place along with
     process changes have given us a lot of confidence in our fine pitch
     process, enough so that I'm not sure how much additional benefit we
     will get from solder mask between the pads, but having always used it
     in a previous life, I'm still concerned. Many of the previous Technet
     discussions and technical publications rave the benefits of solder
     mask between pads.
       Can some of you, assemblers or fab houses, share your spec's
     regarding this issue, specifically:

     1) Do you use/require solder mask (LPI type) between fine pitch pads?
     And if so, what is your specs/tolerances on the web width, and how do
     you spec it to fit it between the pads?

     2) Is a specific copper weight (0.25, 0.5 oz., etc.) specified for top
     layer copper when fine pitch parts are present?
     What kind of tolerances do you require?

     Any info you can share would be appreciated! Thanx in advance.

     Jeff Hempton
     United Technologies Electronic Controls

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