We have no problems printing 20 thou at 40 and 50 mm/s. I don't agree
     that the slower speed is an issue, slower printing should help not
     hinder. It's all down to paste. Recent No-Clean pastes from Indium,
     Kester and Alpha have brilliant print characteristics, so that it
     doesn't seem to matter what printer you use any more. You don't need
     grade 4 powder at 20 thou pitch. The worry is, finer powder has a
     higher percentage of oxide.
     Regards
     Edward Brunker



______________________________ Reply Separator _________________________________
Subject: [TN] Squeegee Speed
Author:  "TechNet E-Mail Forum." <[log in to unmask]>           Ryan Jennens
<[log in to unmask]> at INTERNET
Date:    18/02/99 17:12


Evenin' all!

        My question is this:  My stencil printer operator has said that he has
        to
wipe our 6-mil stencil each pass to get the paste in the 20-mill pitch
aperatures for a QFP to release well.  We are using Amtech NC-559 type 3
paste with 89.5% metal.  The paste is not old.  I considered using type 4
paste, which has a much finer powder in it. I was told by Amtech that this
finer powder paste will pack more densly into the aperatures and I could get
some bridging, unless I order a new stencil with aperature reductions.  Our
squeegee speed is 0.6 inches/s, or 15mm/s.  Is this too slow?  Amtech
suggested that at this slow speed, the paste could be rising out of the
aperature, as if someone pressed on a wet sponge and it rose back to its
original shape.  What is a good squeegee speed for 20 mil pitch parts? Thanks
all!

Ryan Jennens
TelGen Corp.

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